title: Dual phase hepatic CT: influence of scanning direction on liver attenuation.
abstract: OBJECTIVE
  We measured changes in hepatic attenuation during arterial and portal phase acquisition of hepatic CT in the craniocaudal and caudocranial directions.
  
  
  METHODS
  In 10 of 20 patients undergoing dual phase helical CT during staging for colorectal cancer, images in both phases were obtained in the craniocaudal direction. Ten patients underwent imaging in the caudocranial direction. Attenuation values in the aorta and in the peripheral and central liver regions of interest were measured on each slice. Central and peripheral liver attenuation was also measured in 10 additional patients undergoing unenhanced CT.
  
  
  RESULTS
  Both peripheral and central regions of interest revealed progressively increasing attenuation during the arterial phase, irrespective of scanning direction. During the portal phase, hepatic attenuation was stable in the craniocaudal direction but decreased in the caudocranial direction (p < 0.05, Wilcoxon's signed rank sum test). Central hepatic attenuation was lower than peripheral attenuation in unenhanced livers and in enhanced livers during both phases of caudocranial acquisition. We determined no significant difference during the arterial phase of enhancement in the craniocaudal direction.
  
  
  CONCLUSIONS
  The direction of acquisition does not influence sequential liver enhancement during the arterial phase. Craniocaudal acquisition produces more stable enhancement during the portal phase. Differences in attenuation between the central and peripheral areas of the liver are probably unrelated to contrast administration.
authors.affiliation: Department of Clinical Radiology, St James's University Hospital, Leeds, United Kingdom.
authors.forename: E
authors.initials: E
authors.lastname: O'Riordan
authors.forename: C M
authors.initials: CM
authors.lastname: Craven
authors.forename: D
authors.initials: D
authors.lastname: Wilson
authors.forename: P J
authors.initials: PJ
authors.lastname: Robinson
mesh_terms: D000328:Adult; D000368:Aged; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging; D003287:Contrast Media / Q000008:administration & dosage; D005260:Female; D006801:Humans; D007275:Injections, Intravenous; D008099:Liver / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media