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The point spread function (PSF) in MPI has been found to be the derivative of the Langevin function [1,2,3]. This PSF has noticeably longer “tails” than a single Gaussian (see Fig. 1). These tails of the PSF manifest as baseline blurring, which significantly decreases contrast and “glare” in MPI. Here, we develop a robust post-processing method to equalize (similar to deconvolution) the PSF, to essentially...
Both PEGylated NPs were highly stable in biological media, with sustained long-term (tested up to 1 week) signal intensity and half-width in their magnetic particle spectrometry (MPS). However, the terminating functional groups of the PEG molecules altered the efficacy of the phase transfer, polydispersity index (PDI) of their hydrodynamic size (dH) and the MPs signal. When NH2-PEG-SH was used for...
The sensitivity limit of the cytometer system can be determined from the system signal equation, derived using the Principle of Reciprocity and the MPI signal equation [4]: equation where ξ(t) [V] is the received emf signal, B1 [T/A] is the sensitivity of the receive coil, m̂ [Am2] is the magnetic moment of the magnetic nanoparticle, n is the number of nanoparticles, L̇ is the derivative of the Langevin...
MNPs which provide maximum AC magnetization and minimum hysteresis are ideal for MPI applications. Our experimental results show that the interacting MNP clusters have high AC magnetization values that are an order of magnitude larger than unclustered MNPs. We anticipate the enhancement is due to the exchange coupling interaction among nanoparticles in the cluster that tune the magnetic properties...
We applied back projection method and got a 2D image of the bottle as shown in Fig.1. Two separated bright area can be seen. Each spot is corresponding to the 1H of water. Then we applied this technology to the contaminant detection in food. Two water bottles, one with a small aluminum ball of φ1.5 mm, the other without, were prepared. Figure 2 shows the comparison of the 1H signal intensity between...
Several harmonic spectra are plotted in Figure 2. An important result is the comparison of free particles embedded in agar and films (Figure 2c). The particles embedded in the films are “frozen” in place, while those in agar, unless bound within the matrix, should still have some freedom to rotate. Particles in both should have identical Neel relaxation times, as that is dependent only on the structure...
Here our large-angle physical model of the Langevin equation with magneto-viscous relaxation has been found to agree quite well with the results of a Monte Carlo simulation for dynamic particle behavior in a magnetic field. Furthermore, the magneto-viscous relaxation time constant predicted through this model has been shown to agree with experimental data. Such a model to describe magneto-viscous...
Fig. 2 shows the measured results for only one of the two coils since they are similar to each other. The field quality is high with an overall root-mean-square deviation below 2.3 % from the ideal homogeneous case within the considered FOV. A deviation of 2.68° from the desired angular displacement of 90° could be determined considering the main axes of the measured fields.
The reaction has been explored in vitro in solution and the results for a DNA target are provided in Fig. 2. The 24 base pair DNA target can be found with 100 pM sensitivity. Shorter 20 base pair DNA target molecules bound the NPs together with less affinity so the sensitivity is only 2 nM. DNA molecules with incorrect sequencing produced no change in the MSB signal. Thrombin can also be measured...
TRL-NS is a potent MR contrast agent with comparable properties to TRL. Dynamic in-vivo MR measurements after application of TRL-NS showed a two phase SNR change with a rapid exponential SNR decrease in order of vena cava, aorta, portal vein followed by a protracted SNR recovery in all vessels. Liver and BAT showed an exponential SNR decline (rΔSNRliver= −0.60±0.14 (p<0.01); rΔSNRBAT= −0.74±0.13...
Figure 3 shows a comparison between the spatial patterns of the real components the system matrix obtained with the SCU (top) and the M3 (bottom) at 3 frequencies. The SCU system matrix has been corrected using the calibration data shown in figure 2. The grey scale levels used for the SCU and the M3 are the same. The differences in all studied cases are within the noise level. A clear improvement...
In order to identify suitable operating conditions for future clinical Magnetic Particle Imaging, peripheral nerve stimulation (PNS) and specific absorption rate (SAR) experiments have been performed by exposing volunteers to sinusoidally time-varying magnetic fields along and transverse to the body axis at frequencies from 24 kHz to 162 kHz. The findings show that future clinical MPI can advantageously...
Figure 1 compares the accuracy of both methods. In Figure 1a) the temperatures calculated from amplitude sweeps correspond to different values of frequencies. Corrections need to be made at higher frequencies as the error increases with frequency. In Figure 1b) the values of temperature obtained from frequency sweeps correspond to a ‘Lower’ frequency range (290–1050 Hz) and a ‘Higher’ frequency range...
In this work, the first study on the symmetry of the 2D magnetic particle imaging (MPI) system matrix is performed. The matrix symmetries are formed by the symmetries of the drive-field sequence and the characteristic of the Fourier transformation. The symmetries can be exploited for reducing the number of calibration scans that are necessary to acquire the system matrix, which is a time demanding...
All measurements were taken from 10µl undiluted Resovist, averaging 21900 × 10 periods, resulting in 10 s measurement time. An air measurement, taken directly before, was subtracted and the resulting signal was corrected by the transfer function of the receive chain. The advantage of the combination of the separation techniques can be seen in figure 2. While the fundamental frequency is missing with...
The mean magnetostimulation threshold curve is shown in Fig. 1b. The thresholds were well modeled by the hyperbolic amplitude vs. frequency curve. As shown in Fig. 1c, the magnetostimulation thresholds demonstrated an asymptotic behavior as a function of pulse duration, stabilizing for durations longer than 25 ms.
With this simple strategy we are able to proof that the measured mean grey values increase directly proportional with the iron oxide concentration of the ferrofluid. This promises an appropriate determination of the iron oxide concentration based on μCT for evaluation of new tracer materials for MPI.
Therapeutic efficacy was evaluated by comparing survival times of treated animals with untreated animals and control groups. The mean survival time for animals receiving a single treatment of Drug-NC followed by RF exposure was 25.1 days, compared to 15.2 days for untreated and control groups. A two-cycle treatment prolonged survival to an average of 46 days. Significant cell death was observed in...
In magnetic particle imaging the system matrix is commonly obtained by performing a tedious calibration scan, which requires measuring the system response at various positions in the field-of-view. In this work, a method for significantly reducing the number of required calibration scans is proposed. It exploits the fact that the MPI system matrix can be sparsified using certain basis transformations...
Magnetic Particle Imaging (MPI) commonly utilizes a Field Free Point (FFP) magnetic field gradient to localize magnetic nanoparticles [1–2]. With the benefits of two orders of magnitude reduced acquisition time or one order of magnitude signal-to-noise ratio (SNR) improvement, a gradient called a Field Free Line (FFL), which localizes particles to a line instead of a point, has been theoretically...
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