• Daniel I Glazer, Katherine E Maturen, Richard H Cohan, Matthew S Davenport, James H Ellis, Ursula S Knoepp, William J Weadock, and Joel F Platt.
• 1 Department of Radiology, University of Michigan Health System, UH B1 D502, 1500 E Medical Center Dr, Ann Arbor, MI 48109.
• AJR Am J Roentgenol. 2014 Dec 1; 203 (6): 1230-5.

ObjectiveThe 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.Materials And MethodsFifty-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.ResultsMean 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]).ConclusionAggressively 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.

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