title: Conspicuity of hepatic metastases on helical CT: effect of different time delays between contrast administration and scanning.
abstract: OBJECTIVE
  The purpose of this study was to compare two time delays between injection of contrast material and helical CT scanning to determine relative conspicuity of hepatic metastases.
  
  
  METHODS
  Twenty-five patients with hepatic metastases were examined with helical CT. The first imaging phase was initiated at 50 sec and the second 75 sec after the start of contrast material injection (3 ml/sec, 150 ml). Differences in lesion and liver attenuation were measured quantitatively. Four radiologists used a 5-point scale to assess lesion conspicuity subjectively.
  
  
  RESULTS
  Mean differences in enhancement between liver and lesion were 41 H during the first phase and 59 H for the second phase (p = .0001). Radiologists' conspicuity score averaged 2.4 for lesions in the first phase versus 3.3 for lesions in the second phase (p = .0001). In 56 (88%) of 64 lesions, objective measurements showed greater enhancement of lesions during the later phase. Radiologists found 60 (94%) of 64 lesions to be more conspicuous on these later images.
  
  
  CONCLUSIONS
  Our results show that conspicuity of hepatic metastases on helical CT scans is better with a 75-sec scan delay between contrast administration and scanning than with a 50-sec scan delay. The longer delay time should be used when scanning is used to detect metastases.
authors.affiliation: Department of Radiology, Georgetown University Medical Center, Washington, DC 20007.
authors.forename: P M
authors.initials: PM
authors.lastname: Silverman
authors.forename: J
authors.initials: J
authors.lastname: O'Malley
authors.forename: M C
authors.initials: MC
authors.lastname: Tefft
authors.forename: C
authors.initials: C
authors.lastname: Cooper
authors.forename: R K
authors.initials: RK
authors.lastname: Zeman
mesh_terms: D000328:Adult; D000368:Aged; D003287:Contrast Media / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000556:secondary*; D008297:Male; D008875:Middle Aged; D013997:Time Factors; D014057:Tomography, X-Ray Computed
chemical_list: D003287:Contrast Media