FIG 2. Axial CT scan of the PE tubes phantom used to correct for PVA. PE tubes on the left contain 40 mL of distilled water with 2.7 mL of Isovue 300 (300 mg I/mL contrast material) added. PE tubes on the right contain only distilled water to serve as background (ie, unenhanced). A two-pixel-radius ROI was drawn in the center of each tube, and the mean CT number was determined within these circular ROIs