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Quantitative Assessment of Colorectal Cancer Tumor Vascular Parameters by Using Perfusion CT: Influence of Tumor Region of Interest¹

¹ From the Paul Strickland Scanner Centre, Mount Vernon Hospital, Northwood, Middlesex, England (V.G., A.G.); Department of Academic Radiology, University College Hospital, 235 Euston Rd, Level 2 Podium, London NW1 2BU, England (S.H.); Intestinal Imaging Centre, St Mark's Hospital, Harrow, England (A.G., C.I.B.); and Health Research and Development Support Unit, University of Hertfordshire, Hatfield, England (D.W., J.S.). From the 2006 RSNA Annual Meeting. Received March 2, 2007; revision requested May 9; revision received July 19; accepted August 17; final version accepted November 13. Supported in part by a pump priming grant from the Royal College of Radiologists, London, England. Address correspondence to S.H. (e-mail: s.halligan{at}ucl.ac.uk).

Purpose: To prospectively determine whether position and size of tumor region of interest (ROI) influence estimates of colorectal cancer vascular parameters at computed tomography (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 permeability–surface area product were determined for 40- or 120-mm² circular ROIs placed at the tumor edge and center and around (outlining) visible tumor. ROI analysis was repeated by two observers in different subsets of patients to assess intra- and interobserver variation. Measurements 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 ROIs. 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-mm² ROI, means of the three measurements 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 intermediate 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.

© RSNA, 2008