الفهرس 
Anatomy of Cerebral Arterial CirculationOnly 14 pages are availabe for public view
 |  | from | 136 |  |  |
| | | from | 136 | | |
Abstract
The determination of the extent of brain tissue that is ischemic, but still viable and therefore under risk for irreversible injury (i.e., penumbra), is one of the major goals in acute stroke imaging. Advances in technology and the availability of perfusion imaging, either by computed tomography (CT) or magnetic resonance imaging (MRI), are major steps in this regard. Despite these developments, there are certain roadblocks in the utilization of perfusion imaging, with MRI in particular, in acute stroke patients. These include the unavailability of resources; the need for technical and medical personnel for the postprocessing and interpretation of perfusion images; and the use of intravenous contrast agents, which are highly critical in patients with renal failure. Last but not least, the concept of diffusion/perfusion mismatch representing the ischaemic penumbra may not be as reliable as it was earlier thought to be and may not actually represent the threatened tissue.
Another imaging feature suggestive of impaired tissue perfu¬sion is the presence of marked hypointense vessels on susceptibility-weighted imaging (SWI), a high-spatial-resolution 3-dimensional gradient-echo MR technique, which is highly susceptible to paramagnetic substances such as deoxyhemoglobin, Shortly after vascular occlusion, the uncoupling between oxygen supply and demand in the hypoperfused region leads to an elevated oxygen extraction fraction and subsequent increased level of deoxyhemoglobin in the vessel, which contributes to prominent hypointensity of the draining veins on SWI. Thus asymmetric cortical veins, which can be visualized on SWI after acute ischemic stroke (AIS) can be considered an indicator of salvageable ischemic tissue.
Results of this study, like several other studies demonstrate that DWI/SWI mismatch can be a marker for ischaemic penumbra and a reliable but not conclusive predictor of stroke evolution.
To conclude, this study shows that SWI provides valuable information in AIS concerning critically perfused brain tissue at risk of infarct progression, and may guide early treatment options to prevent infarct progression. This suggests that SWI is a valuable MR tool to be added to the battery of neuroimaging techniques for AIS. Nevertheless studies with a larger cohort of patients, and PWI as part of the acute neuroimaging protocol are needed to further validate the value of SWI in AIS.