International Journal on Magnetic Particle Imaging (IJMPI)
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Effect of the PEG functionalization on the saturation magnetization of magnetic nanoporous core-shell nanoparticles
No full textThe treatment of implant-associated infection is still a considerable issue in modern orthopaedical surgery. A promising candidate to improve this are superparamagnetic, drug loaded nanoparticles in combination with a magnetizable implant and an external magnetic field. This set-up enhances the accumulation of the magnetic nanoparticles at the targeted implant, thus reducing the number of nanoparticles needed for a successful treatment. Pivotal for the superparamagnetic nanoparticles are a preferably high magnetization and a sufficient long circulation time within the body. A poly(ethyleneglycol) (PEG) functionalization is widely used to increase the circulation time. Since a PEG functionalization adds mass to a nanoparticle, which influence its properties, we functionalized magnetic nanoporous silica nanoparticles (MNPSNP) with PEG moieties of different chain length and studied the effect of the chain length of the saturation magnetization on the particles
An Arbitrary Waveform MPI Scanner
No full textIn magnetic particle imaging (MPI) systems, impedance matching or tuning circuitry has to be employed at a particular operating frequency to handle the reactive power. In this work, we propose a drive coil design with a Rutherford cable winding that enables arbitrary waveform (AW) characteristics in an MPI scanner. The AW drive coil achieves a 144-fold reduction in inductance and 12-fold reduction in voltage to generate a given drive field (DF) amplitude. With imaging experiments, we show that the proposed design can enable imaging in a wide bandwidth, providing flexibility for different functional imaging applications of MPI
MPI region of interest (ROI) analysis and quantification of iron in different volumes
No full textMPI directly detects superparamagnetic iron oxides (SPIONs), which should enable precise, accurate, and linear quantification. However, selecting a region of interest (ROI) has strong effects on MPI quantification results. Ideally, ROI selection should be simple, user-independent, and widely applicable. In this work, we describe and compare four MPI ROI selection methods and assess their performance in vitro and in vivo. To explore the effect of ROI selection, ten ferucarbotran phantoms were imaged, each contained the same amount of iron but varied in volume. Three users tested the accuracy of the ROI methods for quantification of these samples. Lastly, the four ROI methods were applied to quantify ferucarbotran in vivo after intravenous, intramuscular, and subcutaneous injections in mice. We discuss the strengths and limitations of each ROI method, such as the ability to capture MPI signals of custom shapes (i.e. size of the ROI), degree of user variability, speed of analysis, and quantification accuracy of SPIONs in different volumes.
Int. J. Mag. Part. Imag. 8(1), 2022, Article ID: 2208002, DOI: 10.18416/IJMPI.2022.220800
Displacement measurement of magnetic particles by ultrasonic vibration
No full textSignal detection methods of conventional magnetic particle imaging (MPI) require large coils and multiple power supplies for detecting signals from magnetic nanoparticles (MNPs). In connection to this, there is a concern about the safety of the living body. Therefore, a new signal detection method based on the vibration of MNPs has been proposed in this study. Further, to establish this method using ultrasonic vibration, the displacement of the MNPs by a focused ultrasonic transducer has been evaluated using experiment and the finite element method. Iron oxide particles have been used instead of MNPs to investigate whether ultrasonic waves can be used for generating vibrations in a simulated biological object. From the experimental results, the displacement of the iron oxide particles in agar has been observed to be approximately 51.8 ?m, which is different from the simulation results, indicating that the finite element model requires improvement to match the experimental conditions
Boundary artifact reduction by extrapolating system matrices outside the field-of-view in joint multi-patch MPI
No full textIn multi-patch magnetic particle imaging an artifact-free image can be obtained by using a joint reconstruction and measuring the system matrices not only in the field-of-view but also in a huge overscan. This leads to a long calibration time and heavy memory consumption and therefore an unsuitability of this method for large three-dimensional measurements. In this work we propose to measure the system matrices only in the field-of-view and use a diffusion based extrapolation step to extant the system matrices computationally into the overscan. In this way we massively reduce the calibration time while maintaining a nearly artifact-free image
Uncertainty estimation for 2D magnetic particle imaging
No full textMagnetic Particle Imaging (MPI) has in recent years been established as a powerful imaging tool that measures the non-linear magnetic response of magnetic particles to an applied field. Obtaining quantitative information from these images in the form of a discretized version of the particle distribution in space requires the solution of an inverse problem that can be addressed by linear regression. We demonstrate how the linear regression can be used to also estimate the uncertainty of the reconstructed particle distribution
Comparison of Reconstruction Methods for Measured FFL Data
No full textSystem matrix and x-space resonstruction are two of the main approaches for image reconstruction of field free line magnetic particle imaging. A comparative studiy of both options is performed on data from a phantommeasurement in a permanent magnet-based scanner system. The system matrix reconstruction is performed in a hybrid fashion with data obtained in a spectrometer. This data is also used to obtain the relaxation time and particle diameter of the particles used. A deconvolution can then be used to enhance the image quality of the x-space approach which is compared to the system matrix reconstruction. A slight blurring can be depicted in the x-space reconstruction but overall a good agreement between both approaches is reached with the Structural Similarity Index yielding a value of 0.79
Changing iron content and excitation field: Comparative study of Synomag® nanoparticles
No full textMagnetic nanoparticles (MNPs) are widely used to facilitate magnetic particle imaging (MPI) which has the potential to become the leading diagnostic instrument for biomedical imaging. This comparative study assesses the effects of changing iron content and excitation frequency on point-spread function (PSF) representing the effect of magnetization reversal. PSF is quantified by features of interest for MPI: i.e. gradient amplitude and full-width-at-half-maximum (FWHM). A superparamagnetic quantifier (SPaQ) is used to assess differential magnetic susceptibility of two commercially available MNPs: Synomag®-D50 and Synomag®-D70. For both MNPs, the signal output depends on increase in drive field frequency and amount of iron-oxide, which might be hampering the sensitivity of MPI systems that perform on higher frequencies. Nevertheless, there is a clear potential of Synomag®-D for a stable MPI resolution, especially in case of 70 nm version, that is independent of either drive field frequency or amount of iron-oxide
Compensating model imperfections during image reconstruction via Resesop
No full textTo avoid the time consuming process of measuring the system function of magnetic particle imaging, model-based system matrix simulation is an alternative. However, this is a complex procedure with model imperfections, which influence the accuracy of the resulting system matrix as well as the quality of the image reconstruction. Standard reconstruction algorithms like regularized Kaczmarz are not able to take those inexactnesses into account and produce poor quality images. The Resesop-Kaczmarz algorithm is a novel image reconstruction method, which allows model imperfections or dynamics. We examine and discuss the compensating characteristics of Resesop-Kaczmarz regarding model inexactnesses
Recent impetus in magnetic particle imaging
No full textSince its beginnings in 2001, MPI has shown more than ever a very high innovation potential. As expected, the number of publications is increasing and the interest in MPI is greater than ever. This certainly has to do with the growing number of commercial systems currently in operation. To this end, this editorial introduces topics in the current IJMPI Volume 7 No. 1 (2021) that reflect well the breadth of our field. More particular, these topics ranges from novel reconstruction techniques based on deep image priors, methods to improve spatial selectivity, tracer characterization, and new scanner geometries. These are four very exciting topics on MPI that are worth diving into.
Int. J. Mag. Part. Imag. 7(1), 2021, Article ID: 2201001, DOI: 10.18416/IJMPI.2022.220100