Magnetic Particle Imaging (MPI) is an imaging technique that allows the local distribution of magnetic nanoparticles to be determined. After rapid technological development, the method is currently undergoing preclinical trials, in which it has already shown a high potential in various medical applications. In particular, MPI has already achievedpioneering results in neurological questions such as craniocerebral trauma and stroke, as well as in the imaging of brain aneurysms. So far, however, the results could only be shown in small animal models because the MPI scanners developed so far are too small for measurements on large animals or humans.The goal of this project is the development of an MPI scanner for neurological questions, which is also suitable for human examination. Based on a prototype with which the feasibility has already been demonstrated, we will design a system that is optimally suited for monitoring tasks in the neurological intensive care unit. Due to its small sizeand optimized coils, it does not require a dedicated cooling and can therefore be mounted directly on the patient’s bed. The system can also be operated outside shielded rooms thanks to efficient signal routing and the detection of disturbances in the room. This enables permanent monitoring of the patient in the hours following stroke treatmentwithout exposure to X-rays. Up to now, CT images of these patients are only taken in cases of acute deterioration and at great expense.The existing prototype is implemented as a low-field MPI system and achieves a spatial resolution of up to 6mm in the horizontal direction and 28 mm in the vertical direction with a gradient strength of the selection field of approx. 0.2 T/m. Within the project, a two-dimensional excitation unit and a three-dimensional receiver unit will be designed which meets three essential requirements. They are highly efficient and do not require active cooling, they are electrically safe and can also be used in human experiments without hesitation and they are noise optimized so that the sensitivity of the existing prototype can be further increased. Due to the two-dimensional excitation and three-dimensional reception, the head scanner will achieve an isotropic resolution of approx. 5 mm. By optimizing the measurement sequence, the scanner will achieve a high temporal resolution of approx. 250 ms for a three-dimensional measurement volume with an edge length of 100 mm. For data reconstruction algorithms are developed, which consider imperfections of the magnetic fields. The developed MPI scanner and the reconstruction algorithms are tested on realistic flow phantoms, which simulate the vascular system of a human head.

Magnetic-Particle-Imaging (MPI) ist ein bildgebendes Verfahren für die Darstellung superparamagnetischer Nanopartikel. Derzeit befindet sich MPI im präklinischen Forschungsstadium bei dem Experimente am Kleintiermodel durchgeführt werden können. Da das bei MPI angelegt Magnetfeld physiologische Nebenwirkungen wie Gewebeerwärmung und Nervenstimulation verursachen kann, ist die Messfeldgröße in der Praxis limitiert. Für typische Scanner- und Sequenzparameter ist das Messfeld auf 1-3 cm Seitenlänge beschränkt. Da dies weder für eine Ganzkörpermessung einer Maus noch für anvisierte Humananwendungen reicht, benötigt MPI eine Komponente zum verschieben des Messfeldes. Dies funktioniert mit dem sogenannten Fokusfeld, welches entweder diskret oder kontinuierlich mit niedriger Frequenz angelegt wird. Folglich können deutlich höhere Feldamplituden verwendet werden ohne das Tier / den Patienten zu belasten. Dieses Projekt hat zum Ziel eine MPI-Messsequenz zu entwickeln mit der das Messen großer Messvolumina möglich ist. Hierzu wird das angestrebte Messfeld in mehrere Teilbereiche - sogenannte Patches - unterteilt. Diese können mit dem schnellen Anregungsfeld abgetastet werden. Die einzelnen Patches werden sukzessive gemessen wobei die Patchposition nach jeder Messung durch das Fokusfeld verschoben wird. In dem Projekt wird neben einer effizienten Implementierung untersucht, wie viele Patches benötigt werden, um ein vordefiniertes Messvolumen so schnell wie möglich zu vermessen. Neben der Entwicklung der Messsequenz liegt der Schwerpunkt des Projektes auf der Rekonstruktion von Multi-Patch-Messdaten. Da die Messsignale der einzelnen Patches in der Praxis nicht voneinander unabhängig sind, werden die Daten in einem gemeinsamen Schritt rekonstruiert. Diese Rekonstruktion ist mit hohem zeitlichen Aufwand verbunden und daher nur bei einer geringen Anzahl an Patches praktisch durchführbar. Ziel dieses Projektes ist eine deutliche Beschleunigung der Rekonstruktion von Multi-Patch-MPI-Daten. Hierzu werden Matrixkompressionstechniken genutzt, um effiziente Algorithmen herzuleiten, die schon mit wenigen arithmetischen Operationen ein zufriedenstellendes Rekonstruktionsergebnis liefern. Die entwickelte Messsequenz und Datenrekonstruktion wird zunächst anhand von Phantomen getestet und validiert. Im letzten Schritt werden in-vivo Messdaten erhoben, um zu zeigen, dass mit der Multi-Patch-Messsequenz eine Verfolgung einer Tracerinjektion im ganzen Körper einer Maus möglich ist.

Magnetic particle imaging (MPI) is a tomographic imaging technique for superparamagnetic nanoparticles. Currently, MPI is in the preclinical research stage and allows experiments to be performed on small animal models. Since the magnetic field applied in MPI can cause physiological side effects such as tissue heating and nerve stimulation, the measurement field size is limited in practice. For typical scanner and sequence parameters, the measurement field is limited to 1-3 cm side length. Since this is neither sufficient for a full-body measurement of a mouse nor for targeted human applications, MPI needs a component to shift the measurement field. This works with the so-called focus field, which is applied either discretely or continuously at low frequency. Consequently, much higher field amplitudes can be used without stressing the animal/patient. The aim of this project is to develop MPI measurement sequences that allow the measurement of large measurement volumes. For this purpose, the targeted measurement field is divided into several patches, which can be scanned with the fast excitation field. The individual patches are measured successively, while the patch position is shifted by the focus field after or even during each measurement. The project investigates how many patches are needed to scan a predefined measurement volume as fast as possible. In addition to the development of the measurement sequence, the project focuses on the reconstruction of multi-patch measurement data. Since the measurement signals of the individual patches are not independent of each other, the data are reconstructed in a joint step. This reconstruction is time consuming and requires tailored algorithms that exploit the sparse structure of the multi-patch system matrix. Another challenge is the imperfection of the applied magnetic field, which leads to image artifacts if not taken into account. After measuring the field profiles, these are taken into account in the MPI signal equation, thus reducing image artifacts. The developed measurement sequences and data reconstruction algorithms are first evaluated with static and dynamic particle phantoms. In a second step, in-vivo measurement data are considered to show that the developed methods also allow an enlargement of the measurement field in dynamic small animal experiments without reducing the image quality.

Ischemic stroke is a devastating disease and a leading cause of disability and death worldwide. Thrombolysis of cerebral blood clots with tissue-type plasminogen activator (rt-Pa) is the only evidence-based medical treatment for stroke. Despite 20 years of experience with rt-PA, fifty percent of treated patients remain disabled for life. A narrow therapeutic time window, insufficient thrombolysis rates, serious side effects of this therapy, and time-consuming imaging techniques decrease the efficacy of stroke treatment. MAGneTISe aims to develop a new two-pronged approach by combining therapy and monitoring of stroke patients with Magnetic Particle Imaging (MPI). This new imaging technique enables the rapid assessment of cerebral perfusion (Real-time MPI), as well as the steering of superparamagnetic iron oxide nanoparticles (SPIO) by magnetic fields (Force-MPI). We will develop strategies for continuous bedside cerebral perfusion monitoring by using red blood cells (RBC) as a biomimetic tracer-delivery system for the SPIOs, which otherwise would be quickly eliminated. This method will enable the rapid diagnosis of stroke or bleeding and facilitate faster treatment and better patient outcomes. Additionally, we will couple therapeutics, such as rt-PA, with SPIOs. Using the magnetic fields of the MPI system, we will trap the coupled nanoparticles in the occluded vessel. Through this approach, we will locally increase the amount of active enzyme, resulting in an increased rate of successful revascularization while decreasing systemic side effects. We expect that MPI has the potential to substantially improve stroke therapy and the benefits of nanomedicine by combining targeted therapies with ultrafast imaging.

In this project, we will develop and use magnetic resonance imaging (MRI) methods which allow to non-intrusively quantify a variety of process variables at high spatial and temporal resolution. The measured variables include the spatial distribution, the velocity, the temperature, and the chemical composition of the phases in the reactor, as well as the pore size distribution and diffusion properties of gels. In numerous collaborations within the CRC, these MRI methods are applied to characterise the material and system components of SMART reactors. The experiments of this project are mainly carried out on a globally unique large-scale vertical MRI system located at the TUHH.