title: Positive enteric contrast material for abdominal and pelvic CT with automatic exposure control: what is the effect on patient radiation exposure?
abstract: OBJECTIVE
  To assess the effect of positive enteric contrast administration on automatic exposure control (AEC) CT radiation exposure in (1) a CT phantom, and (2) a retrospective review of patients.
  
  
  METHODS
  We scanned a CT phantom containing simulated bowel that was sequentially filled with water and positive enteric contrast, and recorded the mean volume CT dose index (CTDIvol). We also identified 17 patients who had undergone 2 technically comparable CT scans of the abdomen and pelvis, one with positive enteric contrast and the other with oral water. Paired Student's t-tests were used to compare the mean CTDIvol between scans performed with and without positive enteric contrast. Both the phantom and patient CT scans were performed using AEC with a fixed noise index.
  
  
  RESULTS
  The mean CTDIvol for the phantom with simulated bowel containing water and positive enteric contrast were 8.2 ± 0.2 mGy, and 8.7 ± 0.1 mGy (6.1% higher than water, p=0.02), respectively. The mean CTDIvol for patients scanned with oral water and with positive enteric contrast were 11.8 mGy and 13.1 mGy, respectively (p=0.003). This corresponded to a mean CTDIvol which was 11.0% higher (range: 0.0-20.7% higher) in scans with positive enteric contrast than those with oral water in patients.
  
  
  CONCLUSIONS
  When automatic exposure control is utilized for abdominopelvic CT, the radiation exposure, as measured by CTDIvol, is higher for scans performed with positive enteric contrast than those with oral water.
authors.affiliation: Department of Radiology, University of California San Francisco, 505 Parnassus Avenue, San Francisco, CA 94143-0628, United States. jane.wang@radiology.ucsf.edu
authors.forename: Zhen J
authors.initials: ZJ
authors.lastname: Wang
authors.forename: Katherine S
authors.initials: KS
authors.lastname: Chen
authors.forename: Robert
authors.initials: R
authors.lastname: Gould
authors.forename: Fergus V
authors.initials: FV
authors.lastname: Coakley
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Fu
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Yeh
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003287:Contrast Media / Q000008:administration & dosage*; D003974:Diatrizoate Meglumine / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D007410:Intestinal Diseases / Q000000981:diagnostic imaging*; D007422:Intestines / Q000000981:diagnostic imaging*; D007472:Iohexol / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed
chemical_list: D003287:Contrast Media; D003974:Diatrizoate Meglumine; D007472:Iohexol