Quantitative Assessment of Shockwave Lithotripsy Accuracy and the Effect of Respiratory Motion

Abstract

Background and Purpose: Effective stone comminution during shockwave lithotripsy (SWL) is dependent on precise three-dimensional targeting of the shockwave. Respiratory motion, imprecise targeting or shockwave alignment, and stone movement may compromise treatment efficacy. The purpose of this study was to evaluate the accuracy of shockwave targeting during SWL treatment and the effect of motion from respiration. Patients and Methods: Ten patients underwent SWL for the treatment of 13 renal stones. Stones were targeted fluoroscopically using a Healthtronics Lithotron (five cases) or Dornier Compact Delta II (five cases) shockwave lithotripter. Shocks were delivered at a rate of 1 to 2 Hz with ramping shockwave energy settings of 14 to 26 kV or level 1 to 5. After the low energy pretreatment and protective pause, a commercial diagnostic ultrasound (US) imaging system was used to record images of the stone during active SWL treatment. Shockwave accuracy, defined as the proportion of shockwaves that resulted in stone motion with shockwave delivery, and respiratory stone motion were determined by two independent observers who reviewed the ultrasonographic videos. Results: Mean age was 51 -15 years with 60% men, and mean stone size was 10.5 -3.7 mm (range 5-18 mm). A mean of 2675 -303 shocks was delivered. Shockwave-induced stone motion was observed with every stone. Accurate targeting of the stone occurred in 60% -15% of shockwaves. Conclusions: US imaging during SWL revealed that 40% of shockwaves miss the stone and contribute solely to tissue injury, primarily from movement with respiration. These data support the need for a device to deliver shockwaves only when the stone is in target. US imaging provides real-time assessment of stone targeting and accuracy of shockwave delivery.

A heuristic model of stone comminution in shock wave lithotripsy

“…Removing the ineffectual pulses from the total LSW dose (i.e., 2000 shocks) gives a representation of effective dose (dose eff ), from which it was determined that 39% 6 11% of shock waves missed the target stone during the motion simulations for the original lens compared to 29% 6 18% for the new lens (p < 0.01). These values are consistent with clinical observations of percentages of missed shock waves during SWL (Leighton et al, 2008;Sorensen et al, 2012).…”

Improving the lens design and performance of a contemporary electromagnetic shock wave lithotripter

“…S3B). Clinically, it is well known that kidney stones can move up to 5 cm during inspiration and expiration breath phases (8), which can result in 30-40% of shock waves missing the target stone (55,56). The benefits of a lithotripter field with broad FW, associated high average peak pressure, and strong cavitation activity are supported by the results of in vitro respiratory motion simulations where for excursions of 15 mm the new lens produced statistically higher stone comminution than the original lens (Fig.…”

Evaluation of the LithoGold LG-380 Lithotripter:In VitroAcoustic Characterization and Assessment of Renal Injury in the Pig Model

“…A recent patient study using diagnostic ultrasonography to detect when stones were hit by SWs indicated that *40% of SWs miss the stone entirely. 5 The wider the focal width of the lithotripter, the better the chance of hitting the stone. 3,35 A broad focal width may also play a role in initiating stone breakage.…”

“…[3][4][5] In addition, the generation of stress waves understood to play an important role in stone fragmentation is enhanced when the width of the high pressure region (focal volume) is wider than the stone. [6][7][8] As such, focal width is one factor that may contribute to differences in treatment outcomes observed with different lithotripters.…”