Whole Body Magnetic Particle Imaging Measurement Sequences

• Applicants: Professor Dr.-Ing. Tobias Knopp; Dr. Martin Möddel
• Subject Area: Medical Physics, Biomedical Technology
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 314157186

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.

• DFG Programme: Research Grants