@article{pmid22944790,
Author = {B. Stender and B. Wang and A. Schlaefer},
Title = {Computing Synthetic Echocardiography Volumes for Automatic Validation of 3D Segmentation Results.},
Journal = {Biomed Tech (Berl).},
Year = {(2012).},
Volume = {57.},
Number = {(Suppl. 1),},
Note = {[DOI:10.1515/bmt-2012-449210.1515/bmt-2012-4492] [PubMed:http://www.ncbi.nlm.nih.gov/pubmed/2294479022944790]},
Doi = {10.1515/bmt-2012-4492}
}
@inproceedings{B12b,
Author = {B. Stender and M. Brandenburger and B. Wang and Z.X. Zhang and A. Schlaefer},
Title = {Motion compensation of optical mapping signals from rat heart slices.},
Year = {(2012).},
Volume = {8553.},
Booktitle = {Proc. SPIE 8553 Optics in Health Care and Biomedical Optics V},
Doi = {10.1117/12.2008992},
Url = {http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1485450}
}
@article{C12b,
Author = {C. Otte and G. Hüttmann and A. Schlaefer},
Title = {Feasibility of optical detection of soft tissue deformation during needle insertion.},
Journal = {SPIE Medical Imaging.},
Year = {(2012).},
Volume = {8316.},
Pages = {8316-8316-11},
Doi = {10.1117/12.912538}
}
@article{C12a,
Author = {C. Otte and G. Hüttmann and G. Kovács and A. Schlaefer},
Title = {Phantom validation of optical soft tissue navigation for brachytherapy.},
Journal = {MICCAI Workshop on Image-Guidance and Multimodal Dose Planning in Radiation Therapy.},
Year = {(2012).},
Pages = {96-100},
Abstract = {In high dose rate brachytherapy, needles are inserted into soft tissue and subsequently radioactive sources are used to deliver a high dose inside the target region. While this approach can achieve a steep dose gradient and o ers a focused, organ sparing treatment, it also requires a careful positioning of the needles with respect to the tissue. We have previously proposed to use an optical ber embedded in the needle to detect soft tissue deformation. To validate the approach, we have developed an experimental setup to compare the actual needle motion with the motion estimated via the ber. Our results show a good agreement between actual and estimated motion, indicating that optical deformation detection through the needle is possible.}
}
@article{ERMMBS12a,
Author = {F. Ernst and L. Richter and L. Matthäus and V. Martens and R. Bruder and A. Schlaefer and A. Schweikard},
Title = {Non-orthogonal tool/flange and robot/world calibration.},
Journal = {Int J Med Robot.},
Year = {(2012).},
Volume = {8.},
Number = {(4),},
Pages = {407-420},
PMID = {22508570},
Doi = {10.1002/rcs.1427},
Abstract = {BACKGROUND\: For many robot\-assisted medical applications, it is necessary to accurately compute the relation between the robot\'s coordinate system and the coordinate system of a localisation or tracking device. Today, this is typically carried out using hand\-eye calibration methods like those proposed by Tsai\/Lenz or Daniilidis. METHODS\: We present a new method for simultaneous tool/flange and robot/world calibration by estimating a solution to the matrix equation AX\?\=\?YB. It is computed using a least\-squares approach. Because real robots and localisation are all afflicted by errors, our approach allows for non\-orthogonal matrices, partially compensating for imperfect calibration of the robot or localisation device. We also introduce a new method where full robot\/world and partial tool\/flange calibration is possible by using localisation devices providing less than six degrees of freedom \(DOFs\). The methods are evaluated on simulation data and on real\-world measurements from optical and magnetical tracking devices, volumetric ultrasound providing 3\-DOF data, and a surface laser scanning device. We compare our methods with two classical approaches: the method by Tsai\/Lenz and the method by Daniilidis. RESULTS\: In all experiments, the new algorithms outperform the classical methods in terms of translational accuracy by up to 80\% and perform similarly in terms of rotational accuracy. Additionally, the methods are shown to be stable\: the number of calibration stations used has far less influence on calibration quality than for the classical methods. CONCLUSION\: Our work shows that the new method can be used for estimating the relationship between the robot\'s and the localisation device\'s coordinate systems. The new method can also be used for deficient systems providing only 3\-DOF data, and it can be employed in real\-time scenarios because of its speed.}
}
@inproceedings{F12a,
Author = {F. Gasca and T. Wissel and H. Hadjar and A. Schlaefer and A. Schweikard},
Title = {Sparsely optimized multi-electrode transcranial direct current stimulation.},
Year = {(2012).},
Volume = {6.},
Number = {(136),},
Publisher = {Frontiers Media:},
Booktitle = {Bernstein Conference, Frontiers in Computational Neuroscience},
Organization = {Front. Comput. Neurosci.},
Doi = {10.3389/conf.fncom.2012.55.00136}
}
@inproceedings{H12a,
Author = {H. Hadjar and R. Friedl and H.-H. Sievers and P. Hunold and B. Stender and A. Schlaefer},
Title = {Patient-specific finite-element simulation of aortic valve-sparing surgery.},
Year = {(2012).},
Number = {(Computer Assisted Radiology and Surgery (CARS)),},
Booktitle = {Computer Assisted Radiology and Surgery (CARS)}
}
@article{312a,
Author = {L. Hertel and A. Schlaefer},
Title = {Data Mining for Optimal Sail and Rudder Control of Small Robotic Sailboats.},
Journal = {Robotic Sailing 2012.},
Year = {(2012).},
Pages = {37-48},
Publisher = {Springer:},
Booktitle = {Robotic Sailing, Proceedings of the 5th International Robotic Sailing Conference},
Organization = {Robotic Sailing, Proceedings of the 5th International Robotic Sailing Conference},
Doi = {10.1007/978-3-642-33084-1_4},
Abstract = {Finding the optimal parameter settings to control a sailing robot is an intricate task, as sailing presents a fairly complex problem with a highly non-linear interaction of boat, wind, and water. As no complete mathematical model for sailing is available, we studied how a large set of sensor data gathered in different conditions can be used to obtain parameters. In total, we analyzed approximately 2 million records collected during more than 110 hours of autonomous sailing on 55 different days. The data was preprocessed and episodes of stable sailing were extracted before studying boat, sail and rudder trim with respect to speed, course stability, and energy consumption. Our results highlight the multi-criteria nature of optimizing robotic sailboat control and indicate that a reduced set of preferable parameter settings may be used for effective control.}
}
@article{L12b,
Author = {L. Richter and P. Trillenberg and A. Schweikard and A. Schlaefer},
Title = {Comparison of stimulus intensity in hand held and robotized motion compensated transcranial magnetic stimulation.},
Journal = {Neurophysiologie Clinique/Clinical Neurophysiology.},
Year = {(2012).},
Volume = {42.},
Pages = {61-62},
Doi = {10.1016/j.neucli.2011.11.028},
Url = {http://www.sciencedirect.com/science/article/pii/S0987705311001869},
Abstract = {Transcranial Magnetic Stimulation (TMS) is based on a changing magnetic field passing through the skull and inducing an electric field in the cortex [1,2]. The latter results in cortical stimulation and needs to be aligned with the target region. Conventionally, the TMS coil is mounted to a static holder and the subject is asked to avoid head motion. Additionally, head resting frames have been used [3]. In contrast, our robotized TMS system employs active motion compensation (MC) to maintain the correct coil position [4]. To assess the potential impact of patient motion, we study the induced electric field for the different setups. We recorded 30 min of head motion for six subjects in three scenarios: (a) using a coil holder and avoiding head motion, (b) using a coil holder and a head rest, and (c) using the robotized system with motion compensation. The motion traces were fed into a second robot to mimic head motion for a field sensor integrated in a head phantom. We found that after 30 minutes the induced electric field was reduced by 32.0% and 19.7% for scenarios (a) and (b), respectively. For scenario (c) it was reduced by only 4.9%. Furthermore, the orientation of the induced field changed by 5.5°, 7.6°, and 0.4° for scenarios (a), (b), and (c), respectively. None of the scenarios required rigid head fixation [5], which is often considered impractical and uncomfortable. We conclude that active motion compensation is a viable approach to maintain a stable stimulation during TMS treatments.}
}
@article{FKSBLG12a,
Author = {M. Finke and S. Kantelhardt and A. Schlaefer and R. Bruder and E. Lankenau and A. Giese and A. Schweikard},
Title = {Automatic scanning of large tissue areas in neurosurgery using optical coherence tomography.},
Journal = {Int J Med Robot.},
Year = {(2012).},
Volume = {8.},
Number = {(3),},
Pages = {327-336},
PMID = {22911978},
Doi = {10.1002/rcs.1425},
Abstract = {BACKGROUND: With its high spatial and temporal resolution, optical coherence tomography \(OCT\) is an ideal modality for intra\-operative imaging. One possible application is to detect tumour invaded tissue in neurosurgery, e.g. during complete resection of glioblastoma. Ideally, the whole resection cavity is scanned. However, OCT is limited to a small field of view \(FOV\) and scanning perpendicular to the tissue surface. METHODS: We present a new method to use OCT for scanning of the resection cavity during neurosurgical resection of brain tumours. The main challenges are creating a map of the cavity, scanning perpendicular to the surface and merging the three\-dimensional \(3D\) data for intra\-operative visualization and detection of residual tumour cells. RESULTS: Our results indicate that the proposed method enables creating high\-resolution maps of the resection cavity. An overlay of these maps with the microscope images provides the surgeon with important information on the location of residual tumour tissue underneath the surface. CONCLUSION: We demonstrated that it is possible to automatically acquire an OCT image of the complete resection cavity. Overlaying microscopy images with depth information from OCT could lead to improved detection of residual tumour cells.}
}
@article{HHS12a,
Author = {M. Heinig and U. G. Hofmann and A. Schlaefer},
Title = {Calibration of the motor-assisted robotic stereotaxy system: MARS.},
Journal = {Int J Comput Assist Radiol Surg.},
Year = {(2012).},
Volume = {7.},
Number = {(6),},
Pages = {911-920},
Doi = {10.1007/s11548-012-0676-7},
Abstract = {Background: The motor\-assisted robotic stereotaxy system presents a compact and light\-weight robotic system for stereotactic neurosurgery. Our system is designed to position probes in the human brain for various applications, for example, deep brain stimulation. It features five fully automated axes. High positioning accuracy is of utmost importance in robotic neurosurgery. Methods: First, the key parameters of the robot\’s kinematics are determined using an optical tracking system. Next, the positioning errors at the center of the arc which is equivalent to the target position in stereotactic interventions are investigated using a set of perpendicular cameras. A modeless robot calibration method is introduced and evaluated. To conclude, the application accuracy of the robot is studied in a phantom trial. Results: We identified the bending of the arc under load as the robot\’s main error source. A calibration algorithm was implemented to compensate for the deflection of the robot\’s arc. The mean error after the calibration was 0.26 mm, the 68.27th percentile was 0.32 mm, and the 95.45th was 0.50 mm. Conclusion: The kinematic properties of the robot were measured, and based on the results an appropriate calibration method was derived. With mean errors smaller than currently used mechanical systems, our results show that the robot\’s accuracy is appropriate for stereotactic interventions.}
}
@inproceedings{N12a,
Author = {N. Lessmann and J. Sulikowski and P. Névoa and T. Kral and D. Drömann and A. Schlaefer},
Title = {Ein Ansatz zur bewegungskompensierten stereoskopischen Navigation für die Bronchoskopie.},
Year = {(2012).},
Booktitle = {Jahrestagung der deutschen Gesellschaft für computer- und roboterassistierte Chirurgie (CURAC)},
Abstract = {Die bronchoskopische Diagnostik peripherer Lungentumore wird durch Atembewegungen und die schlechte Sichtbarkeit im Röntgenbild erschwert. Eine genaue 3D Lokalisation von Instrument und Zielgebiet kann nur durch stereoskopische Röntgenbilder erreicht werden. Bei sequentieller Aufnahme mit einem CBogen kann die Atmung zu Verschiebungen führen. Wir beschreiben einen Ansatz, wie anhand eines Markers und eines passiven optischen Lageverfolgungssystems die Lage der Bildebenen unter Ausgleich der Atembewegung bestimmt werden kann. Erste experimentelle Ergebnisse deuten darauf hin, dass mit dem System zum Atemzustand konsistente Bilddaten erfasst werden können. Aus zwei Röntgenbildern aus verschiedenen Richtungen zum gleichen Atemzustand kann die Lage von Bronchoskop und Zielgebiet bestimmt werden}
}
@inproceedings{O12b,
Author = {O. Blanck and G. Hildebrandt and J. Dunst and A. Schweikard and A. Schlaefer},
Title = {Ein Review zur Bestrahlungsplanung für die robotergestützte Radiochirurgie ? Konzepte, Klinikeinsatz und Ausblick auf zukünftige Entwicklungen.},
Year = {(2012).},
Booktitle = {DGMP Jahrestagung 2012 Jena}
}
@inproceedings{O12d,
Author = {O. Blanck and J. Krause and R. Dürichen and N. Andratschke and S. Wurster and A. Kovacs and G. Gaffke and K.R. Bogun and D. Rades and M. Birth and J. Dunst and G. Hildebrandt and A. Schweikard and A. Schlaefer},
Title = {Pilotstudie zur Analyse der klinischen Genauigkeit der robotergestützten Radiochirurgie für Lebermetastasen.},
Year = {(2012).},
Booktitle = {DEGRO - Deutsche Gesellschaft für Radioonkologie e.V. Jahrestagung}
}
@article{O12e,
Author = {O. Blanck and J. Krause and R. Dürichen and S. Wurster and N. Andratschke and D. Rades and G. Hildebrandt and J. Dunst and A. Schweikard and A. Schlaefer},
Title = {Retrospective Accuracy Estimation for Motion Compensated Robotic Radiosurgery of the Liver.},
Journal = {Medical Physics.},
Year = {(2012).},
Volume = {39.},
Number = {(3985),},
Doi = {10.1118/1.4736257},
Abstract = {Purpose: The CyberKnife\™ compensates translational target motion by moving the beams synchronously. While the system was found to operate with sub?millimeter accuracy in phantoms, determining the clinical accuracy is challenging. Measuring the delivered dose distribution inside a patient is impractical. Hence an analysis of treatment data is typically used to estimate residual errors. Methods: We implant 3?5 fiducials for target tracking and treat livertumors in 3?5 fractions with 45Gy at 80% to the PTV (CTV+3mm). Patients are aligned based on X?ray images in expiration breath hold. During delivery, X?ray images are acquired every 60?90s, and the translational and rotational misalignment is computed. We grouped this data into 10 respiratory phases. The mean misalignment for each phase was used to simulate the translation and rotation of the target with respect to the alignment center. The resulting dose distribution was computed and compared to the planned dose. Additionally, the quality of motion prediction was evaluated. Results: We analyzed 5 cases with a total of 17 fractions. The maximal target motion per fraction ranged from 9.2mm to 25.7mm (3D trajectory). The mean error for each patient ranged from ?0.76/?0.01/? 0.32mm to 0.35/0.17/0.10mm (Translation IS/LR/AP) and ?0.94/?0.82/?2.07 degrees to 0.24/1.95/2.36 degrees (Rotation roll/pitch/yaw). The dose simulation showed point dose difference for each patient ranging from ? 0.10Gy to ?0.76Gy (Mean) and ?1.13Gy to ?5.05Gy (Max). The resulting reduction in coverage ranged from 0.37% to 4.19% (PTV) and ?0.43% to +0.94% (CTV). Finally, the mean prediction error over all fractions was 0.33mm. Conclusions: We demonstrated that while maximum point dose differences can be considerable, the coverage of the CTV is maintained even in the presence of substantial respiratory motion. The results indicate that the standard 3mm system uncertainty margin can account for errors due to rotation and deformation during roboticradiosurgery for tumors in the liver.}
}
@conference{O12c,
Author = {O. Blanck and N. Andratschke and H.-W. Breyer and C. Stubert and A. Schlaefer and A. Schweikard and D. Rades and J. Dunst and G. Hildebrandt},
Title = {Erweiterte Qualitätssicherung für die robotergestützte Radiochirurgie.},
Year = {(2012).}
}
@inproceedings{SMBKS12a,
Author = {O. Shahin and V. Martens and A. Beširevic and M. Kleemann and A. Schlaefer},
Title = {Localization of liver tumors in freehand 3D laparoscopic ultrasound.},
Journal = {Medical Imaging.},
Year = {(2012).},
Volume = {8316.},
Pages = {83162C},
Month = {February},
Booktitle = {SPIE Medical Imaging},
Organization = {International Society for Optics and Photonics},
Doi = {10.1117/12.912375},
Abstract = {The aim of minimally invasive laparoscopic liver interventions is to completely resect or ablate tumors while minimizing the trauma caused by the operation. However, restrictions such as limited field of view and reduced depth perception can hinder the surgeon\'s capabilities to precisely localize the tumor. Typically, preoperative data is acquired to find the tumor\(s\) and plan the surgery. Nevertheless, determining the precise position of the tumor is required, not only before but also during the operation. The standard use of ultrasound in hepatic surgery is to explore the liver and identify tumors. Meanwhile, the surgeon mentally builds a 3D context to localize tumors. This work aims to upgrade the use of ultrasound in laparoscopic liver surgery. We propose an approach to segment and localize tumors intra\-operatively in 3D ultrasound. We reconstruct a 3D laparoscopic ultrasound volume containing a tumor. The 3D image is then preprocessed and semi\-automatically segmented using a level set algorithm. During the surgery, for each subsequent reconstructed volume, a fast update of the tumor position is accomplished via registration using the previously segmented and localized tumor as a prior knowledge. The approach was tested on a liver phantom with artificial tumors. The tumors were localized in approximately two seconds with a mean error of less than 0.5 mm. The strengths of this technique are that it can be performed intra\-operatively, it helps the surgeon to accurately determine the location, shape and volume of the tumor, and it is repeatable throughout the operation}
}
@inproceedings{T12a,
Author = {T. Neumann and A. Schlaefer},
Title = {Feasibility of Basic Visual Navigation for Small Robotic Sailboats.},
Journal = {Robotic Sailing.},
Year = {(2012).},
Pages = {13-22},
Publisher = {Springer:},
Abstract = {Image based navigation is a key research focus for many robotic applications. One complication for small sailing robots is their limited buoyancy and rather rapid motion. We studied whether it would still be feasible to use video data for basic navigation in an inshore race course scenario. Particularly, we considered methods for detecting the horizon and buoys, as well as estimating rotations via optical flow. All methods have been tested on a set of manually annotated scenes representing different sailing and lighting conditions. The results show that detection rates of more than 80% for the horizon and more than 94\% for buoys can be achieved. Moreover, a comparison of the average optical flow with compass data indicates that rotations of the boat can be estimated. Hence, the methods should be considered in addition to other sensors.}
}
@inproceedings{T12b,
Author = {T. Viulet and A. Schlaefer},
Title = {SU-E-T-618: Error Compensated Sparse Optimization for Fast Radiosurgery Treatment Planning.},
Journal = {Medical Physics.},
Year = {(2012).},
Volume = {39.},
Number = {(3848-3848),},
Publisher = {Wiley-Blackwell:},
Booktitle = {Medical Physics},
Doi = {10.1118/1.4735708},
Abstract = {Purpose: Radiosurgical treatment planning requires a good approximation of the dose distribution which is typically computed on a high resolution grid. However, the resulting optimization problem is large, and leads to substantial runtime. We study a sparse grid approach, for which we estimate and compensate for the expected deviations from the bounds. Methods: We buildup an estimate of the hotspot error distribution by measuring the maximum dose deviation within a voxel for a large number of randomly generated beam configurations. This results in a conservative estimation of overdosage as a function of upper bound reduction for different grid sizes. We adjust the bounds for voxels inside the target volume (PTV) according to our estimation thus maintaining the likelihood of dose deviations within acceptable limits. The approach was applied to a prostate case, where the volumes of interest are large and close to each other. Our planning objective is a prescribed dose of 36.25 Gy to the 87\% isodose. We employed constrained optimization to optimize the lower PTV bound on 2, 4, and 8mm isotropic grids. Results were computed on 1mm grid. Results: The initial coverage was 93.7\%, 92\%, and 91\%, and the volume exceeding the upper bound was 0.74\%, 1.71\%, and 9\% for grid sizes of 2, 4, and 8mm, respectively. Changing the upper bound by 0.5\% and 2.5\% for the 4 and 8 mm grids resulted in only 0.75\% and 2.2\% of the volume exceeding the bound. The coverage did not change. Mean optimization times were 141.1, 22.6 and 3.4 minutes using the 2, 4 or 8mm grid, respectively. Conclusions: Experiments show that planning on a sparse grid can achieve comparable results with those of a high resolution grid, as long as the bounds are carefully balanced. This leads to substantially lower optimization times which facilitates interactive planning. This work was supported by the Graduate School for Computing in Medicine and Life Sciences funded by Germany\'s Excellence Initiative [DFG GSC 235\/1]}
}
@article{S11a,
Author = {A. Schlaefer},
Title = {Treatment Planning for Motion Adaptation in Radiation Therapy.},
Journal = {Adaptive Motion Compensation in Radiotherapy.},
Year = {(2011).},
Number = {(CRC Press ),},
Pages = {Ch8, 65–75},
Publisher = {CRC Press:},
Isbn = {978-1-4398-2193-0},
Booktitle = {Adaptive Motion Compensation in Radiotherapy},
chapter = {8}
}
@inproceedings{A11b,
Author = {A. Schlaefer and C. Otte and F. Noack and M. Sommerauer and G. Hüttmann and G. Kovacs},
Title = {Preliminary study on optical coherence tomography for brachytherapy guidance.},
Year = {(2011).},
Booktitle = {4th International Symposium on Focal Therapy and Imaging in Prostate & Kidney Cancer},
Url = {http://www.epostersonline.com/focther2011/?q=node/1425},
Abstract = {Preliminary study on optical coherence tomography for brachytherapy guidance Focal therapy requires precise localization of the target, and a navigated treatment. Transrectal ultrasound (TRUS) remains the preferable image modality for the prostate, although needles inserted during brachy-therapy can cause substantial artifacts. Yet, the needles penetrate prostate tissue and could be used for high resolution imaging from within the target region (Fig. 1a). We study how optical coherence tomography (OCT) images can be obtained and mapped against histology data.}
}
@Inbook{A11c,
Author = {A. Schlaefer and D. Beckmann and M. Heinig and R. Bruder},
Title = {A New Class for Robotic Sailing: The Robotic Racing Micro Magic.},
Journal = {Robotic Sailing: Proceedings of the 4th International Robotic Sailing Conference.},
Year = {(2011).},
Pages = {71-84 },
Editor = {In A. Schlaefer and O. Blaurock (Eds.)},
Publisher = {Springer Berlin Heidelberg:},
Isbn = {978-3-642-22836-0},
Booktitle = {Robotic Sailing: Proceedings of the 4th International Robotic Sailing Conference},
Doi = {10.1007/978-3-642-22836-0_5},
Url = {https://doi.org/10.1007/978-3-642-22836-0_5},
Abstract = {A number of boat designs have been proposed for robotic sailing, particularly inspired by competitions like the Microtransat challenge, SailBot, and the World Robotic Sailing Championship. So far, most of the boats are one-offs, often highlighting naval architecture aspects. We propose a new one-design class based on a readily available kit. Small, lightweight and with proven sailing performance the robotic racing Micro Magic presents a more standardized alternative, particularly for algorithm development and multi-boat scenarios. Our intention is to introduce an evolving class, and we propose a set of basic rules and describe the modified boat design, electronics, sensors and control approach for our prototype. Moreover, we have used four identical boats for the past year and we present results illustrating the good and comparable sailing performance, indicating that the class is suitable to study robotic sailing methods}
}
@inproceedings{A11a,
Author = {A. Schlaefer and O. Blaurock (Eds.)},
Title = {Robotic Sailing.},
Journal = {Proceedings of the 4th International Robotic Sailing Conference.},
Year = {(2011).},
Publisher = {Springer:},
Isbn = {978-3-642-22835-3},
Booktitle = {Proceedings of the 4th International Robotic Sailing Conference},
Doi = {10.1007/978-3-642-22836-0}
}
@article{SD11a,
Author = {A. Schlaefer and S. Dieterich},
Title = {Feasibility of case-based beam generation for robotic radiosurgery.},
Journal = {Artif Intell Med.},
Year = {(2011).},
Volume = {52.},
Number = {(2),},
Pages = {67-75},
PMID = {21683563},
Doi = {10.1016/j.artmed.2011.04.008},
Abstract = {OBJECTIVE: Robotic radiosurgery uses the kinematic flexibility of a robotic arm to target tumors and lesions from many different directions. This approach allows to focus the dose to the target region while sparing healthy surrounding tissue. However, the flexibility in the placement of treatment beams is also a challenge during treatment planning. We study an approach to make the search for treatment beams more efficient by considering previous treatment plans. METHODS AND MATERIAL: Conventionally, a beam generation heuristic based on randomly selected candidate beams has been proven to be most robust in clinical practice. However, for prevalent types of cancer similarities in patient anatomy and dose prescription exist. We present a case-based approach that introduces a problem specific measure of similarity and allows to generate candidate beams from a database of previous treatment plans. Similarity between treatments is established based on projections of the organs and structures considered during planning, and the desired dose distribution. Solving the inverse planning problem a subset of treatment beams is determined and adapted to the new clinical case. RESULTS: Preliminary experimental results indicate that the new approach leads to comparable plan quality for substantially fewer candidate beams. For two prostate cases, the dose homogeneity in the target region and the sparing of critical structures is similar for plans based on 400 and 600 candidate beams generated with the novel and the conventional method, respectively. However, the runtime for solving the inverse planning problem for could be reduced by up to 47\%, i.e., from approximately 19 min to less than 11 min. CONCLUSION: We have shown the feasibility of case\-based beam generation for robotic radiosurgery. For prevalent clinical cases with similar anatomy the cased\-based approach could substantially reduce planning time while maintaining high plan quality}
}
@inproceedings{B11a,
Author = {B. Stender and M. Scharfschwerdt and F. Ernst and R. Bruder and H. Hadjar and A. Schlaefer},
Title = {Optical Imaging of Cardiac Function: System setup and calibration.},
Journal = {Proceedings of the 25th International Congress and Exhibition on Computer Assisted Radiology and Surgery (CARS 11).},
Year = {(2011).},
Volume = {6.},
Number = {(1),},
Pages = {42-43},
Booktitle = {Proceedings of the 25th International Congress and Exhibition on Computer Assisted Radiology and Surgery (CARS 11)}
}
@Inbook{C11a,
Author = {C. Otte and R. Ansari and G. Kovács and M. Sommerauer and G. Hüttmann and A. Schlaefer},
Title = {Kompensation von Bewegungsartefakten beim Einbringen von Brachytherapienadeln.},
Journal = {Informatik aktuell.},
Year = {(2011).},
Pages = {444-448},
chapter = {Bildverarbeitung für die Medizin (BVM)},
Abstract = {Beim Einbringen von Nadeln in Weichgewebe kommt es zu Bewegungen und Deformationen. Diese beeinträchtigen besonders hochaufgelöste Bildgebungsverfahren mit geringer Eindringtiefe wie die optische Kohärenztomographie, die jedoch auch kleine Strukturen aufl ösen kann und eine Möglichkeit zur „optischen Biopsie“ darstellt. Die Korrektur von Bewegungsartefakten auf Basis anderer Bilddaten wie beispielsweise perkutaner / transrektaler Ultraschall wird durch die Nadeln erschwert. Wir untersuchen, ob auftretende Gewebedeformationen mit Hilfe einer Kraftmomentensensorik berücksichtigt werden können. Die Ergebnisse deuten auf einen deutlichen Zusammenhang von Gewebedeformation und auftretender Kräfte hin}
}
@article{ESS11a,
Author = {F. Ernst and A. Schlaefer and A. Schweikard},
Title = {Predicting the outcome of respiratory motion prediction.},
Journal = {Med Phys.},
Year = {(2011).},
Volume = {38.},
Number = {(10),},
Pages = {5569-5581},
Doi = {10.1118/1.3633907}
}
@article{EBSS11a,
Author = {F. Ernst and R. Bruder and A. Schlaefer and A. Schweikard},
Title = {Forecasting pulsatory motion for non-invasive cardiac radiosurgery: an analysis of algorithms from respiratory motion prediction.},
Journal = {Int J Comput Assist Radiol Surg.},
Year = {(2011).},
Volume = {6.},
Number = {(1),},
Pages = {93-101},
Doi = {10.1007/s11548-010-0424-9},
Abstract = {Objective: Recently, radiosurgical treatment of cardiac arrhythmia, especially atrial fibrillation, has been proposed. Using the CyberKnife, focussed radiation will be used to create ablation lines on the beating heart to block unwanted electrical activity. Since this procedure requires high accuracy, the inevitable latency of the system \(i.e., the robotic manipulator following the motion of the heart\) has to be compensated for. Materials and methods: We examine the applicability of prediction algorithms developed for respiratory motion prediction to the prediction of pulsatory motion. We evaluated the MULIN, nLMS, wLMS, SVRpred and EKF algorithms. The test data used has been recorded using external infrared position sensors, 3D ultrasound and the NavX catheter systems. Results With this data, we have shown that the error from latency can be reduced by at least 10 and as much as 75\% \(44\% average\), depending on the type of signal. It has also been shown that, although the SVRpred algorithm was successful in most cases, it was outperformed by the simple nLMS algorithm, the EKF or the wLMS algorithm in a number of cases. Conclusion: We have shown that prediction of cardiac motion is possible and that the algorithms known from respiratory motion prediction are applicable. Since pulsation is more regular than respiration, more research will have to be done to improve frequency\-tracking algorithms, like the EKF method, which performed better than expected from their behaviour on respiratory motion traces}
}
@inproceedings{F11a,
Author = {F. Ernst and R. Bruder and A. Schlaefer and A. Schweikard},
Title = {Performance Measures and Pre-Processing for Respiratory Motion Prediction.},
Journal = {53rd Annual Meeting of the AAPM.},
Year = {(2011).},
Volume = {38.},
Number = {(6),},
Pages = {3857},
Booktitle = {53rd Annual Meeting of the AAPM},
Doi = {10.1118/1.3613523},
Abstract = {Purpose: Much research has been done on prediction of respiratory motion traces for motion compensation in radiotherapy. Unfortunately, the results of different groups cannot be compared easily due to different standards in preprocessing and analysis of the results. Furthermore, it has been speculated that the typically used measure for prediction quality, the RMS error, is not sufficient alone. Methods: We propose a set of guidelines for signal preprocessing (i.e., for scaling, detrending, resampling, and denoising) as well as measures for the analysis of the prediction results. The latter complement the RMS error with confidence intervals, the signal\'s smoothness (called jitter) and a measure for the periodicity of the error (called frequency content). Additionally, we have developed an extendable cross?platform prediction toolkit for easy analysis of prediction algorithms. Results: We found that very different signals (corrupted by noise, scaled by a constant factor, delayed in time, and scaled by random factors for each respiratory period) feature the exact same RMS error when compared to the original signal. The fundamental difference in the error signals can only be determined when using spectral measures, like the frequency content. Conclusion: Using the guidelines developed, the proposed evaluation measures, as well as the publicly available prediction toolkit, should help the community in establishing a better understanding for the capabilities and shortcomings of individual prediction methods. Additionally, it should allow others to more readily compare newly developed methods to already published algorithms. In the future, it would be desirable to also create a database of motion traces from various sources. If these signals would represent the characteristics of motion traces observed in the clinic, it could serve as a general benchmark for the quality of algorithms for motion prediction}
}
@inproceedings{BS11a,
Author = {F. Ernst and R. Bruder and A. Schlaefer and A. Schweikard},
Title = {Validating an SVR-based correlation algorithm on human volumetric ultrasound data.},
Journal = {Proceedings of the 25th International Congress and Exhibition on Computer Assisted Radiology and Surgery (CARS’11),.},
Year = {(2011).},
Volume = {6.},
Number = {(S1),},
Pages = {59-60},
Edition = {Proceedings of the 25th International Congress and Exhibition on Computer Assisted Radiology and Surgery (CARS'11) Volume 6 of International Journal of Computer Assisted Radiology and Surgery , page accepted.},
Booktitle = {Computer Assisted Radiology and Surgery (CARS)}
}
@inproceedings{GMBSHS11a,
Author = {F. Gasca and L. Marshall and S. Binder and A. Schlaefer and U.G. Hofmann and A. Schweikard},
Title = {Finite element simulation of transcranial current stimulation in realistic rat head model.},
Journal = {Proceedings of the 5th International IEEE EMBS Conference on Neural Engineering.},
Year = {(2011).},
Pages = {36-39},
Address = {Cancun, Mexico},
Booktitle = {5th International IEEE/EMBS Conference on Neural Engineering (NER)},
Organization = {5th International IEEE/EMBS Conference on Neural Engineering (NER)},
Doi = {10.1109/NER.2011.5910483},
Url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=5910483},
Abstract = {Transcranial current stimulation (tCS) is a method for modulating neural excitability and is used widely for studying brain function. Although tCS has been used on the rat, there is limited knowledge on the induced electric field distribution during stimulation. This work presents the finite element (FE) simulations of tCS in a realistic rat head model derived from MRI data. We simulated two electrode configurations and analyzed the spatial focality of the induced electric field for three implantation depth scenarios: (1) electrode implanted at the surface of the skull, (2) halfway through the skull and (3) in contact with cerebrospinal fluid. We quantitatively show the change in focality of stimulation with depth. This work emphasizes the importance of performing FE analysis in realistic models as a vital step in the design of tCS rat experiments. This can yield a better understanding of the location and intensity of stimulation, and its correlation to brain function.}
}
@inproceedings{H11a,
Author = {H. Hadjar and R. Friedl and H.-H. Sievers and P. Hunold and B. Stender and A. Schlaefer},
Title = {Surgical planning tool for the simulation of the aortic valve-sparing surgery.},
Journal = {Computer Assisted Radiology and Surgery (CARS).},
Year = {(2011).},
Address = {Berlin},
Booktitle = {Computer Assisted Radiology and Surgery (CARS)}
}
@article{RESS11a,
Author = {L. Richter and F. Ernst and A. Schlaefer and A. Schweikard},
Title = {Robust real-time robot-world calibration for robotized transcranial magnetic stimulation.},
Journal = {Int J Med Robot.},
Year = {(2011).},
Volume = {7.},
Number = {(4),},
Pages = {414-422},
Doi = {10.1002/rcs.411},
Abstract = {Background: For robotized transcranial magnetic stimulation (TMS), the magnetic coil is placed on the patient\'s head by a robot. As the robotized TMS system requires tracking of head movements, robot and tracking camera need to be calibrated. However, for robotized TMS in a clinical setting, such calibration is required frequently. Mounting/unmounting a marker to the end effector and moving the robot into different poses is impractical. Moreover, if either system is moved during treatment, recalibration is required. Methods: To overcome this limitation, we propose to directly track a marker at link three of the articulated arm. Using forward kinematics and a constant marker transform to link three, the calibration can be performed instantly. Results: Our experimental results indicate an accuracy similar to standard hand-eye calibration approaches. It also outperforms classical hand-held navigated TMS systems. Conclusion: This robust online calibration greatly enhances the system\'s user-friendliness and safety}
}
@article{L11a,
Author = {L. Richter and F. Ernst and A. Schlaefer and A. Schweikard},
Title = {Robust robot-camera calibration for robotized Transcranial Magnetic Stimulation.},
Journal = {The International Journal of Medical Robotics and Computer Assisted Surgery.},
Year = {(2011).},
Volume = {7.},
Pages = {414-422},
Doi = {10.1002/rcs.411},
Abstract = {Background: For robotized transcranial magnetic stimulation (TMS), the magnetic coil is placed on the patient\'s head by a robot. As the robotized TMS system requires tracking of head movements, robot and tracking camera need to be calibrated. However, for robotized TMS in a clinical setting, such calibration is required frequently. Mounting/unmounting a marker to the end effector and moving the robot into different poses is impractical. Moreover, if either system is moved during treatment, recalibration is required. Methods: To overcome this limitation, we propose to directly track a marker at link three of the articulated arm. Using forward kinematics and a constant marker transform to link three, the calibration can be performed instantly. Results: Our experimental results indicate an accuracy similar to standard hand-eye calibration approaches. It also outperforms classical hand-held navigated TMS systems. Conclusion: This robust online calibration greatly enhances the system\'s user-friendliness and safety}
}
@inproceedings{HGGDHT11a,
Author = {M. Heinig and M.F. Govela and F. Gasca and C. Dold and U.G. Hofmann and V. Tronnier and A. Schlaefer and A. Schweikard},
Title = {MARS - Motor assisted robotic stereotaxy system.},
Journal = {Proceedings of the 5th International IEEE EMBS Conference on Neural Engineering.},
Year = {(2011).},
Pages = {334-337},
Address = {Cancun, Mexico},
Booktitle = {Proceedings of the 5th International IEEE EMBS Conference on Neural Engineering},
Doi = {10.1109/NER.2011.5910555},
Url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=5910555},
Abstract = {We report on the design, setup and first results of a robotized system for stereotactic neurosurgery. It features three translational and two rotational axes, as well as a motorized MicroDrive, thereby resembling the Zamorano-Duchovny (ZD) design of stereotactic frames (inomed Medizintechnik GmbH). Both rotational axes intersect in one point, the Center of the Arc, facilitating trajectory planning. We used carbon fiber-reinforced plastic to reduce the weight of the system. The robot can be mounted to standard operating table\'s side rails and can be transported on an operation theatre (OT) instrument table. We discuss the design paradigms, the resulting design and the actual robot. Kinematic calculations for the robot based on the Denavit-Hartenberg (DH) rules are presented. Positioning accuracy of our system is determined using two perpendicular cameras mounted on an industrial robot. The results are compared to a manual ZD system. We found that the robot\'s mean position deviation is 0.231 mm with a standard deviation of 0.076 mm}
}
@inproceedings{M11a,
Author = {M. Heinig and O. Christ and V. Tronnier and U.G. Hofmann and A. Schlaefer and A. Schweikard},
Title = {Electromagnetic noise measurement of the Motor Assisted Robotic Stereotaxy System (MARS).},
Journal = {Proceedings of the 4th Hamlyn Symposium on Medical Robotics.},
Year = {(2011).},
Number = {(4),},
Pages = {63-64},
Booktitle = {Proceedings of the 4th Hamlyn Symposium on Medical Robotics}
}
@inproceedings{N11a,
Author = {N. Ammann and F. Hartmann and P. Jauer and J. Krüger and T. Meyer and R. Bruder and A. Schlaefer},
Title = {Global data storage for collision avoidance in robotic sailboat racing ? the World Server Approach.},
Journal = {4th International Robotic Sailing Conference.},
Year = {(2011).},
Booktitle = {4th International Robotic Sailing Conference}
}
@inproceedings{O11b,
Author = {O. Shahin and V. Martens and A. Beširevic and M. Kleemann and A. Schlaefer},
Title = {Intraoperative tumor localization in laparoscopic liver surgery.},
Journal = {Proceedings of the Joint Workshop on New Technologies for Computer/Robot Assisted Surgery.},
Year = {(2011).},
Booktitle = {Proceedings of the Joint Workshop on New Technologies for Computer/Robot Assisted Surgery}
}
@conference{R11a,
Author = {R. Bruder and F. Ernst and A. Schlaefer and A. Schweikard},
Title = {A Framework for Real-Time Target Tracking in Radiosurgery using Three-dimensional Ultrasound.},
Journal = {Computer Assisted Radiology and Surgery (CARS).},
Year = {(2011).},
Pages = {306-307},
Booktitle = {Computer Assisted Radiology and Surgery (CARS)}
}
@conference{T11a,
Author = {T. Viulet and N. Rzezovski and A. Schlaefer},
Title = {Towards interactive planning for radiotherapy by three-dimensional iso-dose manipulation.},
Journal = {Proceedings of the 25th International Conference and Exhibition on Computer Assisted Radiology and Surgery (CARS'11)oin AAPM/COMP Meeting.},
Year = {(2011).},
Booktitle = {Proceedings of the 25th International Conference and Exhibition on Computer Assisted Radiology and Surgery (CARS'11) on AAPM/COMP Meeting}
}
@article{T11b,
Author = {T. Viulet and N. Rzezovski and A. Schlaefer},
Title = {Three-Dimensional Isodose Surface Manipulation for Multi-Criteria Inverse Planning in Radiosurgery.},
Journal = {Medical Physics.},
Year = {(2011).},
Volume = {38.},
Number = {(3371),},
Edition = {oin AAPM/COMP Meeting},
Booktitle = {Annual Meeting of the AAPM},
Doi = {10.1118/1.3611475},
Abstract = {Purpose: Traditionally, the planning task for radiotherapy offers the human planner little direct spatial control of the dose distribution. Dose painting methods exist, but they typically suffer from side effects, such as uncontrolled spilling of dose. We developed a tool that allows for local three-dimensional isodose surface manipulation which avoids this problem by employing constrained optimization and inverse planning. Methods: In our approach, the planner operates directly on the three-dimensional dose distribution, e.g., selecting areas to be covered with a certain iso-dose surface. The underlying mathematical model implementing constrained inverse planning prevents dose from shifting into areas that are not explicitly selected. To move towards a desired clinical goal, e.g., coverage of the target, the planner directly controls where to operate trade-offs. First, a local objective is set graphically. Second, the potential trade-offs are visualized. Third, the planner selects where to relax constraints. Notably, the relaxation steps imply quick re-optimization in an interactive manner. We studied the use of the tool for a clinical case, where initially tight bounds on critical structures prevent sufficient target coverage. The dose bounds are then relaxed in specific areas, i.e., shaping the isodose surfaces in a controlled way. Results: Our experiments show that local isodose manipulation is possible, with little to no dose shifting. Outside the local target area, constraints stay in place and maintain the dose distribution. When the isodose surface is deliberately remodeled to relax constraints the some areas, the coverage of the target area is improved. Initial optimization times are below 40 seconds while re-optimization is done in less than 5 seconds. Conclusions: The planning tool implements a novel approach to interactively shape the dose distribution, which would be of particular interest in radiosurgical planning with steep gradients. Our results illustrate that interactive multi-criteria planning in the dose space is feasible.}
}
@Inbook{A10a,
Author = {A. Schlaefer and A. Schweikard},
Title = {Robotiksysteme für die Radiochirurgie.},
Journal = {Computerassistierte Chirurgie.},
Year = {(2010).},
Number = {(Kapitel 16),},
Editor = {In Peter Michael Schlag, Sebastian Eulenstein, Thomas Lange (Hrsg.) (Eds.)},
Publisher = {Elsevier:},
Isbn = {9783437248801},
Booktitle = {Computerassistierte Chirurgie},
Url = {https://www.123library.org/ebook/isbn/9783437593260/},
Abstract = {Das Buch stellt die computerassistierte Chirurgie erstmals in deutscher Sprache grundlegend und umfassend dar. Im ersten Teil werden alle wesentlichen Grundlagen über alle chirurgischen Fachgebiete hinweg behandelt, u.a. Visualisierung, computerassistierte Chirurgieplanung, Lokalisierungssysteme, roboterassistierte minimal-invasive Chirurgie, Analyse und Beschreibung chirurgischer Workflows und Bewertung der Mensch-Maschine-Interaktion. Der zweite Teil beschreibt die klinischen Fragestellungen, Lösungsansätze und bisherigen Erfahrungen in den jeweiligen chirurgischen Fachgebieten. Der Code im Buch schaltet zusätzliche Inhalte im Internet frei: Videos zur virtuellen OP-Planung und zur klinischen Anwendung}
}
@inproceedings{AK10a,
Author = {A. Schlaefer and C. Otte and R. Ansari and G. Hüttmann and L. Richter and R. Bruder and M. Heinig and M. Sommerauer and G. Kovacs},
Title = {Towards high resolution image guided navigation for prostate brachytherapy.},
Journal = {International Journal of Computer Assisted Radiology and Surgery.},
Year = {(2010).},
Volume = {5.},
Number = {(1),},
Pages = {24-25},
Month = {June},
Address = {Geneva, Switzerland},
Booktitle = {Proceedings of the 24th International Conference and Exhibition on Computer Assisted Radiology and Surgery (CARS'10)}
}
@conference{A10b,
Author = {A. Schlaefer and T. Wolschon},
Title = {Optimizing the Trade-Off Between Number of Beam Starting Points and Plan Quality in Robotic Radiosurgery.},
Journal = {XVIth International Conference on the Use of Computers in Radiation Therapy (ICCR).},
Year = {(2010).},
Booktitle = {XVIth International Conference on the Use of Computers in Radiation Therapy (ICCR)}
}
@conference{B10a,
Author = {B. Stender and A. Schlaefer},
Title = {Handling and detecting motion in electrical impedance tomography.},
Year = {(2010).}
}
@article{FDKMWS10a,
Author = {C. Fürweger and C. Drexler and M. Kufeld and A. Muacevic and B. Wowra and A. Schlaefer},
Title = {Patient motion and targeting accuracy in robotic spinal radiosurgery: 260 single-fraction fiducial-free cases.},
Journal = {Int J Radiat Oncol Biol Phys.},
Year = {(2010).},
Volume = {78.},
Number = {(3),},
Pages = {937-945},
Booktitle = {Int J Radiat Oncol Biol Phys},
Doi = {10.1016/j.ijrobp.2009.11.030},
Abstract = {Purpose: The CyberKnife\™ compensates translational target motion by moving the beams synchronously. While the system was found to operate with sub-millimeter accuracy in phantoms, determining the clinical accuracy is challenging. Measuring the delivered dose distribution inside a patient is impractical. Hence an analysis of treatment data is typically used to estimate residual errors. Methods: We implant 3-5 fiducials for target tracking and treat livertumors in 3-5 fractions with 45Gy at 80% to the PTV (CTV+3mm). Patients are aligned based on X-ray images in expiration breath hold. During delivery, X-ray images are acquired every 60-90s, and the translational and rotational misalignment is computed. We grouped this data into 10 respiratory phases. The mean misalignment for each phase was used to simulate the translation and rotation of the target with respect to the alignment center. The resulting dose distribution was computed and compared to the planned dose. Additionally, the quality of motion prediction was evaluated. Results: We analyzed 5 cases with a total of 17 fractions. The maximal target motion per fraction ranged from 9.2mm to 25.7mm (3D trajectory). The mean error for each patient ranged from -0.76/-0.01/- 0.32mm to 0.35/0.17/0.10mm (Translation IS/LR/AP) and -0.94/-0.82/-2.07 degrees to 0.24/1.95/2.36 degrees (Rotation roll/pitch/yaw). The dose simulation showed point dose difference for each patient ranging from - 0.10Gy to -0.76Gy (Mean) and -1.13Gy to -5.05Gy (Max). The resulting reduction in coverage ranged from 0.37% to 4.19% (PTV) and -0.43% to +0.94% (CTV). Finally, the mean prediction error over all fractions was 0.33mm. Conclusions: We demonstrated that while maximum point dose differences can be considerable, the coverage of the CTV is maintained even in the presence of substantial respiratory motion. The results indicate that the standard 3mm system uncertainty margin can account for errors due to rotation and deformation during roboticradiosurgery for tumors in the liver}
}
@conference{C10a,
Author = {C. Otte and R. Ansari and G. Hüttmann and A. Schlaefer},
Title = {Bildverarbeitung für die OCT-Navigation in Weichgewebe.},
Year = {(2010).},
Booktitle = {Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik (BMT)}
}
@inproceedings{F10a,
Author = {F. Ernst and B. Stender and A. Schlaefer and A. Schweikard},
Title = {Using ECG in Motion Prediction for Radiosurgery of the Beating Heart.},
Journal = {The Hamlyn Symposium on Medical Robotics.},
Year = {(2010).},
Volume = {3.},
Pages = {37-38},
Address = {The Royal Society, London},
Booktitle = {The Hamlyn Symposium on Medical Robotics}
}
@conference{EBSS10a,
Author = {F. Ernst and R. Bruder and A. Schlaefer and A. Schweikard},
Title = {Improving the quality of biomedical signal tracking using prediction algorithms.},
Journal = {UKACC International Conference on CONTROL 2010.},
Year = {(2010).},
Pages = {301-305},
Month = {September},
Booktitle = {UKACC International Conference on CONTROL 2010},
Doi = {10.1049/ic.2010.0298},
Url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=6490756},
Abstract = {The use of optical and magnetical tracking systems is widely spread throughout modern operating theatres. One thing that is not taken into account so far is the fact that all systems which need to make two or more sequential measurements to determine an object\'s pose will exhibit systematic measurement errors. These errors can be attributed on the nonsimultaneous acquisition process. We have analysed this problem for the atracsys accuTrack system which is an optical tracking system using three line cameras. Using robotised and manual experiments we found that, using a marker with four LEDs at a single LED acquisition rate of 331.04 Hz, these errors can be as much as 1.4 mm and 2.1\° (RMS). With lower acquisiton rates which are commonplace in other tracking systems\-these errors are expected to be even higher. Using the proposed compensation methods, they may be reduced to as little as 0.2 mm and 0.6\° (RMS), respectively.}
}
@conference{F10b,
Author = {F. Ernst and R. Bruder and M. Pohl and A. Schlaefer and A. Schweikard},
Title = {Prediction of Cardiac Motion.},
Journal = {Proceedings of the 24th International Conference and Exhibition on Computer Assisted Radiology and Surgery (CARS'10).},
Year = {(2010).},
Volume = {5.},
Number = {(1),},
Pages = {273-274},
Booktitle = {Proceedings of the 24th International Conference and Exhibition on Computer Assisted Radiology and Surgery (CARS'10)}
}
@inproceedings{RMSS10a,
Author = {L. Richter and L. Matthäus and A. Schlaefer and A. Schweikard
},
Title = {Fast robotic compensation of spontaneous head motion during Transcranial Magnetic Stimulation (TMS).},
Journal = {UKACC International Conference on CONTROL 2010.},
Year = {(2010).},
Pages = {1-6},
Booktitle = {UKACC International Conference on CONTROL 2010},
Doi = {10.1049/ic.2010.0396},
Url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=6490854},
Abstract = {As Transcranial Magnetic Stimulation (TMS) is spreading fast in neurology and neuroscience, advanced techniques for TMS are required. A robotized system is used for precise and repeatable TMS. The system is based on a serial industrial robot and an infrared tracking system for permanent position tracing of the head. For enhanced precision, a motion compensation module counterbalances head motions during stimulation. This avoids rigid fixations of the patient and leads to increased convenience and significant stress reduction. The motion compensation deals with two main scenarios: While the robot approaches the target point, the trajectory has to be adapted when the head moves. Once the point is reached, the robot keeps the coil at the given target position relative to the head. For safe robot operations around the patient\'s head, a metric is used that restricts big joint changes. Furthermore, a running average is used to compensate jitter in the tracking measurements. As a specific extension of the motion compensation method for TMS, an online coil pose adaptation and a manual coil placement are integrated. Our results have shown that the motion compensation latency is about 110 ms. The associated compensation is about 200 ms. Hence, the original position relative to the head will be re\-established within about 300 ms. Our recent clinical trials for rTMS have practically proved that the motion compensation method is sufficient for medical applications}
}
@inproceedings{L10a,
Author = {L. Richter and R. Bruder and A. Schlaefer},
Title = {Proper Force-Torque Sensor System for robotized TMS: automatic coil calibration.},
Journal = {Proceedings of the 24th International Conference and Exhibition on Computer Assisted Radiology and Surgery (CARS'10).},
Year = {(2010).},
Volume = {5.},
Number = {(1),},
Pages = {422-423},
Address = {Geneva, Switzerland},
Booktitle = {Proceedings of the 24th International Conference and Exhibition on Computer Assisted Radiology and Surgery (CARS'10)}
}
@inproceedings{RBSS10a,
Author = {L. Richter and R. Bruder and A. Schlaefer and A. Schweikard},
Title = {Towards direct head navigation for robot-guided transcranial magnetic stimulation using 3D laserscans: idea, setup and feasibility.},
Journal = {Conf Proc IEEE Eng Med Biol Soc.},
Year = {(2010).},
Pages = {2283-2286},
Booktitle = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society},
Doi = {10.1109/IEMBS.2010.5627660},
Abstract = {Direct tracking is more robust than tracking that is based on additional markers. 3D laser scans can be used for direct tracking because they result in a 3D data set of surface points of the scanned object. For head\-navigated robotized systems, it is crucial to know where the patient\'s head is positioned relatively to the robot. We present a novel method to use a 3D laserscanner for direct head navigation in the robotized TMS system that places a coil on the patient\'s head using an industrial robot. First experimental results showed a translational error <= 2mm in the robot hand\-eye\-calibration with the laserscanner. The rotational error was 0.75\° and the scaling error <= 0.001. Furthermore, we found that the error of a scanned head to a reference head image was <= 0.2mm using ICP. These results have shown that a direct head navigation is feasible for the robotized TMS system. Additional effort has to be made in future systems to speed up the compution time for real time capability}
}
@conference{M10a,
Author = {M. Finke and B. Stender and R. Bruder and A. Schlaefer and A. Schweikard},
Title = {An experimental comparison of control devices for automatic movements of a surgical microscope.},
Year = {(2010).},
Booktitle = {Computer Assisted Radiology and Surgery (CARS)}
}
@inproceedings{HSS10b,
Author = {M. Heinig and A. Schlaefer and A. Schweikard},
Title = {3D localization of ferromagnetic probes for small animal neurosurgery.},
Journal = {Engineering in Medicine and Biology Society (EMBC), 2010 Annual International Conference of the IEEE.},
Year = {(2010).},
Pages = {2321-2324},
Doi = {10.1109/IEMBS.2010.5627435},
Url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=5627435},
Abstract = {We present the design, setup and results for a magnetic navigation system for small animal stereotactic neurosurgery. Our system tracks the position of thin (diameter 0.5 mm), magnetized ferromagnetic probes inserted into brains of small animals, e.g. rats, for electrophysiological recordings. It is used in combination with the spherical assistant for stereotactic surgery (SASSU) robot to obtain online feedback of the probe\'s position. Navigation is based only on the static magnetic field generated by the probes thus no external excitation or wires are needed. The magnetic field created by the probe is measured by three sensors and compared to data of a previously generated lookup table. To account for overlaying magnetic fields (e.g earth\'s field), we determine and adjust for the magnetic background. A nearest neighbor approach is used to identify the best element of the lookup table. The actual position of the probe is found using trilinear interpolation between the best element and its neighbors. To validate the system, the workspace was filled with gelatin to simulate brain\-like, organic structure. Next, several positions were approached by the robot. The difference between the ground truth position and the position determined by the system was calculated. We found that the norm of the mean values are between 0.09 mm and 0.64 mm with a norm of the standard deviation between 0.52 mm and 0.80 mm. No substantial difference between gelatin and non\-gelatin data was observed. Our approach allows the online validation of the probe\'s position in X\-,Y and Z\-axis. We conclude that accurate localization of small ferromagnetic objects is feasible with our system. Currently, we are working on further applications including the use in human surgery, e.g. dermatology}
}
@inproceedings{HBSS10a,
Author = {M. Heinig and R. Bruder and A. Schlaefer and A. Schweikard},
Title = {3D localization of a thin steel rod using magnetic field sensors: feasibility and preliminary results.},
Journal = {4th Int. Conf. Bioinformatics and Biomedical Engineering (iCBBE), 2010.},
Year = {(2010).},
Pages = {1-4},
Address = {Chengdu},
Isbn = {978-1-4244-4713-8},
Booktitle = {4th Int. Conf. Bioinformatics and Biomedical Engineering (iCBBE), 2010},
Doi = {10.1109/ICBBE.2010.5515423},
Url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=5515423},
Abstract = {We present the design, setup and preliminary results for a navigation system based on magnetic field sensors. Our system localizes the tip of a magnetized steel rod with diameter 0.5 mm in a cubic workspace with 30 mm edge length. We plan to localize electrodes and probes during surgeries, e.g. for small animal research like neurosurgery in rats. Only the static magnetic field of the steel rod is needed for localization. Our navigation system does not need any external excitation, wires or alternating magnetic fields. Hence, we avoid undesirable stimulation of the animal\'s brain and we are able to realize small (0.5 mm) probe diameters to reduce brain damage. Localization of the steel rod\'s tip is achieved using a nearest neighbor approach. The currently measured sensor values are compared to data stored in a previously generated lookup table. An industrial robot is used to create the lookup table and later to validate the accuracy of the system. Currently, the system has 3 degrees of freedom (DOF). Mean of the difference between true and determined position is \-0.53; 0.31; \-0.95 [mm] with a standard deviation of 1.13; 1.24; 0.99 [mm] in XYZ, or lower. The influence of different noise sources, e.g. electric currents or metal, on the performance of the system are discussed}
}
@conference{N10b,
Author = {N. Ammann and F. Hartmann and P. Jauer and R. Bruder and A. Schlaefer},
Title = {Design of a robotic sailboat for WRSC/SailBot.},
Journal = {International Robotic Sailing Conference.},
Year = {(2010).},
Pages = {40-42}
}
@conference{N10a,
Author = {N. Ammann and R. Biemann and F. Hartmann and C. Hauft and I. Heinecke and P. Jauer and J. Krüger and T.Meyer and R. Bruder and A. Schlaefer},
Title = {Towards autonomous one-design sailboat racing: navigation, communication and collision avoidance.},
Year = {(2010).}
}
@conference{V10a,
Author = {V. Martens and O. Shahin and A. Beširevic and A. Schlaefer},
Title = {A combined surface and ultrasound image approach for registration in laparoscopic liver surgery.},
Year = {(2010).},
Volume = {5.},
Number = {(1),},
Pages = {285-287},
Month = {June},
Booktitle = {Proceedings of the 24th International Conference and Exhibition on Computer Assisted Radiology and Surgery (CARS 2010)}
}
@inproceedings{S09a,
Author = {A. Schlaefer},
Title = {Workflow-Based Treatment Planning for Robotic Radiosurgery.},
Journal = {Int J CARS 4 (Suppl 1).},
Year = {(2009).},
Pages = {22},
Booktitle = {23st International Congress and Exhibition Computer Assisted Radiology and Surgery CARS'2009},
Organization = {Computer Assisted Radiology and Surgery (CARS)}
}
@conference{A09b,
Author = {A. Schlaefer and D. Ruan and S. Dieterich and W. Kilby},
Title = {A linear implementation of dose-volume constraints for multi-criteria optimization.},
Journal = {Medical Physics and Biomedical Engineering World Congress.},
Year = {(2009).},
Volume = {25.},
Number = {(1),},
Pages = {IFMBE Proceedings 322-325},
Month = {September},
Address = {Munich},
Abstract = {Dose-volume constraints are widely used in inverse planning for radiation therapy. Given the intricate combinatorial nature of the problem, existing approaches suffer from long runtimes, insufficient approximation of the constraints, or the necessity to specify reasonable starting values a priori. This can be problematic, particularly when planning is considered as a multi-criteria optimization problem. We present a new method to handle dose-volume constraints during planning for robotic radiosurgery. Taking into account the typically very conformal nature of the resulting dose distributions, we specify the constraints on a small subset of points instead of the full volume. We show how this allows for an effective relaxation of the problem. Results for a prostate case indicate that the proposed method leads to good approximations of the dose-volume constraints and is independent of the optimization objective.}
}
@conference{C09a,
Author = {C. Fürweger and A. Schlaefer and C. Drexler},
Title = {Robotic radiosurgery with fiducial-free tracking: patient motion and targeting precision in 227 spinal cases.},
Journal = {10th Biennial ESTRO Conference on Physics and Radiation Technology for Clinical Radiotherapy.},
Year = {(2009).},
Volume = {92.},
Number = {(1),},
Pages = {34},
Doi = {10.1016/S0167-8140(12)72675-0}
}
@conference{C09b,
Author = {C. Fürweger and M. Kufeld and A. Schlaefer and C. Drexler},
Title = {Fiducial-free spinal radiosurgery: Patient motion and targeting accuracy in 227 single fraction treatments with the Cyberknife.},
Journal = {World Congress on Medical Physics and Biomedical Engineering IFMBE Proceedings.},
Year = {(2009).},
Volume = {25.},
Number = {(1),},
Pages = {277-280},
Month = {September},
Abstract = {Objective: To evaluate clinical targeting precision in fiducial\-free spinal treatments with a robotic radiosurgery system (Cyberknife). Methods: For assessment of spine tracking system performance, we conducted phantom tracking tests on cervical and thoracic vertebrae. We retrospectively evaluated intrafraction patient movement for cervical (47), thoracic (90) and lumbar (90) treatments. A conservative measure for the expected targeting error due to patient motion was derived. Results: The phantom tests show that spinal targets are detected with an accuracy of \<0.2 mm for the translational and \<0.3\° for the rotational directions. The mean targeting error per beam due to residual patient motion is determined to be as low as 0.28+/\-0.13 mm (X), 0.25+/\-0.15 mm (Y), 0.19+/\-0.11 mm (Z) for translational shifts and 0.40+/\-0.20\° (roll), 0.20+/\- 0.08\° (pitch) and 0.19+/\-0.08\° (yaw) for rotations. Interestingly, the tracked spine section is of little significance for the overall targeting error due to motion, which is below 1 mm for more than 95\% of our spinal treatments (median: 0.48 mm). Conclusions: We could demonstrate that image\-guided spinal radiosurgery with the Cyberknife allows for submillimeter precision in treatment delivery despite of patient motion}
}
@conference{E09a,
Author = {E. Lessard and W. Kilby and J. Dooley and C. Sims and A. Schlaefer and O. Blanck and C. Maurer},
Title = {Sequential Optimization Scripts to Facilitate Treatment Planning for Robotic Radiosurgery Clinical Studies for Prostate and Lung Cancers.},
Journal = {World Congress on Medical Physics and Biomedical Engineering IFMBE Proceedings.},
Year = {(2009).},
Volume = {25.},
Number = {(1),},
Pages = {1031-1034},
Booktitle = {Medical Physics and Biomedical Engineering World Congress},
Abstract = {Sequential Optimization, which features a scriptable optimization process, is the latest inverse planning tool available for robotic radiosurgery. The purpose of this study was to create and evaluate Sequential Optimization scripts to facilitate the treatment planning for clinical studies for radiosurgery treatment of prostate and lung cancer. Four sample scripts were designed to generate treatment plans according to the clinical objectives defined in current prostate and lung cancer protocols. The scripts were evaluated using a group of 10 prostate cancer cases and 10 lung cancer cases with tumors of various sizes and shapes. The scripts generated treatment plans with dose distributions within minor variations defined by the protocols for most cases and provided good starting points for the challenging cases}
}
@article{EKLESS09a,
Author = {G. G. Echner and W. Kilby and M. Lee and E. Earnst and S. Sayeh and A. Schlaefer and B. Rhein and J. R. Dooley and C. Lang and O. Blanck and E. Lessard and C. R. Maurer Jr and W. Schlegel},
Title = {The design, physical properties and clinical utility of an iris collimator for robotic radiosurgery.},
Journal = {Phys Med Biol.},
Year = {(2009).},
Volume = {54.},
Number = {(18),},
Pages = {5359-5380},
PMID = {19687567},
Doi = {10.1088/0031-9155/54/18/001},
Abstract = {Robotic radiosurgery using more than one circular collimator can improve treatment plan quality and reduce total monitor units (MU). The rationale for an iris collimator that allows the field size to be varied during treatment delivery is to enable the benefits of multiple-field-size treatments to be realized with no increase in treatment time due to collimator exchange or multiple traversals of the robotic manipulator by allowing each beam to be delivered with any desired field size during a single traversal. This paper describes the Iris variable aperture collimator (Accuray Incorporated, Sunnyvale, CA, USA), which incorporates 12 tungsten-copper alloy segments in two banks of six. The banks are rotated by 30 degrees with respect to each other, which limits the radiation leakage between the collimator segments and produces a 12-sided polygonal treatment beam. The beam is approximately circular, with a root-mean-square (rms) deviation in the 50% dose radius of <0.8% (corresponding to <0.25 mm at the 60 mm field size) and an rms variation in the 20-80% penumbra width of about 0.1 mm at the 5 mm field size increasing to about 0.5 mm at 60 mm. The maximum measured collimator leakage dose rate was 0.07%. A commissioning method is described by which the average dose profile can be obtained from four profile measurements at each depth based on the periodicity of the isodose line variations with azimuthal angle. The penumbra of averaged profiles increased with field size and was typically 0.2-0.6 mm larger than that of an equivalent fixed circular collimator. The aperture reproducibility is < or =0.1 mm at the lower bank, diverging to < or =0.2 mm at a nominal treatment distance of 800 mm from the beam focus. Output factors (OFs) and tissue-phantom-ratio data are identical to those used for fixed collimators, except the OFs for the two smallest field sizes (5 and 7.5 mm) are considerably lower for the Iris Collimator. If average collimator profiles are used, the assumption of circular symmetry results in dose calculation errors that are <1 mm or <1% for single beams across the full range of field sizes; errors for multiple non-coplanar beam treatment plans are expected to be smaller. Treatment plans were generated for 19 cases using the Iris Collimator (12 field sizes) and also using one and three fixed collimators. The results of the treatment planning study demonstrate that the use of multiple field sizes achieves multiple plan quality improvements, including reduction of total MU, increase of target volume coverage and improvements in conformality and homogeneity compared with using a single field size for a large proportion of the cases studied. The Iris Collimator offers the potential to greatly increase the clinical application of multiple field sizes for robotic radiosurgery}
}
@conference{M09a,
Author = {M. Heinig and A. Schlaefer and A. Schweikard},
Title = {Super resolution in Optical Coherence Tomography (OCT).},
Journal = {Medical Physics and Biomedical Engineering World Congress.},
Year = {(2009).},
Address = {Munich},
Booktitle = {Medical Physics and Biomedical Engineering World Congress},
Abstract = {Introduction: Optical Coherence Tomography (OCT) is a commonly used imaging technology in medicine, for example in ophthalmology, dermatology and urology. Some applications would benefit from higher spatial resolution and speckle noise reduction. We present a robust and effective method to enhance spatial resolution in OCT. The proposed method also reduces the inherent speckle noise. Materials and Methods: The probe of a Thorlabs FD-OCT spectral radar (frequency 1.2kHz, resolution 6.2um) was mounted on a piezo XY stage, pointing in direction of the X-axis. To acquire images, the probe was moved stepwise in longitudinal direction. Every step moved the probe a forth of the spatial resolution of the OCT system. After each step data was gathered from the OCT and stored at the appropriate position of the so called virtual detector array (VDA). The VDA’s data was processed by a super-resolution algorithm. Data for the same depth in the tissue was averaged to account for speckle noise. The resulting 1D image was low-pass filtered, yielding a low noise image at twice the resolution of the OCT system. To acquire 2D images, the probe was moved along the lateral direction using the piezo stage. Results: Canvas tape was used as phantom to test the system. Spatial resolution of the Thorlabs FD-OCT spectral radar was doubled from 6.2um to 3.1um. Images were acquired with and without using the super-resolution algorithm. The results show that speckle noise is substantially reduced and spatial resolution of the image is effectively doubled. Conclusion: Applying super-resolution algorithms to OCT yields promising results in enhancing resolution. A second benefit is clearly visible reduction of speckle noise. We plan to test the presented approach with real tissue and in-vivo to study its potential use for micro-navigation, e.g., in neurosurgery}
}
@conference{O09a,
Author = {O. Witt and A. Schlaefer and L. Ramrath},
Title = {A fuzzy segmentation approach to white matter detection in optical coherence tomography.},
Year = {(2009).},
Volume = {4.},
Number = {(Suppl 1),},
Pages = {328-329},
Booktitle = {Poster Session of 23rd International Congress Computer Assisted Radiology and Surgery CARS'2009},
Doi = {10.1007/s11548-009-0343-9}
}
@conference{R09b,
Author = {R. Bruder and B. Stender and A. Schlaefer},
Title = {Model Sailboats as a Testbed for Artificial Intelligence Methods.},
Journal = {Proceedings of the 3rd International Robotics Sailing Conference.},
Year = {(2009).},
Address = {Kingston},
Booktitle = {International Robotic Sailing Conference},
Organization = {International Robotic Sailing Conference}
}
@article{R09a,
Author = {R. Bruder and F. Ernst and A. Schlaefer and A. Schweikard},
Title = {TH-C-304A-07: Real-Time Tracking of the Pulmonary Veins in 3D Ultrasound of the Beating Heart.},
Journal = {Medical Physics.},
Year = {(2009).},
Volume = {36.},
Number = {(6),},
Pages = {2804-2804},
Publisher = {Medical Physics:},
Doi = {10.1118/1.3182643},
Url = {http://scitation.aip.org/content/aapm/journal/medphys/36/6/10.1118/1.3182643},
Abstract = {Purpose: Currently effort is taken to use radiation therapy to cure heart diseases like arrhythmia. This approach requires high accuracy localisation and tracking of the pulmonary veins. Because of the high speed of motion of the heart, fluoroscopic tracking of fiducials or anatomical structures as in IGRT would on the one hand require high frame rates and, on the other hand, it would be dangerous to place fiducials near the target. We propose to use live 3D ultrasound to perform the landmark localization and tracking. Methods and materials: We have modified a GE Vivid7 dimension 3D cardiovascular ultrasound station for real\-time volume processing and target localisation. It is capable of providing ultrasound volume scans of the target region with more than 20 fps. A framework was established to upload and run image\-processing algorithms directly on the ultrasound machine which is necessary to handle the high amount of data. This prevents the bottleneck of Ethernet data streaming and external processing. We propose to localise the pulmonary veins using a template matching algorithm with multiple templates. Approximately 20 templates are manually generated during one heart beat cycle. To increase the speed and accuracy of the matching process, electrical pulse signals were recorded by the ultrasound station. This allows selecting two or three pulse?dependent templates in the live matching stage. Results: The accuracy of the localization process is highly dependent on the templates chosen. The best results were achieved providing a full heart cycle as template data. As a compromise between speed and accuracy, we used 9×9×9 points as template, corresponding to 4.5×4.5×4.5mm3. Conclusion: The presented approach is a new and robust approach to semi\-automatically track small substructures in the beating heart. Furthermore, the generated signal is suitable as input to numerous prediction algorithms currently used to compensate for breathing motion in radiosurgery}
}
@article{BESS09a,
Author = {R. Bruder and F. Ernst and A. Schlaefer and A. Schweikard},
Title = {THC-C-305A-07: Real-time PV tracking in 3D ultrasound of the beating heart.},
Journal = {Medical Physics.},
Year = {(2009).},
Volume = {36.},
Number = {(2804),},
Pages = {1116-1118},
Booktitle = {Medical Physics},
Doi = {10.1118/1.3182643},
Abstract = {Purpose: Currently effort is taken to use radiation therapy to cure heart diseases like arrhythmia. This approach requires high accuracy localisation and tracking of the pulmonary veins. Because of the high speed of motion of the heart, fluoroscopic tracking of fiducials or anatomical structures as in IGRT would on the one hand require high frame rates and, on the other hand, it would be dangerous to place fiducials near the target. We propose to use live 3D ultrasound to perform the landmark localization and tracking. Methods and materials: We have modified a GE Vivid7 dimension 3D cardiovascular ultrasound station for real-time volume processing and target localisation. It is capable of providing ultrasound volume scans of the target region with more than 20 fps. A framework was established to upload and run image-processing algorithms directly on the ultrasound machine which is necessary to handle the high amount of data. This prevents the bottleneck of Ethernet data streaming and external processing. We propose to localise the pulmonary veins using a template matching algorithm with multiple templates. Approximately 20 templates are manually generated during one heart beat cycle. To increase the speed and accuracy of the matching process, electrical pulse signals were recorded by the ultrasound station. This allows selecting two or three pulse-dependent templates in the live matching stage. Results: The accuracy of the localization process is highly dependent on the templates chosen. The best results were achieved providing a full heart cycle as template data. As a compromise between speed and accuracy, we used 9\¡Á9\¡Á9 points as template, corresponding to 4.5\¡Á4.5\¡Á4.5mm3. Conclusion: The presented approach is a new and robust approach to semi-automatically track small substructures in the beating heart. Furthermore, the generated signal is suitable as input to numerous prediction algorithms currently used to compensate for breathing motion in radiosurgery.}
}
@conference{W09a,
Author = {W. Kilby and A. Schlaefer and J. Dooley and O. Blanck and E. Lessard and C. Maurer},
Title = {Evaluation of the Clinical Utility of an Iris Collimator Combined with a Sequential Optimization Algorithm for Robotic Radiosurgery.},
Year = {(2009).},
Volume = {25.},
Pages = {916-919},
Booktitle = {Proceedings of the World Congress 2009 for Medical Physics and Biomedical Engineering},
Url = {http://www.springer.com/de/book/9783642038976}
}
@article{SS08a,
Author = {A. Schlaefer and A. Schweikard,},
Title = {Stepwise multi-criteria optimization for robotic radiosurgery.},
Journal = {Med Phys.},
Year = {(2008).},
Volume = {35.},
Number = {(5),},
Pages = {2094-2103},
Doi = {10.1118/1.2900716},
Abstract = {Achieving good conformality and a steep dose gradient around the target volume remains a key aspect of radiosurgery. Clearly, this involves a trade\-off between target coverage, conformality of the dose distribution, and sparing of critical structures. Yet, image guidance and robotic beam placement have extended highly conformal dose delivery to extracranial and moving targets. Therefore, the multi\-criteria nature of the optimization problem becomes even more apparent, as multiple conflicting clinical goals need to be considered coordinate to obtain an optimal treatment plan. Typically, planning for roboticradiosurgery is based on constrained optimization, namely linear programming. An extension of that approach is presented, such that each of the clinical goals can be addressed separately and in any sequential order. For a set of common clinical goals the mapping to a mathematical objective and a corresponding constraint is defined. The trade\-off among the clinical goals is explored by modifying the constraints and optimizing a simple objective, while retaining feasibility of the solution. Moreover, it becomes immediately obvious whether a desired goal can be achieved and where a trade\-off is possible. No importance factors or predefined prioritizations of clinical goals are necessary. The presented framework forms the basis for interactive and automated planning procedures. It is demonstrated for a sample case that the linear programming formulation is suitable to search for a clinically optimal treatment, and that the optimization steps can be performed quickly to establish that a Pareto\-efficient solution has been found. Furthermore, it is demonstrated how the stepwise approach is preferable compared to modifying importance factors}
}
@article{A08a,
Author = {A. Schlaefer and J. Gill and A. Schweikard},
Title = {A simulation and training environment for robotic radiosurgery.},
Journal = {International Journal of Computer Assisted Radiology and Surgery.},
Year = {(2008).},
Volume = {3.},
Number = {(3),},
Pages = {267-274},
Doi = {10.1007/s11548-008-0159-z}
}
@article{A08c,
Author = {A. Schlaefer and O. Blanck},
Title = {Establishing a Trade-Off Between Number of Beams and Plan Quality in Robotic Radiosurgery.},
Journal = {Medical Physics.},
Year = {(2008).},
Volume = {35.},
Number = {(5),},
Pages = {2638},
Doi = {10.1118/1.2961382},
Abstract = {Purpose: To study the potential trade\?off between the number of beams and the plan quality in roboticradiosurgery. Specifically, to assess, whether the number of beams can be reduced by repeating the series of optimization steps on a subset of substantially weighted beams. Method and Materials: We use a linear programming formulation of the planning problem, where objective terms are matched by corresponding constraints. The optimization is decomposed into a series of steps. When a plan with acceptable quality has been obtained, the activation time of the beams is studied. Beams with an activation time below a threshold are removed from the plan. We then compare the effect of (A) rescaling the weight of the remaining beams to obtain at least 98% of the previous coverage, and (B) to re\-optimize the beam weights by applying the series of optimization steps to the reduced set of beams. The methods are applied to three clinical cases, a spinal lesion, a head and neck tumor, and a prostate case. Results: We removed up to 17.6%, 52.3%, and 28.4% of the beams for the spinal, the head and neck, and the prostate case, respectively, while retaining the plan quality with reoptimization. In contrast, rescaling changed the dose distribution substantially and the plan quality metrics degraded to an unacceptable level. Conclusion: Removing low weighted beams can reduce the number of active beams, and hence the overall treatment time. Reoptimization using the original series of optimization steps leads to better plan quality compared with rescaling. The potential to reduce the number of beams while retaining plan quality depends on the clinical case, and the fraction of beams that is removed. Conflict of Interest: Research partially sponsored by Accuray Inc}
}
@article{A08b,
Author = {A. Schlaefer and O. Blanck},
Title = {TU-EE-A1-05: Exploring the Spatial Trade-Off in Treatment Planning.},
Journal = {Medical Physics.},
Year = {(2008).},
Volume = {35.},
Number = {(6),},
Pages = {2910},
Booktitle = {Medical Physics},
Doi = {10.1118/1.2962609},
Abstract = {Purpose: To include spatial information during multi\-criteria treatment planning. Particularly, to study whether constrained optimization on the voxel level allows to deliberately trade\-off the dose delivered to one region of a volume of interest (VOI) with respect to other clinical goals. Method and Materials: We extended a stepwise optimization method for roboticradiosurgery to interactively modify dose constraints on a voxel level. The optimization problem is solved using linear programming, and every term in the objective function is matched by a corresponding constraint. Clinical goals are addressed separately and maintained using the constraints. A trade\-off among the clinical goals is then explored by a series of optimization steps. For visualization, VOIs are represented by a 3D grid of spheres, where each sphere represents a voxel and can be selected in a 3D scene. Constraints on the dose in the selected voxels can be considered independently for subsequent optimization steps. The method was applied to a prostate case, where we studied trade\-offs with respect to the maximum dose in the rectum. Results: Relaxing the upper dose bound on a set of voxels in the prostate lobes by 150 cGy allowed to reduce the maximum rectum dose by 100 cGy. Likewise, a relaxation of the lower dose bound on a few voxels on the prostate surface by 100 cGy allowed to further reduce the maximum dose in th rectum by 157 cGy. Conclusion: Spatial information is not available from cumulative statistics typically used as criteria for treatment planning. Our results indicate that it is possible to include spatial information in interactive multi\-criteria optimization. The proposed method can be used when clinical goals can be expressed with respect to a subregion of a VOI. Conflict of Interest: Research partially sponsored by Accuray Inc}
}
@conference{A08d,
Author = {A. Schlaefer and O. Jungmann},
Title = {Plan quality versus number of beam source positions in image guided robotic radiosurgery.},
Year = {(2008).},
Booktitle = {Computer Assisted Radiology and Surgery (CARS'2008)}
}
@article{F08a,
Author = {F. Ernst and A. Schlaefer and S. Dieterich and A. Schweikard},
Title = {A Fast Lane Approach to LMS Prediction of Respiratory Motion Signals.},
Journal = {Biomedical Signal Processing and Control.},
Year = {(2008).},
Volume = {3.},
Number = {(4),},
Pages = {291-299},
Month = {October},
Doi = {doi:10.1016/j.bspc.2008.06.001},
Abstract = {As a tool for predicting stationary signals, the Least Mean Squares (LMS) algorithm is widely used. Its improvement, the family of normalised LMS algorithms, is known to outperform this algorithm. However, they still remain sensitive to selecting wrong parameters, being the learning coefficient u and the signal history length M. We propose an improved version of both algorithms using a Fast Lane Approach, based on parallel evaluation of several competing predictors. These were applied to respiratory motion data from motion\-compensated radiosurgery. Prediction was performed using arbitrarily selected values for the learning coefficient u € [0,0.3] and the signal history length M € [1,15]. The results were compared to prediction using the globally optimal values of u and M found using a grid search. When the learning algorithm is seeded using locally optimal values (found using a grid search on the first 96 s of data), more than 44% of the test cases outperform the globally optimal result. In about 38% of the cases, the result comes to within 5% and, in about 9% of the cases, to within 5\-10% of the global optimum. This indicates that the Fast Lane Approach is a robust method for selecting the parameters u and M}
}
@article{S08a,
Author = {S. Dieterich and A. Schlaefer},
Title = {SU-GG-J-76: Dosimetric Consequences of Patient Setup Decisions in Image-Guided Procedures Based On Soft-Tissue Fiducials for Imaging.},
Journal = {Medical Physics.},
Year = {(2008).},
Volume = {35.},
Number = {(6),},
Pages = {2696-2696},
Organization = {50th Annual Meeting of the AAPM},
Doi = {10.1118/1.2961626},
Abstract = {Purpose: The purpose of this work is to demonstrate the dosimetric consequences of patient setup and tracking technique decisions for 4D adaptive SBRT treatments. Method and Materials: Clinical fiducial tracking scenarios of 450 SBRT cases, 120 of them treated with 4D adaptive SBRT, were analyzed and classified into different case scenarios. A flowchart was created to systematically display each clinical tracking scenario and the decision options. Based on the flowchart, scenarios which could cause a deviation from delivered dose to planned dose were identified. For these situations, each tracking decision was evaluated for dosimetric impact by simulating the situation in treatment planning software using a patient CT and an artificially created elliptical tumor.Results: Only two clinical scenarios were identified as having dosimetric consequences. One scenario contains tumors which rotate significantly (>5 degrees) during the respiratory cycles. For rotations smaller than 5 degrees we saw no differences in the DVH than non-rotating tumors. For tumors with rotation angles larger than 6 degrees, the DVH shows increasing, but still small, tumor underdose. The second scenario with potential dosimetry changes was a small rotational change (<5 degrees) of the tumor position relative to the global patient position. Our calculations show that changing the global patient position to move the tumor into the treatment field did change the DVH, because the SSD and obliquity of incoming beams changes. A third tracking scenario was identified in which a repeat simulation is necessary. Conclusion: Fiducial setup and rotational tumor tracking decisions for SBRT treatments were classified. Dosimetric impact was studied for the two relevant class decisions. A class of patients which needed re-CT was identified. Our flowchart and dosimetry studies will help in the future to systematically identify and address soft-tissue fiducial tracking scenarios and choice of tracking technique for SBRT.}
}
@conference{A07a,
Author = {A. Schlaefer and O. Blanck and A. Schweikard},
Title = {Interactive Multi-criteria Inverse Planning for Robotic Radiosurgery.},
Journal = {XVth International Conference on the Use of Computers in Radiation Therapy (ICCR 2007).},
Year = {(2007).},
Address = {Toronto, Canada},
Booktitle = {XVth International Conference on the Use of Computers in Radiation Therapy (ICCR)}
}
@conference{A07b,
Author = {A. Schlaefer and O. Jungmann and W. Kilby and A. Schweikard},
Title = {Objective specific beam generation for image guided robotic radiosurgery.},
Year = {(2007).},
Address = {Berlin, Germany},
Booktitle = {21st International Congress and Exhibition Computer Assisted Radiology and Surgery CARS'2007}
}
@inproceedings{ESS07a,
Author = {F. Ernst and A. Schlaefer and A. Schweikard},
Title = {Prediction of respiratory motion with wavelet-based multiscale autoregression.},
Year = {(2007).},
Volume = {10.},
Number = {(Pt 2),},
Pages = {668-675},
Address = {Brisbane, Australia},
Isbn = {978-3-540-75759-7},
Booktitle = {Med Image Comput Comput Assist Interv},
Organization = {10th International Conference on Medical Image Computing and Computer Assisted Intervention (MICCAI 2007)},
PMID = {18044626},
Doi = {10.1007/s11548-007-0083-7},
Institution = {Institute of Robotics and Cognitive Systems, University of Lübeck, DE. ernst@rob.uni-luebeck.de},
Keywords = {Computer Simulation; Humans; Models, Biological; Movement, physiology; Radiosurgery, methods; Regression Analysis; Reproducibility of Results; Respiratory Mechanics, physiology; Sensitivity and Specificity; Signal Processing, Computer-Assisted; Surgery, Computer-Assisted, methods},
Abstract = {In robotic radiosurgery, a photon beam source, moved by a robot arm, is used to ablate tumors. The accuracy of the treatment can be improved by predicting respiratory motion to compensate for system delay. We consider a wavelet-based multiscale autoregressive prediction method. The algorithm is extended by introducing a new exponential averaging parameter and the use of the Moore-Penrose pseudo inverse to cope with long-term signal dependencies and system matrix irregularity, respectively. In test cases, this new algorithm outperforms normalized LMS predictors by as much as 50\%. With real patient data, we achieve an improvement of around 5 to 10\%.}
}
@conference{F07a,
Author = {F. Ernst and R. Bruder and A. Schlaefer},
Title = {Processing of Respiratory Signals from Tracking Systems for Motion Compensated IGRT.},
Journal = {Medical Physics.},
Year = {(2007).},
Volume = {34.},
Number = {(6),},
Pages = {2565},
Month = {July},
Booktitle = {47th Annual Meeting of the American Association of Physicists in Medicine},
Doi = {10.1118/1.2761413},
Abstract = {Purpose: Improving the quality of signals obtained with optical and magnetic tracking systems. Special focus is placed on the measurement of respiratory motion signals for motion compensated IGRT and the possibility of filtering this data to obtain low-noise breathing signals. Method and Materials: The accuracy of five different tracking systems (NDI Polaristexttrademark, active and passive, Clarion MicronTrackertexttrademark, BIG FP5000, NDI Auroratexttrademark) was examined by (a) tracking stationary markers over several hours, and (b) by attaching the markers to a Kuka KR16 robot to simulate human respiration. The à trous wavelet decomposition was used to decompose the measured signal into scales, and to remove scales related to high frequencies, i.e., noise. The method was applied to a sinusoidal signal with artificial noise modeled according to (a), to real measurements for a sinusoidal motion of the robot, and to a set of breathing motion data from an actual patient treated with the CyberKnifetextregistered. Motion prediction was applied to the data. Results: The error on the measurements of the stationary marker approaches a Gaussian distribution. For a tracking rate of 60 Hz, information related to breathing motion is represented by higher scales of the à trous wavelet decomposition. Removing the first three scales and resconstructing the signal from the remaining scales and trend it is possible to obtain close and smooth approximations of the original signal. The normalized RMS error for motion prediction is 0.3368 mm and 0.1378 mm for a simulated and the smoothed signal using normalized LMS prediction. Conclusion: Data from tracking devices is subject to device specific measurement noise. The à trous wavelet decomposition can be used to remove frequencies related to noise from measured breathing signals. The resulting signal is suitable for further processing, e.g., correlation with or prediction of tumor motion in the context of motion compensated IGRT.}
}
@inproceedings{RSEDS07a,
Author = {L. Ramrath and A. Schlaefer and F. Ernst and S. Dieterich and A. Schweikard},
Title = {Prediction of respiratory motion with a multi-frequency based Extended Kalman Filter.},
Year = {(2007).},
Volume = {21.},
Number = {(2),},
Pages = {56-58},
Booktitle = {International Journal of Computer Assisted Radiology and Surgery CARS'2007},
Organization = {Computer Assisted Radiology and Surgery (CARS)},
Doi = {10.1007/s11548-007-0083-7},
Abstract = {In this work, an Extended Kalman Filter formulation for respiration motion tracking is introduced. Based on the assumption of multiple sinusoidal components contributing to respiratory motion, a state-space model is developed. Performance of the filter is tested on data sets of patients subject to radiotherapy. Comparison to an nLMS predictor shows that the Kalman filter is less sensitive to systematic errors during target prediction.}
}
@conference{A06a,
Author = {A. Schlaefer and O. Blanck and A. Muacevic and A. Schweikard},
Title = {Inverse Planung für die robotergestützte Strahlentherapie: Strahlauswahl und Gewichtung.},
Year = {(2006).}
}
@article{A06b,
Author = {A. Schlaefer and O. Blanck and H. Shiomi and A. Schweikard},
Title = {An iterative beam placement approach for image guided robotic radiosurgery.},
Journal = {International Journal of Computer Assisted Radiology and Surgery (CARS).},
Year = {(2006).},
Volume = {1, Supplement 1.},
Pages = {226-228}
}
@article{SSA06a,
Author = {A. Schweikard and A. Schlaefer and J. R. Adler Jr},
Title = {Resampling: an optimization method for inverse planning in robotic radiosurgery.},
Journal = {Med Phys.},
Year = {(2006).},
Volume = {33.},
Number = {(11),},
Pages = {4005-4011},
Doi = {10.1118/1.2357020},
Abstract = {By design, the range of beam directions in conventional radiosurgery are constrained to an isocentric array. However, the recent introduction of roboticradiosurgery dramatically increases the flexibility of targeting, and as a consequence, beams need be neither coplanar nor isocentric. Such a nonisocentric design permits a large number of distinct beam directions to be used in one single treatment. These major technical differences provide an opportunity to improve upon the well-established principles for treatment planning used with GammaKnife or LINACradiosurgery. With this objective in mind, our group has developed over the past decade an inverse planning tool for roboticradiosurgery. This system first computes a set of beam directions, and then during an optimization step, weights each individual beam. Optimization begins with a feasibility query, the answer to which is derived through linear programming. This approach offers the advantage of completeness and avoids local optima. Final beam selection is based on heuristics. In this report we present and evaluate a new strategy for utilizing the advantages of linear programming to improve beam selection. Starting from an initial solution, a heuristically determined set of beams is added to the optimization problem, while beams with zero weight are removed. This process is repeated to sample a set of beams much larger compared with typical optimization. Experimental results indicate that the planning approach efficiently finds acceptable plans and that resampling can further improve its efficiency}
}
@inproceedings{O06a,
Author = {O. Blanck and A. Schlaefer and A. Schweikard},
Title = {3D visualization of radiosurgical treatment plans experience with Java3D and VTK.},
Journal = {Computational Modeling of Objects Represented in Images-Fundamentals, Methods and Applications, First International Symposium CompIMAGE.},
Year = {(2006).},
Pages = {101-106},
Month = {October},
Address = {Coimbra, Portugal},
Booktitle = {Computational Modelling of Objects Represented in Images, Proceedings of the International Symposium CompIMAGE},
Organization = {Computational Modelling of Objects Represented in Images, Proceedings of the International Symposium CompIMAGE},
Url = {http://dblp.uni-trier.de/rec/bib/conf/compimage/BlanckSS06}
}
@article{RSSA06a,
Author = {P. Romanelli and A. Schweikard and A. Schlaefer and J. Adler},
Title = {Computer aided robotic surgery.},
Journal = {Comput Aided Surg.},
Year = {(2006).},
Volume = {11.},
Number = {(4),},
Pages = {161-174},
PMID = {17060075},
Doi = {10.3109/10929080600886393},
Abstract = {Radiosurgery involves the precise delivery of sharply collimated high-energy beams of radiation to a distinct target volume along selected trajectories. Historically, accurate targeting required the application of a stereotactic frame, thus limiting the use of this procedure to single treatments of selected intracranial lesions. However, the scope of radiosurgery has undergone a remarkable broadening since the introduction of image-guided robotic radiosurgery. Recent developments in real-time image guidance provide an effective frameless alternative to conventional radiosurgery and allow both the treatment of lesions outside the skull and the possibility of performing hypofractionation. As a consequence, targets in the spine, chest and abdomen can now also be radiosurgically ablated with submillimetric precision. Meanwhile, the combination of image guidance, robotic beam delivery, and non-isocentric inverse planning can greatly enhance the conformality and homogeneity of radiosurgery. The aim of this article is to describe the technological basis of image-guided radiosurgery and provide a perspective on future developments. The current clinical usage of robotic radiosurgery will be reviewed with an emphasis on those applications that may represent a major shift in the therapeutic paradigm}
}
@article{SFDSCS05a,
Author = {A. Schlaefer and J. Fisseler and S. Dieterich and H. Shiomi and K. Cleary and A. Schweikard},
Title = {Feasibility of four-dimensional conformal planning for robotic radiosurgery.},
Journal = {Med Phys.},
Year = {(2005).},
Volume = {32.},
Number = {(12),},
Pages = {3786-3792},
Doi = {10.1118/1.2122607},
Abstract = {Organ motion can have a severe impact on the dose delivered by radiation therapy, and different procedures have been developed to address its effects. Conventional techniques include breath hold methods and gating. A different approach is the compensation for target motion by moving the treatment beams synchronously. Practical results have been reported for robot based radiosurgery, where a linear accelerator mounted on a robotic arm delivers the dose. However, not all organs move in the same way, which results in a relative motion of the beams with respect to the body and the tissues in the proximity of the tumor. This relative motion can severely effect the dose delivered to critical structures. We propose a method to incorporate motion in the treatment planning for roboticradiosurgery to avoid potential overdosing of organs surrounding the target. The method takes into account the motion of all considered volumes, which is discretized for dose calculations. Similarly, the beam motion is taken into account and the aggregated dose coefficient over all discrete steps is used for planning. We simulated the treatment of a moving target with three different planning methods. First, we computed beam weights based on a 3D planning situation and simulated treatment with organ motion and the beams moving synchronously to the target. Second, beam weights were computed by the 4D planning method incorporating the organ and beam motion and treatment was simulated for beams moving synchronously to the target. Third, the beam weights were determined by the 4D planning method with the beams fixed during planning and simulation. For comparison we also give results for the 3D treatment plan if there was no organ motion and when the plan is delivered by fixed beams in the presence of organ motion. The results indicate that the new 4D method is preferable and can further improve the overall conformality of motion compensated roboticradiosurgery.}
}
@article{A05d,
Author = {A. Schlaefer and O. Blanck and A. Schweikard},
Title = {WE-C-I-609-09: Autostereoscopic Display of the 3D Dose Distribution to Assess Beam Placement for Robotic Radiosurgery.},
Journal = {Medical Physics.},
Year = {(2005).},
Volume = {32.},
Number = {(6),},
Pages = {2122},
Doi = {10.1118/1.1998500},
Abstract = {Purpose: To study whether a 3D view of the dose distribution and treatment beams on an autostereoscopic display facilitates a \‘smart\’ placement of additional beams for roboticradiosurgery. Method and Materials:Treatment plans for roboticradiosurgery with the CyberKnife system (Accuray Inc., Sunnyvale) consist of a large number of non?isocentrical, cylindrical beams directed towards arbitrary points within the target volume. We implemented a tool to visualize the resulting 3D dose distribution and the beam directions using the visualization toolkit (VTK). A hypsometric color scheme allows to identify cold and hot spots in the target volume, i.e. regions where the dose is close to the lower or upper bound specified for the target. Given this information we manually added a 20 beams to an existing treatment plan with 1200 beams for an intracranial tumor. The beams where placed such that a large number of cold voxels were hit but hot voxels were avoided. To assess the spatial extent of the cold and hot regions and the orientation of the beams an autostereoscopic display (SeeReal Technologies GmbH, Dresden) was used. An inverse planning algorithm similar to the one used by the CyberKnife system was implemented to re?optimize the plan, the result was compared to the original plan. Results: The original plan consisted of 119 weighted beams with an accumulated weight of 21763.3 MU. Adding 20 beams we obtained a plan with 123 beams with the total weight reduced to 21610.7 MU. All 20 new beams got the maximum weight of 250 MU per beam, i.e. other, less efficient beams were discarded by the optimizer. Conclusion: The visualization tool proved to be useful in the guidance of beam placement. A direction of additional beams towards cold spots in the target volume can improve the plan quality}
}
@inproceedings{A05c,
Author = {A. Schlaefer and O. Blanck and H. Shiomi and A. Schweikard},
Title = {Radiochirurgie: Identifizierung effizienter Behandlungsstrahlen mittels autostereoskopischer Visualisierung.},
Year = {(2005).},
Booktitle = {Jahrestagung der Deutschen Gesellschaft für Computer- und Roboterassistierte Chirurgie CURAC'2005}
}
@conference{A05b,
Author = {A. Schlaefer and S. Dieterich and A. Schweikard},
Title = {Berücksichtigung interfraktionaler Bewegungen bei der Behandlungsplanung für die bewegungskompensierte Strahlenchirurgie.},
Year = {(2005).},
Booktitle = {Jahrestagung der Deutschen Gesellschaft für Computer- und Roboterassistierte Chirurgie CURAC'2005}
}
@article{FHBRNF05a,
Author = {L. Fritsche and J. Hoerstrup and K. Budde and P. Reinke and H. H. Neumayer and U. Frei and A. Schlaefer},
Title = {Accurate prediction of kidney allograft outcome based on creatinine course in the first 6 months posttransplant.},
Journal = {Transplant Proceedings.},
Year = {(2005).},
Volume = {37.},
Number = {(2),},
Pages = {731-733},
Doi = {10.1016/j.transproceed.2004.12.067},
Abstract = {Most attempts to predict early kidney allograft loss are based on the patient and donor characteristics at baseline. We investigated how the early posttransplant creatinine course compares to baseline information in the prediction of kidney graft failure within the first 4 years after transplantation. Two approaches to create a prediction rule for early graft failure were evaluated. First, the whole data set was analysed using a decision-tree building software. The software, rpart, builds classification or regression models; the resulting models can be represented as binary trees. In the second approach, a Hill-Climbing algorithm was applied to define cut-off values for the median creatinine level and creatinine slope in the period between day 60 and 180 after transplantation. Of the 497 patients available for analysis, 52 (10.5%) experienced an early graft loss (graft loss within the first 4 years after transplantation). From the rpart algorithm, a single decision criterion emerged: Median creatinine value on days 60 to 180 higher than 3.1 mg/dL predicts early graft failure (accuracy 95.2% but sensitivity = 42.3%). In contrast, the Hill-Climbing algorithm delivered a cut-off of 1.8 mg/dL for the median creatinine level and a cut-off of 0.3 mg/dL per month for the creatinine slope (sensitivity = 69.5% and specificity 79.0%). Prediction rules based on median and slope of creatinine levels in the first half year after transplantation allow early identification of patients who are at risk of loosing their graft early after transplantation. These patients may benefit from therapeutic measures tailored for this high-risk setting}
}
@inproceedings{A04a,
Author = {A. Schlaefer and P. Kneschaurek and A. Schweikard},
Title = {Beam placement for robotic radiosurgery.},
Journal = {Computer Assisted Radiology and Surgery. Proceedings of the 18th International Congress and Exhibition CARS'2004.},
Year = {(2004).},
Volume = {1268.},
Pages = {1235},
Month = {June},
Publisher = {Elsevier:},
Address = {Chicago, USA},
Booktitle = {Computer Assisted Radiology and Surgery (CARS), Proceedings of the 18th International Congress and Exhibition},
Doi = {10.1016/j.ics.2004.03.025}
}
@article{FSBSN02a,
Author = {L. Fritsche and A. Schlaefer and K. Budde and K. Schroeter and H. H. Neumayer},
Title = {Recognition of critical situations from time series of laboratory results by case-based reasoning.},
Journal = {J Am Med Inform Assoc.},
Year = {(2002).},
Volume = {9.},
Number = {(5),},
Pages = {520-528},
PMID = {12223504},
Abstract = {OBJECTIVE: To develop a technique for recognizing critical situations based on laboratory results in settings in which a normal range cannot be defined, because what is \'normal\' differs widely from patient to patient. To assess the potential of this approach for kidney transplant recipients, where recognition of acute rejections is based on the pattern of changes in serum creatinine. DESIGN: We developed a case\-based reasoning algorithm using dynamic time\-warping as the measure of similarity which allows comparison of series of infrequent measurements at irregular intervals for retrieval of the most similar historical cases for the assessment of a new situation. MEASUREMENTS: The ability to recognize creatinine courses associated with an acute rejection was tested for a set of cases from a database of transplant patient records and compared with the diagnostic performance of experienced physicians. Tests were performed with case bases of various sizes. RESULTS: The accuracy of the algorithm increased steadily with the size of the available case base. With the largest case bases, the case\-based algorithm reached an accuracy of 78 +/\- 2\%, which is significantly higher than the performance of experienced physicians (69 +/\- 5.3\%) (p \< 0.001). CONCLUSION: The new case\-based reasoning algorithm with dynamic time warping as the measure of similarity allows extension of the use of automatic laboratory alerting systems to conditions in which abnormal laboratory results are the norm and critical states can be detected only by recognition of pathological changes over time}
}
@article{A01a,
Author = {A. Schlaefer and K. Schroeter and L. Fritsche},
Title = {A Case-Based Approach for the Classification of Medical Time Series.},
Journal = {J. Crespo, V. Maojo, F. Martin (Eds.): Medical Data Analysis.},
Year = {(2001).},
Volume = {2199.},
Pages = {258-263},
Note = {Springer LNCS 2199},
Url = {http://link.springer.com/chapter/10.1007%2F3-540-45497-7_39},
Abstract = {An early and reliable detection of rejections is most important for the successful treatment of renal transplantation patients. A good indicator for the renal function of transplanted patients is the course over time of the parameter creatinine. Existing systems for the analysis of time series usually require frequent and equidistant measurements or a well defined medical theory. These requirements are not fulfilled in our application domain. In this paper we present a case-based approach to classify a creatinine course as critical or non-critical. The distance measure used to find similar cases is based on linear regression. Our results show that while having a good specificity, our sensitivity is significantly higher than that of physicians}
}
@article{FSBSN01a,
Author = {L. Fritsche and A. Schlaefer and K. Budde and K. Schroeter and H. H. Neumayer},
Title = {Case-based reasoning algorithm for kidney transplant monitoring.},
Journal = {Transplant Proc.},
Year = {(2001).},
Volume = {33.},
Number = {(7-8),},
Pages = {3331-3333},
Month = {November-December},
Doi = {10.1016/S0041-1345(01)02434-4}
}
@article{F00a,
Author = {F. Müller and J. Nolte and A. Schlaefer},
Title = {CLIX - A Hybrid Programming Environment for Distributed Objects and Distributed Shared Memory.},
Journal = {J. Rolim et al. (Eds.): Parallel and Distributed Processing - Workshop on High-Level Parallel Programming Models and Supportive Environments.},
Year = {(2000).},
Pages = {285-292},
Note = {Springer LNCS 1800},
Abstract = {Parallel programming with distributed object technology becomes increasingly popular but shared-memory programming is still a common way of utilizing parallel machines. In fact, both models can coexist fairly well and software DSM systems can be constructed easily using distributed object systems. In this paper, we describe the construction of a hybrid programming platform based on the Arts distributed object system. We describe how an object-oriented design approach provides a compact and flexible description of the system components. A sample implementation demonstrates that three classes of less than 100 lines of code each suffice to implement sequential consistency}
}
@article{G00a,
Author = {G. Lindemann and L. Fritsche and K. Schröter and A. Schlaefer and K. Budde and H. H. Neumayer},
Title = {A Web-Based Patient Record for Hospitals - The Design of TBase2.},
Journal = {Bruch, Köckerling, Bouchard, Schug-Paß (Eds.): New Aspects of High Technology in Medicine.},
Year = {(2000).}
}
@COMMENT{Bibtex file generated on 2026-5-3 with typo3 si_bibtex plugin. Data from https://www.tuhh.de/mtec/publications/2012-2000 }