Purpose: To prospectively determine whether position and size of tumor region of interest (ROI) influence estimates of colo-rectal cancer vascular parameters at computed tomogra-phy(CT).
Materials and Methods: After institutional review board approval and informed consent, 25 men and 22 women (mean age, 65.8 years) with colorectal adenocarcinoma underwent 65-second CT perfusion study. Blood volume, blood flow, and perme-ability-surface area product were determined for 40- or 120-mm2 circular ROIs placed at the tumor edge and cen-ter and around (outlining) visible tumor. ROI analysis was repeated by two observers in different subsets of patients to assess intra- and interobserver variation. Measure-ments were compared by using analysis of variance; a difference with P = .002 was significant.
Results: Blood volume, blood flow, and permeability-surface area product measurements were substantially higher at the edge than at the center for both 40- and 120-mm2 ROls. For 40-mm2 ROI, means of the three measurements were 6.9 mL/100 g (standard deviation [SD], 1.4), 108.7 mL/ 100 g per minute (SD, 39.2), and 16.9 mL/100 g per minute (SD, 4.2), respectively, at the edge versus 5.1 mL/100 g (SD, 1.5), 56.3 mL/100 g per minute (SD, 33.1), and 13.9 mL/100 g per minute (SD, 4.6), respectively, at the center. For 120-mm" ROI, means of the three mea-surements were 6.6 mL/100 g (SD, 1.3), 96.7 mL/100 g per minute (SD, 42.5), and 16.3 mL/100 g per minute (SD, 5.6), respectively, at the edge versus 5.1 mL/100 g (SD, 1.4), 58.3 mL/100 g per minute (SD, 32.5), and 13.4 mL/100 g per minute (SD, 4.3) at the center {P < .0001). Measurements varied substantially depending on the ROI size; values for the ROI for outlined tumor were interme-diate between those at the tumor edge and center. Inter-and intraobserver agreement was poor for both 40- and 120-mm2 ROIs.
Conclusion: Position and size of tumor ROI and observer variation substantially influence ultimate perfusion values. ROI for outlined entire tumor is more reliable for perfusion measurements and more appropriate clinically than use of arbitrarily determined smaller ROIs.