Diffusion-weighted MR imaging of acute cerebral ischemia

Abstract

Diffusion-weighted MR imaging has been used in studies on experimental animal models and on patients with acute cerebral ischemia. Compared with CT and conventional MR techniques, diffusion-weighted imaging can provide earlier and more precise detection of the location and the extent of an ischemic lesion during the critical first few hours after the onset of stroke. Quantitative apparent diffusion coefficient (ADC) mapping of the brain water can also be carried out by recording a series of diffusion-weighted images with different amplitudes of the displacement encoding gradients. ADC maps can provide important information about the extra- and intracellular water homeostasis. ADC reduction of the tissue water is one of the early signals of the pathophysiological cascade resulting from ischemic tissue injury. Diffusion MR imaging has become a valuable tool in stroke research. It may also prove a valuable tool in monitoring the efficiency of therapeutic effects in stroke patients. It is our intention to provide an overview of the recent development in this area with emphasis on the diffusion-weighted MR techniques, and to discuss the possible underlying biophysical mechanisms responsible for the contrast of diffusion-weighted imaging.

Cerebral White Matter Disruption in Creutzfeldt-Jakob Disease

“…Identifying the tissue substrate of FA changes is complicated by the fact that diffusion of water molecules occurs in at least 2 compartments: intracellular and extracellular. FA was shown to be elevated with increasing myelination, [40][41][42] and it is tempting to interpret our data as proof of degraded myelination. However, the axonal environment can be altered by other mechanisms that would modify diffusion, such as geometry.…”

Significance of Early CT Signs in Acute Stroke

“…It has been reported that the acute decrease in diffusion and apparent diffusion coefficient (ADC) on ADC maps occurs at the point at which Na + -ATPase activity fails and cytotoxic edema ensues [22]. Associated with these changes there is a decrease in the intracellular and extracellular diffusion of water [14, 18, 22, 23]. Vasogenic edema or increased tissue water content will appear hyperintense in T2WI and tend to cause an increase in ADC.…”

“…The introduction of ultrafast echo planar imaging (EPI) methods in DWI [18]allowed the elimination of movement artifact and the reduction of imaging time and led to promote the major role of DWI in acute stroke diagnosis. Numerous studies have demonstrated the high sensitivity of diffusion and perfusion MR imaging in detecting and assessing acute stroke within the first hours [17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29], and some have of them have compared DWI and CT scan in the diagnosis acute stroke, showing a higher sensitivity for DWI. Comparing the extent of areas of early CT scan signs and DWI in patients with hyperacute stroke, a positive correlation was found between lesion volume on acute DWI and CT [30, 31].…”

ADC mapping by means of a single-shot spiral MRI technique with application in acute cerebral ischemia

“…Compared with CT and conventional T 2 -and T 1 -weighted MRI techniques, diffusionweighted imaging (DWI) can provide earlier and more precise detection of the location and extent of ischemic infarct within the early stage of stroke (6,7), which is considered to be the most critical time window necessary to guide acute therapeutic interventions promising improved patient outcome. Quantitative measurement of the apparent diffusion coefficient (ADC) of the brain tissue water provides direct information about the extracellular and intracellular water homeostasis without confounding T 2 effects.…”