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

Probing electronic and structural properties of single molecules on the atomic scale

In this thesis work, a combination of low-temperature scanning tunneling microscopy (STM) and atomic force microscopy (AFM) was used to study single atoms and molecules on thin insulating films. We show that noncontact-AFM can yield important additional information for these systems, which had previously been studied only with STM. In particular, we demonstrate that the charge states of single gold adatoms can be detected with Kelvin probe force microscopy (KPFM). Furthermore, it is described how AFM can be used to image the chemical structure of a molecule with atomic resolution if the microscope tip is functionalized with suitable single atoms or molecules. This method was then applied to study the exact geometry of a molecular switch consisting of a single gold atom and a PTCDA molecule, and to help in the elucidation of the structure of an unknown molecule from the deep sea. Finally, we were able to combine the high resolution of our AFM molecular imaging technique with the charge sensitivity of KPFM to directly image for the first time the charge distribution within a single molecule. These investigations show that by combining STM and AFM, the electronic and structural properties of single molecules can be revealed in unprecedented detail. The possibility of directly imaging the chemical structure and the intramolecular charge distribution could lead to new fundamental insights into single-molecule switching and bond formation – processes that are usually accompanied by a structural rearrangement and/or an intra- or intermolecular redistribution of charge

Heat dissipation for power switches

Systems, methods, techniques and apparatuses of power switches are disclosed. One exemplary embodiment is a power switch comprising an outer housing; a power electronics board disposed within the housing and including a semiconductor switch structured to selectively conduct a current between a first power terminal and a second power terminal; a first heat sink coupled to the power electronics board; a plurality of thermally conductive connectors; a second heat sink coupled to the plurality of thermally conductive connectors, a control electronics board structured to control the semiconductor switch, the control electronics board being located within an enclosure formed of the second heat sink, the plurality of thermally conductive connectors, and the power electronics board

Role of Phase Encoding in Pulsed Magnetic Particle Imaging

Non-sinusoidal excitation waveforms have the ability to improve the signal-to-noise ratio and image resolution under certain conditions. Yet, the ability to use phase information for spatial encoding is expected to diminish as sharp pulses lead to concurrent signal response due to steep slopes and therefore less phase information. This motivates investigations into alternate sampling approaches that mitigate a loss in spatial encoding. However, measurements and image reconstruction results indicate that 10 times faster slew rates compared to sine excitation lead to enough phase information to resolve basic features using system matrix reconstruction