TAIPEI, TAIWAN (UroToday.com) - Introduction and Objectives: Ultrasound images of kidney stones display a bright stone with a distal shadow. We hypothesize the width of the shadow is a more accurate predictor of true stone size than width of the stone image.
Methods: Forty five calcium oxalate monohydrate kidney stones ranging from 1–10mm were imaged in a water bath. The width of the stone and the shadow was measured at depths of 6, 10, and 14 cm. A linear mixed-effect model was used to compare measurements of shadow width and depth versus true stone size. Subgroup analysis was performed to determine the percentage of stones that were over-classified as greater than 5mm when true stone size was less than 5 mm.
Results: Measurement of stone width compared to true stone size resulted in mean overestimation at 0.9 +/- 0.8mm, 1.5 +/- 1.0mm, 2.0 +/- 1.2mm at 6, 10, 14cm depths, respectively. Overestimation of stone width increased with depth (p < 0.001). Measurement of shadow width compared to true stone size resulted in an underestimation of -0.02 +/- 0.4mm, - 0.04 +/- 0.6mm, and - 0.19 +/- 0.8mm at 6, 10, 14cm depths, respectively. The acoustic shadow was a better predictor of true stone size at all depths (p < 0.001). Subgroup analysis demonstrated that over-classification occurred in 17/60 cases (28%) when the stone width was measured and 7/60 cases (12%) when the shadow width was measured.
Conclusions: Stone size was consistently overestimated when directly measuring stone width and worsened with increasing depth. Measuring shadow width significantly reduced overestimation of true stone size.
Source of Funding: This work was supported by NIH DK043881 andDK092197, andNSBRI throughNASANCC 9-58.
|Listen to an interview with Ryan Hsi, one of the authors of this study.|
Presented by Franklin Lee,1 Barbrina Dunmire,2 Jonathan Harper,1 Ziyue Liu,3 Ryan Hsi,1 Michael Bailey,1, 2 and Mathew Sorensen1 at the 32nd World Congress of Endourology & SWL - September 3 - 7, 2014 - Taipei, Taiwan
1University of Washington Department of Urology, USA
2Applied Physics Laboratory, USA
3Indiana University Department of Biostatistics, USA