International Journal on Magnetic Particle Imaging (IJMPI)
Not a member yet
555 research outputs found
Sort by
Effect of matrix compressibility and temperature on MPI signal intensity
No full textA major advantage of MPI compared to other in vivo imaging modalities is a linear relationship between the label (SPIO) concentration and MPI signal. However, the MPI signal can be affected by intrinsic tissue matrix parameters, which are often not known a priori, presenting challenges for proper SPIO quantification in vivo. We report here on the effects of matrix compressibility and temperature on MPI signal in tissue-mimicking phantoms, which has direct relevance to MPI-guided magnetic fluid hyperthermia.
 
Extent determination of stent heating in MPI
No full textMPI offers a huge potential for cardiovascular imaging and interventional guidance. Especially, stent lumen imaging is an advantageous feature of MPI. Due to the presence of oscillating magnetic fields some metallic objects show temperature increase during MPI scans. Regarding first available human size MPI scanners and thus, future clinical application, the extent of stent heating becomes an important safety issue which could limit the application of MPI for specific patient groups. In this work, the temperature increase of stents with large diameters was investigated to determine the extent of stent heating in MPI
DiffMag handheld probe for perioperative lymph node harvesting
No full textMagnetic nanoparticles (MNPs) are used in many biomedical applications, including sentinel lymph node biopsy (SLNB) and magnetic particle imaging (MPI). DiffMag handheld probe ,based upon nonlinear detection principles has been developed by University of Twente for SLNB with MNPs. This method uses an excitation coil to activate the MNPs, and a detection coil to acquire the consequent magnetization of the MNPs. The hydrodynamic size and surface properties of MNPs are changed when introduced to new environment with different viscosity. Consequently, the number of mechanical degrees of freedom for rotation and translation in MNPs is reduced. This alteration in mechanical behavior has an effect on their magnetic behavior and particles Brownian relaxation time. In this study, we optimize the protocol settings for the nonlinear handheld detection probe during the SLNB procedure and investigate the detection depth in two environments
Stability of Fe3N nanoparticles as possible candidates for biomedical applications
No full textSuperparamagnetic iron oxide nanoparticles (SPIONs) have been the material of choice for the biomedical industry as well as scientific community due to their extreme stability, well-known metabolism of iron in the human body, acceptable magnetic properties, easiness, low cost and scalability of production[1]. However, recently alternative iron-based[2] materials with enhanced magnetic properties have been considered for improved performance in biomedical applications.
In this work, we study iron nitride Fe3N nanoparticles, as alternative candidates in biomagnetic applications due to their larger saturation magnetization values(Ms (Fe3N) = 128 Am2/kg vs Ms (Fe3O4) = 61 Am2/kg). Calorimetry results demonstrate significantly enhanced magnetic fluid hyperthermia heating performance compared to iron oxides as shown in Fig. 1.
Crucial question for further development of Fe3N particles is stability in biological environment. The as-synthesized spherical Fe3N nanoparticles (13.5 nm) demonstrate very good stability of magnetic properties in water (Fig 2.). Transmission electron microscopy studies show that the reason for this is formation of a thin oxide layer that protects particles from further oxidation
A system function component model for magnetic particle imaging with anisotropic particles
No full textIn 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
Single-Pass Relaxation Mapping at Multiple Frequencies Using an Arbitrary Waveform MPI Scanner
No full textIn Magnetic Particle Imaging (MPI), relaxation behavior of magnetic nanoparticles (MNPs) has enabled the inference of information about different MNP types and their local environments, such as viscosity and temperature. Previously, we have proposed and demonstrated an arbitrary waveform (AW) MPI scanner that facilitates operation in a wide range of drive field (DF) frequencies by eliminating the need for impedance matching. In this work, we propose a technique for simultaneous relaxation mapping at multiple DF frequencies in a single pass using an AW MPI scanner
Model-based Calibration and Image Reconstruction with Immobilized Nanoparticles
No full textThe model-based reconstruction problem is still one of the key challenges in magnetic particle imaging (MPI) when using multi-dimensional Lissajous-type excitations. One aspect, which is often highlighted in the literature, is the magnetization behavior of the magnetic nanoparticles in fluids, which is typically modeled by a coupling of Brown and N\\u27{e}el rotation mechanisms. Another aspect, which is at least as important as the particle model itself but sometimes treated less prominently, is a very careful calibration of the model input, respectively the scanner parameters such as analog filter and applied magnetic fields. The careful consideration of both aspects is the essential requirement for a proper solution to the model-based problem. In the present work we combine calibrated scanner components with polydisperse particle models for immobilized nanoparticles to derive a model-based system function and an efficient calibration routine. It is experimentally validated on the Bruker preclinical MPI system using 2D Lissjous trajectories
A Dictionary-Based Algorithm for MNP Signal Prediction at Unmeasured Drive Field Frequencies
No full textThe 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
Gradient-based pulsed excitation for catheter tracking in MPI
No full textThe visualization and tracking of a catheter is crucial in clinical vascular intervention process. Gradient-based pulsed excitation may enable a large field of view (FOV) and high spatial resolution in vascular magnetic particle imaging (MPI). A 5 × 5 cm2 digital phantom was designed to mimic a catheter with solidified MNPs inside vessels with suspended MNPs. The signal curve of normal vessel tissue was adapted from the synomag-D sample with a 1 wt% glycerol concentration. The catheter signal curve was adapted from the sample with 30 wt% gelatin to mimic solidified MNPs. The FFL was initially horizontal and then vertical to the digital phantom. The excitation gradient field amplitude along the FFL varied from 0.5 to 10 mT through the FOV. The signal curves of synomag-D with 1 wt% glycerol at different field amplitudes (0.5 to 10 mT) were interpolated to form the system matrix. By applying gradient-based pulsed excitation along a field-free line (FFL), a catheter molded from granulate incorporating solidified MNPs can be located according to the stripe artifacts in the system-matrix-based reconstructed images. The scan time of the proposed method can be reduced by using a smaller number of periods for signal averages if a reduction in the image quality is acceptable. Accelerated scanning may allow real-time tracking of the catheter during the clinical intervention process
Hands-free Reconstruction for MPI
No full textIn iterative system-matrix-based reconstruction in Magnetic Particle Imaging, three major parameters controlthe amount of regularization. Finding the right choice for these parameters is commonly done by user input andrequires time and experience. We propose a method that enables automatic reconstruction and achieves goodresults on a measured concentration series