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By identifying brain tissue that has been damaged due to lack of blood supply (ischemia), computerized tomography (CT) helps confirm the diagnosis of acute stroke. However, because normal noncontrast CT (NCCT) scans are relatively common when the scans are performed very early after onset of stroke symptoms, they introduce diagnostic uncertainty for the stroke neurologist. CT angiography-source images (CTA-SI) ASPECTS (Alberta Stroke Program Early CT Score), or enhanced CT, has a greater sensitivity to ischemic changes and more accurately identifies the volume of tissue that will ultimately infarct (die) compared with NCCT (unenhanced CT) alone, according to a recent study supported in part by the Agency for Healthcare Research and Quality (HS11392). The study was conducted by researchers at the University of Calgary, Alberta, and Harvard Medical School.
In seven of ten study cases, the ischemia would have been totally missed by one of the expert raters with use of NCCT alone, according to the researchers. They used two expert raters to assign ASPECTS on the acute NCCT, CTA-SI, and followup imaging and then compared the mean baseline ASPECTS of acute NCCT and CTA-SI with the followup ASPECTS. Nearly two-thirds (62 percent) of the 39 patients studied had proximal occlusion (of the internal carotid artery or middle cerebral artery), 18 percent had M2 occlusion, and 20 percent had no occlusion. The median time between symptom onset and CT imaging was 1.9 hours.
There was a significantly larger difference of 1.4 between the mean baseline NCCT and CTA-SI ASPECTS in patients who had more ischemic changes (follow-up ASPECTS of 0 to 3) compared with a difference of 0.6 in patients who had near-to-normal CT scans (follow-up ASPECTS of 8 to 10). Twice as many patients with near-to-normal CT scans (52 percent) had favorable outcomes compared with those who had more ischemic changes (NCCT ASPECTS of 0 to 7) (25 percent). For patients with acute CTA-SI ASPECTS of 8 to 10, the rate of favorable outcome was 59 percent versus 32 percent for those with 0 to 7.
See "ASPECTS on CTA source images versus unenhanced CT: Added value in predicting final infarct extent and clinical outcome," by Shelagh B. Coutts, M.B., Ch.B., Michael H. Lev, M.D., Michael Eliasziw, Ph.D., and others, in the November 2004 Stroke 35, pp. 2472-2476.
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