International Journal on Magnetic Particle Imaging (IJMPI)
Not a member yet
555 research outputs found
Sort by
Real-time and high-resolution magnetic particle optical imaging
No full textMagnetic nanoparticles (MNPs) have emerged as a promising medical imaging contrast agent due to their nontoxic and non-invasive properties, among others. This suggests that they possess significant potential for future applications. However, when it comes to imaging dynamic and rapid physiological processes, real-time visualization becomes crucial. In order to address this challenge, we propose a magnetic particle optical imaging (MPOI) approach that enables real-time imaging of MNPs under the influence of an external magnetic field. Our experimental results demonstrate that MPOI can achieve a frame rate of 20 frames per second (FPS), allowing for the accurate tracking of the movement of a copper wire within an MNPs suspension. This finding highlights the spatial resolution and real-time performance advantages of the MPOI method. Consequently, this method opens up exciting possibilities for the real-time imaging of various rapid physiological activities in the future
Linear magnetic nanoparticle structures for theranostic applications of nanomodified implants in magnetic particle imaging and magnetic hyperthermia
No full textMagnetic particle imaging (MPI) combined with magnetic hyperthermia (MH) is a promising hybrid modality for theranostic applications. It enables localized and controlled heat deposition in the target area and allows accurate treatment planning. In this regard it must be considered that the MPI signal and MH heating output is dependent on magnetic nanoparticle (MNP) interactions and MNP mobility. For MNP immobilized in implants, these effects have a tremendous impact on the quality of diagnosis and therapy.In fiber-based implants, linear MNP agglomerations are formed during production, which are roughly aligned with the major axis direction of the fibers. The MPI and MH investigations of these fibers showed that the MPI frequency spectrum of the MNP signal is dependent on the fiber orientation relative to the direction of the excitation field. This effect was attributed to the interaction between the linearly aligned MNP inside the fibers. The results were confirmed by independent measurements with linearly aligned MNP inside hydrogels. In accordance with experimental results, simulation showed the same trends on MPI and MH heating output. The determined influence of the interactions must therefore be considered for future models. Based on extensive investigations, it will be possible to develop a model that reliably reflects the relations between measured signals and the MNP properties of the linear structures and thus enables accurate MPI images and prediction of MNP heating behavior inside the implants
RegularizedLeastSquares.jl: Modality Agnostic Julia Package for Solving Regularized Least Squares Problems
No full textImage reconstruction in Magnetic Particle Imaging (MPI) is an ill-posed linear inverse problem. A standard methodfor solving such a problem is the regularized least squares approach, which uses, a regularization function toreduce the impact of measurement noise in the reconstruced image by leveraging prior knowledge. Variousoptimization algorithms, including the Kazcmarz method or the Alternating Direction Method of Multipliers(ADMM), and regularization functions, such as l2 or Fused Lasso priors have been employed. Therefore, thecreation and implementation of cutting-edge image reconstruction techniques necessitate a robust and adaptableoptimization framework. In this work, we present the open-source Julia package RegularizedLeastSquares.jl, whichprovides a large selection of common optimization algorithms and allows flexible inclusion of regularizationfunctions. These features enable the package to achieve state-of-the-art image reconstruction in MP
Design of a magnetic particle imaging integrated with magnetic hyperthermia by aiming at pediatric cancer treatment
No full textMagnetic Particle Imaging (MPI) is an emerging non-invasive medical imaging method capable of determining the concentration and spatial distribution of superparamagnetic iron oxide (SPIO) nanoparticles. Ongoing research is exploring technology to estimate the temperature of particles based on MPI signals. In magnetic hyperthermia treatment, volumetric temperature measurement is crucial for ensuring the safety of healthy tissues. While the efficacy of magnetic hyperthermia and simulation-based methods for estimating temperature and damage is now recognized, no prior studies have reported a human-sized MPI system that integrates hyperthermia and MPI. Such integration could potentially allow for non-invasive treatments. In this paper, we present the design and manufacture of a theranostic platform with the potential for MPI, magnetic hyperthermia and thermometry. The development of such technology could greatly extend the application of MPI in planning magnetic hyperthermia treatments
Influence of the System Matrix on Channel Leakage Artifacts in Multi-Contrast MPI
No full textMagnetic Particle Imaging (MPI) is a tracer-based medical imaging modality with great potential due to its high sensitivity, high spatiotemporal resolution, and ability to quantify the tracer concentration. Image reconstruction in MPI is an ill-posed problem, which can be addressed by the use of regularization methods. Single- and multi-contrast MPI reconstructions produce different kinds of artifacts. In this work, the multi-contrast MPI channel leakage is introduced and an analysis of the multi-contrast MPI system matrix properties is conducted to understand the source of the multi-contrast MPI channel leakage
Proof-of-Concept Simulation Study: An Open-sided Hybrid MPI and Low-Field MRI Scanner
No full textThis work aims to investigate the feasibility of performing hybrid magnetic particle imaging (MPI) and low-field magnetic resonance imaging (MRI) on our in-house preclinical open-sided MPI prototype system. The primary advantage of the system lies in the interchangeable use of coil groups between MPI and MRI modes, facilitating the generation of a hybrid image that features high sensitivity and contrast imaging of magnetic nanoparticle distribution by MPI, together with the anatomical information from MRI. In the prototype system, the selection field of MPI is generated via two bi-planar gradient coil groups, producing a Field-Free Line (FFL) in the xy-plane. These coil groups generate the gradient fields in x- and y-directions in MRI mode. A coil group in Helmholtz configuration produces the focus field in MPI mode, while generating the main static B0 field in z-direction in MRI mode. Another coil group creates the drive field when used in Helmholtz configuration in MPI mode, and provides the z-gradient field when used in Maxwell configuration in MRI mode. In this work, experimental measurements were conducted to obtain magnetic field maps for all coil groups. The acquired field maps reveal that the system creates an FFL featuring a 0.3 T/m gradient for MPI mode and B0 field ranging from 5 mT to 65 mT , exhibiting approximately 3500 ppm inhomogeneity for low-field MRI mode. Simulations performed using the measured fields affirm the capability of the system to perform hybrid MPI and low-field MRI imaging
Flexible Selection Field Generator Based On Adjustable Halbach Dipole Configurations
No full textIn magnetic particle imaging, a promising high-performance diagnostic technique, spatial encoding is based on a selection field with a field gradient forming a field-free region. The here proposed field generator assemblies enable a complete 3D encoding requiring only one electromagnetic excitation coil, while the trajectory is generated by exploiting the use of mechanically moving double-layer permanent magnet arrangements, implemented as adjustable Halbach dipole configurations. A simulation study and demonstrator implementation were conducted to provide an understanding and assessment of the trajectories and associated scanner sequences. The study serves as a basis for evaluating the imaging capabilities of this field generator type. Magnetic dipole moments are used to approximate the far field of the magnets, and the scaled moments are organized with the appropriate angular position and orientation. The magnetic flux density of the field generator is computed for each discrete sequential step by superposition of all Halbach array fields, using a solid spherical harmonic expansion as efficient representation. For comparison purposes, a demonstrator, designed using finite-element methods, was constructed, fabricated, and measured using the same expansion. A maximum absolute deviation of 2.2mT was observed between measurements and simulation, while both confirmed a gradient strength of 0.8 T/m for the initial antiparallel dipole configuration. Although currently rather specific to the initial chosen configuration, the developed simulation environment provides a tool for the validation of possible field generators based on adjustable Halbach dipoles, with results that can be compared qualitatively and quantitatively with those of other simulation environments and the developed demonstrator
Dual Mode Imaging of Phantoms in Two Orthogonal Planes with a Single-Sided FFL MPI Scanner
No full textA number of MPI scanner configurations have recently emerged in pursuit of clinical imaging capabilities. A single-sided scanner stands out as one of the promising designs, featuring hardware located exclusively on one side of the device. This approach grants the scanner access to an unhindered imaging volume. Our research group has suggested and developed a variant of the single-sided scanner employing Field-Free Line (FFL) for spatial encoding. In this work, we present the complete small-scale prototype of an FFL MPI scanner by demonstrating imaging phantoms in two orthogonal planes using two different imaging methods
Preliminary Results: Large Bore Clinical MPI System Imaging Human Head-sized FOVs
No full textClinical-scale MPI development has, so far, typically been optimized toward specific body parts and/or clinical applications, including functional brain imaging[1], perfusion[2], interventional[3], and cardiac imaging[4]. These systems have magnet free bore sizes in the range of 20-45 cm[1]–[3], [5], [6]. To date, the largest field of view MPI images published are 10 x 14 cm2[2] and 11 x 12 cm2[3]. Also, previous assessments of magnetostimulation have focused on the transmit field[7]–[9].
In this work, we present progress in our development of a general-purpose, human-scale MPI system capable of imaging large fields of view used clinically in MRI and CT. We show the overall hardware design, phantom imaging results, and human magnetostimulation results for all magnetic fields (i.e., gradient, drive, and slow shift) experienced during imaging.
The main magnet has a 60 cm magnet free bore and is designed to fit the shoulders. The magnet produces a field-free point with a measured performance of 0.6 T/m at 40 kW of power dissipation. A water-cooled head/extremity coil produces a transmit field of up to 7 mTp continuous, requiring a reactive power of 0.5 MW. As a general-purpose system, the imaging FOV is limited by coil size, and we set it to 23 x 23 x 6 cm3 to match FOVs seen in MRI head imaging. We present imaging results of phantoms filled with VivoTrax (Magnetic Insight, Inc.) tracer, including spiral phantoms, sensitivity, resolution, and dynamic range phantoms. We conclude by demonstrating safe, magnetostimulation-free imaging sequences in the feet of three healthy volunteers.  
Minimizing Induced Electric Fields in Human Head-Size MPI Systems
No full textMagnetic Particle Imaging (MPI) utilizes time-varying magnetic fields called drive fields to excite the magnetic nanoparticles for imaging. Time-varying magnetic fields induce electric fields within the human body, which can result in peripheral nerve stimulation (PNS) above a certain threshold. A conventional single-channel drive coil, while possessing a large homogeneous region, presents a challenge by exposing a large portion of the human head to the time-varying magnetic field, consequently leading to larger induced electric field. In this work, we propose using drive array coils to gain versatility by individualizing each winding with varying currents to enable safer imaging by minimizing the induced electric fields in MPI systems designed for human head imaging. To find the optimal current amplitudes for this array configuration, an optimization problem was formulated. Specifically, the objective of the optimization was defined as minimizing the peak induced electric field on the surface of a body model. This goal was accomplished by considering a set of constraints, setting a maximum current amplitude and an upper bound for the deviation from the targeted magnetic field within a specified region of interest. We utilized a realistic and simplified body model and performed simulations in COMSOL to compute the magnetic field sensitivity maps and the induced electric field maps on the body model. These essential data are then fed to the subsequent optimization algorithm to minimize the induced electric fields on the simplified body model using a drive array with optimized current amplitudes