Limited Reliability of Computed Tomographic Perfusion Acute Infarct Volume Measurements Compared With Diffusion-Weighted Imaging in Anterior Circulation Stroke Pamela W. Schaefer, MD; Leticia Souza, MD; Shervin Kamalian, MD; Joshua A. Hirsch, MD; Albert J. Yoo, MD; Shahmir Kamalian, MD; R. Gilberto Gonzalez, MD, PhD; Michael H. Lev, MD Background and Purpose—Diffusion-weighted imaging (DWI) can reliably identify critically ischemic tissue shortly after stroke onset. We tested whether thresholded computed tomographic cerebral blood flow (CT-CBF) and CT-cerebral blood volume (CT-CBV) maps are sufficiently accurate to substitute for DWI for estimating the critically ischemic tissue volume. Methods—Ischemic volumes of 55 patients with acute anterior circulation stroke were assessed on DWI by visual segmentation and on CT-CBF and CT-CBV with segmentation using 15% and 30% thresholds, respectively. The contrast:noise ratios of ischemic regions on the DWI and CT perfusion (CTP) images were measured. Correlation and Bland–Altman analyses were used to assess the reliability of CTP. Results—Mean contrast:noise ratios for DWI, CT-CBF, and CT-CBV were 4.3, 0.9, and 0.4, respectively. CTP and DWI lesion volumes were highly correlated (R2=0.87 for CT-CBF; R2=0.83 for CT-CBV; P4× higher than the corresponding CT-CBF and CT-CBV values. There was no correlation between the CNRs of DWI and CTP-CBF Table 1.  Admission Variables Variable

All Patients, n=55

Female sex, n, %

26 (47%)

Age, y, mean (SD)

66 (62%–71%)

Right hemisphere, n, %

23 (42%)

Baseline NIHSS, median (IQR)

14 (6%–18%)

DWI volume, mL, mean (95% CI)

58 (36%–79%)

15% CBF volume, mL, mean (95% CI)

60 (42%–78%)

30% CBV volume, mL, mean (95% CI) Ictus to CTP, h:min, mean (±SD) CTP to DWI, min, median (IQR)

32 (13%–50%) 3:48 (±1 min:47 h) 51 (41%–65%)

CBF indicates cerebral blood flow; CBV, cerebral blood volume; CI, confidence interval; CTP, computed tomographic perfusion; DWI, diffusion-weighted imaging; IQR, interquartile range; and NIHSS, National Institutes of Health Stroke Scale.

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Schaefer et al   CTP vs DWI to Assess Acute Infarct Volume    421 Table 2.  SNRs and CNRs of Ischemic Lesions for DWI Were Significantly Higher Than Those for CT-CBV and CT-CBF (All P124 mL, it would be difficult to determine confidently that a DWI lesion volume was >70 mL for potential exclusion from intra-arterial therapy.29 Conversely, any lesion >11 mL on CT-CBF could represent a DWI lesion >70 mL and instituting intra-arterial therapy could cause harm. Thus, if a 70 mL threshold is used, all cases in which CBF ischemic lesion volume measured between 10 and 125 mL would be indeterminate. In the cases analyzed for the present study, ≈45% would be indeterminate. The problem is similar if another volume threshold is used. Our findings of CTP measurement variability are similar to those of other investigators. Campbell et al,6 comparing 31% relative CBF with DWI lesion volumes, found a mean difference of −11.3 mL with CIs of −46.7 to 24.2 mL. Thierfelder et al30 found a mean difference of 4.86 with CIs of −41.20 to 50.87 mL for inter-reader whole brain CT-CBF measurements. By contrast, DWI measurement variability is considerably lower. In 1 article, the overall intrarater and inter-rater percent differences in DWI lesion volume measurements were