Localized high-resolution DTI of the human midbrain using single-shot EPI, parallel imaging, and outer-volume suppression at 7T

Abstract

Localized high-resolution diffusion tensor images (DTI) from the midbrain were obtained using reduced field-of-view (rFOV) methods combined with SENSE parallel imaging and single-shot echo planar (EPI) acquisitions at 7 T. This combination aimed to diminish sensitivities of DTI to motion, susceptibility variations, and EPI artifacts at ultra-high field. Outer-volume suppression (OVS) was applied in DTI acquisitions at 2- and 1-mm2 resolutions, b=1000 s/mm2, and six diffusion directions, resulting in scans of 7- and 14-min durations. Mean apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were measured in various fiber tract locations at the two resolutions and compared. Geometric distortion and signal-to-noise ratio (SNR) were additionally measured and compared for reduced-FOV and full-FOV DTI scans. Up to an eight-fold data reduction was achieved using DTI-OVS with SENSE at 1 mm2, and geometric distortion was halved. The localization of fiber tracts was improved, enabling targeted FA and ADC measurements. Significant differences in diffusion properties were observed between resolutions for a number of regions suggesting that FA values are impacted by partial volume effects even at a 2-mm2 resolution. The combined SENSE DTI-OVS approach allows large reductions in DTI data acquisition and provides improved quality for high-resolution diffusion studies of the human brain.

Distinguishing and quantification of the human visual pathways using high-spatial-resolution diffusion tensor tractography

“…Diffusion-sensitized MRI methods applied to the human visual pathways have utilized regions-of-interest [9, 10], deterministic [11, 12, 13, 14] and probabilistic tractography [15, 16, 17] on separate components of the visual system including optic nerves [9, 18], optic chiasm [19, 20, 21], optic tracts [10], and optic radiations [11–14] including Meyer loop [7, 8]. Qualitatively, the methods adopted to-date to quantify components of the human visual system using diffusion-weighted imaging were different on several aspects including spin history preparation (i.e.…”

High spatial resolution in vivo magnetic resonance imaging of the human eye, orbit, nervus opticus and optic nerve sheath at 7.0 Tesla

“…Especially contrast enhanced T 1 w images can demonstrate subtle enhancement indicating an active inflammatory process (Kollia et al, 2009). In combination with high resolution diffusion tensor imaging (Wargo and Gore, 2013) this may facilitate qualitative and quantitative assessment of optic nerve involvement in these patients and may improve differential diagnosis of optic neuropathies (Erb-Eigner et al, 2013b;Khanna et al, 2012).…”

Cervical Spinal Cord DTI Is Improved by Reduced FOV with Specific Balance between the Number of Diffusion Gradient Directions and Averages

“…Finally, as additional techniques are being developed, we can expect further improvement: 1) The combination of parallel imaging and r-FOV, which has already been performed for the pons at 7T 27 , can still increase DTI quality; 1) multisegmented 3D-EPI could increase the SNR and could be associated with r-FOV and parallel imaging to reduce the echo train 28 ; 3) a more accurate diffusion model could be used such as neurite orientation dispersion and density imaging, 29 which might provide more accurate quantitative diffusion metrics, especially for anisotropic structures like gray matter; and 4) improved postprocessing methods are being developed, 30 with improved eddy current and motion corrections.…”