Water diffusion and acute stroke

Abstract

The occlusion of the middle cerebral artery was used as an experimental acute stroke model in 30 cats. The diffusion of water was followed by diffusion-sensitized MRI between 1 and 15 h after induction of stroke. It is demonstrated that images representing the trace of the diffusion tensor provide a much more accurate delineation of affected area than images representing the diffusion in one direction only. The reason is that the strong contrast caused by the anisotropy and orientation of myelin fibers is completely removed in the trace of the diffusion tensor. The trace images show a small contrast between white and gray matter. The diffusion coefficient of white matter is decreased in acute stroke to approximately the same extent as gray matter. It is further shown that the average lifetime of water in extra and intracellular space is shorter than 20 ms both for healthy and ischemic tissue indicating that myelin fibers are permeable to water. The anisotropy contrast did not change before or after induction of stroke, nor after sacrifice. Together, these observations are consistent with the view that the changes in water diffusion during acute stroke are directly related to cytotoxic oedema, i.e., to the change in relative volume of intra- and extracellular spaces. Changes in membrane permeability do not appear to contribute significantly to the changes in diffusion.

Diffusion tensor MRI of the human kidney

“…Therefore, any method exploiting rotationally-dependent ADC data to access the metabolic state of the kidney is likely to be severely error biased due to the internal structure of the kidney having a varying orientation within the slice. This situation is comparable to recent advances in brain diffusion imaging, in which either the full diffusion tensor is measured to obtain both the full anisotropy information and the magnitude (10), or the experiment focuses only on the measurement of the trace of the diffusion tensor and thus reduces the obtained information to the overall diffusion magnitude without any directional influence (28).…”

Diffusion tensor fiber tracking of human brain connectivity: aquisition methods, reliability analysis and biological results

“…2,3 Various groups have used DTT to track fibers in fixed rodent brain 1,25 and in living humans. [2][3][4][5]26 Physical basis of using DT-MRI to track ®bers DTT is based on diffusion tensor-encoded MRI (DT-MRI), in which diffusion-weighted imaging (DWI) data are acquired for computing the effective diffusion tensor 27 and its derived properties such as directionally averaged diffusion 28,29 and anisotropy. [30][31][32][33] Early DWI studies observed a faster diffusion along the WM fibers, [34][35][36] thought to be due in part to membranes that slow diffusion perpendicular to the fiber.…”

Fiber tracking: principles and strategies – a technical review

“…These applications employ both the directional anisotropy that can be measured by DTI 4,5 as well as removal of this anisotropy through the use of the tensor trace. [6][7][8] For example, DTI is presently being explored as a research tool to study brain development, 9,10 multiple sclerosis, 11,12 amyotrophic lateral sclerosis (ALS), 13 stroke, 14,15, schizophrenia 16,17 and reading disability, 18 while trace imaging has become an essential part of clinical acute stroke assessment. [19][20][21][22] As first shown by Basser et al, 4 the diffusion ellipsoid obtained from DTI can not only provide a quantitative orientation-independent measure of diffusion anisotropy, 23,24 but also the predominant direction of water diffusion in image voxels.…”