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Image reconstruction in Magnetic Particle Imaging (MPI) is an ill-posed linear inverse problem. A standard method for solving such a problem is the regularized least squares approach, which uses, a regularization function to reduce the impact of measurement noise in the reconstructed image by leveraging prior knowledge. Various optimization algorithms, including the Kazcmarz method or the Alternating Direction Method of Multipliers (ADMM), and regularization functions, such as l2 or Fused Lasso priors have been employed. Therefore, the creation and implementation of cutting-edge image reconstruction techniques necessitate a robust and adaptable optimization framework. In this work, we present the open-source Julia package RegularizedLeastSquares.jl, which provides a large selection of common optimization algorithms and allows flexible inclusion of regularization functions. These features enable the package to achieve state-of-the-art image reconstruction in MPI.

The Kaczmarz algorithm is widely used for image reconstruction in magnetic particle imaging (MPI) because it converges rapidly and provides good image quality even after a few iterations. It is often combined with Tikhonov regularization to cope with noisy measurements and the ill-posed nature of the imaging problem. In this abstract, we propose to combine the Kaczmarz method with a plug-and-play (PnP) denoiser for regularization, which can provide more specific prior knowledge than handcrafted priors. Using measurement data of a spiral phantom, we show that Kaczmarz-PnP yields excellent image quality, while speeding up the already fast convergence. Since the PnP denoiser is not coupled to the imaging operator, the Kaczmarz-PnP method is very generic and can be used for image reconstruction independently of the measurement sequence and MPI tracer type.

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 system for 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-plane that is shifted with low frequency 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 crucial for future brain examinations. Advanced reconstruction techniques reach a system sensitivity of 4 µgFe with respect to the iron mass in a sensitivity study., Deutsche Forschungsgemeinschaft (DFG)

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.

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. 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., Deutsche Forschungsgemeinschaft (DFG), Europäischer Fonds für Regionale Entwicklung (EFRE)

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

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 anMPI 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 and 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.

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.