Highly Accelerated Distortion-Free Diffusion-Weighted MR Imaging at Ultra High Field (7T): Gray Matter Characterization
Human Cognitive and Systems Neuroscience
Final Report Abstract
Diffusion-weighted MRI is a unique modality to measure connectivity between brain regions in the human brain non-invasively. This modality has led to the term “brain connectome” as a representation of all the brains white matter fiber connections. The method most frequently used to measure diffusion-weighted MRI is echo planar imaging (EPI). EPI, however, is very sensitive to geometric distortions that can arise from the object under study as well as hardware imperfections. This limits not only the anatomic interpretation of the data but also leads to quantitative errors in the analysis. With higher magnetic field strength, higher spatial resolution is possible. However, even stronger geometric distortions and signal variations occur. Thus, the goal to map the diffusion properties in the thin cortical ribbon at high magnetic field strength is compromised. We developed an extension to the EPI method that allows correction of geometric distortions based on the point-spread-function mapping method. This method directly measures spatial distortions and corrects them during reconstruction. Since distortions can change for each of many diffusion-weighted scans, the scan time becomes prohibitively long. The main goal of the work was thus to reduce the measurement time and to investigate the diffusion properties of the human cortex in detail. For this purpose, we extended the PSF-mapping method to allow aggressive acceleration of the underlying EPI measurement, added a 2D phase navigator to allow segmented acquisition, included view angle tilting to reduce the distortions that need to be corrected and further accelerated the measurement through simultaneous multi slice acquisition. The combination of these efforts allowed for very high-resolution diffusion-weighted measurement of the entire human brain in a single session (submillimeter resolution with high SNR and free of distortions). The data clearly demonstrated diffusion anisotropy in the cortex with a reproducible pattern from the white matter to the cortical surface across the entire brain. In addition, we were able to demonstrate that the main diffusion direction within the cortex is orthogonal to the cortical surface and within white matter directly underneath the cortex is largely parallel to the cortical surface at the banks of gyri and perpendicular at their crowns. With the method developed in this project, diffusion tensor imaging (DTI) can be extended from a formerly pure white matter modality into the brain’s gray matter and investigate the cortical microstructure. Since many neurological and neurodegenerative diseases originate in the cortex, this opens a new window into brain imaging and may enable earlier diagnosis of neurologic and neurodegenerative disease.
Publications
- (2017) High-resolution distortion-free diffusion imaging using hybrid spin-warp and echo-planar PSF-encoding approach, NeuroImage 148: 20-30
Myung-Ho In, Oleg Posnansky, Oliver Speck
(See online at https://doi.org/10.1016/j.neuroimage.2017.01.008) - (2018) Accelerated Distortion-Free Diffusion Imaging at 7T – by Fusing PSF and VAT, Joint Annual Meeting ISMRM-ESMRMB 2018, Paris, France
Yi-Hang Tung, Myung-Ho In, Sinyeob Ahn, Alessandro Sciarra, and Oliver Speck
- (2018) Dynamic 2D self‐ phase‐map Nyquist ghost correction for simultaneous multi‐slice echo planar imaging, Magnetic Resonance in Medicine 80(4): 1577-1587
Uten Yarach, Yi-Hang Tung, Kawin Setsompop, Myung-Ho In, Itthi Chatnuntawech, Renat Yakupov, Frank Godenschweger and Oliver Speck
(See online at https://doi.org/10.1002/mrm.27123) - (2019), Isotropic High-Resolution DIADEM-VAT at UHF, ESMRMB Congress 2019, Rotterdam, Netherlands
Yi-Hang Tung, Myung-Ho In, Alessandro Sciarra, and Oliver Speck
