Assessment of 1 mSv Urinary Tract Stone CT With Model-Based Iterative Reconstruction

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. MATERIALS AND 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]). CONCLUSION. Aggressively dose-reduced (similar to 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.