Assessment of 1 mSv urinary tract stone CT with model-based iterative reconstruction

• Published in: American journal of roentgenology (1976) Vol. 203; no. 6; pp. 1230 - 1235
• Main Authors: Glazer, Daniel I, Maturen, Katherine E, Cohan, Richard H, Davenport, Matthew S, Ellis, James H, Knoepp, Ursula S, Weadock, William J, Platt, Joel F
• Format: Journal Article
• Language: English
• Published: United States 01-12-2014
• Subjects: Adult; Aged; Aged, 80 and over; Algorithms; Computer Simulation; Female; Humans; Male; Middle Aged; Models, Biological; Radiation Dosage; Radiation Protection - methods; Radiographic Image Enhancement - methods; Radiographic Image Interpretation, Computer-Assisted - methods; Reproducibility of Results; Sensitivity and Specificity; Tomography, X-Ray Computed - methods; Urolithiasis - diagnostic imaging; Young Adult; dose reduction; urolithiasis; CT; iterative reconstruction
• ISSN: 0361-803X; 1546-3141
• DOI: 10.2214/AJR.13.12271

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.
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.
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]).
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.