IMAGE-BASED RENAL STONE TRACKING TO IMPROVE EFFICACY IN EXTRACORPOREAL LITHOTRIPSY

Purpose: We describe a method to reduce the number of shocks necessary to fragment renal stones during extracorporeal shock wave lithotripsy by automatically taking into account stone movements. Materials and M ethods: Echotrack computer software was developed and implemented on a lithotriptor. One software module uses image processing to detect ins tantaneous stone location based on ultrasound images generated by the lithotriptor. A second module uses the detected location to control th e shock wave generator position, and automatically adjusts it to impro ve coincidence between the focal volume and stone. The reliability of the tracking algorithm was clinically tested in 65 patients with renal stones. These in vivo tests were qualitative and the goal was to asse ss software ability to track stones during actual treatments. A quanti tative evaluation of the reduction in shocks necessary for fragmentati on was performed in vitro. Artificial stones were moved according to c omputer generated trajectories. Each trajectory was applied once with and once without automatic adjustment of the generator position. Resul ts: The in vivo tests demonstrated software ability to track stones as far as they were visible in the images. During in vitro tests automat ic adjustments of the generator position reduced the number of shocks necessary to fragment stones completely by a factor of 1.64. Conclusio ns: Image based renal stone tracking software that automatically adjus ts the shock wave generator position according to the displacement of renal stones is useful during extracorporeal shock wave lithotripsy. T reatment time was significantly shorter with this software.