IN VITRO STUDY OF ULTRASOUND BASED REAL-TIME TRACKING OF RENAL STONES FOR SHOCK WAVE LITHOTRIPSY: PART 1

PURPOSE: We developed a real-time tracking system for renal stones that decreases the number of shock waves and treatment time of shock wave lithotripsy. MATERIALS AND METHODS: Ultrasound images were analyzed to identify the renal stones. A computer software module for ultrasound image processing was developed to monitor stone location instantaneously. Another computer software module controlled generator movement in real time for tracking the stone. We used 13 ultrasound stone trajectories recorded from patients to test the system in vitro. Two tests were established to verify tracking system reliability. One test focused on improvement in the coincidence ratio, which denotes the matching extent of the stone within the effective focal area. The other test focused on improvement in the efficiency ratio, that is a decrease in the number of shocks for stone fragmentation. For each recorded stone trajectory 2 experiments were done under tracking and nontracking conditions. RESULTS: The average coincidence and efficiency ratios plus or minus standard deviation were 79.6% +/- 9.8% and 45.0% +/- 12.7% without tracking, and 97.0% +/- 3.0% and 85.5 +/- 6.8% with tracking, respectively. All tests were statistically significant (paired t test p <0.01). CONCLUSIONS: An ultrasound based real-time tracking system proved to be significantly helpful for in vitro lithotripsy. It appears that the tracking system may greatly decrease the number of shocks and treatment time for renal stones.