Effect of temporal interval between scan acquisitions on quantitative vascular parameters in colorectal cancer: implications for helical volumetric perfusion CT techniques.

OBJECTIVE: The purpose of this study was to determine how the temporal interval between scan acquisitions influences quantitative perfusion CT vascular parameters in colorectal cancer. SUBJECTS AND METHODS: Forty-five patients with colorectal adenocarcinoma prospectively underwent a 65-second single-anatomic-level perfusion CT study. Blood flow, blood volume, transit time, and permeability-surface area product for a 2-cm tumor coverage were determined with commercial software based on distributed parameter analysis for four temporal intervals (1, 2, 3, and 4 seconds) between acquisitions. Mean vascular values obtained for these intervals were compared by use of analysis of variance with posttesting by the Bonferroni method. Statistical significance was set at 5%.
RESULTS: Mean +/- SD blood flow, volume, transit, and permeability-surface area product were 71.5 +/- 34.8 mL/min/100 g tissue, 6.33 +/- 1.96 mL/100 g tissue, 10.8 +/- 5.54 seconds, and 14.9 +/- 3.51 mL/min/100 g tissue, respectively, at 1 second; 86.6 +/- 40.6 mL/min/100 g tissue, 6.30 +/- 2.53 mL/100 g tissue, 10.7 +/- 7.12 seconds, and 14.5 +/- 3.55 mL/min/100 g tissue at 2 seconds; 97.8 +/- 42.7 mL/min/100 g tissue, 5.98 +/- 1.72 mL/100 g tissue, 8.11 +/- 4.37 seconds, and 14.5 +/- 3.58 mL/min/100 g tissue at 3 seconds; and 108.8 +/- 46.0 mL/min/100 g tissue, 6.69 +/- 3.46 mL/100 g tissue, 7.12 +/- 3.54 seconds, and 13.9 +/- 3.49 mL/min/100 g tissue at 4 seconds. Blood flow was overestimated (p = 0.0002) and transit underestimated (p = 0.03) with lengthening acquisition interval. Posttesting revealed that in a comparison with 1-second data, this difference was significant for 3- and 4-second data for blood flow and 4-second data for transit.
CONCLUSION: Increasing the temporal interval from 1 to 4 seconds leads to overestimation of tumor blood flow and underestimation of blood transit in distributed parameter analysis. Use of the helical perfusion CT techniques being developed may lead to inaccurate assessment unless the acquisition interval is shorter than 3 seconds.