Highly Accelerated Distortion-Free Diffusion-Weighted MR Imaging at Ultra High Field (7T): Gray Matter Characterization

• Applicant: Professor Dr. Oliver Speck
• Subject Area: Medical Physics, Biomedical Technology ; Human Cognitive and Systems Neuroscience
• Term: from 2012 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 215187497

Single-shot echo-planar imaging (EPI) at ultra-high field (UHF) enables fast brain imaging with high spatial resolution. It is very beneficial for functional magnetic resonance imaging (fMRI) and diffusion weighted imaging (DWI) studies to measure brain function and to characterize information about brain tissue microstructure and used as a standard method. However, a well-known problem in EPI is strong susceptibility-induced geometric distortion, especially at UHF such as 7T. In DWI, in addition, distortions in EPI vary due to eddy-currents depending on the direction of diffusion encoding gradients and become a major challenge. During the first funding period of this project (2012-2015) we have successfully implemented an online distortion correction package for fMRI and extended the method to DWI. Due to limited spatial resolution of EPI, strong distortions, and signal loss appear in cortical regions. Therefore, DWI has been applied almost exclusively to the investigation of structure and pathology in white matter (WM) up to now. As an alternative to standard EPI, we developed a novel distortion-free technique that allows unprecedented high spatial resolution and fidelity of in vivo human brain DWI. With our new method, gray matter microstructure becomes accessible non-invasively although measurement times are prolonged. In the continuation of this project, our goal covers i) full development of a comprehensive (i.e. susceptibility- and eddy-current-induced) distortion correction package and its implementation for standard DWI, ii) further research on our new technique for very high-resolution DWI to reduce scan time and improve the image fidelity by suppressing flow- and motion-induced artifacts, and iii) detailed in vivo characterization of gray matter diffusion using very high-resolution diffusion images. This will allow comprehensive characterization of gray matter diffusion in the entire human brain in vivo for the first time and serve as a reference for future scientific and clinical applications.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Myung-Ho In