title: Helical CT during arterial portography: optimization of contrast enhancement and scanning parameters.
abstract: OBJECTIVE
  To determine the optimal scanning parameters for helical computed tomography during arterial portography (CTAP) of the liver.
  
  
  METHODS
  Single- and double-helix CTAP were performed in 11 and 20 adult patients, respectively, with 200 mL of contrast material (300 mg of iodine per milliliter) injected at a rate of 3 mL/sec via the superior mesenteric artery. Scanning delays were adjusted for single-helix CTAP so the last scan was obtained at 66 seconds. Delays were adjusted for double-helix CTAP so the last scan during the first helix (CTAP-1) was obtained 10 seconds before the end of the injection at 56 seconds and the first scan during the second helix (CTAP-2) was obtained at the end of the injection at 66 seconds.
  
  
  RESULTS
  Single-helix CTAP scans were of poor quality owing to multiple perfusion abnormalities. Lesion detection for double-helix CTAP-1 was 93.2% and was 100% for CTAP-2, and CTAP-2 scans had significantly fewer perfusion abnormalities.
  
  
  CONCLUSIONS
  A scanning delay of 60-66 seconds appears to be optimal. The CTAP-1 scans showed no useful information and need not be acquired.
authors.affiliation: Department of Radiology SB-05, University of Washington School of Medicine, Seattle 98195.
authors.forename: P C
authors.initials: PC
authors.lastname: Freeny
authors.forename: H V
authors.initials: HV
authors.lastname: Nghiem
authors.forename: T C
authors.initials: TC
authors.lastname: Winter
mesh_terms: D006528:Carcinoma, Hepatocellular / Q000098:blood supply / Q000000981:diagnostic imaging* / Q000378:metabolism; D005260:Female; D006801:Humans; D008099:Liver / Q000098:blood supply / Q000000981:diagnostic imaging*; D008113:Liver Neoplasms / Q000098:blood supply / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D011172:Portography / Q000379:methods*; D012509:Sarcoma / Q000000981:diagnostic imaging / Q000378:metabolism; D014057:Tomography, X-Ray Computed / Q000379:methods*