The overall objective of the proposed project is to develop, optimize and validate an artifact-free diffusion mapping protocol based on echo-planar imaging (EPI), to enable a fast and accurate quantitative diffusion mapping in clinical examinations. EPI based diffusion mapping is a powerful tool to assess the microstructure of the biological tissues, and is valuable in the clinical examinations and the detection of pathological changes in various diseases, such as the ischemic stroke, multiple sclerosis, and tumor. However, the accuracy of EPI based diffusion mapping is usually degraded by various EPI artifacts, such as the Nyquist artifact and geometric distortions due to the eddy current. In this proposal, we aim to further improve the state-of-the-art EPI artifact removal methods, and integrate them into a diffusion mapping protocol in such a way that the clinical scan time is not increased. This project has three specific aims. Firstly, we plan to design techniques to remove artifacts in diffusion-weighted EPI, based on the distortion correction and Nyquist artifact removal techniques we have previously developed. Secondly, we plan to integrate the developed artifact removal methods into a diffusion mapping protocol without increasing the clinical scan time. Specifically, the time-consuming procedure for characterizing the eddy current phase errors (which are subject independent) will be performed on a phantom. In the clinical scan sessions, only the subject dependent phase errors will be measured using a modified EPI sequence. The phase error information obtained from phantom and clinical scans will be combined for an effective artifact removal. Finally, we will evaluate the effectiveness of the developed diffusion mapping protocol on eight normal subjects at 3 Tesla. The levels of artifacts before and after correction will be quantified, and the stability of the correction methods over multiple scan sessions will also be evaluated. A successful outcome from this study will generate a robust and rigorously validated diffusion mapping protocol free from EPI artifacts.
