In Vitro Study of the Revised Ultrasound Based Real-Time Tracking of Renal Stones for Shock Wave Lithotripsy: Part 1

Purpose: Extracorporeal shock wave lithotripsy has been popular since the 1980s. Only 30% to 50% of the shock waves of all conventional lithotripters are focused on stones. We developed an ultrasound based, real-time stone tracking system (version 1) to improve accuracy and treatment efficiency. However, some problems remained. We revised the existing system (version 2) and tested its reliability and performance. Materials and Methods: We revised the system by adding more algorithms to decrease renal stone misidentification. We verified the advanced system by 2 tests using no tracking and tracking with 13 stone trajectories for versions 1 and 2. We performed the coincidence test to evaluate the accuracy of targeting the stone within the effective focal area and the stone fragmentation efficiency test to clarify the decrease in the number of shocks needed for stone fragmentation. Results: In the coincidence test the mean +/- SD results of the nontracking system, and tracking versions 1 and 2 were 68.8% +/- 18.8%, 89.9% +/- 5.2% and 94.3% +/- 4.5%, respectively. Version 2 was statistically significantly better than version 1 (p = 1.5 x 10(-4)). In the stone fragmentation efficiency test the mean results of the nontracking system, and versions 1 and 2 were 49.5% +/- 14.2%, 85.1% +/- 4.5% and 89.5% +/- 4.2%, respectively. Version 2 was statistically significantly better than version 1 (p = 1.9 x 10(-8)). Conclusions: The revised tracking system is better than version 1. It improves treatment efficiency, decreases stone misidentification and can shorten treatment time.