title: Effect of temporal interval between scan acquisitions on quantitative vascular parameters in colorectal cancer: implications for helical volumetric perfusion CT techniques.
abstract: 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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Paul Strickland Scanner Centre, Mount Vernon Hospital, Rickmansworth Rd., Northwood, Middlesex, HA6 2RN, United Kingdom. vicky.goh@stricklandscanner.org.uk
authors.forename: Vicky
authors.initials: V
authors.lastname: Goh
authors.forename: Jonathan
authors.initials: J
authors.lastname: Liaw
authors.forename: Clive I
authors.initials: CI
authors.lastname: Bartram
authors.forename: Steve
authors.initials: S
authors.lastname: Halligan
mesh_terms: D000230:Adenocarcinoma / Q000098:blood supply / Q000000981:diagnostic imaging*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015179:Colorectal Neoplasms / Q000098:blood supply / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D055414:Myocardial Perfusion Imaging / Q000379:methods*; D009389:Neovascularization, Pathologic / Q000000981:diagnostic imaging*; D011856:Radiographic Image Enhancement / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors; D036542:Tomography, Spiral Computed / Q000379:methods*