International Journal on Magnetic Particle Imaging (IJMPI)
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VivoTrax+ improves the detection of cancer cells with magnetic particle imaging
No full textCellular imaging is a rapidly growing field as novel tracers and imaging techniques are developed. Magnetic particle imaging (MPI) detects superparamagnetic iron oxide nanoparticles (SPIO), which can be used to label cells. The unique detection of SPIO-labeled cells boasts MPI as a sensitive modality; as such, the type of SPIO has a critical role in determining sensitivity and resolution. For cell tracking applications, the ideal SPIO should label cells efficiently and retain its sensitivity after cellular uptake. VivoTraxTM, a commercially available and commonly used SPIO for MPI, was recently re-released as VivoTrax+TM with an improved size distribution enriched for larger particles. In this study, VivoTrax+TM is shown to enhance cellular labeling and improve in vitro/in vivo sensitivity. Importantly, the sensitivity of both SPIO significantly decreased after cellular internalization. The results from this study emphasize the importance of translating SPIO performance in vivo to maintain its utility for cell tracking applications
Vicinity Effects of Field Free Point on the Relaxation Behavior of MNPs
No full textIn Magnetic Particle Imaging (MPI), the distribution of magnetic nanoparticles (MNPs) is imaged by moving a field free point (FFP) in space. All MNPs in close vicinity of the FFP contribute to the signal induced on the receive coil. The relaxation behavior of these MNPs are subject to a DC field due to the selection field (SF). In this work, we investigate the effects of the DC field on the relaxation behavior of the MNPs, with the goal of understanding the differences between the measured relaxations in Magnetic Particle Spectrometer (MPS) setups vs. MPI scanners
MPI tracer interactions and their effect on signal stability
No full textNanoparticles tend to agglomerate following their in vivo or in vitro application. This leads to particle interaction and, for magnetic particle imaging (MPI) tracers, to magnetic coupling phenomena. Here, we investigate these effects and their influence on magnetic particle spectroscopy (MPS) and MPI signal stability. Highly magnetic flame-made Zn-ferrites with controlled interparticle distance are suggested as a stable MPI tracer system. Due to their pre-aggregated morphology, additional agglomeration does not substantially alter their magnetic response. This is in strong contrast to frequently investigated polymer-coated iron oxide nanoparticles, which show a massive MPS signal loss in a biologically relevant dispersion medium compared to water. This effect is also shown during MPI and renders these tracers inapplicable to further applications. Our flame-made Zn-ferrites, on the other hand, show sufficient signal stability, which allows their detailed quantification via MPI
Deep learning MPI super-resolution by implicit representation of the system matrix
No full textImage reconstruction in MPI is often performed with the system matrix (SM) approach, where the signal of a reference particle sample is measured on a predefined grid in the scanner. This calibration measurement is not only very time-consuming but also places an upper limit to the spatial resolution of the reconstructed image, given by the spacing between two adjacent SM grid points. Recently, implicit neural representations have shown great results in computer vision. They allow for oversampling to gain a higher frequency explicit representation of an object without fixing a certain upsampling scale. We show that this can be used to mostly restore an SM with up to 16x subsampling in 2D and to generate SMs of arbitrary size as an additional tool for image quality improvement. However, we also found that classic spline interpolation is a reasonable tool for this task as well
Efficient 3D Drive-Field Characterization for Magnetic Particle Imaging Systems
No full textMagnetic particle imaging uses time-dependent drive fields for signal generation, which are designed to be homogeneous in order to achieve a similar image quality all over the volume of interest. In practice, the fields are not exactly homogeneous and in turn a precise knowledge of the spatial field profile is necessary when using a model-based reconstruction approach. In this work, we propose an efficient method for the measurement and compact representation of the drive fields using a small 3D calibration coil and solid harmonics
Imaging of the lumen of intracranial flow diverter stents with MPI
No full textFlow diverter (FD) for the endovascular treatment of intracranial aneurysms are an innovative new stent design. These nitinol stents modulate the turbulent inflow into an aneurysm, offering the potential of occlusion through thrombosis. After treatment follow-up imaging is necessary. Digital subtraction angiography is the gold-standard in follow-up of flow-diverters, yet its invasiveness with an 1% complication rate and patient exposure to ionizing radiation limit its application. The metallic stent material causes artifacts in computed tomography and magnetic resonance imaging compromising clinical interpretation. Magnetic particle imaging (MPI) is a fast and sensitive tomographic imaging modality that uses magnetic fields to visualize superparamagnetic iron-oxide nanoparticles (SPIOs). Inherent advantages of MPI are the background- and radiation-free visualization of tracer material. Thus, magnetic particle imaging (MPI) may be beneficial for patients with FD treated aneurysms. The aim of this work was to illustrate the feasibility of MPI visualizing the stent lumen of flow diverters in a phantom stud
Non-radioactive imaging of bone marrow using antibody-conjugated nanoparticles in magnetic particle imaging
No full textBone marrowserves a crucial role in the body, producing hematopoietic stem cells and blood products. Imaging bone marrow could help doctors determine bone marrow disorders and have an early understanding of the metastatic distribution of tumors in the bone. Colloidal tracers that target the reticuloendothelial system (RES) such as the liver, spleen and bone marrow are commonly used to image bone marrow. Alternatively, antibodies specific to granulocytes, especially neutrophils, can be used to image the myeloid distribution of bone marrow. Using antibody functionalized superparamagnetic iron oxide (SPIO) nanoparticles as tracers, magnetic particle imaging (MPI) could image bone marrow in vivo. In this work, we imaged bone marrow in vivo using anti-Ly6G antibody functionalized nanoparticles that are specific towards surface antigens expressed on granulocytes
Demonstration of the new detection limit for the single-sided FFL MPI scanner with a surface gradiometer receive coils
No full textTraditional MPI scanners utilize cylindrical bore geometry which prevents scaling up the scanner to accommodate human subject. Our single-sided MPI device utilizes a field-free line topology with a single drive coil and a surface receive coil that detects the response of nanoparticles. Common to all single-sided devices, however, excitation field results in saturation in the receive chain concealing the small SPIO response and impinging potential sensitivity gain. In this work we show how a surface gradiometer receive coil provides highest sensitivity to date and demonstrate a new detection limit in a single-sided scanner of 100 ng of iron
PNS Limits for Human Head-Size MPI Systems: Preliminary Results
No full textMagnetic Particle Imaging (MPI) utilizes kHz-range sinusoidal drive fields to excite the magnetic nanoparticles. These time-varying magnetic fields form electric fields within the human body, which in turn can induce peripheral nerve stimulation (PNS), also known as magnetostimulation. In this work, we report the preliminary results of human subject experiments for human head-size MPI systems. These experiments were performed on a solenoidal head coil that achieved an order of magnitude reduction in the voltages needed to generate the targeted magnetic fields
MPI system using the mechanically movement of a three-dimensionally arranged permanent magnets
No full textWe present a magnetic particle imaging (MPI) system arranging permanent magnets three dimensionally to form a Field Free Line (FFL) and then moving the FFL mechanically. FFL was formed in the center of the magnet structure and the FFL was moved in the sample volume translationally and rotationally. Securing the signal due to the nonlinear magnetic properties of Nano Magnetic Particle (NMP) was obtained by applying electromagnetic waves with two different frequencies. The performance of the system was tested using the silicone tube with a spiral structure filled with NMP, and it was shown that 3D images can be obtained using the system proposed