@article{Foerger2026IEEESensors,
author = {F. Foerger, M. Boberg, N. Hackelberg, P. Heinisch, K. Ostaszewski, J. Faltinath, P. Suskin, F. Thieben, F. Mohn, P. Jürß, M. Möddel and T. Knopp},
title = {3-D Magnetic Field Camera With Subsecond Temporal Resolution.},
journal = {IEEE Sensors Journal.},
year = {2026},
volume = {26.},
number = {(1),},
note = {article},
doi = {https://doi.org/10.1109/JSEN.2025.3629803},
url = {https://ieeexplore.ieee.org/document/11244237},
abstract = {Accurate and efficient volumetric magnetic field measurements are essential for a wide range of applications. Conventional methods are often limited in terms of measurement speed and applicability or suffer from scaling problems at larger volumes. This work presents a proof-of-concept field camera designed to measure magnetic fields within a spherical volume at a frame rate of 10 Hz. The camera features an array of 3-D Hall magnetometers positioned according to a spherical t-design, allowing simultaneous magnetic field data acquisition from the surface of the sphere. The approach enables the efficient representation of all three components of the magnetic field inside the sphere using a sixth-degree polynomial, significantly reducing measurement time compared with sequential methods. This work details the design, calibration, and measurement methods of the field camera. To evaluate its performance, we compare it with a sequential single-sensor measurement by examining a magnetic gradient field. The obtained measurement uncertainties of approximately 1% demonstrate the feasibility of the approach and its potential applicability to a variety of future applications.}
}

@article{Faltinath2025natural,
author = {J. Faltinath, F. Mohn, F. Foerger, M. Möddel, and T. Knopp},
title = {Natural Frequency Dependence of Magneto-Mechanical Resonators on Magnet Distance.},
journal = {IEEE Sensors Journal.},
year = {2025},
volume = {25.},
number = {(20),},
pages = {38073-38081},
note = {article, openaccess, mmr},
doi = {https://doi.org/10.1109/JSEN.2025.3600007},
url = {https://ieeexplore.ieee.org/document/11139087},
abstract = {The precise derivation of physical quantities like temperature or pressure at arbitrary locations is useful in numerous contexts, e.g., medical procedures or industrial process engineering. The novel sensor technology of magneto-mechanical resonators (MMRs), based on the interaction of a rotor and stator permanent magnet, allows for the combined tracking of the sensor position and orientation while simultaneously sensing an external measurand. Hence, the quantity is coupled to the torsional oscillation frequency, e.g., by varying the magnet distance. In this article, we analyze the (deflection angle-independent) natural frequency dependence of MMR sensors on the rotor-stator distance and evaluate the performance of theoretical models. The three presented sensors incorporate magnets of spherical and/or cylindrical geometry and can be operated at adjustable frequencies within the range of 61.9–307.3 Hz. Our proposed method to obtain the natural frequency demonstrates notable robustness to variations in the initial deflection amplitudes and quality factors, resulting in statistical errors on the mean smaller than 0.05%. We find that the distance–frequency relationship is well-described by an adapted dipole model accounting for material and manufacturing uncertainties. Their combined effect can be compensated by an adjustment of a single parameter, which drives the median model deviation generally below 0.2%. Our depicted methods and results are important for the design and calibration process of new sensor types utilizing the MMR technique.}
}

@article{scheffler2025efficient,
author = {K. Scheffler, L. Meyn, F. Foerger, M. Boberg, M. Möddel, and T. Knopp},
title = {Efficient measurement and representation of magnetic fields in tomographic imaging using ellipsoidal harmonics.},
journal = {Communications Physics.},
year = {2025},
volume = {8.},
number = {(112),},
month = {January},
note = {article, openaccess, magneticfield},
publisher = {Nature:},
doi = {10.1038/s42005-025-02012-5},
keywords = {magnetic resonance imaging, magnetic particle imaging, magneticfield
},
abstract = {Given the pivotal role of magnetic fields in modern medicine, there is an increasing necessity for a precise characterization of their strength and orientation at high spatial and temporal resolution. As source-free magnetic fields present in tomographic imaging can be described by harmonic polynomials, they can be efficiently represented using spherical harmonic expansions, which allows for measurement at a small set of points on a sphere surrounding the field of view. However, the majority of closed-bore systems possess a cylindrical field of view, making a sphere an inadequate choice for coverage. Ellipsoids represent a superior geometrical choice, and the theory of ellipsoidal harmonic expansions can be applied to magnetic fields in an analogous manner. Despite the mathematical principles underpinning ellipsoidal harmonics being well-established, their utilization in practical applications remains relatively limited. In this study, we present an effective and flexible approach to measuring and representing magnetic fields present in tomographic imaging, which draws upon the theory of ellipsoidal harmonic expansions.}
}

@article{Foerger2024AIS,
author = {F. Foerger, M. Boberg, J. Faltinath, T. Knopp, M. Möddel},
title = {Design and Optimization of a Magnetic Field Generator for Magnetic Particle Imaging with Soft Magnetic Materials.},
journal = {Advanced Intelligent Systems.},
year = {2024},
volume = {6.},
number = {(11),},
note = {article},
doi = {https://doi.org/10.1002/aisy.202400017},
url = {https://advanced.onlinelibrary.wiley.com/doi/full/10.1002/aisy.202400017},
abstract = {Magnetic field generators are a key component of Magnetic Particle Imaging (MPI) systems, and their power consumption is a major obstacle on the path to human-sized scanners. Despite their importance, a focused discussion of these generators is rare, and a comprehensive description of the design process is currently lacking. This work presents a methodology for the design and optimization of selection field generators operating with soft magnetic materials outside the linear regime in the context of MPI. Key elements are a mathematical model of magnetic field generators, a formalism for defining field sequences, and a relationship between power consumption and field sequence. These are used to define the design space of a field generator given its system requirements and constraints. The design process is then formulated as an optimization problem. Subsequently, this methodology is then utilized to design a new magnetic field generator specifically for cerebral imaging studies. The optimization result outperforms our existing MPI field generator in terms of power consumption and field of view size, providing a proof-of-concept for the entire methodology. As the approach is very general, it can be extended beyond the MPI context to other areas such as magnetic manipulation of medical devices and micro-robotics.}
}

@article{mohn_resonant_2024,
author = {F. Mohn, F. Foerger, F. Thieben, M. Möddel, I. Schmale, T. Knopp and M. Graeser},
title = {Resonant Inductive Coupling Network for Human-Sized Magnetic Particle Imaging.},
journal = {Review of Scientific Instruments.},
year = {2024},
volume = {95.},
number = {(4),},
pages = {044701},
note = {article, openaccess, brainimager},
doi = {10.1063/5.0192784},
keywords = {Mohn},
abstract = {In magnetic particle imaging, a field-free region is maneuvered throughout the field of view using a time-varying magnetic field known as the drive-field. Human-sized systems operate the drive-field in the kHz range and generate it by utilizing strong currents that can rise to the kA range within a coil called the drive field generator. Matching and tuning between a power amplifier, a band-pass filter, and the drive-field generator is required. Here, for reasons of safety in future human scanners, a symmetrical topology and a transformer called an inductive coupling network are used. Our primary objectives are to achieve floating potentials to ensure patient safety while attaining high linearity and high gain for the resonant transformer. We present a novel systematic approach to the design of a loss-optimized resonant toroid with a D-shaped cross section, employing segmentation to adjust the inductance-to-resistance ratio while maintaining a constant quality factor. Simultaneously, we derive a specific matching condition for a symmetric transmit--receive circuit for magnetic particle imaging. The chosen setup filters the fundamental frequency and allows simultaneous signal transmission and reception. In addition, the decoupling of multiple drive field channels is discussed, and the primary side of the transformer is evaluated for maximum coupling and minimum stray field. Two prototypes were constructed, measured, decoupled, and compared to the derived theory and method-of-moment based simulations.}
}

@article{thieben_system_2024,
author = {F. Thieben, F. Foerger, F. Mohn, N. Hackelberg, M. Boberg, J.-P. Scheel, Möddel,  M. Graeser, and T. Knopp},
title = {System Characterization of a Human-Sized 3D Real-Time Magnetic Particle Imaging Scanner for Cerebral Applications.},
journal = {Communications Engineering.},
year = {2024},
volume = {3.},
number = {(1),},
pages = {47},
note = {article, openaccess, brainimager},
doi = {10.1038/s44172-024-00192-6},
keywords = {Mohn},
abstract = {Abstract Since the initial patent in 2001, the Magnetic Particle Imaging community has endeavored to develop a human-applicable Magnetic Particle Imaging scanner, incorporating contributions from various research fields. Here we present an improved head-sized Magnetic Particle Imaging scanner with low power consumption, operated by open-source software and characterize it with an emphasis on human safety. The focus is on the evaluation of the technical components and on phantom experiments for brain perfusion. We achieved 3D single- and multi-contrast imaging at 4 Hz frame rate. The system characterization includes sensitivity, resolution, perfusion and multi-contrast experiments as well as field measurements and sequence analysis. Images were acquired with a clinically approved tracer and within human peripheral nerve stimulation thresholds. This advanced scanner holds potential as a tomographic imager for diagnosing conditions such as ischemic stroke (different stages) or intracranial hemorrhage in environments lacking electromagnetic shielding, such as the intensive care unit.}
}

@article{Thieben2023receive,
author = {F. Thieben, T. Knopp, M. Boberg, F. Foerger, M.Graeser, and M. Möddel},
title = {On the Receive Path Calibration of Magnetic Particle Imaging Systems.},
journal = {IEEE Transactions on Instrumentation and Measurement.},
year = {2023},
volume = {72.},
pages = {1-15},
note = {article, instrumentation},
doi = {10.1109/TIM.2022.3219461},
url = {https://ieeexplore.ieee.org/document/9939022},
abstract = {Magnetic nanoparticles are a valuable tool in many biomedical applications and can be used for diagnostic and therapeutic purposes. In magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS), the particles are subjected to a dynamic magnetic field and the particle magnetization response is simultaneously measured using one or multiple receive coils. Separating the particle signal from the feed-through signal is commonly done by advanced passive filtering, which distorts the particle signal. To correct this distortion, the transfer function of the receive chain needs to be known. While in principle, the transfer function can be simulated, due to imperfections in the electronic components, it is often more accurate to determine the transfer function in a calibration procedure. Although this system calibration, utilizing a calibration-coil setup has been done by several research groups in the past, a general description of the underlying calibration model and methodology is still missing. In this paper we provide a general multi-channel calibration procedure for inductive receive paths in MPI and a blueprint to investigate model and method uncertainties. We generalized the calibration procedure to also cover non-orthogonal and non-homogeneous receive coils. Finally, we showcase the calibration procedure and uncertainty analysis on our custom MPS system and use the MPI transfer functions of misaligned receive coils to decouple their superimposed receive signals from the receive path. The findings enable the comparison of MPI signals from different devices and can be used to normalize measurements and system functions in devices with exchangeable receive coils.}
}

@article{Ludewig2022MPICerebralPerfusionIschemia,
author = {P. Ludewig, M. Graeser, N. D. Forkert, F. Thieben, J. Rández-Garbayo, J. Rieckhoff, K. Lessmann, F. Foerger, P. Szwargulski, T. Magnus, and T. Knopp},
title = {Magnetic particle imaging for assessment of cerebral perfusion and ischemia.},
journal = {Wiley Interdiscip Rev Nanomed Nanobiotechnol.},
year = {2022},
note = {article, openaccess},
doi = {10.1002/wnan.1757},
url = {https://pubmed.ncbi.nlm.nih.gov/34617413/},
abstract = {Stroke is one of the leading worldwide causes of death and sustained disability. Rapid and accurate assessment of cerebral perfusion is essential to diagnose and successfully treat stroke patients. Magnetic particle imaging (MPI) is a new technology with the potential to overcome some limitations of established imaging modalities. It is an innovative and radiation-free imaging technique with high sensitivity, specificity, and superior temporal resolution. MPI enables imaging and diagnosis of stroke and other neurological pathologies such as hemorrhage, tumors, and inflammatory processes. MPI scanners also offer the potential for targeted therapies of these diseases. Due to lower field requirements, MPI scanners can be designed as resistive magnets and employed as mobile devices for bedside imaging. With these advantages, MPI could accelerate and improve the diagnosis and treatment of neurological disorders. This review provides a basic introduction to MPI, discusses its current use for stroke imaging, and addresses future applications, including the potential for clinical implementation. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease.}
}

@article{Graeser2020,
author = {M. Graeser, P. Ludewig, P. Szwargulski, F. Foerger, T. Liebing, N. D. Forkert, F. Thieben, T. Magnus, and T. Knopp},
title = {Design of a head coil for high resolution mouse brain perfusion imaging using magnetic particle imaging.},
journal = {Physics in Medicine and Biology.},
year = {2020},
volume = {65.},
number = {(23),},
pages = {235007},
note = {article, magneticfield},
doi = {10.1088/1361-6560/abc09e},
url = {https://arxiv.org/abs/2004.11728},
abstract = {Magnetic Particle Imaging (MPI) is a novel and versatile imaging modality developing towards human application. When up-scaling to human size, the sensitivity of the systems naturally drops as the coil sensitivity depends on the bore diameter. Thus, new methods to push the sensitivity limit further have to be investigated to cope for this loss. In this paper a dedicated surface coil improving the sensitvity in cerebral imaging applications was developed. Similar to MRI the developed surface coil improves the sensitivity due to the closer vicinity to the region of interest. With the developed surface coil presented in this work, it is possible to image tracer samples containing only 896 pg iron and detect even small vessels and anatomical structures within a wild type mouse model. As current sensitivity measures are dependent on the tracer system a new method for determining a sensitivity measure without this dependence on the tracer is presented and verified to enable comparison between MPI receiver systems.}
}

@COMMENT{Bibtex file generated on 2026-5-29 with typo3 si_bibtex plugin. Data from https://www.tuhh.de/ibi/people/fynn-foerger }