Accuracy of the Alberta Stroke Program Early CT Score during the first 3 hours of middle cerebral artery stroke: comparison of noncontrast CT, CT angiography source images, and CT perfusion

Abstract

Background and purpose: The Alberta Stroke Program Early CT Score (ASPECTS) is a reliable method of delineating the extent of middle cerebral artery (MCA) stroke. Our aim was to retrospectively compare the accuracy of ASPECTS on noncontrast CT, CT angiography (CTA) source images, and CT perfusion maps of cerebral blood volume (CBV) during the first 3 hours of middle cerebral artery (MCA) stroke.

Materials and methods: First-time patients with MCA stroke who presented <3 hours from symptom onset and were evaluated by noncontrast CT/CTA/CT perfusion, had confirmed acute nonlacunar MCA infarct on diffusion-weighted MR imaging (DWI) within 7 days, and had follow-up angiography were included. Patients were excluded for persistent MCA occlusion or stenosis. Two raters through consensus assigned an ASPECTS on the noncontrast CT, CTA source images, and the section-selective (2 x 12 mm coverage) CT perfusion CBV maps. ASPECTS on follow-up DWI served as the reference standard. For each CT technique, the detection rates of regional infarction, the mean ASPECTS, and the linear correlation to final ASPECTS were determined and compared. P values <.05 were considered significant.

Results: Twenty-eight patients satisfied the criteria with DWI performed at a mean of 50.3 hours (range, 22-125 hours) post-CT imaging. Of 280 ASPECTS regions, 100 were infarcted on DWI. The accuracy of noncontrast CT, CTA source images, and CT perfusion CBV for detecting regional infarct was 80.0%, 84.3%, and 96.8%, respectively (P < .0001). The mean ASPECTSs of noncontrast CT, CTA source images, CT perfusion CBV, and DWI were 8.4 +/- 1.8, 8.0 +/- 1.8, 6.8 +/- 1.9, and 6.5 +/- 1.8, respectively. The mean noncontrast CT and CTA source image ASPECTS was different from that of DWI (P < .05). Correlation of noncontrast CT, CTA source images, and CT perfusion CBV ASPECTS with final ASPECTS was r(2) = 0.34, r(2) = 0.42, and r(2) = 0.91, respectively.

Conclusion: In a retrospective cohort of MCA infarcts imaged <3 hours from stroke onset, ASPECTS was most accurately determined on CT perfusion CBV maps.

Fig 1.

A 62-year-old man imaged <3 hours after sudden onset of right hemiparesis. From left to right, baseline noncontrast CT (NCCT), CTA source images (CTA-SI), CT perfusion CBV color maps (CT-CBV), and follow-up DWI. Noncontrast CT, by using a window center of 35 HU and a width of 15 HU to visualize optimally the gray-white interface, fails to demonstrate a focal region of parenchymal hypoattenuation, yielding an ASPECTS of 10. CTA source images reveal a focal hypoattenuation at the caudate nucleus consistent with acute infarction, yielding an ASPECTS of 9. CT perfusion CBV map shows relative hypoperfusion in the caudate nucleus as well as at the anterior inferior frontal lobe (M1) and anterior superior frontal lobe (M4), yielding an ASPECTS of 7. Follow-up DWI at 37 hours post-CT imaging confirms acute infarctions in the caudate nucleus, M1, and M4, yielding a final ASPECTS of 7.

Fig 2.

Plots of linear regression between noncontrast CT (NCCT) ASPECTS (r² = 0.34, P = .0011), CTA source images (CTA-SI) ASPECTS (r² = 0.42, P = .0002), and CT perfusion CBV (CT-CBV) ASPECTS (r² = 0.91, P < .0001), with follow-up DWI ASPECTS.