title: Low-dose and standard-dose unenhanced helical computed tomography for the assessment of acute renal colic: prospective comparative study.
abstract: OBJECTIVE
  To compare the efficacy of low-dose and standard-dose computed tomography (CT) for the diagnosis of ureteral stones.
  
  
  METHODS
  Unenhanced helical CT was performed with both a standard dose (260 mAs, pitch 1.5) and a low dose (50 mAs, pitch 1.5) in 121 patients suspected of having acute renal colic. The two studies were prospectively and independently interpreted for the presence and location of ureteral stones, abnormalities unrelated to stone disease, identification of secondary signs, i.e. hydronephrosis and perinephric stranding, and tissue rim sign. The standard-dose CT images were interpreted by one reviewer and the low-dose CT images independently by two reviewers unaware of the standard-dose CT findings. The findings of the standard and low-dose CT scans were compared with the exact McNemar test. Interobserver agreements were assessed with kappa analysis. The effective radiation doses resulting from two different protocols were calculated by means of commercially available software to which the Monte-Carlo phantom model was given.
  
  
  RESULTS
  The sensitivity, specificity, and accuracy of standard-dose CT for detecting ureteral stones were 99%, 93%, and 98%, respectively, whereas for the two reviewers the sensitivity of low-dose CT was 93% and 95%, specificity 86%, and accuracy 92% and 94%. We found no significant differences between standard-dose and low-dose CT in the sensitivity and specificity for diagnosing ureter stones (P >0.05 for both). However, the sensitivity of low-dose CT for detection of 19 stones less than or equal to 2 mm in diameter was 79% and 68%, respectively, for the two reviewers. Low-dose CT was comparable to standard-dose CT in visualizing hydronephrosis and the tissue rim sign. Perinephric stranding was far less clear on low-dose CT. Low-dose CT had the same diagnostic performance as standard-dose CT in diagnosing alternative diseases. Interobserver agreement between the two low-dose CT reviewers in the diagnosis of ureter stones and alternative diseases, the identification of secondary signs, and tissue rim sign were high, with kappa values ranging from 0.769 to 0.968. On standard-dose CT scans, the calculated mean effective radiation dose was 7.30 mSv for males and 10.00 mSv for females. On low-dose CT scans, the calculated mean effective radiation dose was 1.40 mSv for males and 1.97 mSv for females.
  
  
  CONCLUSIONS
  Compared with standard scans using 260 mAs, low-dose unenhanced helical CT using a reduced tube current of 50 mAs results in a concomitant decrease in the radiation dose of 81%. Although low-dose CT was limited in its ability to depict small-sized calculi less than or equal to 2 mm, it is still comparable to standard-dose CT for the diagnosis of ureter stones and alternative disease.
authors.affiliation: Department of Diagnostic Radiology, Cheju National University College of Medicine, Jeju, Korea. 67kbs@medimail.co.kr
authors.forename: Bong Soo
authors.initials: BS
authors.lastname: Kim
authors.forename: Im Kyung
authors.initials: IK
authors.lastname: Hwang
authors.forename: Yo Won
authors.initials: YW
authors.lastname: Choi
authors.forename: Sook
authors.initials: S
authors.lastname: Namkung
authors.forename: Heung Cheol
authors.initials: HC
authors.lastname: Kim
authors.forename: Woo Cheol
authors.initials: WC
authors.lastname: Hwang
authors.forename: Kuk Myung
authors.initials: KM
authors.lastname: Choi
authors.forename: Ji Kang
authors.initials: JK
authors.lastname: Park
authors.forename: Tae Il
authors.initials: TI
authors.lastname: Han
authors.forename: Weechang
authors.initials: W
authors.lastname: Kang
mesh_terms: D000208:Acute Disease; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003085:Colic / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D006869:Hydronephrosis / Q000000981:diagnostic imaging; D007674:Kidney Diseases / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D019047:Phantoms, Imaging; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D036542:Tomography, Spiral Computed / Q000379:methods*; D014057:Tomography, X-Ray Computed; D014514:Ureteral Calculi / Q000000981:diagnostic imaging*