Quantitative CT Perfusion: Does CT Dose and Vascular Flow Rate Affect Measures of Parametric Maps?

摘要

The variation in quantitative measures extracted from computed tomography (CT) perfusion parametric maps due to changes in dose was evaluated. A CT perfusion phantom was scanned on a Philips CT scanner using AAPM recommendations at 2 different speeds and varying x-ray exposure. The acquired images were post-processed using the TeraRecon software. The software outputted Cerebral Blood Flow (CBF), Cerebral Blood Volume (CBV), Mean Transit Time (MTT) maps and Time Attenuation Curves (TAC) of the artery and the vein rods of the phantom. Measurements were made in regions of interest (ROIs) in the two tissue rods (foreground) and 5 regions in the background, across the different parametric maps, respectively. Mixed effect model with AR (1) covariance structure was used to compare measurements across different dose levels as repeated measured random effect. Dunnet adjustment was used for post-hoc pairwise comparisons. For the foreground ROI, no significant changes in the measured mean CBF, CBV, and MTT values were observed with changes in dose. As expected, the standard deviation (SD) of CBF and CBV decreased as dose increased. At each dose, higher speed settings were consistently associated with higher SD of CBF and lower MTT. For the background ROI, the measured mean CBF and CBV were significantly higher at lower dose levels, and the SD of CBF decreased as the dose increased. The MTT of the background did not vary with dose. We conclude that radiation dose affects perfusion metrics especially for low or no flow conditions.