3,812 research outputs found
L1 data fitting for robust reconstruction in magnetic particle imaging: quantitative evaluation on Open MPI dataset
Magnetic particle imaging is an emerging quantitative imaging modality,
exploiting the unique nonlinear magnetization phenomenon of superparamagnetic
iron oxide nanoparticles for recovering the concentration. Traditionally the
reconstruction is formulated into a penalized least-squares problem with
nonnegativity constraint, and then solved using a variant of Kaczmarz method
which is often stopped early after a small number of iterations. Besides the
phantom signal, measurements additionally include a background signal and a
noise signal. In order to obtain good reconstructions, a preprocessing step of
frequency selection to remove the deleterious influences of the noise is often
adopted. In this work, we propose a complementary pure variational approach to
noise treatment, by viewing highly noisy measurements as outliers, and
employing the l1 data fitting, one popular approach from robust statistics.
When compared with the standard approach, it is easy to implement with a
comparable computational complexity. Experiments with a public domain dataset,
i.e., Open MPI dataset, show that it can give accurate reconstructions, and is
less prone to noisy measurements, which is illustrated by quantitative (PSNR /
SSIM) and qualitative comparisons with the Kaczmarz method. We also investigate
the performance of the Kaczmarz method for small iteration numbers
quantitatively
Radon-based Image Reconstruction for MPI using a continuously rotating FFL
Magnetic particle imaging is a relatively new tracer-based medical imaging
technique exploiting the non-linear magnetization response of magnetic
nanoparticles to changing magnetic fields. If the data are generated by using a
field-free line, the sampling geometry resembles the one in computerized
tomography. Indeed, for an ideal field-free line rotating only in between
measurements it was shown that the signal equation can be written as a
convolution with the Radon transform of the particle concentration. In this
work, we regard a continuously rotating field-free line and extend the forward
operator accordingly. We obtain a similar result for the relation to the Radon
data but with two additive terms resulting from the additional
time-dependencies in the forward model. We jointly reconstruct particle
concentration and corresponding Radon data by means of total variation
regularization yielding promising results for synthetic data.Comment: YRM & CSE Workshop on Modeling, Simulation & Optimization of Fluid
Dynamic Applications 202
Unique Compact Representation of Magnetic Fields using Truncated Solid Harmonic Expansions
Precise knowledge of magnetic fields is crucial in many medical imaging
applications like magnetic resonance imaging or magnetic particle imaging (MPI)
as they are the foundation of these imaging systems. For the investigation of
the influence of field imperfections on imaging, a compact and unique
representation of the magnetic fields using real solid spherical harmonics,
which can be obtained by measuring a few points of the magnetic field only, is
of great assistance. In this manuscript, we review real solid harmonic
expansions as a general solution of Laplace's equation including an efficient
calculation of their coefficients using spherical t-designs. We also provide a
method to shift the reference point of an expansion by calculating the
coefficients of the shifted expansion from the initial ones. These methods are
used to obtain the magnetic fields of an MPI system. Here, the field-free-point
of the spatial encoding field serves as unique expansion point. Lastly, we
quantify the severity of the distortions of the static and dynamic fields in
MPI by analyzing the expansion coefficients.Comment: 25 page
System Characterization of a Human-Sized 3D Real-Time Magnetic Particle Imaging Scanner for Cerebral Applications
Since the initial patent in 2001, the Magnetic Particle Imaging (MPI)
community has been striving to develop an MPI scanner suitable for human
applications. Numerous contributions from different research fields, regarding
tracer development, reconstruction methods, hardware engineering, and sequence
design have been employed in pursuit of this objective. In this work, we
introduce and thoroughly characterize an improved head-sized MPI scanner with
an emphasis on human safety. The scanner is operated by open-source software
that enables scanning, monitoring, analysis, and reconstruction, designed to be
handled by end users. Our primary focus is to present all technical components
of the scanner, with the ultimate objective to investigate brain perfusion
imaging in phantom experiments. We have successfully achieved full 3D single-
and multi-contrast imaging capabilities at a frame rate of 4 Hz with sufficient
sensitivity and resolution for brain applications. To assess system
characterization, we devised sensitivity, resolution, perfusion, and
multi-contrast experiments, as well as field measurements and sequence
analysis. The acquired images were captured using a clinically approved tracer
and suitable magnetic field strengths, while adhering to the established human
peripheral nerve stimulation thresholds. This advanced scanner holds potential
as a tomographic imager for diagnosing conditions such as ischemic stroke or
intracranial hemorrhage in environments lacking electromagnetic shielding.
Furthermore, due to its low power consumption it may have the potential to
facilitate long-term monitoring within intensive care units for various
applications.Comment: 22 pages, 9 figure
TranSMS: Transformers for Super-Resolution Calibration in Magnetic Particle Imaging
Magnetic particle imaging (MPI) offers exceptional contrast for magnetic
nanoparticles (MNP) at high spatio-temporal resolution. A common procedure in
MPI starts with a calibration scan to measure the system matrix (SM), which is
then used to set up an inverse problem to reconstruct images of the MNP
distribution during subsequent scans. This calibration enables the
reconstruction to sensitively account for various system imperfections. Yet
time-consuming SM measurements have to be repeated under notable changes in
system properties. Here, we introduce a novel deep learning approach for
accelerated MPI calibration based on Transformers for SM super-resolution
(TranSMS). Low-resolution SM measurements are performed using large MNP samples
for improved signal-to-noise ratio efficiency, and the high-resolution SM is
super-resolved via model-based deep learning. TranSMS leverages a vision
transformer module to capture contextual relationships in low-resolution input
images, a dense convolutional module for localizing high-resolution image
features, and a data-consistency module to ensure measurement fidelity.
Demonstrations on simulated and experimental data indicate that TranSMS
significantly improves SM recovery and MPI reconstruction for up to 64-fold
acceleration in two-dimensional imaging
Quantification of Lipoprotein Uptake in Vivo Using Magnetic Particle Imaging and Spectroscopy
Lipids are a major source of energy for most tissues, and lipid uptake and storage is therefore crucial for energy homeostasis. So far, quantification of lipid uptake in vivo has primarily relied on radioactive isotope labeling, exposing human subjects or experimental animals to ionizing radiation. Here, we describe the quantification of in vivo uptake of chylomicrons, the primary carriers of dietary lipids, in metabolically active tissues using magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS). We show that loading artificial chylomicrons (ACM) with iron oxide nanoparticles (IONPs) enables rapid and highly sensitive post hoc detection of lipid uptake in situ using MPS. Importantly, by utilizing highly magnetic Zn-doped iron oxide nanoparticles (ZnMNPs), we generated ACM with MPI tracer properties superseding the current gold-standard, Resovist, enabling quantification of lipid uptake from whole-animal scans. We focused on brown adipose tissue (BAT), which dissipates heat and can consume a large part of nutrient lipids, as a model for tightly regulated and inducible lipid uptake. High BAT activity in humans correlates with leanness and improved cardiometabolic health. However, the lack of nonradioactive imaging techniques is an important hurdle for the development of BAT-centered therapies for metabolic diseases such as obesity and type 2 diabetes. Comparison of MPI measurements with iron quantification by inductively coupled plasma mass spectrometry revealed that MPI rivals the performance of this highly sensitive technique. Our results represent radioactivity-free quantification of lipid uptake in metabolically active tissues such as BAT
Quantification of Lipoprotein Uptake in Vivo Using Magnetic Particle Imaging and Spectroscopy
Lipids are a major source of energy for most tissues, and lipid uptake and storage is therefore crucial for energy homeostasis. So far, quantification of lipid uptake in vivo has primarily relied on radioactive isotope labeling, exposing human subjects or experimental animals to ionizing radiation. Here, we describe the quantification of in vivo uptake of chylomicrons, the primary carriers of dietary lipids, in metabolically active tissues using magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS). We show that loading artificial chylomicrons (ACM) with iron oxide nanoparticles (IONPs) enables rapid and highly sensitive post hoc detection of lipid uptake in situ using MPS. Importantly, by utilizing highly magnetic Zn-doped iron oxide nanoparticles (ZnMNPs), we generated ACM with MPI tracer properties superseding the current gold-standard, Resovist, enabling quantification of lipid uptake from whole-animal scans. We focused on brown adipose tissue (BAT), which dissipates heat and can consume a large part of nutrient lipids, as a model for tightly regulated and inducible lipid uptake. High BAT activity in humans correlates with leanness and improved cardiometabolic health. However, the lack of nonradioactive imaging techniques is an important hurdle for the development of BAT-centered therapies for metabolic diseases such as obesity and type 2 diabetes. Comparison of MPI measurements with iron quantification by inductively coupled plasma mass spectrometry revealed that MPI rivals the performance of this highly sensitive technique. Our results represent radioactivity-free quantification of lipid uptake in metabolically active tissues such as BAT
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