International Journal on Magnetic Particle Imaging (IJMPI)
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A portable single-sided magnetic particle imaging concept using amplitude modulation for breast conserving sugery
No full textIn breast-conserving surgery (BCS), complete removal of breast cancers and minimal expulsion of normal cells are very important. Since surgery is a burdensome treatment for the patient, the surgical procedures should be minimally invasive while ensuring the maximum degree of completion. Before and after surgery, the location of the tumor and the presence of residual tumor can be checked through examination outside the operating room. However, if residual tumors are identified in the postoperative examination, reoperation or additional chemotherapy is required. Therefore, in order to improve the degree of completion during surgery, a small real-time device that can be used inside the operating room is presented. Using these devices, the presence of residual tumor can be examined before suturing the affected area. Furthermore, this article proposes how detecting the exact location will improve the completion of the initial surgery
MPI visualization of hybrid implant fibers using different system matrices
No full textHybrid stents can be used in cardiovascular applications and in hollow organ tumor therapy. They open the occluded area and can induce local hyperthermia by application of an alternating magnetic field (AMF) destroying cancer cells. Here, we investigate hybrid fibers made of polypropylene (PP) fibers with incorporated magnetic nanoparticles (MNP) via magnetic particle imaging (MPI). An influence of the MNP mobility and MNP agglomeration state as well as the orientation of elongated MNP agglomerations with respect to the drive field of the system matrix reference on the image reconstruction were determined. Best image resolution for a phantom consisting of two parallel fibers was achieved with reconstructions using system matrices of a fiber where MNP agglomerations point in the same direction as the ones of the phantom with respect to the drive field. Changes in MNP mobility, agglomeration state and their preferred directions have effects on the resulting image quality and must be considered in future measurements of complex structures of hybrid fibers
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 (SPIO) particles, which can be used to label cells., The type of SPIO has a critical role in determining MPI 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+ with an improved size distribution enriched for larger particles. In this study, VivoTrax+ 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.
Int. J. Mag. Part. Imag. 8(2), 2022, Article ID: 2210001, DOI: 10.18416/IJMPI.2022.221000
1D Imaging with a Single-Sided FFL Magnetic Particle Imaging Scanner
No full textOver the past decade, various MPI scanner topologies have been demonstrated, which included a single-sided scanner. Such a scanner features all its hardware located on one side, offering accessibility without limitations due to the size of the object of interest. The original scanner design utilized a field-free point making it very robust in the hardware implementation. In our design of a single-sided scanner we utilize a field-free line, which provides higher sensitivity and robust image reconstruction. In this work we demonstrate first one-dimensional imaging with a single-sided field-free line MPI scanner
Assessing excitation field frequency for various magnetic nanoparticles
No full textMagnetic detection is presently used in a handheld probe to identify metastasis bearing lymph nodes (LNs) fora variety of oncology applications. This approach utilises the underlying assumption that injected magneticnanoparticles (MNPs) will migrate to LNs with the shortest path to a tumor and therefore will generate a localizedmagnetic signal. Nonlinear magnetic detection is specific for magnetic nanoparticles and negates the influenceof human tissue and surgical instruments. Our nonlinear DiffMag principle uses a combination of an AC and DCmagnetic field to activate MNPs and records the consequent magnetic signal. MNP detection can be optimised tomaximise detection parameters, such as iron sensitivity and detection depth. Tuning the excitation field frequencyto physical properties of MNPs (such as particle diameter) leads to improved detection.This study assesses the magnetic properties of various MNPs (SHP15, SHP20, SHP25, SHP30) and compare thefindings to clinically available MNP (Magtrace®). Magnetization response of these MNPs was acquired using theSuperParamagnetic Quantifier (SPaQ) at various AC field frequencies (1, 2.5, 5, 7.5, 10, 12.5 and 15 kHz). Two featurescapturing magnetization response (maximum signal difference and full width at half maximum) were extracted tocompare MNPs. Additional acquisition captured AC susceptibility (ACS) in the range 10Hz-1MHz.SPaQ results show an optimal excitation frequency between 5 and 12.5 kHz for the various types of MNPs. ACSresults show small particles (SHP15) are Néel dominated, large MNPs (SHP30) are Brownian dominated and thesizes in between show a combination of Néel and Brownian relaxation. The larger, Brownian dominated MNPsperform best in nonlinear magnetic detection
Computational modeling of superferromagnetism in finite-length chains of superparamagnetic Iron Oxide tracers for use in super-resolution Magnetic Particle Imaging
No full textMagnetic Particle Imaging (MPI) is a novel tracer imaging modality that images the spatial distribution of super- paramagnetic iron oxide nanoparticles (SPIOs), allowing for the sensitive and radiation-free imaging of labeled cells and targeted disease. Recent works have shown that at high concentrations, SPIOs display extremely sharp magnetic responses, resulting in 10-fold resolution and signal improvements. Dubbed superferromagnetic iron oxide particles (SFMIOs), these particles appear to interact with neighbours, effectively amplifying applied fields. This work performs a simulation of ensembles of linear chains of interacting SPIOs to elucidate SFMIO behavior and guide practical constraints in SFMIO synthesis. We show that working within certain physical constraints (chain length distributions and SPIO separation) preserves the improvements observed from SFMIOs
MPI of soft ferromagnetic needles
No full textThe combination of magnetic particle imaging with magnetic actuation is a promising additional application of MPI field generators aside from the imaging of SPIO tracers, because similar field configurations are needed. Since ferromagnetic materials can be manipulated easily using magnetic fields, the MPI properties of these materials are of interest to achieve a good combination of both functionalities. This work investigates the MPI signal of needle-like soft ferromagnetic objects as markers for tracking magnetic devices. Our results confirm the influence of demagnetization fields on the magnetization curve of macroscopic ferromagnetic objects and the importance of aspect ratio for the strength of the MPI signal. In addition, the spatial encoding properties of the system function are evaluated. The results show that the localization of ferromagnetic needles is possible but only in the spatial direction which is aligned with the object\u27s long axis
Increasing the efficiency of open-sided field free line scanning MPI system using silicon-steel core
No full textCurrently available preclinical magnetic particle imaging (MPI) systems can provide mm/sub mm -scale resolution for bore diameter of few centimeters. A human-scale system that preserves mm-scale resolution requires large coil sizes and high amount of current and power. Since the resolution in MPI mainly depends on the magnetic field gradient of the selection field coils, core loading may help to obtain a sufficient resolution with a feasible coil size and power consumption. Here, we present an open-sided small-size MPI system in which the outer selection field coils are loaded with a planar magnetic core. We investigated the effect of core loading on the magnetic field efficiencies and the impedances of the coils. For the measurements, three different type of silicon-steels with varying thicknesses are used as core material. Conducted simulation and experimental studies showed that gradient efficiency of the inner and outer coils can be increased by approximately 1.25 and 2 times, respectively
Heat it up: Thermal stabilization by active heating to reduce impedance drifts in capacitive matched networks
No full textThe achievable sensitivity in Magnetic Particle Imaging is not only limited by noise, but also depends on the stability of the system. Thermal dependencies of the current carrying components lead to drive-field distortions in amplitude and phase causing drifting background signals. In this work, an active capacitor heating system is developed that allows for thermal stabilization and trimming a resonance circuit to the desired frequency
Magnetic Microspheres for MPI and magnetic actuation
No full textMagnetic particle imaging (MPI) systems do not only allow for the visualization of the distribution of magnetic nanoparticles, but the magnetic fields of an MPI scanner can be also used to apply a magnetic force or a torque. This enables the actuation of magnetic particles. Here, we demonstrate that magnetic microspheres (MMS) are well suitable candidates for the actuation and visualization with MPI. By means of magnetic particle spectrometer (MPS) measurements, a promising imaging performance of the MMS for MPI was confirmed. We show that MMS can be actuated by rotating focus fields of a preclinical MPI scanner. Since the used MMS can carry therapeutics, which can be released by means of hyperthermia, this approach paves the way towards an MPI monitored targeted drug delivery