Modeling the magnetization dynamics for large ensembles of immobilized magnetic nanoparticles in multi-dimensional magnetic particle imaging
TL;DR: In this paper, a model-based approach where the magnetization response is simulated by a Neel rotation model for the particle's magnetic moments and the ensemble magnetization is obtained by solving a Fokker-Planck equation approach is presented.
About: This article is published in Journal of Magnetism and Magnetic Materials.The article was published on 2022-02-01 and is currently open access. It has received 1 citations till now. The article focuses on the topics: Magnetization & Magnetic particle imaging.
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TL;DR: In this article , a general multi-channel calibration procedure for inductive receive paths in magnetic particle imaging (MPI) and a blueprint to investigate model and method uncertainties is provided. And the calibration procedure is generalized to also cover nonorthogonal and nonhomogeneous receive coils.
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 article, 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 nonorthogonal and nonhomogeneous 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.
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TL;DR: This paper discusses targeted drug delivery and triggered release, novel contrast agents for magnetic resonance imaging, cancer therapy using magnetic fluid hyperthermia, in vitro diagnostics and the emerging magnetic particle imaging technique that is quantitative and sensitive enough to compete with established imaging methods.
Abstract: Biomedical nanomagnetics is a multidisciplinary area of research in science, engineering and medicine with broad applications in imaging, diagnostics and therapy. Recent developments offer exciting possibilities in personalized medicine provided a truly integrated approach, combining chemistry, materials science, physics, engineering, biology and medicine, is implemented. Emphasizing this perspective, here we address important issues for the rapid development of the field, i.e., magnetic behavior at the nanoscale with emphasis on the relaxation dynamics, synthesis and surface functionalization of nanoparticles and core-shell structures, biocompatibility and toxicity studies, biological constraints and opportunities, and in vivo and in vitro applications. Specifically, we discuss targeted drug delivery and triggered release, novel contrast agents for magnetic resonance imaging, cancer therapy using magnetic fluid hyperthermia, in vitro diagnostics and the emerging magnetic particle imaging technique, that is quantitative and sensitive enough to compete with established imaging methods. In addition, the physics of self-assembly, which is fundamental to both biology and the future development of nanoscience, is illustrated with magnetic nanoparticles. It is shown that various competing energies associated with self-assembly converge on the nanometer length scale and different assemblies can be tailored by varying particle size and size distribution. Throughout this paper, while we discuss our recent research in the broad context of the multidisciplinary literature, we hope to bridge the gap between related work in physics/chemistry/engineering and biology/medicine and, at the same time, present the essential concepts in the individual disciplines. This approach is essential as biomedical nanomagnetics moves into the next phase of innovative translational research with emphasis on development of quantitative in vivo imaging, targeted and triggered drug release, and image guided therapy including validation of delivery and therapy response.
717 citations
TL;DR: The quality of the least-squares solution can be improved by incorporating a weighting matrix using the reciprocal of the matrix-row energy as weights and this weighting strategy in combination with the conjugate gradient method improves the image quality and substantially shortens the reconstruction time.
Abstract: Magnetic particle imaging (MPI) is a new imaging technique capable of imaging the distribution of superparamagnetic particles at high spatial and temporal resolution. For the reconstruction of the particle distribution, a system of linear equations has to be solved. The mathematical solution to this linear system can be obtained using a least-squares approach. In this paper, it is shown that the quality of the least-squares solution can be improved by incorporating a weighting matrix using the reciprocal of the matrix-row energy as weights. A further benefit of this weighting is that iterative algorithms, such as the conjugate gradient method, converge rapidly yielding the same image quality as obtained by singular value decomposition in only a few iterations. Thus, the weighting strategy in combination with the conjugate gradient method improves the image quality and substantially shortens the reconstruction time. The performance of weighting strategy and reconstruction algorithms is assessed with experimental data of a 2D MPI scanner.
173 citations
TL;DR: For the first time, the system function is calculated using a model of the signal chain and allows for reconstruction of the particle distribution in a 1-D MPI experiment, enabling fast generation of system functions on arbitrarily dense grids.
Abstract: Magnetic particle imaging (MPI) is a new imaging modality capable of imaging distributions of superparamagnetic nanoparticles with high sensitivity, high spatial resolution and, in particular, high imaging speed. The image reconstruction process requires a system function, describing the mapping between particle distribution and acquired signal. To date, the system function is acquired in a tedious calibration procedure by sequentially measuring the signal of a delta sample at the positions of a grid that covers the field of view. In this work, for the first time, the system function is calculated using a model of the signal chain. The modeled system function allows for reconstruction of the particle distribution in a 1-D MPI experiment. The approach thus enables fast generation of system functions on arbitrarily dense grids. Furthermore, reduction in memory requirements may be feasible by generating parts of the system function on the fly during reconstruction instead of keeping the complete matrix in memory.
168 citations
TL;DR: Experimental evidence of the separability of signals from different particle types and aggregation states using a 'multi-color' reconstruction approach is presented and several mechanisms are discussed that may form the basis for successful signal separation.
Abstract: Magnetic particle imaging is a new approach to visualizing magnetic nanoparticles. It is capable of 3D real-time in vivo imaging of particles injected into the blood stream and is a candidate for medical imaging applications. To date, only one particle type has been imaged at a time, however, the ability to separate signals acquired simultaneously from different particle types or from particles in different environments would substantially increase the scope of the method. Different colors could be assigned to different signal sources to allow for visualization in a single image. Successful signal separation has been reported in spectroscopic experiments, but it was unclear how well separation would work in conjunction with spatial encoding in an imaging experiment. This work presents experimental evidence of the separability of signals from different particle types and aggregation states (fluid versus powder) using a 'multi-color' reconstruction approach. Several mechanisms are discussed that may form the basis for successful signal separation.
167 citations