Ureteroscopic ultrasound technology to size kidney stone fragments: Proof of principal using a miniaturized probe in a porcine model.

Abstract

Background: the ability to measure stone fragment size could help prevent attempting to extract too large a stone fragment. We evaluated the ability of a 1.2 mm (3.6 French) ultrasound probe to measure stone fragments in a porcine kidney. Methods: 15 human stones of three types (five each calcium oxalate, cystine, calcium phosphate) sized 3–7 mm were placed deep in a porcine kidney collecting system. The sound speed of each stone type was determined using a separate reference stone. A 2 MHz, 1.2 mm needle hydrophone was used to send and receive ultrasound pulses. Stone thickness was calculated as d=c*t/2 by determining the signal transit time through the stone, t, and the stone sound speed, c. Calculated stone thicknesses were compared to digital caliper measurements. Results: Stone size was determined for all 15 stones. Correlation between ultrasound‐determined thickness and caliper measurements was excellent (r2=0.90, p<0.0001) with ultrasound performing well in all three stone types. All stone measurements were accurate within 1 mm, and ten (66%) stone measurements were accurate within 0.5 mm. Conclusions: Ultrasound‐based measurements are accurate and precise using a 3.6 French probe with stone fragments placed deep in a porcine kidney. [Work supported by Grants NIH DK43881 and NSBRI SMST01601.]