Advancing Spatial and Temporal Resolution of MRI for Biological and Physical Applications

Increasing the spatial and temporal resolution of Magnetic Resonance Imaging (MRI) has been two major challenges in MRI for several decades. Despite substantial advances in MRI technologies, barriers to high spatiotemporal resolution remain in many applications such as diffusion MRI and visualization of ultra-fast biological and physical processes. Therefore, the goal of this PhD research project is to advance the spatial and temporal resolution of MRI to enable new biological and physical applications. To increase the spatial resolution, a novel high spatial resolution MRI technique has been developed to produce distortion-reduced diffusion images with sub-millimeter resolution. The images were analyzed by using an advanced diffusion model to probe tissue micro-structural abnormalities in the brain stem of patients with Parkinson’s disease, followed by a comparison with healthy control subjects. To advance the temporal resolution, a novel ultra-fast acquisition technique, coined Sub-millisecond Periodic Event Encoded Imaging or SPEEDI, has been developed. This technique improved the temporal resolution by 2-4 orders of magnitude from what is used clinically, making it possible to use MRI for the study of ultrafast biological and physical processes on a time scale of milliseconds or sub-milliseconds. Using this novel technique, we have successfully observed the dynamics of fast-changing current signals that mimic an action potential and characterized transient eddy currents in an MRI system. More importantly, we have applied SPEEDI to visualizing the rapid opening and closing processes of the aortic valve in human subjects with an unprecedented temporal resolution of 0.6-ms. These advances in spatiotemporal resolution of MRI are expected to open new opportunities to expand the scope of MRI applications in research and patient care.