title: Assessment of 1 mSv urinary tract stone CT with model-based iterative reconstruction.
abstract: OBJECTIVE
  The purpose of this study was to evaluate stone detection, assessment of secondary signs of stone disease, and diagnostic confidence utilizing submillisievert CT with model-based iterative reconstruction (MBIR) in a North American population with diverse body habitus.
  
  
  METHODS
  Fifty-two adults underwent stone CT using a split-dose protocol; weight-based projected volume CT dose index (CTDIvol) and dose-length product (DLP) were divided into two separate acquisitions at 80% and 20% dose levels. Images were reconstructed with MBIR. Five blinded readers counted stones in three size categories and rated "overall diagnostic confidence" and "detectability of secondary signs of stone disease" on a 0-4 scale at both dose levels. Effective dose (ED) in mSv was calculated as DLP multiplied by conversion coefficient, k, equal to 0.017.
  
  
  RESULTS
  Mean ED (80%, 3.90±1.44 mSv; vs 20%, 0.97±0.34 mSv [p<0.001]) and number of stones detected (80%, 193.6±25.0; vs 20%, 154.4±15.4 [p=0.03]) were higher in scans at 80% dose level. Intrareader correlation between scans at 80% and 20% dose levels was excellent (0.83-0.97). With 80% scans as reference standard, mean sensitivity and specificity at 20% varied with stone size (<3 mm, 74% and 77%; ≥3 mm, 92% and 82%). The 20% scans scored lower than 80% scans in diagnostic confidence (2.46±0.50; vs 3.21±0.36 [p<0.005]) and detectability of secondary signs (2.41±0.39; vs 3.19±0.29 [p<0.005]).
  
  
  CONCLUSIONS
  Aggressively dose-reduced (~1 mSv) MBIR scans detected most urinary tract stones of 3 mm or larger but underperformed the low-dose reference standard (3-4 mSv) scans in small (<3 mm) stone detection and diagnostic confidence.
authors.affiliation: 1 Department of Radiology, University of Michigan Health System, UH B1 D502, 1500 E Medical Center Dr, Ann Arbor, MI 48109.
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Glazer
authors.forename: Katherine E
authors.initials: KE
authors.lastname: Maturen
authors.forename: Richard H
authors.initials: RH
authors.lastname: Cohan
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Davenport
authors.forename: James H
authors.initials: JH
authors.lastname: Ellis
authors.forename: Ursula S
authors.initials: US
authors.lastname: Knoepp
authors.forename: William J
authors.initials: WJ
authors.lastname: Weadock
authors.forename: Joel F
authors.initials: JF
authors.lastname: Platt
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D003198:Computer Simulation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods*; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D052878:Urolithiasis / Q000000981:diagnostic imaging*; D055815:Young Adult
keywords: CT; dose reduction; iterative reconstruction; urolithiasis