k-space and q-space: Combining ultra-high spatial and angular resolution in diffusion imaging using ZOOPPA at 7T

• Published in: NeuroImage (Orlando, Fla.) Fla.), 2012-04, Vol.60 (2), p.967-978
• Main Authors: Heidemann, Robin M., Anwander, Alfred, Feiweier, Thorsten, Knösche, Thomas R., Turner, Robert
• Format: Article
• Language: English
• Subjects: Acquisitions & mergers; Brain; Diffusion; Diffusion MRI; Fiber-tracking; Magnetic fields; Methods; NMR; Nuclear magnetic resonance; Parallel imaging; Ultra-high field MRI; Zoomed imaging
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2011.12.081

There is ongoing debate whether using a higher spatial resolution (sampling k-space) or a higher angular resolution (sampling q-space angles) is the better way to improve diffusion MRI (dMRI) based tractography results in living humans. In both cases, the limiting factor is the signal-to-noise ratio (SNR), due to the restricted acquisition time. One possible way to increase the spatial resolution without sacrificing either SNR or angular resolution is to move to a higher magnetic field strength. Nevertheless, dMRI has not been the preferred application for ultra-high field strength (7T). This is because single-shot echo-planar imaging (EPI) has been the method of choice for human in vivo dMRI. EPI faces several challenges related to the use of a high resolution at high field strength, for example, distortions and image blurring. These problems can easily compromise the expected SNR gain with field strength. In the current study, we introduce an adapted EPI sequence in conjunction with a combination of ZOOmed imaging and Partially Parallel Acquisition (ZOOPPA). We demonstrate that the method can produce high quality diffusion-weighted images with high spatial and angular resolution at 7T. We provide examples of in vivo human dMRI with isotropic resolutions of 1mm and 800μm. These data sets are particularly suitable for resolving complex and subtle fiber architectures, including fiber crossings in the white matter, anisotropy in the cortex and fibers entering the cortex. [Display omitted] ► Diffusion MRI (dMRI) at ultra-high field strength. ► Using ZOOPPA to exploit the SNR benefit of the high field strength. ► Enables dMRI with sub-millimeter isotropic resolution. ► High spatial and angular resolution with sufficient SNR to resolve crossing fibers.