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Item type:Publication, Access status: with files , Low-power Iron selection and focus field generator(Infinite Science Publishing, 2022-03-21); ; ; ; A major issue for human-sizedMagnetic Particle Imaging scanners is the generation of sufficiently large magnetic gradient fields. By taking advantage of the field amplification properties of soft-iron, a considerable amount of power can be saved. In this work, an optimized selection and focus field generator is presented, that can generate flexible and high gradient fields at comparatively lowpower consumption. Coil spacing and possible field-free-point positions are similar to conventional MPI scanners designed with air coils, but with significantly less demands on infrastructure and cooling design. The optimization process is discussed and first field measurements are presented.Publicationtype: Journal ArticleScopus© Citations 2 36 85 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Multi-channel current control system for coupled multi-coil arrays(Infinite Science Publishing, 2022-03-21); ; ; ; For imaging and magnetic manipulation experiments in Magnetic Particle Imaging several field generating coils are required to produce sufficiently high and flexible magnetic fields. To minimize the power consumption, coils with iron cores are the best choice for low and medium frequency ranges. Such coils have comparatively high reactance and are often inductively coupled. The trivial approach to ensure target currents is to provide each coil with a current controlled source resulting in high system complexity and high costs. This paper presents a circuit design to distribute bipolar target currents from a single unipolar source with high accuracy, reducing unwanted coil coupling by a feedback controller. Thus, the number of current sources can be significantly reduced. With a regenerative concept, reactive power is stored and can be reused, allowing efficient and fast current switching.Publicationtype: Journal ArticleScopus© Citations 1 45 93 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Estimating the spatial orientation of immobilized magnetic nanoparticles with parallel-aligned easy axes(American Physical Society (APS), 2021-10-28); ; ; Advances in micromachinery and nanotechnology, such as magnetically actuated microrobots for navigating in viscous environments, are important driving forces in medicine. Recently, it has been shown that the spatial orientation of an ensemble of immobilized nanoparticles with parallel-aligned magnetic easy axes has an effect on the magnetization response to an external dynamic magnetic field. Here, we introduce a method that allows us to estimate the spatial orientation of this axis from the magnetization response and experimentally study a potential application scenario.Publicationtype: Journal ArticleScopus© Citations 3 94 182 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Towards accurate modeling of the multidimensional MPI physicsThe MPI image reconstruction problem requires, particularly for 2D and 3D excitation patterns, a measured system matrix due to the lack of an accurate model that is capable of describing the nanoparticles’ magnetization behavior in the MPI setup. Here we exploit a model based on Néel rotation for large particle ensembles and we find model parameters that describe measured 2D MPI data with higher precision than state of the art MPI models, which is also illustrated in phantom experiments. This is a short summary of the recent work (4) to which we refer to for all further details.Publicationtype: Journal ArticleScopus© Citations 1 58 93 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Quasi-simultaneous magnetic particle imaging and navigation of nanomag/synomag-D particles in bifurcation flow experiments(Infinite Science Publishing, 2020-09-02); ; ; ; Magnetic Particle Imaging (MPI) is used to visualize the distribution of superparamagnetic nanoparticles within 3D volumes with high sensitivity in real time. Recently, MPI is utilized to navigate micron-sized particles and micron-sized swimmers, since the magnetic field topology of the MPI scanner is well suited to apply magnetic forces. In this work, we analyze the magnetic mobility and imaging performance of nanomag/synomag-D for Magnetic Particle Imaging/Navigation (MPIN). With MPIN the focus fields are constantly switching between imaging and magnetic force mode, thus enabling quasi-simultaneous navigation and imaging of particles. In flow bifurcation experiment with a 100 % stenosis on one branch, we determine the limiting flow velocity of 1.36 mL/s, which allows all particles to flow only through one branch towards the stenosis. During this experiment, we image the accumulation of the particles within the stenosis. In combination with therapeutic substances, this approach has high potential for targeted drug delivery.Publicationtype: Journal ArticleScopus© Citations 4 109 82 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Reducing displacement artifacts by warping system matrices in efficient joint multi-patch magnetic particle imagingThe reconstruction of multi-patch magnetic particle imaging data requires a compromise between image quality and calibration time. While optimal image quality is ensured by the joint reconstruction approach, a system matrix needs to be acquired for each patch. One can reuse system matrices by shifting them in space, which decreases the calibration effort but leads to distortions due to field imperfections. In this work, we introduce a method for reducing displacement artifacts in the efficient joint multi-patch reconstruction. Based on the magnetic fields we propose a mapping that warps the central system matrix to capture the spatial displacement of off-center system matrices. In this way, we can maintain the low calibration time while significantly improving the image quality.Publicationtype: Journal ArticleScopus© Citations 8 71 98 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Simultaneous Magnetic Particle Imaging and Navigation of large superparamagnetic nanoparticles in bifurcation flow experiments(2020-03-15); ; ; ; Magnetic Particle Imaging (MPI) has been successfully used to visualize the distribution of superparamagnetic nanoparticles within 3D volumes with high sensitivity in real time. Since the magnetic field topology of MPI scanners is well suited for applying magnetic forces on particles and micron-sized ferromagnetic devices, MPI has been recently used to navigate micron-sized particles and micron-sized swimmers. In this work, we analyze the magnetophoretic mobility and the imaging performance of two different particle types for Magnetic Particle Imaging/Navigation (MPIN). MPIN constantly switches between imaging and magnetic modes, enabling quasi-simultaneous navigation and imaging of particles. We determine the limiting flow velocity to be 8.18 mL s−1 using a flow bifurcation experiment, that allows all particles to flow only through one branch of the bifurcation. Furthermore, we have succeeded in navigating the particles through the branch of a bifurcation phantom narrowed by either 60% or 100% stenosis, while imaging their accumulation on the stenosis. The particles in combination with therapeutic substances have a high potential for targeted drug delivery and could help to reduce the dose and improve the efficacy of the drug, e.g. for specific tumor therapy and ischemic stroke therapy.Publicationtype: Journal Article256 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , OpenMPIData: an initiative for freely accessible magnetic particle imaging dataMagnetic particle imaging is a tomographic imaging technique capable of measuring the local concentration of magnetic nanoparticles that can be used as tracers in biomedical applications. Since MPI is still at a very early stage of development, there are only a few MPI systems worldwide that are primarily operated by technical research groups that develop the systems themselves. It is therefore difficult for researchers without direct access to an MPI system to obtain experimental MPI data. The purpose of the OpenMPIData initiative is to make experimental MPI data freely accessible via a web platform. Measurements are performed with multiple phantoms and different image sequences from 1D to 3D. The datasets are stored in the magnetic particle image data format (MDF), an open document standard for storing MPI data. The open data is mainly intended for mathematicians and algorithm developers working on new reconstruction algorithms. Each dataset is designed to pose a specific challenge to image reconstruction. In addition to the measurement data, computer aided design (CAD) drawings of the phantoms are also provided so that the exact dimensions of the particle concentrations are known. Thus, the phantoms can be reproduced by other research groups using additive manufacturing. These reproduced phantoms can be used to compare different MPI systems.Publicationtype: Data PaperScopus© Citations 54 341 281 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , IVOCT catheter tracking and targeted drug delivery using magnetic particle imaging and magnetic particle navigation(2020); The modality Magnetic Particle Imaging (MPI) visualizes the quantitative distribution of magnetic nanoparticles by using static and oscillating magnetic fields. In this work, a submillimeter-accurate localization method is developed to identify fiducial markers more precisely for the registration of MRI and MPI volumes. With this method a IVOCT catheter is also tracked in 4D for bimodal imaging of IVOCT and MPI. Further, the method of Magnetic Particle Imaging and Magnetic Particle Navigation is used to navigate magnetic particles through a bifurcation within a vascular flow. Finally, the novel easy-axis aligned MPI contrast is used to determine the easy-axis orientation of samples.Publicationtype: Doctoral Thesis353 253 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Discriminating nanoparticle core size using multi-contrast MPI(2019-03-29); ; ; ; Magnetic particle imaging (MPI) is an imaging modality that detects the response of a distribution of magnetic nanoparticle tracers to alternating magnetic fields. There has recently been exploration into multi-contrast MPI, in which the signal from different tracer materials or environments is separately reconstructed, resulting in multi-channel images that could enable temperature or viscosity quantification. In this work, we apply a multi-contrast reconstruction technique to discriminate between nanoparticle tracers of different core sizes. Three nanoparticle types with core diameters of 21.9 nm, 25.3 nm and 27.7 nm were each imaged at 21 different locations within the scanner field of view. Multi-channel images were reconstructed for each sample and location, with each channel corresponding to one of the three core sizes. For each image, signal weight vectors were calculated, which were then used to classify each image by core size. With a block averaging length of 10 000, the median signal-to-noise ratio was 40 or higher for all three sample types, and a correct prediction rate of 96.7% was achieved, indicating that core size can effectively be predicted using signal weight vector classification with close to 100% accuracy while retaining high MPI image quality. The discrimination of the core size was reliable even when multiple samples of different core sizes were placed in the measuring field.Publicationtype: Journal ArticleScopus© Citations 25 37