Alberta Stroke Program Early CT Scoring of CT perfusion in early stroke visualization and assessment

Abstract

Background and purpose: Qualitative CT perfusion (CTP) assessment by using the Alberta Stroke Program Early CT Score (ASPECTS) allows rapid calculation of infarct extent for middle cerebral artery infarcts. Published thresholds exist for noncontrast CT (NCCT) ASPECTS, which may distinguish outcome/complication risk, but early ischemic signs are difficult to detect. We hypothesized that different ASPECTS thresholds exist for CTP parameters versus NCCT and that these may be superior at predicting clinical and radiologic outcome in the acute setting.

Materials and methods: Thirty-six baseline acute stroke NCCT and CTP studies within 3 hours of symptoms were blindly reviewed by 3 neuroradiologists, and ASPECTS were assigned. Treatment response was defined as major neurologic improvement when a > or =8-point National Institutes of Health Stroke Scale improvement at 24 hours occurred. Follow-up NCCT ASPECTS and 90-day modified Rankin score (mRS) were radiologic and clinical reference standards. Receiver operating characteristic curves derived optimal thresholds for outcome.

Results: Cerebral blood volume and NCCT ASPECTS had similar radiologic correlations (0.6 and 0.5, respectively) and best predicted infarct size in the absence of major neurologic improvement. A NCCT ASPECT threshold of 7 and a cerebral blood volume threshold of 8 discriminated patients with poor follow-up scans (P < .0002 and P = .0001) and mRS < or =2 (P = .001 and P < .001). Only cerebral blood volume predicted major neurologic improvement (P = .02). Interobserver agreement was substantial (intraclass correlation coefficient, 0.69). Cerebral blood volume ASPECTS sensitivity, specificity, positive predictive value, and negative predictive value for clinical outcome were 60%, 100%, 100%, and 45%, respectively. No patients with cerebral blood volume ASPECTS <8 achieved good clinical outcome.

Conclusion: Cerebral blood volume ASPECTS is equivalent to NCCT for predicting radiologic outcome but may have an additional benefit in predicting patients with major neurologic improvement.

Fig 1.

A 75-year-old man, within 2 hours of right-sided stroke and presentation of NIHSS 20. A, NCCT demonstrates subtle loss of the left posterior putamen, internal capsule, and posterior insular cortex (white arrowhead) (ASPECTS 7). B, Cerebral blood flow. C, Cerebral blood volume. D, Mean transit time. Cerebral blood volume demonstrates an abnormality confined to the posterior putamen and internal capsule (ASPECTS 8), with larger cerebral blood flow and mean-transit-time abnormalities corresponding to the left middle cerebral artery M1 segment occlusion (not shown). E, Follow-up NCCT at day 6 shows an indistinct posterior putamen confirmed on diffusion-weighted MR imaging (F). The patient recovered by 18 points with a final NIHSS of 2.

Fig 2.

A plot of mean baseline ASPECTS NCCT, cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) against major neurologic improvement, demonstrating that only CBV is predictive of 24-hour NIHSS change.

Fig 3.

A plot of mean baseline ASPECTS NCCT, cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT). Results are dichotomized for clinical outcome by using 2-sample t tests. Favorable outcome was defined as mRS ≤2. Comparison of mean clinical outcomes was based on dichotomized mRS (0–2 versus 3–6), by using unequal variance 2-sample t tests.