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

Multi-Channel Current Control System for Coupled Multi-Coil Arrays

For imaging and force experiments in Magnetic Particle Imaging several field generating coils are required to produce sufficiently high and flexible magnetic fields. To minimize power consumption, coils with iron cores are the best choice for low and medium frequency ranges. Such coils have comparatively high reactance and often are inductively coupled. The trivial approach to ensure target currents is to provide each coil with a current controlled source resulting in high system complexity and high costs. This paper presents a circuit design to distribute bipolar target currents from a single unipolar source with high accuracy, reducing unwanted coil coupling by a feedback controller. Thus, the number of current sources can be significantly reduced. With a regenerative concept, reactive power is stored and can be reused, allowing efficient and fast current switching

Low-Power Iron Selection and Focus Field Generator

A major issue for human-sized Magnetic Particle Imaging (MPI) scanners is the generation of sufficiently large magnetic gradient fields. By taking advantage of the field amplification properties of soft iron, a considerable amount of power can be saved. In this work, an optimized selection and focus field generator is presented, that can generate flexible and high gradient fields at comparatively low power consumption. Coil spacing and possible field-free-point positions are similar to conventional MPI scanners designed with air coils, but with significantly less demands on infrastructure and cooling design. The optimization process is discussed and first field measurements are presented

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