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

PURPOSE A prototype ultrasound-based probe for use in ureteroscopy was used for in vitro measurements of stone fragments in a porcine kidney. METHODS Fifteen human stones consisting of three different compositions were placed deep in the collecting system of a porcine kidney. A 2 MHz, 1.2 mm (3.6F) needle hydrophone was used to send and receive ultrasound pulses for stone sizing. Calculated stone thicknesses were compared with caliper measurements. RESULTS Correlation between ultrasound-determined thickness and caliper measurements was excellent in all three stone types (r(2) = 0.90, p < 0.0001). All 15 ultrasound measurements were accurate to within 1 mm, and 10 measurements were accurate within 0.5 mm. CONCLUSION A 3.6F ultrasound probe can be used to accurately size stone fragments to within 1 mm in a porcine kidney.