title: Iterative reconstructions versus filtered back-projection for urinary stone detection in low-dose CT.
abstract: OBJECTIVE
  To evaluate prospectively, in patients with suspected or known urinary stone disease, the image quality and diagnostic confidence of nonenhanced abdominal low-dose computed tomography (CT) with iterative reconstruction (IR) compared to filtered back-projection (FBP).
  
  
  METHODS
  Fifty consecutive patients with suspected (n = 33) or known (n = 17) urinary stone disease underwent nonenhanced abdominal low-dose CT (120 kVp, 30 effective mAs, 1.6 ± 0.5 mSv). Reconstructions were performed with sinogram-affirmed IR and with FBP. Attenuation (in Hounsfield units) was measured in subcutaneous fat and urinary bladder; image noise was determined. Two readers assessed image quality, number and location of urinary calculi were recorded, and diagnostic confidence was assessed. Statistical analyses included Mann-Whitney, Friedman's two-way, Wilcoxon signed rank, Pearson's, and Spearman's rank order correction tests.
  
  
  RESULTS
  Attenuation of urinary bladder (P = .208, reader 1; P = .123, reader 2) and fat (P = .568, reader 1; P = .834, reader 2) was similar among FBP and IR datasets. Image noise was reduced in IR datasets by 40.1% (P < .001). IR improved image quality (P < .01), and obesity as factor impairing image quality was noted in FBP but not in IR images (P < .05). There was no significant difference in number of calculi in datasets reconstructed with IR and FBP (P = .102, reader 1; P = .059, reader 2). Diagnostic confidence regarding identification of urinary calculi improved with IR (P < .05, reader 1; P < .01, reader 2).
  
  
  CONCLUSIONS
  IR improves image quality and confidence for diagnosing urinary stone disease in abdominal low-dose CT.
authors.affiliation: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Raemistrasse 100, CH-8091, Zurich, Switzerland.
authors.forename: Anna
authors.initials: A
authors.lastname: Winklehner
authors.forename: Iris
authors.initials: I
authors.lastname: Blume
authors.forename: Sebastian
authors.initials: S
authors.lastname: Winklhofer
authors.forename: Daniel
authors.initials: D
authors.lastname: Eberli
authors.forename: Ralph
authors.initials: R
authors.lastname: Gnannt
authors.forename: Thomas
authors.initials: T
authors.lastname: Frauenfelder
authors.forename: Hatem
authors.initials: H
authors.lastname: Alkadhi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011860:Radiography, Abdominal / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods*; D052878:Urolithiasis / Q000000981:diagnostic imaging*
keywords: Computed tomography; iterative reconstruction; low radiation dose; urinary stone disease