title: In vitro CT evaluation of intrahepatic stones: correlation with chemical composition.
abstract: OBJECTIVE
  To describe in vitro CT features of intrahepatic stones and to correlate CT attenuation with chemical composition.
  
  
  METHODS
  Of the patients who underwent choledochoscopic intrahepatic stone removal between 1998 and 2001, 54 patients with stones larger than 3 mm were enrolled in this study. In each case, a chemical compositional analysis was performed to determine calcium, cholesterol, total bilirubin, and inorganic phosphorus compositions. The three largest stones obtained from each patient were imaged by CT. CT attenuation numbers were measured in the center images of each stone by drawing free-hand region of interest (ROI). The measured CT attenuation numbers were correlated with their chemical composition. Also, CT attenuation numbers of stones were compared with that of the liver on non-contrast CT (50-70 HU).
  
  
  RESULTS
  Stone size ranged from 3.1 to 10.5 mm (mean +/- S.D.: 6.0 +/- 1.4). The CT attenuation numbers (HU) of stones ranged from 36.4 to 410.19 (mean +/- S.D.: 94.6 +/- 49.9). CT numbers of stones were below 70 HU in 11 patients (20.4%), and below 90 HU in 33 patients (59.3%). The chemical analysis data of the stones were as follows: calcium (0.5-6.5 wt.%; mean +/- S.D., 2.6 +/- 1.4), total bilirubin (0.45-24.4 wt.%; 13.1 +/- 6.2), cholesterol (5.4-73.9 wt.%; 29.3 +/- 17.4), phosphorus (0.1-1.2 wt.%; 0.6 +/- 0.3), and non-soluble residue (17.6-85.4 wt.%; 57.0 +/- 22.6). There was a weak but significant correlation between calcium composition and CT attenuation (r = 0.38, P < 0.01) and no significant correlation between other chemical compositions and the CT attenuation (cholesterol, r = 0.01, P > 0.01; total bilirubin, r = 0.05, P > 0.01; phosphorus, r = 0.01, P > 0.01).
  
  
  CONCLUSIONS
  On non-contrast CT, intrahepatic stones would not be hyperattenuating with respect to liver parenchyma in about one fifth of patients. The CT attenuation of stones correlates with calcium and does not correlate with any other chemical composition.
authors.affiliation: Department of Radiology and Institute of Radiation Medicine, Seoul National University College of Medicine, 28 Yongon-dong, Chongno-gu, Seoul 110-744, Republic of Korea.
authors.forename: Young Jun
authors.initials: YJ
authors.lastname: Kim
authors.forename: Joon Koo
authors.initials: JK
authors.lastname: Han
authors.forename: Jun Yong
authors.initials: JY
authors.lastname: Jeong
authors.forename: Kyoung Ho
authors.initials: KH
authors.lastname: Lee
authors.forename: Se Hyung
authors.initials: SH
authors.lastname: Kim
authors.forename: Young Il
authors.initials: YI
authors.lastname: Kim
authors.forename: Jeong Min
authors.initials: JM
authors.lastname: Lee
authors.forename: Byung Ihn
authors.initials: BI
authors.lastname: Choi
authors.forename: Youn-Chan
authors.initials: YC
authors.lastname: Park
authors.forename: Sun-Whe
authors.initials: SW
authors.lastname: Kim
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001663:Bilirubin / Q000032:analysis; D002118:Calcium / Q000032:analysis; D002137:Calculi / Q000737:chemistry* / Q000000981:diagnostic imaging*; D002784:Cholesterol / Q000032:analysis; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008107:Liver Diseases / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010758:Phosphorus / Q000032:analysis; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D010758:Phosphorus; D002784:Cholesterol; D001663:Bilirubin; D002118:Calcium