International Journal on Magnetic Particle Imaging (IJMPI)
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Hybrid harmonic projection reconstruction for magnetic particle imaging
No full textX-space is a rapid reconstruction technique based on time domain signals for magnetic particle imaging (MPI). However, due to particle relaxation effect, signal distortion and image blur will inevitably occur in high drive field and low gradient field. In this work, we propose a hybrid harmonic projection (HHP) reconstruction method based on time-frequency spectrum, which uses the response harmonic amplitude in a short time for continuous projection reconstruction. In order to more accurately simulate the actual dynamic magnetic field distribution, a 3D finite element model of MPI scanner was constructed. Simulation and reconstruction results show that harmonic projection has the advantage of realizing high resolution in high drive field compared with time domain projection. In addition, HHP can significantly reduce the high order harmonic artifacts and show good quantitative imaging performance
Multi-Channel Current Control System for Coupled Multi-Coil Arrays
No full textFor imaging and force experiments in Magnetic Particle Imaging several field generating coils are required to produce sufficiently high and flexible magnetic fields. To minimize power consumption, coils with iron cores are the best choice for low and medium frequency ranges. Such coils have comparatively high reactance and often are 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
A synthesis apparatus for the continuous flow synthesis of Magnetic Nanoparticles
No full textIn magnetic particle imaging, superparamagnetic iron oxide nanoparticles are used as a tracer material. By utilizing the non-linear magnetization of the particles, their concentration in the body can be determined with high spatial and temporal resolution. Some of the important properties of the particles are their core diameter, hydrodynamic diameter, size distribution, and magnetic properties. In order to be able to produce particles with adequate quality and high reproducibility, a prototype of a continuous-flow synthesis apparatus is designed and tested. This research deals with the design and construction of a device that can use the co-precipitation synthesis method to synthesis particles in continuous flow
Investigating methods for temperature reconstruction based on simulated data
No full textMagnetic particles imaging (MPI) leverages the nonlinear response of magnetic particles for imaging. Since the response of the particles is dependent on the environment like temperature or viscosity it can reconstruct images of these properties. It has been shown that magnetic particle imaging is a promising tool to monitor temperatures using a reconstruction approach called multi-color MPI. Multi-color MPI can reconstruct the temperatures of the particles within the field of view and enables temperature imaging in applications such as magnetic particle hyperthermia. This work investigates different approaches to reconstruct temperature differences as well as different reconstruction schemes for multi-color MPI. The performed reconstructions are based on simulated 2D system matrices providing a reliable baseline for comparisons. The simulated system matrices are obtained by simulations of the magnetic particles in the per voxel different applied magnetic fields
Fully mechanically driven Traveling Wave MPI
No full textMagnetic Particle Imaging (MPI) is a novel imaging technique utilizing time-varying magnetic fields to determine the distribution of superparamagnetic iron-oxide nanoparticles in 3D. The usage of electrical coils for the generation of the desired strong magnetic field gradient as well as the time-varying magnetic fields allows flexible and fast imaging, but the corresponding high energy consumption also requires sophisticated cooling. The usage of permanent magnets provides the advantage of generating high magnetic field gradients without requiring electrical power and cooling, but also brings limitations with respect of flexibility and the size of the field of view. A novel approach utilizing rotatable Halbach rings is introduced, which overcomes the restrictions of static permanent magnet designs and provides the flexibility of a mechanically driven Traveling Wave MPI scanner
MPI region of interest (ROI) analysis and quantification of iron in different volumes
No full textMPI directly detects superparamagnetic iron oxides (SPIOs), which should enable precise, accurate and linear quantification. However, selecting a region of interest (ROI) has strong effects on MPI quantification results. Ideally, ROI selection should be simple, user-independent, and widely applicable. In this work, we describe and compare four MPI ROI selection methods and assesses their performance in vitro and in vivo. To explore the effect of ROI selection, ten ferucarbotran phantoms were imaged, each contained the same amount of iron but varied in volume. Three users tested the accuracy of the ROI methods for quantification of these samples. Lastly, quantification of ferucarbotran-labeled stem cells in vivo was demonstrated with the four ROI methods. We demonstrate that each ROI method has strengths. We conclude there is an important trade-off between ROI size and the accuracy of iron quantification, therefore the choice of ROI selection method for each study must be carefully informed
Role of Phase Encoding in Pulsed Magnetic Particle Imaging
No full textNon-sinusoidal excitation waveforms have the ability to improve the signal-to-noise ratio and image resolution under certain conditions. Yet, the ability to use phase information for spatial encoding is expected to diminish as sharp pulses lead to concurrent signal response due to steep slopes and therefore less phase information. This motivates investigations into alternate sampling approaches that mitigate a loss in spatial encoding. However, measurements and image reconstruction results indicate that 10 times faster slew rates compared to sine excitation lead to enough phase information to resolve basic features using system matrix reconstruction
Optimizing magnetic particle image resolution using superferromagnetic nanoparticles modified through post-synthesis oxidation
No full textMagnetic Particle Imaging (MPI) is a novel tracer-based imaging modality that allows for exquisitely sensitive celltherapy trackingin vivo, cancer imaging, lung ventilation/perfusion imaging, and hemorrhage detection. MPIuses superparamagnetic iron oxide Particles (SPIOs) as tracers with linear contrast, zero tissue attenuation, andmicromolar sensitivity, all with zero ionizing radiation and infinite reporter persistence. However, MPI’s poor spatialresolution (roughly 1 mm in a 7T/m gradient) is holding back clinical translation. Our lab recently reported theuse of superferromagnetic nanoparticles (SFMIOs) for MPI demonstrating a 10-fold improvement (?100?m) inresolution compared to the approximately mm for commercially available SPIOs. In the current work, we detail theproduction of SFMIO for MPI using a modified extended LaMer synthesis. We implement a post-oxidation step tothe process for repeated and reproducible production of high resolution SFMIO particles
An iron-oxide nanoparticle with therapeutic capability in Magnetic Fluid Hyperthermia and diagnostic capability in MRI and MPI
No full textM55 belongs to a class of innovative nanomaterials, constituted by doped ferrite, with potential application in tumor therapy, as agents for Magnetic Fluid Hyperthermia (MFH), and in diagnosis, as contrast agents for MRI and MPI. Interestingly, such nanomaterials are characterized by a self-limiting temperature that can be modulated by adjusting the composition of the nanomaterial itself. M55 was coated with a double shell of citrate and glucose. We demonstrated that it has good capability as contrast agent for MRI and MPI. Moreover we tested its biocompatibility in a triple negative human breast cancer line and its efficacy as MFH agent in the same cell line. Despite relatively low SAR values in water solution, this agents was highly efficient in decreasing cell viability after two MFH treatments. Finally, we demonstrated that it can be useful to label cells for cell tracking in MPI. Although preliminary, these results are encouraging and push toward in vivo tests of such material. 
Design of a more easily shimmable gradiometric coil using linear programming
No full textMagnetic particle imaging (MPI) is a tracer imaging modality that detects superparamagnetic iron oxide nanoparticles (SPIOs), enabling sensitive, radiation-free imaging of cells and disease pathologies. The arbitrary waveform relaxometer (AWR) is an indispensable platform for developing magnetic nanoparticle tracers and evaluating tracer performace for magnetic particle imaging applications. One of the biggest challenges in arbitrary waveform excitation is direct feedthrough interference, which is usually six orders of magnitude larger than the signal from magnetic nanoparticles. Direct feedthrough is often mitigated with a gradiometric cancellation coil which requires extremely precise placement in order to achieve adequate decoupling from the transmit excitation coil. This work will showcase a coil design of a transmit coil that meets excitation capability requirements with an order of magnitude more forgiving mechanical tolerance