Purpose: To evaluate the effects of total scanning time (TST), inter-scan delay (ISD), inclusion of image at peak vascular enhancement (IPVE), and selection of the input function vessel on the accuracy of tumor blood flow (BF) calculatior with computed tomography (CT) in an animal model.
Materials and Methods: All animal protocols and experiments were approved by the institutional animal care and use committee prior to study initiation. After injection of 0.2 or 0.4 mL of iodin-ated contrast material, six rats with mammary adenocarcinoma (three tumors each) were scanned in the axial mode for 5 minutes with 1-second ISD (reference scan), 2.5-mm section thickness, 2.5-mm interval, pitch of 1.3, 120 kV, 240 mA, and 0.5-second rotation time. A total of 126 dynamic data sets were created with commercial software by varying TST and ISD, including or excluding the IPVE, and using the aorta or inferior vena cava (IVC) as the input function. Comparative analyses were used to test for significant differences (t test, Wilcoxon signed rank test). Regression analysis was performed to assess the relationship between attenuation of the input function vessel and BF.
Results: No significant difference was observed (P > .05) when TST was as short as 30 seconds (range, 20-23 mL/100 g). In sequences performed with an ISD longer than 8 seconds, BF was significantly elevated (P < .01). Inclusion of the IPVE eliminated this difference (P > .10). Use of the IVC as the input function resulted in significantly higher BF (P < .02), with a correlation between peak attenuation and BF (R2 = 0.43).
Conclusion: To reduce radiation dose in tumor perfusion with CT, TST can be reduced without causing significant changes in BF calculation in an animal model. Scanning the aortic reference with peak contrast enhancement reduces variability sufficiently to allow for longer ISDs.