publications | Matthias Gräser

2023

Saline bolus for negative contrast perfusion imaging in magnetic particle imaging

Fabian Mohn, and 5 more authors

Arxive, 2023

10.48550/arXiv.2303.05439
On the Receive Path Calibration of Magnetic Particle Imaging Systems

Florian Thieben, and 5 more authors

IEEE Transactions on Instrumentation and Measurement, 2023

10.1109/TIM.2022.3219461
In situ theranostic platform uniting highly localized magnetic fluid hyperthermia, magnetic particle imaging, and thermometry in 3D

Oliver Buchholz, and 12 more authors

2023

10.48550/arXiv.2304.06554
Functional magnetic particle imaging (fMPI) of cerebrovascular changes in the rat brain during hypercapnia

Erica Ellis Mason, and 9 more authors

Physics in Medicine and Biology, 2023

10.1088/1361-6560/acecd1

2022

Magnetic particle imaging

Matthias Graeser, and 12 more authors

Die Radiologie, 2022

10.1007/s00117-022-01011-9
System Matrix based Reconstruction for Pulsed Sequences in Magnetic Particle Imaging

Fabian Mohn, and 5 more authors

IEEE Transactions on Medical Imaging, 2022

10.1109/tmi.2022.3149583
Heating of Large Endovascular Stents and Stent Grafts in Magnetic Particle Imaging—Influence of Measurement Parameters and Isocenter Distance

Franz Wegner, and 10 more authors

CardioVascular and Interventional Radiology, 2022

10.1007/s00270-022-03324-7
A sensitive, stable, continuously rotating FFL MPI system for functional imaging of the rat brain

Eli Mattingly, and 6 more authors

International Journal on Magnetic Particle Imaging, 2022

10.18416/IJMPI.2022.2212001

2021

Efficient Joint Estimation of Tracer Distribution and Background Signals in Magnetic Particle Imaging Using a Dictionary Approach

T. Knopp, and 4 more authors

IEEE Transactions on Medical Imaging, 2021

10.1109/TMI.2021.3090928
Magnetic particle imaging for assessment of cerebral perfusion and ischemia

P. Ludewig, and 10 more authors

WIREs Nanomedicine and Nanobiotechnology, 2021

10.1002/wnan.1757
Pulmonary blood volume estimation in mice by magnetic particle imaging and magnetic resonance imaging

Michael Gerhard Kaul, and 8 more authors

Scientific Reports, 2021

10.1038/s41598-021-84276-9

2020

Investigating Spatial Resolution,Field Sequences and Image ReconstructionStrategies using Hybrid Phantoms in MPI

Anselm Gladiss, and 6 more authors

International Journal of Magnetic Particle Imaging, 2020

Article ID 2003004

10.18416/ijmpi.2020.2003004
OpenMPIData: An initiative for freely accessible magnetic particle imaging data

T. Knopp, and 3 more authors

Data in Brief, 2020

Paper ID: 104971

10.1016/j.dib.2019.104971
In-Vitro MPI-guided IVOCT catheter tracking in real time for motion artifact compensation

F. Griese, and 6 more authors

PLOS ONE, Mar 2020

10.1371/journal.pone.0230821
Design of a head coil for high resolution mouse brain perfusion imaging using magnetic particle imaging

Matthias Graeser, and 8 more authors

Physics in Medicine & Biology, Mar 2020

Publisher: IOP Publishing

Abs 10.1088/1361-6560/abc09e

Magnetic particle imaging (MPI) is a novel and versatile imaging modality developing toward human application. When up-scaling to human size, the sensitivity of the systems naturally drops as the coil sensitivity depends on the bore diameter. Thus, new methods to push the sensitivity limit further have to be investigated to cope for this loss. In this paper a dedicated surface coil for mice is developed, improving the sensitivity in cerebral imaging applications. Similar to magnetic resonance imaging the developed surface coil improves the sensitivity due to the closer vicinity to the region of interest. With the developed surface coil presented in this work, it is possible to image tracer samples containing only 896 pgfe and detect even small vessels and anatomical structures within a wild type mouse model. As current sensitivity measures require a tracer system a new method for determining a sensitivity measure without this requirement is presented and verified to enable comparison between MPI receiver systems.
Efficient hybrid 3D system calibration for magnetic particle imaging systems using a dedicated device

Anselm Gladiss^∗, and 4 more authors

Scientific Reports, Oct 2020

Abs 10.1038/s41598-020-75122-5

Image reconstruction in magnetic particle imaging is often performed using a system matrix based approach. The acquisition of a system matrix is a time-consuming calibration which may take several weeks and thus, is not feasible for a clinical device. Due to hardware characteristics of the receive chain, a system matrix may not even be used in similar devices but has to be acquired for each imager. In this work, a dedicated device is used for measuring a hybrid system matrix. It is shown that the measurement time of a 3D system matrix is reduced by 96%. The transfer function of the receive chains is measured, which allows the use of the same system matrix in multiple devices. Equivalent image reconstruction results are reached using the hybrid system matrix. Furthermore, the inhomogeneous sensitivity profile of receive coils is successfully applied to a hybrid system matrix. It is shown that each aspect of signal acquisition in magnetic particle imaging can be taken into account using hybrid system matrices. It is favourable to use a hybrid system matrix for image reconstruction in terms of measurement time, signal-to-noise ratio and discretisation.
Monitoring Intracranial Cerebral Hemorrhage Using Multicontrast Real-Time Magnetic Particle Imaging

Patryk Szwargulski, and 11 more authors

ACS Nano, Sep 2020

Abs 10.1021/acsnano.0c06326

Magnetic particle imaging (MPI) is an innovative radiation-free tomographic imaging method providing excellent temporal resolution, contrast, sensitivity, and safety. Mobile human MPI prototypes suitable for continuous bedside monitoring of whole-brain perfusion have been developed. However, for the clinical translation of MPI, a crucial gap in knowledge still remains: while MPI can visualize the reduction in blood flow and tissue perfusion in cerebral ischemia, it is unclear whether MPI works in intracranial hemorrhage. Our objective was to investigate the capability of MPI to detect intracranial hemorrhage in a murine model. Intracranial hemorrhage was induced through the injection of collagenase into the striatum of C57BL/6 mice. After the intravenous infusion of a long-circulating MPI-tailored tracer consisting of superparamagnetic iron oxides, we detected the intracranial hemorrhage in less than 3 min and could monitor hematoma expansion in real time. Multicontrast MPI can distinguish tracers based on their physical characteristics, core size, temperature, and viscosity. By employing in vivo multicontrast MPI, we were able to differentiate areas of liquid and coagulated blood within the hematoma, which could provide valuable information in surgical decision making. Multicontrast MPI also enabled simultaneous imaging of hemorrhage and cerebral perfusion, which is essential in the care of critically ill patients with increased intracranial pressure. We conclude that MPI can be used for real-time diagnosis of intracranial hemorrhage. This work is an essential step toward achieving the clinical translation of MPI for point-of-care monitoring of different stroke subtypes.

2019

Bimodal intravascular volumetric imaging combining OCT and MPI

Sarah Latus, and 8 more authors

Medical Physics, Sep 2019

Abs 10.1002/mp.13388

Abstract Purpose Intravascular optical coherence tomography (IVOCT) is a catheter based image modality allowing for high resolution imaging of vessels. It is based on a fast sequential acquisition of A-scans with an axial spatial resolution in the range of 5 to 10 μm, i.e., one order of magnitude higher than in conventional methods like intravascular ultrasound or computed tomography angiography. However, position and orientation of the catheter in patient coordinates cannot be obtained from the IVOCT measurements alone. Hence, the pose of the catheter needs to be established to correctly reconstruct the three-dimensional vessel shape. Magnetic particle imaging (MPI) is a three-dimensional tomographic, tracer-based and radiation-free image modality providing high temporal resolution with unlimited penetration depth. Volumetric MPI images are angiographic and hence suitable to complement IVOCT as a co-modality. We study simultaneous bimodal IVOCT MPI imaging with the goal of estimating the IVOCT pullback path based on the 3D MPI data. Methods We present a setup to study and evaluate simultaneous IVOCT and MPI image acquisition of differently shaped vessel phantoms. First, the inuence of the MPI tracer concentration on the optical properties required for IVOCT is analyzed. Second, using a concentration allowing for simultaneous imaging, IVOCT and MPI image data is acquired sequentially and simultaneously. Third, the luminal centerline is established from the MPI image volumes and used to estimate the catheter pullback trajectory for IVOCT image reconstruction. The image volumes are compared to the known shape of the phantoms. Results We were able to identify a suitable MPI tracer concentration of 2.5 mmol L−1 with negligible influence on the IVOCT signal. The pullback trajectory estimated from MPI agrees well with the centerline of the phantoms. Its mean absolute error ranges from 0.27mm to 0.28mm and from 0.25mm to 0.28mm for sequential and simultaneous measurements, respectively. Likewise, reconstructing the shape of the vessel phantoms works well with mean absolute errors for the diameter ranging from 0.11mm to 0.21mm and from 0.06mm to 0.14mm for sequential and simultaneous measurements, respectively. Conclusions MPI can be used in combination with IVOCT to estimate the catheter trajectory and the vessel shape with high precision and without ionizing radiation. This article is protected by copyright. All rights reserved.
Human-sized Magnetic Particle Imaging for Brain Applications

Matthias Graeser, and 13 more authors

Nature Communications, Sep 2019

10.1038/s41467-019-09704-x
3D Printed Anatomical Model of a Rat for Medical Imaging

M. Exner, and 4 more authors

Current Directions in Biomedical Engineering, Sep 2019

10.1515/cdbme-2019-0048
Correction of linear system drifts in magnetic particle imaging

T. Knopp, and 4 more authors

Physics in Medicine & Biology, Sep 2019

10.1088/1361-6560/ab2480

2018

First Measurement and SNR Results of a 3D Magnetic Particle Spectrometer

Xin Chen, and 4 more authors

International Journal on Magnetic Particle Imaging, Sep 2018

Abs 10.18416/ijmpi.2018.1810001

Magnetic Particle Imaging (MPI) is capable of imaging the spatial distribution of superparamagnetic iron oxide (SPIO) nanoparticles with high sensitivity and high resolution. A Magnetic Particle Spectrometer (MPS) can simulate the magnetic field inside an MPI imaging device and measure the response of the nanoparticles without moving the samples. Therefore, it is used to estimate the characteristics of SPIO nanoparticles, as well as achieve the system matrix of imaging devices. A one-dimensional and a two-dimensional MPS were introduced before and showed good usability. A three-dimensional transmit coil setup was presented lately, and its corresponding signal chains have been partially described. This paper is a continuation work and aims at presenting the first measurement and signal to noise ratio (SNR) results of the three-dimensional MPS.Int. J. Mag. Part. Imag. 4(1), 2018, Article ID: 1810001, DOI: 10.18416/IJMPI.2018.1810001
Moving table magnetic particle imaging: a stepwise approach preserving high spatio-temporal resolution

P. Szwargulski, and 7 more authors

Journal of Medical Imaging, Sep 2018

10.1117/1.JMI.5.4.046002

2017

Magnetic Particle Imaging for Real-Time Perfusion Imaging in Acute Stroke

Peter Ludewig, and 16 more authors

ACS Nano, Sep 2017

PMID: 28976180

10.1021/acsnano.7b05784
Towards picogram detection of superparamagnetic iron-oxide particles using a gradiometric receive coil

Matthias Graeser, and 9 more authors

Scientific reports, Sep 2017

10.1038/s41598-017-06992-5
Hybrid system calibration for multidimensional magnetic particle imaging

A Gladiss^∗, and 4 more authors

Physics in Medicine and Biology, Sep 2017

10.1088/1361-6560/aa5340
Two dimensional magnetic particle spectrometry

Matthias Graeser, and 3 more authors

Physics in Medicine & Biology, Sep 2017

10.1088/1361-6560/aa5bcd
SNR and Discretization Enhancement for System Matrix Determination by Decreasing the Gradient in Magnetic Particle Imaging

Matthias Graeser, and 3 more authors

International Journal on Magnetic Particle Imaging, Sep 2017

Abs 10.18416/ijmpi.2017.1703019

In system matrix (SM) based reconstruction, the physical resolution is often within the range of the SM discretization. This is caused by the signal to noise ratio (SNR) decrease following a discretization increase due to the smaller particle sample volume. As the SNR affects the resolution of the image as well, it is necessary to decouple the SNR and discretization. In this work, a calibration protocol is presented which enhances either the SNR or discretization by reducing the gradient strength within the system calibration. This new protocol results in higher resolution and better image quality.
Experimental Validation of the Selection Field of a Rabbit-Sized FFL Scanner

Anna Bakenecker, and 5 more authors

International Journal on Magnetic Particle Imaging, Sep 2017

Abs http://dx.doi.org/10.18416/ijmpi.2017.1703013

There are two different field topologies in magnetic particle imaging which enable the spatial encoding of the signal. Scanners using a field-free line (FFL) are promising regarding their sensitivity, because the low field volume is larger compared to a field-free point (FFP) and therefore, more particles contribute to the signal. A rabbit-sized FFL scanner with a bore diameter of 173 mm was presented in . After planning and assembling the scanner an experimental validation of the designated field topology of the selection field is presented. With a hall probe the field topologies of the z-gradient coil and the two quadrupoles forming together the selection field of the scanner were investigated. These magnetic field measurements show the expected field topologies: an FFP formed by the z-gradient coil and an FFL parallel to the bore of the scanner formed by each quadrupole. From these measurements the field gradients were calculated and approximated towards the designated currents. The results are in good agreement with the expected field gradients. In order to determine the best suitable frequency for rotating the FFL measurements were done on the power loss in the shielding taking place for higher frequencies. And the power transmission of the transformer, which is problematic for low frequencies. A rotation frequency of 20 Hz is chosen as it represents a compromise between transformer performance and power loss in the shielding.
Measurements Inside a Rabbit Sized FFL-MPI Device Using a Gradiometric Receive Coil

Jan Stelzner, and 5 more authors

International Journal on Magnetic Particle Imaging, Sep 2017

Abs http://dx.doi.org/10.18416/ijmpi.2017.1703012

This work continues prior investigations on the currently world’s largest field-free line (FFL) magnetic-particle- imaging (MPI) scanner. The bore of the imaging device provides a diameter of 180 mm and is designed to accomodate measurement objects up to rabbit size. It has already been shown that the drive-field coil is capable of conducting an alternating current with a frequency of 25 kHz and an amplitude of above 500 A. With this current input, the drive-field generator produces a magnetic flux density of more than 20 mT amplitude in the center of the bore. As the associated magnetic field strength is already sufficient to excite super-paramagnetic iron oxide nano particles (SPIONs), this work presents an approach to further increase the sensitivity of the system by testing a gradiometric receive-coil arrangement.

2016

Imaging Characterization of MPI Tracers Employing Offset Measurements in a two Dimensional Magnetic Particle Spectrometer

Daniel Schmidt, and 4 more authors

International Journal on Magnetic Particle Imaging, Sep 2016

Abs 10.18416/ijmpi.2016.1604002

We developed a method to characterize the imaging performance of MPI tracers from virtual MPI measurements that can be synthesized using measurement data from a Magnetic Particle Spectrometer (MPS) at different static magnetic field offsets. MPI system functions were obtained from measurements on a FeraSpin™ R (nanoPET GmbH, Berlin) sample in a 2D MPS comprising two excitation coils and two receive coils. Software phantoms of spatial MPI tracer distributions with different size and shape were constructed. With the measured MPI system function, a synthetic MPI measurement of the software phantoms was simulated. By adding noise to the virtual MPI data, the detection limit of each harmonic in dependence of the noise level was obtained. An MPI reconstruction of the virtual tracer distribution was performed using the virtual MPI data as input. By comparing the reconstructed images with the actual software phantoms, we obtained the spatial resolution of MPI of the investigated tracers. This method might help predicting the image resolution for real MPI setups. Our characterization method provides a valuable link between pure spectroscopic characterization and time consuming MPI phantom experiments.

2015

Dynamic single-domain particle model for magnetite particles with combined crystalline and shape anisotropy

Matthias Graeser, and 2 more authors

Journal of Physics D: Applied Physics, Sep 2015

Abs 10.1088/0022-3727/48/27/275001

The dynamical behaviour of superparamagnetic iron oxide nanoparticles (SPIONs) is not yet fully understood. In magnetic particle imaging (MPI) SPIONs are used to determine quantitative real-time medical images of a tracer material distribution. For reaching spatial resolution in the sub-millimetre range, MPI requires a well engineered instrumentation providing a magnetic field gradient exceeding 2 T m\{}^{-{1}} . However, as the particle performance strongly affects the sensitivity of the imaging process, optimization of the particle parameters is a crucial factor, which is not easy to address. Today most simulations of MPI use the Langevin model to describe the particle behaviour. In equilibrium, the model matches the measured data. If alternating fields in the mid kHz frequency range are applied, the dynamic behaviour of the particles differs from the Langevin theory due to anisotropy effects, particle–particle-interactions and/or exchange interaction in case of multi-core particles. In this paper a model based on previous work is introduced, which was adopted to include crystal and shape anisotropy of immobilised mono-domain single-core particles. The model is applied to typical MPI frequencies and field strengths with different possible superposition of the anisotropy effects, leading to differences in the particle response. It is shown that, despite comparatively high anisotropy constants, the magnetocrystalline anisotropy energy does not quench the signal response for MPI. The constructive superposition of shape and crystal anisotropy leads to the best performance in terms of sensitivity and resolution of the associated imaging modality and slightly reduces the energy barriers compared to a sole-shape anisotropy.
Trajectory dependent particle response for anisotropic mono domain particles in magnetic particle imaging

Matthias Graeser, and 3 more authors

Journal of Physics D: Applied Physics, Sep 2015

Paper ID: 045007

10.1088/0022-3727/49/4/045007
Introducing a frequency tunable magnetic particle spectrometer

A. Behrends, and 2 more authors

Current Directions in Biomedical Engineering, Sep 2015

10.1515/cdbme-2015-0062
Electronic field free line rotation and relaxation deconvolution in Magnetic Particle Imaging

K. Bente, and 5 more authors

IEEE Transactions on Medical Imaging,, Sep 2015

Abs 10.1109/TMI.2014.2364891

It has been shown that magnetic particle imaging (MPI), an imaging method suggested in 2005, is capable of measuring the spatial distribution of magnetic nanoparticles. Since the particles can be administered as biocompatible suspensions, this method promises to perform well as a tracer-based medical imaging technique. It is capable of generating real-time images, which will be useful in interventional procedures, without utilizing any harmful radiation. To obtain a signal from the administered superparamagnetic iron oxide (SPIO) particles, a sinusoidal changing external homogeneous magnetic field is applied. To achieve spatial encoding, a gradient field is superimposed. Conventional MPI works with a spatial encoding field that features a field free point (FFP). To increase sensitivity, an improved spatial encoding field, featuring a field free line (FFL) can be used. Previous FFL scanners, featuring a 1-D excitation, could demonstrate the feasibility of the FFL-based MPI imaging process. In this work, an FFL-based MPI scanner is presented that features a 2-D excitation field and, for the first time, an electronic rotation of the spatial encoding field. Furthermore, the role of relaxation effects in MPI is starting to move to the center of interest. Nevertheless, no reconstruction schemes presented thus far include a dynamical particle model for image reconstruction. A first application of a model that accounts for relaxation effects in the reconstruction of MPI images is presented here in the form of a simplified, but well performing strategy for signal deconvolution. The results demonstrate the high impact of relaxation deconvolution on the MPI imaging process.
Contribution of Brownian rotation and particle assembly polarisation to the particle response in Magnetic Particle Spectrometry

A. Gladiss, and 3 more authors

Current Directions in Biomedical Engineering, Sep 2015

10.1515/cdbme-2015-0074
Sequences for real-time magnetic particle imaging

M. Weber, and 4 more authors

Current Directions in Biomedical Engineering, Sep 2015

10.1515/cdbme-2015-0087
System matrix recording and phantom measurements with a single-sided Magnetic Particle Imaging device

K. Gräfe, and 4 more authors

IEEE Transactions on Magnetics, Sep 2015

Paper ID: 6502303

Abs 10.1109/TMAG.2014.2330371

Magnetic particle imaging (MPI) is a new imaging method, which uses superparamagnetic iron oxide nanoparticles as tracer material. Due to their tube-like design, most MPI devices have limited patient access. In this paper, an improved oil-cooled single-sided MPI device is presented that has the advantage that all coils, which are generating the magnetic fields or receiving the particle signal, are coplanar and on one side of the patient only. In consequence, the object, which will be scanned, is not limited in size. In this paper, a first 1-D image recorded with the new device is presented.
Construction of a device for magnetic separation of superparamagnetic iron oxide nanoparticles

K. Kläser, and 3 more authors

Current Directions in Biomedical Engineering, Sep 2015
Magnetic particle imaging: current developments and future directions

Nikolaos Panagiotopoulos, and 13 more authors

International Journal of Nanomedicine, Sep 2015

Abs 10.2147/IJN.S70488

Magnetic particle imaging (MPI) is a novel imaging method that was first proposed by Gleich and Weizenecker in 2005. Applying static and dynamic magnetic fields, MPI exploits the unique characteristics of superparamagnetic iron oxide nanoparticles (SPIONs). The SPIONs’ response allows a three-dimensional visualization of their distribution in space with a superb contrast, a very high temporal and good spatial resolution. Essentially, it is the SPIONs’ superparamagnetic characteristics, the fact that they are magnetically saturable, and the harmonic composition of the SPIONs’ response that make MPI possible at all. As SPIONs are the essential element of MPI, the development of customized nanoparticles is pursued with the greatest effort by many groups. Their objective is the creation of a SPION or a conglomerate of particles that will feature a much higher MPI performance than nanoparticles currently available commercially. A particle’s MPI performance and suitability is characterized by parameters such as the strength of its MPI signal, its biocompatibility, or its pharmacokinetics. Some of the most important adjuster bolts to tune them are the particles’ iron core and hydrodynamic diameter, their anisotropy, the composition of the particles’ suspension, and their coating. As a three-dimensional, real-time imaging modality that is free of ionizing radiation, MPI appears ideally suited for applications such as vascular imaging and interventions as well as cellular and targeted imaging. A number of different theories and technical approaches on the way to the actual implementation of the basic concept of MPI have been seen in the last few years. Research groups around the world are working on different scanner geometries, from closed bore systems to single-sided scanners, and use reconstruction methods that are either based on actual calibration measurements or on theoretical models. This review aims at giving an overview of current developments and future directions in MPI about a decade after its first appearance.
Implementation of a high-precision 2-D receiving coil set for Magnetic Particle Imaging

M. Weber, and 4 more authors

IEEE Transactions on Magnetics, Sep 2015

Abs 10.1109/TMAG.2014.2331987

In the medical imaging technique magnetic particle imaging, tomographic images of the spatial distribution of superparamagnetic particles are produced in real time. To generate images in a plane, the particles are excited in two dimensions. A specific particle response can be measured via receiving coils and the measured signal gives quantitative information about the particle distribution and local concentration. To achieve a high-spatial resolution with x-space reconstruction, the receiving coils have to feature a preferably homogeneous sensitivity in the field of view. To achieve this for a cylindrical bore, which is the typical medical scenario, an optimized coil set is implemented and tested in this paper. Two orthogonal receiving coil pairs are wound inside a negative form, which is custom made by a 3-D printer. Further, a well performing receiving chain is utilized, which transmits the particle signal from the receiving coils to the data acquisition unit. For performance evaluation, a hardware phantom with three delta samples is used. A field free line is chosen as a selection field, for which the presented coils may be used in an application scenario. The receiving coils perform well in the sense that no coupling in between the data paths is apparent and the recorded signals clearly represent the used phantom.

2014

Magnetic particle imaging: kinetics of the intravascular signal in vivo

Julian Haegele, and 8 more authors

International Journal of Nanomedicine, Sep 2014

Abs 10.2147/IJN.S49976

BACKGROUND: Magnetic particle imaging (MPI) uses magnetic fields to visualize superparamagnetic iron oxide nanoparticles (SPIO). Today, Resovist(®) is still the reference SPIO for MPI. The objective of this study was to evaluate the in vivo blood half-life of two different types of Resovist (one from Bayer Pharma AG, and one from I’rom Pharmaceutical Co Ltd) in MPI. METHODS: A Resovist concentration of 50 μmol/kg was injected into the ear artery of ten New Zealand White rabbits. Five animals received Resovist distributed by I’rom Pharmaceutical Co Ltd and five received Resovist by Bayer Pharma AG. Blood samples were drawn before and directly after injection of Resovist, at 5, 10, and 15 minutes, and then every 15 minutes until 120 minutes after the injection. The MPI signal of the blood samples was evaluated using magnetic particle spectroscopy. RESULTS: The average decline of the blood MPI signal from the two distributions differed significantly (P=0.0056). Resovist distributed by Bayer Pharma AG showed a slower decline of the MPI signal (39.7% after 5 minutes, 20.5% after 10 minutes, and 12.1% after 15 minutes) compared with Resovist produced by I’rom Pharmaceutical Co Ltd (20.4% after 5 minutes, 7.8% after 10 minutes, no signal above noise level after 15 minutes). CONCLUSION: In MPI, the blood half-life of an SPIO tracer cannot be equalized to the blood half-life of its MPI signal. Resovist shows a very rapid decline of blood MPI signal and is thus not suitable as a long circulating tracer. For cardiovascular applications in MPI, it may be used as a bolus tracer.
Toward the optimization of D-shaped coils for the use in an open Magnetic Particle Imaging scanner

H. Wojtczyk, and 7 more authors

IEEE Transactions on Magnetics, Sep 2014

Abs 10.1109/TMAG.2014.2303113

Magnetic particle imaging (MPI) is a novel medical imaging modality that allows for the quantitative detection of superparamagnetic iron oxide nanoparticles using static and oscillating magnetic fields. Essential aspects in the coil optimization for MPI include the magnetic field generated per unit current and the magnetic field homogeneity. For a set of D-shaped coils, which can be used in an open MPI scanner with lateral patient access to enable multidimensional imaging, these quantities were analyzed for a range of configurations. The results were compared with the situation in a four-wire-model and a four-wire-model with return paths (called eight-wire-model). It was found that for large coil radii, the effects of the D-coil set resemble those of the eight-wire-model; however, the local minimum in the magnetic field inhomogeneity is less pronounced.

2013

Analog receive signal processing for magnetic particle imaging

Matthias Graeser, and 4 more authors

Medical Physics, Sep 2013

Abs 10.1118/1.4794482

PURPOSE: Magnetic particle imaging (MPI) applies oscillating magnetic fields to determine the distribution of magnetic nanoparticles in vivo. Using a receive coil, the change of the particle magnetization can be detected. However, the signal induced by the nanoparticles is superimposed by the direct feedthrough interference of the sinusoidal excitation field, which couples into the receive coils. As the latter is several magnitudes higher, the extraction of the particle signal from the excitation signal is a challenging task. METHODS: One way to remove the interfering signal is to suppress the excitation signal by means of a band-stop filter. However, this technique removes parts of the desired particle signal, which are essential for direct reconstruction of the particle concentration. A way to recover the entire particle signal is to cancel out the excitation signal by coupling a matching cancellation signal into the receive chain. However, the suppression rates that can be achieved by signal cancellation are not as high as with the filtering method, which limits the sensitivity of this method. In order to unite the advantages of both methods, in this work the authors propose to combine the filtering and the cancellation technique. All methods were compared by measuring 10 μl Resovist, in the same field generator only switching the signal processing parts. RESULTS: The reconstructed time signals of the three methods, show the advantage of the proposed combination of filtering and cancellation. The method preserves the fundamental frequency and is able to detect the tracer signal at its full bandwidth even for low concentrations. CONCLUSIONS: By recovering the full particle signal the SNR can be improved and errors in the x-space reconstruction are prevented. The authors show that the combined method provides this full particle signal and makes it possible to improve image quality.
Toward cardiovascular interventions guided by magnetic particle imaging: first instrument characterization

Julian Haegele, and 7 more authors

Magnetic Resonance in Medicine, Sep 2013

Abs 10.1002/mrm.24421

Magnetic particle imaging has emerged as a new technique for the visualization and quantification of superparamagnetic iron oxide nanoparticles. It seems to be a very promising application for cardiovascular interventional radiology. A prerequisite for interventions is the artifact-free visualization of the required instruments and implants. Various commercially available catheters, guide wires, and a catheter experimentally coated with superparamagnetic iron oxide nanoparticles were tested regarding their signal characteristics using magnetic particle spectroscopy to evaluate their performance in magnetic particle imaging. The results indicate that signal-generating and non-signal-generating instruments can be distinguished. Furthermore, coating or loading non-signal-generating instruments with superparamagnetic iron oxide nanoparticles seems to be a promising approach, but optimized nanoparticles need yet to be developed.

2012

Experimental thresholds of magnetically induced currents via a figure-of-eight coil up to 25 kHz

Julia Bohnert, and 3 more authors

Biomedizinische Technik. Biomedical Engineering, Sep 2012

Abs 10.1515/bmt-2012-0007

Magnetic particle imaging, uses magnetic fields of frequencies in the kilo-hertz range. Little research has been carried out upon effects on excitable tissue caused by time-varying magnetic fields in that frequency range. To learn about magnetic stimulation thresholds, a system that is capable of generating a very focused magnetic field strong enough to induce a muscular reaction was built. Stimulation thresholds at 7.38, 12.04, 16.5, and 25.27 kHz have been recorded in 31 trial participants. It has been proved that magnetic stimulation is possible up to even 25 kHz, and respective thresholds have been determined. This article presents the trial setup, procedure, and evaluation of field quantities.
Magnetic particle imaging: introduction to imaging and hardware realization

Thorsten M. Buzug, and 13 more authors

Zeitschrift Für Medizinische Physik, Sep 2012

Abs 10.1016/j.zemedi.2012.07.004

Magnetic Particle Imaging (MPI) is a recently invented tomographic imaging method that quantitatively measures the spatial distribution of a tracer based on magnetic nanoparticles. The new modality promises a high sensitivity and high spatial as well as temporal resolution. There is a high potential of MPI to improve interventional and image-guided surgical procedures because, today, established medical imaging modalities typically excel in only one or two of these important imaging properties. MPI makes use of the non-linear magnetization characteristics of the magnetic nanoparticles. For this purpose, two magnetic fields are created and superimposed, a static selection field and an oscillatory drive field. If superparamagnetic iron-oxide nanoparticles (SPIOs) are subjected to the oscillatory magnetic field, the particles will react with a non-linear magnetization response, which can be measured with an appropriate pick-up coil arrangement. Due to the non-linearity of the particle magnetization, the received signal consists of the fundamental excitation frequency as well as of harmonics. After separation of the fundamental signal, the nanoparticle concentration can be reconstructed quantitatively based on the harmonics. The spatial coding is realized with the static selection field that produces a field-free point, which is moved through the field of view by the drive fields. This article focuses on the frequency-based image reconstruction approach and the corresponding imaging devices while alternative concepts like x-space MPI and field-free line imaging are described as well. The status quo in hardware realization is summarized in an overview of MPI scanners.