Retrospective comparison of measured stone size and posterior acoustic shadow width in clinical ultrasound images
Posterior acoustic shadow width has been proposed as a more accurate measure of kidney stone size compared to direct measurement of stone width on ultrasound (US). Published data in humans to date have been based on a research using US system. Herein, we compared these two measurements in clinical US images.
Thirty patient image sets where computed tomography (CT) and US images were captured less than 1 day apart were retrospectively reviewed. Five blinded reviewers independently assessed the largest stone in each image set for shadow presence and size. Shadow size was compared to US and CT stone sizes.
Eighty percent of included stones demonstrated an acoustic shadow; 83% of stones without a shadow were ≤ 5 mm on CT. Average stone size was 6.5 ± 4.0 mm on CT, 10.3 ± 4.1 mm on US, and 7.5 ± 4.2 mm by shadow width. On average, US overestimated stone size by 3.8 ± 2.4 mm based on stone width (p < 0.001) and 1.0 ± 1.4 mm based on shadow width (p < 0.0098). Shadow measurements decreased misclassification of stones by 25% among three clinically relevant size categories (≤ 5, 5.1–10, > 10 mm), and by 50% for stones ≤ 5 mm.
US overestimates stone size compared to CT. Retrospective measurement of the acoustic shadow from the same clinical US images is a more accurate reflection of true stone size than direct stone measurement. Most stones without a posterior shadow are ≤ 5 mm.
KeywordsUltrasonography Calculi Nephrolithiasis Urolithiasis Computed tomography Size
Body mass index
This work is part of a large collaborative effort, and we appreciate the help of our many collaborators at the University of Vermont, University of Washington (UW) Center for Industrial and Medical Ultrasound, the UW Department of Urology, and within National Institute of Diabetes and Digestive Kidney Diseases (NIDDK) Program Project DK043881.
JCD: Project development, data collection and management, data analysis, manuscript writing/editing. BD: Project development, data collection and management, data analysis, manuscript writing/editing. KMS: Project development, data collection, manuscript editing. ZL: Data analysis, manuscript editing. TL: Data collection and management, manuscript editing. JT: Data collection, manuscript editing. HCC: Data collection, manuscript editing. JDH: Project development, manuscript editing. MRB: Project development, manuscript writing/editing. MDS: Project development, data collection, manuscript editing.
Compliance with ethical standards
Conflict of interest
Michael R. Bailey, Barbrina Dunmire, and Mathew D. Sorensen have equity in and consulting agreements with SonoMotion Inc. which has licensed intellectual property from the University of Washington related to this technology. For the remaining authors, no competing conflicts of interest exist.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. For this type of study formal consent is not required.