A Dictionary-Based Algorithm for MNP Signal Prediction at Unmeasured Drive Field Frequencies

The signal in MPI depends on magnetic nanoparticle (MNP) parameters and environmental conditions, as well as drive field (DF) settings and system-induced deviations. In this study, we propose a dictionary-based algorithm using a coupled Brown-Néel rotation model to simultaneously estimate the MNP parameters together with system transfer function. We then propose an empirical method that enables signal prediction at unmeasured DF frequencies

First Human-scale Magnetic Particle Imaging System with Superconductor

Magnetic particle imaging (MPI) is an emerging non-invasive molecular imaging method that can image the concentration and position of superparamagnetic iron oxide (SPIO) nanoparticles. However, the scalability of magnetic particle imaging (MPI) is the major barrier to its clinical use now.  For a human bore size of MPI, it is important to achieve a high magnetic gradient for high image resolution with a large enough field-of-view (FOV) for most of body part. In this paper, we present a human-scale amplitude modulation (AM) MPI system with a bore size (200 mm) and using a superconductor that generated a high MPI magnetic gradient of up to 2.5 T/m/µ0 and a 1D-FOV of 100 mm (with a feasible 3D FOV of 140 × 140 × 100 mm). The results of this paper show that the promise of MPI for human application is not far away

A system function component model for magnetic particle imaging with anisotropic particles

In this work, it is demonstrated how an extended equilibrium magnetization model that allows modeling of uniaxial anisotropy for the nanoparticles can be integrated into the system function component model for magnetic particle imaging with a field-free point moving along a Lissajous trajectory. In previous works, the particle model with anisotropy has been shown to describe the measured system function better than the classical Langevin model of paramagnetism. However, the question arises how this model relates to the observed tensor products of the Chebyshev polynomials in the Fourier series components of the system function. Static uniaxial anisotropy is assumed in this work. It is shown that the structure compared to the isotropic solution can be preserved in this case

Phase offset Calibration of Instantaneous Position for Magnetic Particle Imaging

Magnetic 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

3D System Matrix Calibration by Using Coil Information and Transformer

System Matrix-based image reconstruction approach requires a time-consuming calibration measurement. Existing methods such as compressed sensing and deep learning-based methods treat each row of the system matrix as independent data sample and lack the ability to modelling the relationships between SM rows. We firstly propose to model SM row relationships by the coil position and frequency value, which can be regarded as the additional and multimodal information. we propose a transformer-based neural network for 3D fast SM calibration, which encodes the information of coil position and frequency value into SM with self-attention mechanism in transformer

Relaxation spectral analysis in multi-contrast vascular magnetic particle imaging

Magnetic nanoparticles (MNPs) are used as tracers for vascular imaging without ionizing radiation. There is a high demand for the simultaneous detection of multiple particle states in multi-contrast magnetic particle imaging (MPI). In this study, the Néel and Brownian relaxation times were decoupled and measured separately to characterize different particle states using interventional vascular imaging as an example. The relaxation spectrum was generated via inverse Laplace transform (ILT)-based spectral analysis of the decay signals in the field-flat phase of pulsed excitation. The Néel and Brownian relaxation components were investigated through experiments involving the excitation of synomag-D samples using a trapezoidal-waveform relaxometer. The Brownian relaxation time was identified in the relaxation spectra due to a linear increase with increasing viscosity and disappeared at high gelatin concentrations. The sensitivity of viscosity prediction of the decoupled relaxation times under different excitation-field amplitudes was evaluated. Spectral imaging of a digital vascular phantom was simulated by combining a field-free point with homogeneous pulsed excitation. The plaque region with bounded MNPs and the catheter region with solidified MNPs were simultaneously differentiated from the vessel region in the Brownian relaxation time map. We demonstrated the quantitative assessment of the Néel and Brownian relaxation times through ILT-based spectral analysis in pulsed excitation, highlighting their potential for use in multi-contrast vascular MPI

From bench to bedside: does a human-sized MPI scanner work with endoprosthesis of the hip and knee?

Investigation of influence of metallic endoprostheses on MPI functionality in a human-sized MPI scanner. No relevant impairment of imaging from the presence of endoprosthesis could be found

Single-sided magnetic particle imaging devices using ferrite core to improve penetration depth

Single-sided MPI devices provide an object unrestricted to the scanned area, but the inadequate penetration depth limits the application scenarios of single-sided MPI devices. In order to solve this problem, we propose adding a ferrite core to the coil to enhance the magnetic flux density. To improve the performance of the receiver coil, we use a spiral receiving coil to improve the sensitivity of the system. In addition, this work uses the Halbach array permanent magnets with adjustable magnetic block angle to generate a variable gradient magnetic field and move the FFP position. The single-sided MPI system we designed in this work is a portable device, which is expected to achieve more accurate detection of tumor location and minimal removal of normal cells during breast-conserving surgery. The feasibility of the device proposed in this work is verified through the analysis of simulation and measurement results

Resotran® meets MPI – clinically approved Ferucarbotran reintroduced: a major leap towards MPI in humans

MPI 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®

Investigating the Influence of Sampling Frequency on X-Space MPI Image Reconstructions

In this presentation we employ a direct X-space deconvolution to estimate particle distributions from MPI data. We report on how the accuracy of those estimations changes as a function of sampling frequency and compare the findings to the MPI core operator approach found in literature