International Journal on Magnetic Particle Imaging (IJMPI)
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Submillimeter magnetic particle imaging with low symmetrical field gradient
No full textMagnetic particle imaging (MPI) requires high field gradient to acquire sharp point spread function used to refine spatial resolution for submillimeter imaging of cells and small animal models. Since the steep field gradient potentially causes difficulty in the sample handling and the signal processing, minimizing the field gradient is more practical even though it degrades the spatial resolution. By modulating relaxation responses of magnetic nanotracers at two distinctive frequencies: 2 kHz and 1MHz, we reconstructed images of Resovist® sample placed in a 1.4×1.4 mm2 field of view. This modulated MPI implements 2 sets of permanent magnets of which the same polarity faces one another to create a 2 Tm-1 symmetrical field gradient on the xy plane and 3 Tm-1 on the z axis. Although the spatial resolution appears poor to differentiate two-neighboring circular phantoms of dense liquid samples, we could visualize a 1-mm ring-shaped solid sample with 0.1 mm thickness.
Int. J. Mag. Part. Imag. 6(2), Suppl. 1, 2020, Article ID: 2009013, DOI: 10.18416/IJMPI.2020.200901
Individual observation of Néel and Brownian relaxations in magnetic nanoparticles
No full textMagnetic relaxation divided into the Néel and Brownian regimes determines the magnetization dynamics. To develop the signal intensity and resolution of magnetic particle imaging, understanding the magnetization dynamics was required. In this study, the Ne?el and Brownian relaxations were individually evaluated. The two-step magnetization response of magnetic nanoparticles dispersed in a fluid as the Brownian regime occurred after the Ne?el regime was observed by applying a fast responding pulse field. To clarify the magnetic relaxation in detail, it is necessary to individually observe the Ne?el and Brownian relaxations in the superposition system. By fitting the theoretical calculation to the measured time evolution of the magnetization response, we isolated Ne?el and Brownian relaxations from the experimentally observed superposition relaxation system. Moreover, the effect of dipole interactions on Ne?el and Brownian relaxation were confirmed by measuring the dependence of magnetization responses on the particle concentration in a magnetic fluid.
Int. J. Mag. Part. Imag. 6(2), Suppl. 1, 2020, Article ID: 2009005, DOI: 10.18416/IJMPI.2020.200900
Towards accurate modeling of the multidimensional MPI physics
No full textThe MPI image reconstruction problem requires, particularly for 2D and 3D excitation patterns, a measured system matrix due to the lack of an accurate model that is capable of describing the nanoparticles’ magnetization behavior in the MPI setup. Here we exploit a model based on Néel rotation for large particle ensembles and we find model parameters that describe measured 2D MPI data with much higher precision than state of the art MPI models, which is also illustrated in phantom experiments. This is a short summary of the recent work [4] to which we refer to for all further details.
Int. J. Mag. Part. Imag. 6(2), Suppl. 1, 2020, Article ID: 2009004, DOI: 10.18416/IJMPI.2020.200900
Design of a Magnetostimulation Head Coil with Rutherford Cable Winding
No full textMagnetic Particle Imaging (MPI) uses sinusoidal drive fields to excite the magnetic nanoparticles. These time-varying magnetic fields form electric fields within the body, which in turn can cause peripheral nerve stimulation, also known as magnetostimulation. In this work, we propose a design for a human head-size magnetostimulation coil with a Rutherford cable winding. This design achieves 12-fold decrease in the voltages needed to generate a given magnetic field, facilitating the safety of human subject experiments. With electromagnetic simulations, we determine the electric field patterns on a human head model to determine the potential primary locations of magnetostimulation.
Int. J. Mag. Part. Imag. 6(2), Suppl. 1, 2020, Article ID: 2009063, DOI: 10.18416/IJMPI.2020.200906
Volumetry in magnetic particle imaging
No full textIn this work, we investigate the suitability of MPI as a volumetry tool for the determination of retrograde voiding cystography of the bladder. Measurements were performed in two different experimental coil settings: first with a novel gradiometer providing three orthogonal channels and second a single-channel gradiometer at varying gradient strengths. The volumes were calculated using two different approaches: a calibration approach based on the amount of SPIOs and a threshold approach. We show that with both approaches MPI volumetry is feasible. Finally we present initial in vivo results of a retrograde voiding cystography in rats.
Int. J. Mag. Part. Imag. 6(2), Suppl. 1, 2020, Article ID: 2009057, DOI: 10.18416/IJMPI.2020.200905
Organ specific mouse head coil for improved image quality in magnetic particle imaging
No full textMagnetic particle imaging is a very useful tool in the detection of stroke. To study the ability of stroke in a mouse model the data acquisition is challenging as a mouse brain contains only a very small ratio of blood compared to large animals or humans. The effective concentration within the whole organ is therefore very small, especially compared to the heart or the liver. Typical MPI receiver coils however cover a sensitive region of around 30 mm to 50 mm and have a bore size of above 40 mm. This leads on the one hand to non-optimal signal coupling due to the distance to the particles and on the other hand strong signals from the heart can cause artifacts in the low signal regions. In this work we present a coil optimized for mouse brain imaging, which due to its small size, also dampens signal from regions outside of the coil.
Int. J. Mag. Part. Imag. 6(2), Suppl. 1, 2020, Article ID: 2009046, DOI: 10.18416/IJMPI.2020.200904
Parameter Robustness Analysis for System Function Reconstruction
No full textThe quality of images in system function reconstruction (SFR) depends on an extensive calibration scan that acquires the system matrix (SM). A change in parameters of the scanner, trajectory, or magnetic nanoparticle requires the acquisition of a new SM. In this work, we analyze the parameter robustness of SFR with simulations. We investigate the effect of utilizing an existing SM in the case of a change in the aforementioned parameters. The results show that a new calibration scan is not needed, as long as the change is sufficiently small.
Int. J. Mag. Part. Imag. 6(2), Suppl. 1, 2020, Article ID: 2009045, DOI: 10.18416/IJMPI.2020.200904
Safety of a new stent design during magnetic particle imaging
No full textAortic coarctation is a potentially life-threatening disease in newborns that requires early treatment. Recently, a new stent was developed for this purpose, which can be redilatated and thus adapted to the growth of the infant’s aorta. Due to the lack of ionizing radiation MPI is a very promising imaging technique for this clinically very important application in children. Therefore, the safety of this stent with regard to heating by oscillating magnetic fields must be investigated before the stent can be used
Quasi-simultaneous magnetic particle imaging and navigation of nanomag/synomag-D particles in bifurcation flow experiments
No full textMagnetic Particle Imaging (MPI) is used to visualize the distribution of superparamagnetic nanoparticles within 3D volumes with high sensitivity in real time. Recently, MPI is utilized to navigate micron-sized particles and micron-sized swimmers, since the magnetic field topology of the MPI scanner is well suited to apply magnetic forces. In this work, we analyze the magnetic mobility and imaging performance of nanomag/synomag-D for Magnetic Particle Imaging/Navigation (MPIN). With MPIN the focus fields are constantly switching between imaging and magnetic force mode, thus enabling quasi-simultaneous navigation and imaging of particles. In flow bifurcation experiment with a 100 % stenosis on one branch, we determine the limiting flow velocity of 1.36 mL/s, which allows all particles to flow only through one branch towards the stenosis. During this experiment, we image the accumulation of the particles within the stenosis. In combination with therapeutic substances, this approach has a high potential for targeted drug delivery.
Int. J. Mag. Part. Imag. 6(2), Suppl. 1, 2020, Article ID: 2009025, DOI: 10.18416/IJMPI.2020.200902
Towards bimagnetic nanoparticle thermometry
No full textMagnetic nanoparticle (MNP) thermometry is a promising approach for non-invasive and remote temperature sensing for applications in both fundamental and applied sciences. However, the small thermosensitivity (temperature-dependent magnetization) of conventional single magnetic material MNPs (e.g. magnetite or other ferrites) limit the requisite sensitivity needed for practical applications. Bimagnetic nanoparticles with tunable thermosensitivity and operating temperature ranges represent a potential route to overcome these limitations. Here we present results on the temperature-dependent AC magnetization of synthesized cobalt-doped ferrite MNPs and demonstrate the feasibility of engineered material composition and structure towards the realization of a highly sensitive MNP thermometer.
Int. J. Mag. Part. Imag. 6(2), Suppl. 1, 2020, Article ID: 2009010, DOI: 10.18416/IJMPI.2020.200901