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Thorsten M Buzug - One of the best experts on this subject based on the ideXlab platform.

  • Simultaneous patch reconstruction in Magnetic Particle Imaging
    2015 5th International Workshop on Magnetic Particle Imaging (IWMPI), 2015
    Co-Authors: Mandy Ahlborg, Christian Kaethner, Thorsten M Buzug
    Abstract:

    In Magnetic Particle Imaging (MPI) the drive field generated field of view (FOV) size is limited by the applied amplitudes that need to be small for a safe use in human applications [1]. A possible solution is to scan and reconstruct several patches that are merged in a post processing step to one large FOV [2,3]. However, this technique often results in truncation artefacts [4]. In this contribution different possibilities of combined reconstruction of patches are proposed to reduce truncation artefacts.

  • Simultaneous Reconstruction and Resolution Enhancement for Magnetic Particle Imaging
    IEEE Transactions on Magnetics, 2015
    Co-Authors: Osama A. Omer, Hanne Wojtczyk, Thorsten M Buzug
    Abstract:

    Spatial resolution is an essential parameter for Magnetic Particle imaging (MPI). The spatial resolution of MPI depends, among other things, on the Particles diameter and sampling frequency. The spatial resolution increases when increasing the Particle diameter. However, large Particles suffer from relaxation effects and are not preferred in some applications. On the other hand, spatial resolution increases with the sampling frequency, which in turn increases the number of sampling points. As an alternative solution for resolution enhancement, super-resolution (SR) is proved to be beneficial in improving the image quality of many medical imaging systems without the need for significant hardware alteration. In this paper, we propose to use small Particle diameter and low sampling frequency to obtain multiple low-resolution (LR) Magnetic Particle measurements and apply a resolution enhancement technique to reconstruct a higher resolution Magnetic Particle concentration. Unlike the conventional SR techniques, we propose to reconstruct a high-resolution concentration from the measured LR signals instead of reconstructing LR concentrations and then post-process these concentrations to get a higher resolution concentration. Simulation results show that the resolution of MPI can be increased by incorporating resolution enhancement technique without increasing the Particle diameter. In addition, simulation results show that using simultaneous reconstruction and resolution enhancement results in sharper concentrations and that this procedure is more robust against noise than using SR as a post-process.

  • Reconstruction Enhancement by Denoising the Magnetic Particle Imaging System Matrix Using Frequency Domain Filter
    IEEE Transactions on Magnetics, 2015
    Co-Authors: Alexander Weber, Jurgen Weizenecker, Ulrich Heinen, Michael Heidenreich, Thorsten M Buzug
    Abstract:

    Magnetic Particle imaging is a new modality, which allows the determination of the spatial distribution of Magnetic nanoParticles in-vivo. A standard approach for Magnetic Particle image reconstruction employs a so-called system matrix. The system matrix is typically acquired by a calibration measurement, whereby the system response at numerous positions in the field-of-view is measured. Due to the measurement process, the system matrix contains noise, which affects the reconstruction of the Particle distribution. In this paper, the special structure of the system matrix is exploited for noise reduction by applying frequency domain filters. It is shown that image reconstruction with the denoised system matrix yields an improved resolution and a better signal-to-noise ratio.

  • toward cardiovascular interventions guided by Magnetic Particle imaging first instrument characterization
    Magnetic Resonance in Medicine, 2013
    Co-Authors: Julian Haegele, Sven Biederer, Thorsten M Buzug, Tobias Knopp, Hanne Wojtczyk, Matthias Graser, J Barkhausen, Florian M Vogt
    Abstract:

    Poster: "ECR 2012 / B-0287 / Towards cardiovascular interventions guided by Magnetic Particle imaging (MPI): first instrument characterisation" by: "J. Haegele, S. Biederer, H. Wojtczyk, M. Graeser, T. Knopp, T. M. Buzug, J. Barkhausen, F. M. Vogt; Lubeck/DE"

  • Magnetic Particle imaging an introduction to imaging principles and scanner instrumentation
    2012
    Co-Authors: Tobias Knopp, Thorsten M Buzug
    Abstract:

    Introduction.- How Magnetic Particle Imaging Works.- How to Build an MPI Scanner.- Prior to Reconstruction.- From Data to Images.- Special System Topologies.- Putting MPI to Use.-Fundamentals of Electromagnetism.

Steven Conolly - One of the best experts on this subject based on the ideXlab platform.

  • Pulsed Excitation in Magnetic Particle Imaging
    IEEE Transactions on Medical Imaging, 2019
    Co-Authors: Daniel Hensley, Patrick Goodwill, Prashant Chandrasekharan, Bo Zheng, Steven Conolly
    Abstract:

    Magnetic Particle imaging (MPI) is a promising new tracer-based imaging modality. The steady-state, nonlinear magnetization physics most fundamental to MPI typically predicts improving resolution with increasing tracer Magnetic core size. For larger tracers, and given typical excitation slew rates, this steady-state prediction is compromised by dynamic processes that induce a significant secondary blur and prevent us from achieving high resolution using larger tracers. Here, we propose a new method of excitation and signal encoding in MPI we call pulsed MPI to overcome this phenomenon. Pulsed MPI allows us to directly encode the steady-state Magnetic physics into the time-domain signal. This in turn gives rise to a simple reconstruction algorithm to obtain images free of secondary relaxation-induced blur. Here, we provide a detailed description of our approach in 1D, discuss how it compares with alternative approaches, and show experimental data demonstrating better than 500-μm resolution (at 7 T/m) with large tracers. Finally, we show experimental images from a 2D implementation.

  • Optimal Broadband Noise Matching to Inductive Sensors: Application to Magnetic Particle Imaging
    IEEE Transactions on Biomedical Circuits and Systems, 2017
    Co-Authors: Bo Zheng, Patrick Goodwill, Kuan Lu, Greig C. Scott, Neerav Dixit, Di Xiao, Wencong Zhang, Beliz Gunel, Steven Conolly
    Abstract:

    Inductive sensor-based measurement techniques are useful for a wide range of biomedical applications. However, optimizing the noise performance of these sensors is challenging at broadband frequencies, owing to the frequency-dependent reactance of the sensor. In this work, we describe the fundamental limits of noise performance and bandwidth for these sensors in combination with a low-noise amplifier. We also present three equivalent methods of noise matching to inductive sensors using transformer-like network topologies. Finally, we apply these techniques to improve the noise performance in Magnetic Particle imaging, a new molecular imaging modality with excellent detection sensitivity. Using a custom noise-matched amplifier, we experimentally demonstrate an 11-fold improvement in noise performance in a small animal Magnetic Particle imaging scanner.

  • Projection Reconstruction Magnetic Particle Imaging
    IEEE Transactions on Medical Imaging, 2013
    Co-Authors: Justin J. Konkle, Patrick Goodwill, Oscar M. Carrasco-zevallos, Steven Conolly
    Abstract:

    We acquire the first experimental 3-D tomographic images with Magnetic Particle imaging (MPI) using projection reconstruction methodology, which is similar to algorithms employed in X-ray computed tomography. The primary advantage of projection reconstruction methods is an order of magnitude increase in signal-to-noise ratio (SNR) due to averaging. We first derive the point spread function, resolution, number of projections required, and the SNR gain in projection reconstruction MPI. We then design and construct the first scanner capable of gathering the necessary data for nonaliased projection reconstruction and experimentally verify our mathematical predictions. We demonstrate that filtered backprojection in MPI is experimentally feasible and illustrate the SNR and resolution improvements with projection reconstruction. Finally, we show that MPI is capable of producing three dimensional imaging volumes in both phantoms and postmortem mice.

  • an x space Magnetic Particle imaging scanner
    Review of Scientific Instruments, 2012
    Co-Authors: Patrick Goodwill, Bo Zheng, Kuan Lu, Steven Conolly
    Abstract:

    Magnetic Particle imaging (MPI) is an imaging modality with great promise for high-contrast, high-sensitivity imaging of iron oxide tracers in animals and humans. In this paper, we present the first x-space MPI hardware and reconstruction software; show experimentally measured signals; detail our reconstruction technique; and present images of resolution and “angiography” phantoms.

  • Capacitor Distortion in Magnetic Particle Imaging
    Springer Proceedings in Physics, 2012
    Co-Authors: Bo Zheng, Patrick Goodwill, Wisely Yang, Steven Conolly
    Abstract:

    The signal-to-noise ratio in Magnetic Particle imaging can be limited by distortion interference arising in the imaging system. In this work, we investigate the contribution of resonant transmit capacitors to system interference. Feedthrough interference spectra obtained using four capacitors with varying voltage ratings in a custom MPI interference testbed show a 20dB reduction in distortion interference with higherrated capacitors. Finally, we discuss the applicability of the interference testbed to treat other interference mechanisms in Magnetic Particle imaging.

Tobias Knopp - One of the best experts on this subject based on the ideXlab platform.

  • Novel Field Sequences, Reconstruction Algorithms, and Particle Synthesis Approaches for Magnetic Particle Imaging
    2020
    Co-Authors: Tobias Knopp
    Abstract:

    The second issue of the third volume of the International Journal on Magnetic Particle Imaging ( IJMPI ) includes 12 papers that were most presented in short form at the 7th International Workshop on Magnetic Particle Imaging. The papers cover the major MPI research areas imaging sequences, reconstruction algorithms, Particle synthesis, and preclinical applications. In addition this issue features a technical report on the open source software SFView, which allows for analyzing 1D , 2D, and 3D MPI system functions. Int. J. Mag. Part. Imag. 3(2), 2018, Article ID: 1803001, DOI: 10.18416/IJMPI.2018.1803001

  • MDF: Magnetic Particle Imaging Data Format
    arXiv: Medical Physics, 2016
    Co-Authors: Tobias Knopp, Mandy Ahlborg, Jurgen Rahmer, Thilo Viereck, Gael Bringout, Anselm Von Gladiss, Christian Kaethner, Alexander Neumann, Patrick Vogel, Martin Möddel
    Abstract:

    Magnetic Particle imaging (MPI) is a tomographic method to determine the spatio-temporal distribution of Magnetic nanoParticles. In this document, a file format for the standardized storage of MPI and Magnetic Particle spectroscopy (MPS) data is introduced. The aim of the Magnetic Particle Imaging Data Format (MDF) is to provide a coherent way of exchanging MPI and MPS data acquired with different devices worldwide. The focus of the MDF is on sequence parameters, measurement data, calibration data, and reconstruction data. The format is based on the hierarchical document format in version 5 (HDF5). This document discusses the MDF version 2.1.0, which is not backward compatible with version 1.x.y.

  • Chebyshev reconstruction of measured 1D Magnetic Particle imaging data
    2015 5th International Workshop on Magnetic Particle Imaging (IWMPI), 2015
    Co-Authors: Tobias Knopp
    Abstract:

    Magnetic Particle imaging (MPI) is a quantitative imaging technique that allows to determine the spatial distribution of Magnetic nanoParticles. In the present work, a model-based system matrix was generated and applied for the first time to the reconstruction of experimental 1D MPI data. The building elements of the simulated system matrix consist of properly altered Chebyshev polynomials. This special structure closely resembles the experimentally measured system matrix and is a main key towards an efficient and memory saving reconstruction in MPI.

  • Local compression of the Magnetic Particle imaging system matrix for efficient image reconstruction
    2015 5th International Workshop on Magnetic Particle Imaging (IWMPI), 2015
    Co-Authors: Tobias Knopp, Alexander Weber
    Abstract:

    Magnetic Particle imaging (MPI) is a quantitative method for determining the spatial distribution of Magnetic nanoParticles, which can be used as tracers for cardiovascular imaging [1,2,3]. For reconstructing a spatial map of the Particle distribution, the system matrix describing the Magnetic Particle imaging equation has to be known. Due to the complex dynamic behavior of the Magnetic Particles, the system matrix is commonly measured in a calibration procedure. In order to speed-up the reconstruction process, in [4], a matrix compression technique has been proposed that makes use of a basis transformation in order to sparsify the MPI system matrix. By thresholding the resulting matrix and storing the remaining entries in compressed row storage format, only a fraction of the data has to be processed when reconstructing the Particle distribution. The purpose of this work is to improve the compression rate for this technique.

  • toward cardiovascular interventions guided by Magnetic Particle imaging first instrument characterization
    Magnetic Resonance in Medicine, 2013
    Co-Authors: Julian Haegele, Sven Biederer, Thorsten M Buzug, Tobias Knopp, Hanne Wojtczyk, Matthias Graser, J Barkhausen, Florian M Vogt
    Abstract:

    Poster: "ECR 2012 / B-0287 / Towards cardiovascular interventions guided by Magnetic Particle imaging (MPI): first instrument characterisation" by: "J. Haegele, S. Biederer, H. Wojtczyk, M. Graeser, T. Knopp, T. M. Buzug, J. Barkhausen, F. M. Vogt; Lubeck/DE"

Volker C. Behr - One of the best experts on this subject based on the ideXlab platform.

  • Zero dead time rotational drift spectroscopy for Magnetic Particle ensembles
    2015 5th International Workshop on Magnetic Particle Imaging (IWMPI), 2015
    Co-Authors: Martin A. Rückert, Patrick Vogel, Anna Vilter, Thomas Kampf, Volker C. Behr
    Abstract:

    Rotational drift spectroscopy (RDS) aims at measuring the nonlinear rotation of Magnetic nanoParticles in suspension in rotating Magnetic fields. This drift has been measured on single Particles. The first experimental realization was limited by a long dead time of 3 ms between the initial pulse and the actual measurement. The signal decay time after the initial pulse is typically rather short, e.g., 340 μs for Magnetic Particles with a hydrodynamic diameter of 100 nm if suspended in water. Therefore a dead time of 3 ms severely limits the range of Particle systems that can be measured. The presented work suggests a new measurement sequence which reduces the dead time of the measurement by orders of magnitude. Shown are simulation results of the Magnetic Particle response of the suggested measurement sequence. Previous methods couldn't measure typical Magnetic Particle suspensions because of its long dead time of 3 ms. The new RDS sequence modification offers a possibility for completely overcome this limitation.

  • Superspeed Traveling Wave Magnetic Particle Imaging
    IEEE Transactions on Magnetics, 2015
    Co-Authors: Patrick Vogel, Martin A. Rückert, Peter Klauer, Walter H. Kullmann, Peter M. Jakob, Volker C. Behr
    Abstract:

    Since the first publication in 2005, several different scanner types for Magnetic Particle imaging (MPI) have been presented. One of these scanner concepts is traveling wave MPI (TWMPI). It uses a dynamic linear gradient array, which generates and moves a field free point with a strong gradient, which is necessary for scanning the sample in 3-D. Due to the linear properties of the TWMPI device, very fast 2-D imaging with frame rates higher than 1500 frames/s is possible (superspeed mode). Using the superspeed mode different high speed measurements are conceivable, e.g., fluid-dynamic investigations.

  • Rotational Drift Spectroscopy for Magnetic Particle Ensembles
    IEEE Transactions on Magnetics, 2015
    Co-Authors: Martin A. Rückert, Patrick Vogel, Peter M. Jakob, Anna Vilter, Walter H. Kullman, Volker C. Behr
    Abstract:

    Magnetic Particles have become a core ingredient for many applications in chemistry, biology, and medical diagnostics, e.g., as a basis for bioanalytical methods or as tracer material for medical imaging. This paper presents a new method called rotational drift spectroscopy (RDS) which uses rotating Magnetic fields for measuring the properties of Magnetic nanoParticles (MNPs) in liquid suspensions. The RDS signal is based on the nonlinear rotational drift behavior of MNPs in rotating Magnetic fields, which is highly dependent on the properties of the MNPs as well as their interaction with the environment. This dependency allows detecting the binding of functionalized MNPs with, e.g., proteins, viruses, or cells with potentially very high sensitivity. This paper presents first experiments demonstrating rotational drift behavior on aggregated Magnetic Particle ensembles and the corresponding experimental setup.

  • traveling wave Magnetic Particle imaging
    IEEE Transactions on Medical Imaging, 2014
    Co-Authors: Patrick Vogel, Martin A. Rückert, Peter Klauer, Walter H. Kullmann, Peter M. Jakob, Volker C. Behr
    Abstract:

    Most 3-D Magnetic Particle imaging (MPI) scanners currently use permanent magnets to create the strong gradient field required for high resolution MPI. However, using permanent magnets limits the field of view (FOV) due to the large amount of energy required to move the field free point (FFP) from the center of the scanner. To address this issue, an alternative approach called “Traveling Wave MPI” is here presented. This approach employs a novel gradient system, the dynamic linear gradient array, to cover a large FOV while dynamically creating a strong Magnetic gradient. The proposed design also enables the use of a so-called line-scanning mode, which simplifies the FFP trajectory to a linear path through the 3-D volume. This results in simplified mathematics, which facilitates the image reconstruction.

Patrick Goodwill - One of the best experts on this subject based on the ideXlab platform.

  • Pulsed Excitation in Magnetic Particle Imaging
    IEEE Transactions on Medical Imaging, 2019
    Co-Authors: Daniel Hensley, Patrick Goodwill, Prashant Chandrasekharan, Bo Zheng, Steven Conolly
    Abstract:

    Magnetic Particle imaging (MPI) is a promising new tracer-based imaging modality. The steady-state, nonlinear magnetization physics most fundamental to MPI typically predicts improving resolution with increasing tracer Magnetic core size. For larger tracers, and given typical excitation slew rates, this steady-state prediction is compromised by dynamic processes that induce a significant secondary blur and prevent us from achieving high resolution using larger tracers. Here, we propose a new method of excitation and signal encoding in MPI we call pulsed MPI to overcome this phenomenon. Pulsed MPI allows us to directly encode the steady-state Magnetic physics into the time-domain signal. This in turn gives rise to a simple reconstruction algorithm to obtain images free of secondary relaxation-induced blur. Here, we provide a detailed description of our approach in 1D, discuss how it compares with alternative approaches, and show experimental data demonstrating better than 500-μm resolution (at 7 T/m) with large tracers. Finally, we show experimental images from a 2D implementation.

  • Optimal Broadband Noise Matching to Inductive Sensors: Application to Magnetic Particle Imaging
    IEEE Transactions on Biomedical Circuits and Systems, 2017
    Co-Authors: Bo Zheng, Patrick Goodwill, Kuan Lu, Greig C. Scott, Neerav Dixit, Di Xiao, Wencong Zhang, Beliz Gunel, Steven Conolly
    Abstract:

    Inductive sensor-based measurement techniques are useful for a wide range of biomedical applications. However, optimizing the noise performance of these sensors is challenging at broadband frequencies, owing to the frequency-dependent reactance of the sensor. In this work, we describe the fundamental limits of noise performance and bandwidth for these sensors in combination with a low-noise amplifier. We also present three equivalent methods of noise matching to inductive sensors using transformer-like network topologies. Finally, we apply these techniques to improve the noise performance in Magnetic Particle imaging, a new molecular imaging modality with excellent detection sensitivity. Using a custom noise-matched amplifier, we experimentally demonstrate an 11-fold improvement in noise performance in a small animal Magnetic Particle imaging scanner.

  • Projection Reconstruction Magnetic Particle Imaging
    IEEE Transactions on Medical Imaging, 2013
    Co-Authors: Justin J. Konkle, Patrick Goodwill, Oscar M. Carrasco-zevallos, Steven Conolly
    Abstract:

    We acquire the first experimental 3-D tomographic images with Magnetic Particle imaging (MPI) using projection reconstruction methodology, which is similar to algorithms employed in X-ray computed tomography. The primary advantage of projection reconstruction methods is an order of magnitude increase in signal-to-noise ratio (SNR) due to averaging. We first derive the point spread function, resolution, number of projections required, and the SNR gain in projection reconstruction MPI. We then design and construct the first scanner capable of gathering the necessary data for nonaliased projection reconstruction and experimentally verify our mathematical predictions. We demonstrate that filtered backprojection in MPI is experimentally feasible and illustrate the SNR and resolution improvements with projection reconstruction. Finally, we show that MPI is capable of producing three dimensional imaging volumes in both phantoms and postmortem mice.

  • an x space Magnetic Particle imaging scanner
    Review of Scientific Instruments, 2012
    Co-Authors: Patrick Goodwill, Bo Zheng, Kuan Lu, Steven Conolly
    Abstract:

    Magnetic Particle imaging (MPI) is an imaging modality with great promise for high-contrast, high-sensitivity imaging of iron oxide tracers in animals and humans. In this paper, we present the first x-space MPI hardware and reconstruction software; show experimentally measured signals; detail our reconstruction technique; and present images of resolution and “angiography” phantoms.

  • Capacitor Distortion in Magnetic Particle Imaging
    Springer Proceedings in Physics, 2012
    Co-Authors: Bo Zheng, Patrick Goodwill, Wisely Yang, Steven Conolly
    Abstract:

    The signal-to-noise ratio in Magnetic Particle imaging can be limited by distortion interference arising in the imaging system. In this work, we investigate the contribution of resonant transmit capacitors to system interference. Feedthrough interference spectra obtained using four capacitors with varying voltage ratings in a custom MPI interference testbed show a 20dB reduction in distortion interference with higherrated capacitors. Finally, we discuss the applicability of the interference testbed to treat other interference mechanisms in Magnetic Particle imaging.