CT angiographic source images: flow- or volume-weighted?

Abstract

Background and purpose: CTA-SI have been previously reported to correlate with CBV. We hypothesized that CTA-SI performed by modern multisection CT scanners are CBF-, not CBV-weighted.

Materials and methods: Sixty-four consecutive patients with anterior circulation stroke symptoms were selected from a stroke data base between June 2007 and January 2009. Two independent blinded readers calculated defect volumes of CTA-SI and PCCT, CBF, and CBV images. Spearman correlation of lesion volumes was performed. Linear regression and residual analysis demonstrated factors associated with outliers for CTA or PCCT for CBF and CBV volumes.

Results: We found a strong positive correlation between CTA with CBF (r = 0.89, P < .0001) and between PCCT and CBV (r = 0.79, P < .0001). CTA to CBV (r = 0.5, P < .0001) and PCCT to CBF (r = 0.52, P < .0001) correlations were weaker. Positive CTA outliers had lower ASPECTS (P = .01), larger baseline CTA (149 ± 46 cm(3) versus 83 ± 32 cm(3); P = .002, respectively), and final infarct (190 ± 100 cm(3) versus 80 ± 50 cm(3); P = .09, respectively) volumes than nonoutliers. No baseline features were significantly related to PCCT outliers. There was no difference in the vessel occlusion sites for positive or negative outliers for CTA or PCCT (P = .55 and P = 1.00, respectively).

Conclusions: Our results indicate that CTA-SI are CBF- rather than CBV-weighted.

Fig 1.

A, Fitted regression line and scatterplot of hypoattenuation volumes of CTA-SI and CBF defect volumes in cubic centimeters. B, logPCCT hypoattenuation volumes and logCBV defect volumes.

Fig 2.

Plots of residuals for CBF defect volumes (A) and logCBV defect volumes (B) based on the linear regression equation. The residual is the difference between the predicted and actual observed value.

Fig 3.

CBF (A) and CBV (B) maps. C, The hypoattenuation of CTA source image and gray-white matter differentiation loss correspond more closely with the CBF than with the CBV map. D, PCCT hypoattenuation corresponds most closely with CBV defect.

Fig 4.

CBF map (A) reveals a large defect within the right MCA territory, while the CBV map (B) shows a substantially smaller region of infarction. C, CTA source image show hypoattenuation and gray-white matter differentiation loss in the right MCA territory corresponding to the CBF defect. D, PCCT image demonstrates subtle questionable posterior Sylvian hypoattenuation.