@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{Merbach2025, Author = {T. Merbach, F. Kexel, J. Faltinath, M. Möddel, M. Schlüter, T. Knopp, F. Mohn}, Title = {Wireless and passive pressure detection using magneto-mechanical resonances in process engineering.}, Journal = {Measurement Science and Technology.}, Year = {(2025).}, Volume = {36.}, Number = {(8),}, Pages = {085109}, Month = {aug}, Note = {article, mmr}, Doi = {10.1088/1361-6501/adf2c8}, Url = {https://dx.doi.org/10.1088/1361-6501/adf2c8}, Abstract = {A custom-developed magneto-mechanical resonator (MMR) for wireless pressure measurement is investigated for potential applications in process engineering. The MMR sensor utilises changes in the resonance frequency caused by pressure on a flexible 3D printed membrane. The thickness of the printed membrane plays a crucial role in determining the performance and sensitivity of MMRs and can be tailored to meet the requirements of specific applications. The study includes static and dynamic measurements to determine the pressure sensitivity and temporal resolution of the sensor. The results show a minimum sensitivity of and are in agreement with theoretical calculations and measurements. The maximum sensor readout frequency is 2 Hz in this study. Additionally, the temperature dependence of the sensor is investigated, revealing a significant dependence of the resonance frequency on temperature. The developed MMR offers a promising and versatile method for precise pressure measurements in process engineering environments.} } @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{mohn_characterization_2024, Author = {F. Mohn, K. Scheffler, J. Ackers, A. Weimer, F. Wegner, F. Thieben, M. Ahlborg, P. Vogel, M. Graeser, and T. Knopp}, Title = {Characterization of the Clinically Approved MRI Tracer Resotran for Magnetic Particle Imaging in a Comparison Study.}, Journal = {Physics in Medicine & Biology.}, Year = {(2024).}, Volume = {69.}, Number = {(13),}, Pages = {135014}, Note = {article, openaccess}, Doi = {10.1088/1361-6560/ad5828}, Abstract = {Abstract Objective. The availability of magnetic nanoparticles (MNPs) with medical approval for human intervention is fundamental to the clinical translation of magnetic particle imaging (MPI). In this work, we thoroughly evaluate and compare the magnetic properties of an magnetic resonance imaging (MRI) approved tracer to validate its performance for MPI in future human trials. Approach. We analyze whether the recently approved MRI tracer Resotran is suitable for MPI. In addition, we compare Resotran with the previously approved and extensively studied tracer Resovist, with Ferrotran, which is currently in a clinical phase III study, and with the tailored MPI tracer Perimag. Main results. Initial magnetic particle spectroscopy (MPS) measurements indicate that Resotran exhibits performance characteristics akin to Resovist, but below Perimag. We provide data on four different tracers using dynamic light scattering, transmission electron microscopy, vibrating sample magnetometry measurements, MPS to derive hysteresis, point spread functions, and a serial dilution, as well as system matrix based MPI measurements on a preclinical scanner (Bruker 25/20 FF), including reconstructed images. Significance. Numerous approved MNPs used as tracers in MRI lack the necessary magnetic properties essential for robust signal generation in MPI. The process of obtaining medical approval for dedicated MPI tracers optimized for signal performance is an arduous and costly endeavor, often only justifiable for companies with a well-defined clinical business case. Resotran is an approved tracer that has become available in Europe for MRI. In this work, we study the eligibility of Resotran for MPI in an effort to pave the way for human MPI trials.} } @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{mohn2023saline, Author = {F. Mohn, M. Exner, P. Szwargulski, M. Möddel, T. Knopp, and M. Graeser}, Title = {Saline bolus for negative contrast perfusion imaging in magnetic particle imaging.}, Journal = {Physics in Medicine & Biology.}, Year = {(2023).}, Volume = {68.}, Number = {(17),}, Pages = {5026}, Month = {aug}, Note = {article, openaccess}, Isbn = {0031-9155, 1361-6560}, Doi = {10.1088/1361-6560/ace309}, Keywords = {Mohn}, Abstract = {Magnetic Particle Imaging is capable to measure the spatial distribution of magnetic nanoparticles with high temporal resolution. As a quantitative tracer based imaging method, the signal is linear in the tracer concentration for any location that contains nanoparticles and zero in the surrounding tissue which does not provide any intrinsic signal. After tracer injection, the concentration over time (positive contrast) can be utilized to calculate dynamic diagnostic parameters like perfusion parameters in vessels and organs, which are an important tool in medical diagnosis. Every acquired perfusion image thus requires a new bolus of tracer with a sufficiently large iron dose to be visible above the background. We propose a method, where a bolus of physiological saline solution without any particles (negative contrast) displaces the remaining steady state concentration which in turn contributes to the image contrast. Perfusion parameters are calculated based on the time response of this negative bolus and compared to a positive bolus. Results from phantom experiments show that normalized signals from positive and negative boli are concurrent and deviations of calculated perfusion maps are low. Our method opens up the possibility to increase the total monitoring time of a future patient by utilizing a positive-negative contrast sequence, while minimizing the iron dose per acquired image.} } @article{mohn_real-time_2023, Author = {F. Mohn, P. Szwargulski, M. G. Kaul, M. Graeser, T. Mummert, K. M. Krishnan, T. Knopp, G. Adam, J. Salamon and C. Riedel}, Title = {Real-Time Multi-Contrast Magnetic Particle Imaging for the Detection of Gastrointestinal Bleeding.}, Journal = {Scientific Reports.}, Year = {(2023).}, Volume = {13.}, Number = {(1),}, Pages = {22976}, Note = {article, openaccess}, Doi = {10.1038/s41598-023-50041-3}, Keywords = {Mohn}, Abstract = {Gastrointestinal bleeding, as a potentially life-threatening condition, is typically diagnosed by radiation-based imaging modalities like computed tomography or more invasively catheter-based angiography. Endoscopy enables examination of the upper gastrointestinal tract and the colon but not of the entire small bowel. Magnetic Particle Imaging (MPI) enables non-invasive, volumetric imaging without ionizing radiation. The aim of this study was to evaluate the feasibility of detecting gastrointestinal bleeding by single- and multi-contrast MPI using human-sized organs. A 3D-printed small bowel phantom and porcine small bowel specimens were prepared with a defect within the bowel wall as the source of a bleeding. For multi-contrast MPI, the bowel lumen was filled with an intestinal tracer representing an orally administered tracer. MPI was performed to evaluate the fluid exchange between the vascular compartment of the bowel wall and the lumen while a blood pool tracer was applied. Leakage of the blood pool tracer was observed to the bowel lumen. Multi-contrast MPI enabled co-registration of both tracers at the same location within the bowel lumen indicating gastrointestinal bleeding. Single- and multi-contrast MPI are feasible to visualize gastrointestinal bleeding. Therefore, MPI might emerge as a useful tool for radiation-free detection of bleeding within the entire gastrointestinal tract.} } @article{Mohn2022pulsed, Author = {F. Mohn, T. Knopp, M. Boberg, F. Thieben, P. Szwargulski, and M. Graeser}, Title = {System Matrix Based Reconstruction for Pulsed Sequences in Magnetic Particle Imaging.}, Journal = {IEEE Transactions on Medical Imaging.}, Year = {(2022).}, Volume = {41.}, Number = {(7),}, Pages = {1862-1873}, Month = {July}, Note = {article, instrumentation}, Doi = {10.1109/TMI.2022.3149583}, Url = {https://ieeexplore.ieee.org/document/9706173}, Abstract = {Improving resolution and sensitivity will widen possible medical applications of magnetic particle imaging. Pulsed excitation promises such benefits, at the cost of more complex hardware solutions and restrictions on drive field amplitude and frequency. State-of-the-art systems utilize a sinusoidal excitation to drive superparamagnetic nanoparticles into the non-linear part of their magnetization curve, which creates a spectrum with a clear separation of direct feed-through and higher harmonics caused by the particles response. One challenge for rectangular excitation is the discrimination of particle and excitation signals, both broad-band. Another is the drive-field sequence itself, as particles that are not placed at the same spatial position, may react simultaneously and are not separable by their signal phase or shape. To overcome this potential loss of information in spatial encoding for high amplitudes, a superposition of shifting fields and drive-field rotations is proposed in this work. Upon close view, a system matrix approach is capable to maintain resolution, independent of the sequence, if the response to pulsed sequences still encodes information within the phase. Data from an Arbitrary Waveform Magnetic Particle Spectrometer with offsets in two spatial dimensions is measured and calibrated to guarantee device independence. Multiple sequence types and waveforms are compared, based on frequency space image reconstruction from emulated signals, that are derived from measured particle responses. A resolution of 1.0 mT (0.8 mm for a gradient of (−1.25,−1.25,2.5) T/m ) in x- and y-direction was achieved and a superior sensitivity for pulsed sequences was detected on the basis of reference phantoms.} } @COMMENT{Bibtex file generated on 2026-5-18 with typo3 si_bibtex plugin. Data from https://www.tuhh.de/ibi/people/fabian-mohn }