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

A graph-based approach to access control migration

Der in dieser Arbeit verwendete Ansatz zur Migration der Zugangskontrolle ist die Erstellung eines graphenbasierten Zugriffskontrollmodell als Zwischenschritt im Migrationsprozess.Das Graphenmodell wird als gemeinsames Modell aller beteiligten Mechanismen entworfen und ermöglicht die Migration von Zugriffskontrolle, unabhängig von welchem Mechanismus ein Graph erstellt wurde. Dies ermöglicht die Migration zwischen allen Mechanismen, die durch ein gegebenes Graphenmodell dargestellt werden können und dem Vergleich zwischen den gewährten Zugang bei den verschiedenen Mechanismen.The approach to access control migration used in this thesis is the creation of a graph-based access control model as an intermediate step in the migration process. The graph-model designed to be a common model of all involved mechanisms, enabling access control to be migrated from the graph to another mechanism, independent of which mechanism a graph was created from. This allows for the migration between any mechanisms represented by a given graph-model, but also for the comparison of the access granted by the different mechanisms

A Flexible High-Performance Signal Generation and Digitization Plattform based on Low-Cost Hardware

Modern imaging modalities, such as magnetic particle imaging (MPI), are based on complex sequences which require synchronous multi-channel signal generation and reception. The component of an MPI scanner responsible for this functionality is the data acquisition (DAQ) system. Different scanner topologies and the nature of (digital) signal processing impose varying requirements on such a system. In this work, we introduce the RedPitayaDAQServer project, which implements a flexible scalable DAQ system. It is based on the low-cost hardware RedPitaya STEMlab 125-14 and is able to meet the requirements of most MPI scanner concepts that have been proposed to date

Model-based voltage predictions for arbitrary waveform excitation in Magnetic Particle Imaging

In recent works, arbitrary waveform or pulsed excitation in Magnetic Particle Imaging (MPI) was proposed to offer better resolution and sensitivity. Generating these excitation fields poses a new challenge in MPI hardware design. This work proposes a method which models the excitation chain as a linear system and predicts the required input voltage for the desired output field. The initial prediction is then iteratively improved to compensate for inaccuracies of the model. The method is demonstrated to achieve accurate field waveforms in both linear and slew rate limited regions of the amplifier

MPIMeasurements.jl: An Extensible Julia Framework for Composable Magnetic Particle Imaging Devices

Magnetic particle imaging (MPI) is a pre-clinical imaging modality, whose system design is still evolving, in particular towards human studies and clinical use. Therefore, many MPI scanners are custom-made distributed systems, both on the hard- and the software side. In this work we present the open-source Julia framework MPIMeasurements.jl, which implements a composable representation of imaging systems. It also offers flexible data structures that allow the implementation of specific imaging protocols, such as online/offline measurements, repeated measurements and system matrix calibrations. %that are reusable across systems. The project is designed to be expanded to new systems through community development and component reuse. To showcase the versatility of the software package, we give an overview of four very different MPI systems, which were realized with MPIMeasurements.jl

Safe and Rapid 3D Imaging: Upgrade of a Human-Sized Brain MPI System

Magnetic Particle Imaging hardware has reached human scale and thus patient safety questions and clinical application scenarios are in the focus of current research. In this work, we present a safe real-time 3D MPI systemfor cerebral applications. High voltages are avoided to ensure patient safety by a low voltage-high current transmit coil design. The developed 2D drive-field generator generates a field-free-point trajectory in the sagittal xz-planethat is shifted by a dynamic selection-field sequence along the y-axis. The scanner generates 3D images with 4 frames/second and allows for direct visualization of the clinically preferred transversal yz-plane, which is crucialfor future brain examinations. Advanced reconstruction techniques reach a system sensitivity of 4 ?gFe with respect to the iron mass in a sensitivity study

Flexible Selection Field Generation using Iron Core Coil Arrays

Many different concepts for selection-field generators have been introduced for Magnetic Particle Imaging so far. Inthis work, the field generation characteristics of an optimized iron core selection-field generator consisting of twocoil arrays with a total of 18 coils are presented. Due to the high number of degrees of freedom, a wide variety offield configurations are possible. The setup allows the generation of arbitrarily shaped fields, including the standardMagnetic Particle Imaging fields such as field-free points and field-free lines. In this work, field measurements arepresented and the current calculation method for generating a specific field configuration is discussed

MagneticParticleImaging/MPIFiles.jl: v0.14.0

MPIFiles v0.14.0 Diff since v0.13.0 Merged pull requests: Change getindex to return KeyError (#62) (@jonschumacher) Tubular regular positions (#63) (@jonschumacher) Update actions (#64) (@jonschumacher) Fix CI for docs (#65) (@jonschumacher) Add Aqua and fix arising issues (#67) (@jonschumacher) Closed issues: Error with keys that are unavailable in the MDF (#61) Failing CI for docs (#66

MagneticParticleImaging/MPIFiles.jl: v0.13.0

MPIFiles v0.13.0 Diff since v0.12.9 Merged pull requests: Move to cartesian index for frequency filtering (#60) (@nHackel

MagneticParticleImaging/MPIFiles.jl: v0.12.9

MPIFiles v0.12.9 Diff since v0.12.8 Merged pull requests: Additions to RegularGridPositions iteration (#58) (@jonschumacher) Fix plural (#59) (@jonschumacher