International Journal on Magnetic Particle Imaging (IJMPI)
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Gradient-based rotational drift and frequency encoding for high-resolution magnetic particle imaging
No full textMagnetic particles exhibit nonlinear rotational drift in rotating magnetic fields, which is dependent on the particle properties and external fields. The rotational drift frequency difference from the particles on an FFL in a gradient rotational excitation field may generate a free-induction decay signal and can be used as a phase encoding method for simultaneous high-resolution and large field-of-view MPI. We propose the use of gradient-based rotational drift to excite magnetic nanoparticles on an FFL. The different rotational drift frequencies from different FFL locations induce free induction decay and refocused echo signals. Magnetic particle concentrations on the FFL can be solved by using Fourier-transform-based reconstruction. The simulation was performed using in-house developed software based on the Interactive Data Language. IDL. The 2D Shepp-Logan phantom and the digital vessel phantom were used for an FFL-based raster scan and image reconstruction simulation. The correlation coefficient between the original and reconstructed images was used for image quality assessment. The dephasing signals and echos form a k-space for image reconstruction. Reconstructed images exhibited an increasing resolution from left to right with an increasing rotational drift frequency slope under a spatially linear excitation field. In the reconstructed brain TOF-MRA image with multi-angle gradient-based rotational excitation from filtered back-projection, the main branches and small vessels are visible with a high peak SNR. In conclusion, we propose the use of gradient-based rotational drift to excite magnetic nanoparticles for high-resolution MPI
Empowered in-vivo functional brain imaging with Ferucarbotran-loaded red blood cells
No full textOur previous MPI data validated that engineered SPIO-loaded RBCs have improved in-vivo stability over the corresponding free SPIO-based contrast agents. We now demonstrate the efficiency of these biomimetic constructs in the field of functional brain imaging using Functional Magnetic Resonance Imaging (fMRI). Data was obtained in an anesthetised rodent model using a 7 Tesla preclinical MRI system (Bruker, Biospec 70/30). Responses to i) neuronal activation of the somatosensory barrel cortex (via repeated electrical stimulation of the whisker pad) and ii) respiratory challenge (10% increased FiCO2) were recorded pre and post injection of 1.5 ml of human Ferucarbotran-loaded-RBCs (corresponding to 16 µmoles Fe) as an intravenous SPIO-based tracer. Post injection we found high contrast-to-noise, Cerebral Blood Volume (CBV) weighted signal changes in line with previous preclinical fMRI studies using free SPIO nanoparticles. CBV-fMRI offers functional sensitivity at cortical laminar resolutions as a significant advantage over routine Blood Oxygenation Level Dependent (BOLD) fMRI. Furthermore, RBCs are biocompatible and biodegradable iron oxide-carriers. Hence, our novel approach permits the easier targeting of CBV markers with higher contrast (over BOLD fMRI) and in the future could drive development of longitudinal assessment of brain function using safe and long half-life SPIO-based tracers
Phase offset Calibration of Instantaneous Position for Magnetic Particle Imaging
No full textMagnetic particle imaging using X-space reconstruction typically requires the knowledge of the Field-Free Point (FFP) position at each time point. Due to the fixed sampling delay caused by imperfections in electronic components, it is necessary to calibrate the phase of the periodic position signal. In this study, we use the current sensor signal mapping to obtain the initial value of the instantaneous position, the eigenvalues of the reconstructed images are used to reflect the degree of phase offset, and the calibration result is calculated automatically by the program through the software modulation. Experimental results show that our phase calibration for correcting instantaneous position is simple, effective, and fast
A high resolution permanent magnet MPI device
No full textMagnetic particle imaging (MPI) is a novel emerging tomographic technique with high resolution and high sensitivity.Typically, the magnetic fields of MPI scanners are generated electromagnetically, resulting in an immense power consumption and making it difficult to apply in clinical research. The MPI device based on Halbach array provide a new solution. In this device, a mechanically driven scanning MPI device was designed using a Halbach permanent magnet array. The device consists of four layers of Halbach arrays, and is ultimately capable of achieving a FOV of 70mmdiameter, and a resolution better than 0.5mm. Compared with the previous Halbach permanent magnet MPI device, this device generates three dimensions of gradients that can be used for 3D imaging. Moreover, the stability of the structure was analyzed by structural mechanics calculations and magnetic field error simulations, and the feasibility of the device was analyzed by simulations of the system scan trajectory and image reconstruction
High resolution magnetic nanoparticle tracers for CAR-T cell tracking, stroke, GI bleed and pulmonary embolism imaging in Magnetic Particle Imaging
No full textMagnetic Particle Imaging (MPI) is a breakthrough in medical imaging technology. MPI already showed great promise towards cancer, gastrointestinal bleeds, pulmonary embolisms, stroke and WBC imaging, and it could soon provide a rapid, high-resolution and zero-radiation alternative to Nuclear Medicine studies like PET and SPECT. MPI could soon give unequivocal CAR-T cell immunotherapy treatment efficacy feedback in just 3 days instead of 3 months, allowing nimble treatment optimization for each patient. Currently, the biggest obstacle in MPI is the poor spatial resolution of MPI tracers. In this work, we report a recently discovered commercially available tracer — Synomag®-D — that shows a 3.5-fold resolution boost when imaged with a weaker drive field. This resolution boost could reduce the gradient cost and hardware constraints and bring MPI a step closer to clinical translation
MPI Transfer-Function Estimation with Receive-Coil Coupling
No full textTime- and memory-consuming calibration measurements are a major drawback in system-matrix-based reconstructions in magnetic particle imaging (MPI). Especially, exchanging the receive coils requires new system matrices and therefore new calibration measurements. To reduce the number of such measurements, the MPI transfer function can be used to transfer the system matrix of one receive coil set to another. The transfer function can be obtained by a direct measurement or by estimation using a measured system matrix of each setup. In this abstract, we extend the latter to incorporate coupling of the receive coils while using only a few voxels of the system matrices. In this way, we can transfer system matrices between two different receive setups, both of which may contain non-orthogonal coils
Modular MPI Component Testing Facility
No full textThe image quality of magnetic particle imaging depends on the interference-free measurement of the particlespectrum. Systematic errors due to harmonic distortions in the components used for implementation complicatethe development of efficient imaging devices. To test the suitability of parts for the development of MPIscanners, a test bench was developed in which the components to be tested can be integrated, to evaluate theirsuitability using the measured spectrum. Different forms of connectors integrated into the high-current pathwere analyzed for their influence on the signal quality using this test bench. An evaluation of this componentscan be made from the clearly visibible distortions in the spectrum recorded with the high-sensitive test system
Evaluation of magnetization dynamics influenced by Brownian relaxation in magnetic nanoparticles
No full textMagnetic relaxations determine the magnetization properties of magnetic nanoparticles for biomedical applications such as the tracer of magnetic particle imaging. In this study, the magnetization dynamics influenced by the dynamics of the particle body as the easy axes of magnetic nanoparticles of different structures were evaluated measuring the magnetization curves, intensity of harmonic components in magnetization, and oscillation and orientation of the easy axis. To observe the effects of the Brownian relaxation associated with particle rotation, we prepared magnetic nanoparticles fixed with epoxy resin to inhibit the particle rotation and dispersed them in water where the particle rotation occurred. It is indicated that the Brownian relaxation observed as the particle oscillation and orientation significantly affected the magnetization dynamics of magnetic nanoparticles in the ferromagnetic regime
Linear structures of magnetic nanoparticles in hyperthermia and magnetic particle imaging
No full textThe development of theranostic devices combining magnetic particle imaging (MPI) and magnetic hyperthermia opens new possibilities for clinical applications of magnetic nanoparticles (MNP), e.g., hyperthermia-mediated drug delivery. Enhancing MNP performance for such applications can be achieved by using linear structures of MNP (i.e. chains, elongated clusters) instead of randomly distributed MNP. Here, we investigate the hyperthermia and MPI performance of two types of MNP linear structures: one generated by exposing MNP to a static magnetic field inside a hydrogel and the other by extruding a mixture of polypropylene and MNP to hybrid fibers. For both types of linear structures, an increase in heating efficiency and MPI signal was observed when the linear structure orientation is in the direction of the excitation field. In summary, the generation of MNP linear structures is a promising approach to increase their performance in MPI and magnetic hyperthermia. For MPI image reconstruction, the orientation of the linear structures relative to the drive field direction should be considered
Resotran® meets MPI – clinically approved Ferucarbotran reintroduced: a major leap towards MPI in humans
No full textMPI has been on a trajectory towards clinical application in humans for years. As scanners and techniques mature, clinical testing is effectively prohibited by the lack of a clinically approved tracer. This changes now by the reintroduction of a Ferucarbotran-based tracer into the market, Resotran®. Although initially intended for use in MRI, we tested Resotran® for its viability in MPI. The other Ferucarbotran-based tracer fit for MRI and MPI is Resovist®, which is well known and characterized but was discontinued years ago. We present initial data on the characterization of Resotran® in comparison to Resovist®