Head Motion Correction in Magnetic Resonance Imaging Using NMR Field Probes

Abstract

Magnetic Resonance Imaging (MRI) is a widely used imaging technology in medicine. Its advantages include good soft tissue contrast and the use of non-ionizing radiation in contrast to for example computed tomography (CT). One drawback are the long acquisition times that are needed. They depend on the diagnostic use case but are usually within the range of minutes. These long scan times make the images prone to patient motion during image acquisition which can lead to blurring or ghosting artifacts. Those artifacts might render the diagnostic value of the images useless which requires the image to be reacquired or the patient to be sedated before the scan to prevent motion artifacts. This is where motion correction comes into play. One can distinguish between retrospective and prospective motion correction (PMC) methods. Retrospective motion correction tries to improve image quality after the image acquisition by post-processing and possibly using additional motion tracking information, if available. Prospective motion correction relies on a motion tracking modality that is used to provide motion information to update imaging parameters during image acquisition. Both motion correction methods can also be used in combination with each other. This thesis, however, will focus on the implementation and validation of a system for prospective head motion correction. The system consisted of four nuclear magnetic resonance (NMR) field probes using. Those feld probes were attached to the head and used to measure the spatiotemporal evolution of magnetic felds. By switching spatially varying magnetic fields, this information can be used to track the field probes' positions and calculate the corresponding head motion in order to perform prospective motion correction