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 dec reases the number of shock waves and treatment time of shock wave lithotrip sy. Materials and Methods: Ultrasound images were analyzed to identify. the ren al stones. A computer software module for ultrasound image processing was d eveloped to monitor stone location instantaneously. Another computer softwa re module controlled generator movement in real time for tracking the stone . We used 13 ultrasound stone trajectories recorded from patients to test t he system in vitro. Two tests were established to verify tracking system re liability. One test focused on improvement in the coincidence ratio, which denotes the matching extent of the stone within the effective focal area. T he other test focused on improvement in the efficiency ratio, that is a dec rease in the number of shocks for stone fragmentation. For each recorded st one trajectory 2 experiments were done under tracking and nontracking condi tions. Results: The average coincidence and efficiency ratios plus or minus standa rd 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 wer e statistically significant (paired t test p <0.01). Conclusions: An ultrasound based real-time tracking system proved to be sig nificantly helpful for in vitro lithotripsy. It appears that the tracking s ystem may greatly decrease the number of shocks and treatment time for rena l stones.