Diffusion tensor MR imaging of the human brain.

Abstract

Summary: Diffusion-tensor MR imaging of the brain is an objective method that can measure diffusion of water in tissue noninvasively. Five adult volunteers participated in this study that was performed to evaluate the potential of gradient-and spin-echo readout for diffusion-tensor imaging by comparing it with single-shot spin-echo echo-planar imaging. Gradient-and spin-echo readout provides comparable measures of water diffusion to single-shot spinecho echo-planar readout with significantly less geometrical distortion at the expense of a longer imaging time.Diffusion-tensor MR imaging of the brain has been proposed as a noninvasive technique that provides microstructural and physiological information regarding brain tissue in vivo by measuring the diffusion of water (1, 2). Most current applications of diffusion-tensor MR imaging implement ultrafast single-shot echo-planar readouts, which effectively freeze physiological effects (3-5) despite severe geometrical distortions caused by local magnetic field inhomogeneity. Gradient-and spinecho (GRASE) MR imaging has less distortion compared with single-shot echo-planar imaging because the multiple refocusing RF pulses implemented in GRASE MR imaging are responsible for reducing errors originating from static field inhomogeneity (6). For this technical note, we compared the signal-to-noise ratio (SNR), isotropic apparent diffusion coefficient (ADCi), fractional anisotropy (FA), and geometrical distortions from diffusion-tensor MR imaging by use of GRASE and echo-planar readout techniques. Description of the Technique MR Imaging and Data ProcessingMR imaging studies were performed on a 1.5-T MR system (ACS-NT; Philips Medical Systems, Best, The Netherlands) using a quadrature head coil operating in receive mode. The ᭧ American Society of Neuroradiology whole-brain MR imaging protocol included axial T1-weighted spin-echo 517/14/2 (TR/TE/excitations) imaging and axial diffusion-tensor imaging using peripheral gating. The diffusion tensor MR imaging was performed using single-shot spin-echo echo-planar and GRASE readouts. Diffusion sensitization was applied sequentially in six different non-colinear directions (G xx , G yy , G zz , G xy , G xz , G yz ). The parameters for single-shot spin-echo echo-planar diffusion-tensor imaging were 3429-5538/96/4 (TR/effective TE/excitations), with a b value of 600 s·mm Ϫ2 . The parameters for GRASE diffusion-tensor imaging with four spin echoes each comprising five gradient echoes were 4000-4615/119 (TR/TE eff ), with a b value of 600 s·mm Ϫ2 . To eliminate phase errors that originated during the diffusion preparation period, a dephasing gradient and a 90-degree RF pulse before the GRASE readout were used (7). The T1-weighted spin-echo sequence and both the diffusiontensor sequences were matched for total brain coverage (number of sections, 18; section thickness, 5 mm; intersection gap, 1 mm; field of view, 23 cm). The GRASE experiment was performed twice, once with four excitations (4-GRASE) and once with 10 excitations (10-GRASE)....

Diffusion‐tensor MRI: theory, experimental design and data analysis – a technical review

“…For example, why is it so uniform within normal adult brain parenchyma? In particular, why is its value so similar in normal white and gray matter, 31 even though these tissues are so different histologically? This spatial uniformity has contributed to the increasing clinical utility of Trace(D) in disease assessment and monitoring since it makes diseased regions more conspicuous when juxtaposed against the homogeneous background of normal parenchyma.…”

“…In fact, it appears to be quite similar across a range of normal mammalian brains including mice, rats, cats, 32,33 monkeys 34 and humans. 31,35 It is worth considering whether mammalian brains are 'designed' to force Trace(D) to lie within such a narrow range of values and, if so, what these optimal design criteria are.…”

Diffusion tensor magnetic resonance imaging strategies for color mapping of human brain anatomy

“…Indeed, connecting the observed anisotropy for isotropic media to errors in calibration, misalignment, and cross-talk between the imaging and diffusion gradients has to be assessed. [212202122232425262728]…”

Magnetic Resonance Imaging in Neuropsychiatric Lupus

“…Diffusion-tensor imaging (DTI) is based on the measurement of water diffusion through cellular compartments, and was demonstrated to provide better resolution than conventional sequences regarding white matter microstructure ( Figure 3a–b) 73, 74 . Compared to more isotropic movement of water in gray matter, the diffusion in white matter presents higher anisotropy, with preferential diffusion along the length of the axon.…”