Improvement of SWL Efficacy: Reduction of the Respiration-Induced Kidney Motion by Using an Abdominal Compression Plate.

BACKGROUND AND PURPOSE: In extracorporeal shockwave lithotripsy (SWL), respiratory-induced motion of the upper urinary tract may hamper stone targeting and disintegration. The objective of this study is to analyze the effect of abdominal compression (AC) to kidney motion and to shock wave efficacy. SUBJECTS AND METHODS: The study included 10 volunteers and 10 kidney stone patients. AC was achieved by a wedge-shaped compression plate. Patients underwent a routine ultrasound-guided SWL. For analgosedation, remifentanil (∼0.1 µg/kg/min) was administered. The respiratory-induced kidney motion, as well as with free breathing and AC, was quantitatively evaluated on basis of recorded ultrasound videos. By definition, shock wave efficacy was 100%, if the stone center was aligned with the shock wave focus. Its decrease depending on off-focus distance was obtained by model stone tests. On this basis, a mean shock wave efficacy value was attributed to the displacement function resulting from each measured kidney motion. RESULTS: In volunteers, the amplitude of the displacement function with AC (mean: 8 mm; range: 3-11 mm) was significantly lower than with free breathing (mean: 12 mm; range: 5-19 mm) (paired samples t-test, p < 0.001). Correspondingly, the mean efficacy improved to 91% (range: 78%-99%) from 79% (range: 59%-94%) (p < 0.01). In the patient cohort, the amplitudes were similar and the efficacy even higher because of the respiratory depressant effect of remifentanil. By AC, the efficacy improved to 93% (range: 85%-98%) compared with 87% (range: 77%-96%) (p < 0.01). CONCLUSIONS: AC with a compression plate is easy to perform and well tolerated by patients. It significantly reduces respiratory-induced kidney motion and improves shock wave efficacy.

Monitoring the coupling of the lithotripter therapy head with skin during routine shock wave lithotripsy with a surveillance camera.

PURPOSE: With lithotripters today the shock waves are typically transmitted into the body via water filled bellows using coupling gel to make contact with the skin. Usually the coupling zone is not visible to the operator. We investigated coupling quality during routine clinical shock wave lithotripsy and the associated effect on shock wave disintegration efficiency. MATERIALS AND METHODS: During 30 routine shock wave lithotripsy treatments the coupling zone was continuously monitored by a video camera integrated into a DoLi SII lithotripter (Dornier MedTech, Wessling, Germany). However, it was not shown to the blinded operator to resemble the standard clinical situation. We used 3 coupling gels, including LithoClear®, Sonogel® and a custom-made gel of low viscosity. The ratio of air in the relevant coupling area was measured. Lithotripter disintegration efficiency was evaluated by in vitro model stone tests at an air ratio of 0%, 5%, 10% and 20%. RESULTS: Only in 10 of 30 treatments was good coupling achieved with an air ratio of less than 5%. In 8 treatments the ratio was greater than 20%. The best coupling conditions were achieved with low viscosity gel. The mean ± SD number of shock waves needed for complete fragmentation in the model stone tests was 100 ± 4 for bubble-free coupling, and 126 ± 3 for 5%, 151 ± 8 for 10% and 287 ± 5 for 20% air bubbles. CONCLUSIONS: At 20 of 30 shock wave lithotripsy sessions there was imperfect coupling, accompanied by significant loss of disintegration capability. A surveillance camera is useful to monitor and improve coupling.

Ultrasound monitoring of kidney stone extracorporeal shockwave lithotripsy with an external transducer: does fatty tissue cause image distortions that affect stone comminution?

INTRODUCTION: Ultrasound imaging, using either an inline or an external transducer, is a standard method for extracorporeal shockwave lithotripsy (SWL) monitoring. This study investigates whether image distortions caused by the low sound speed of fatty tissue could lead to incorrect stone positioning such that disintegration is affected. MATERIALS AND METHODS: To define the accuracy needed for SWL monitoring, the dependency of fragmentation efficiency on the distance between stone center and SWL focus was examined by in vitro model stone tests. In a clinical study, 15 patients with kidney stones were treated with a Dornier Sigma FarSight. This lithotripter was equipped with both an inline and an external transducer. They were operated alternately to check for inconsistencies, which would indicate ultrasound image distortions. In addition, the ultrasound paths from the transducer to the SWL focus were analyzed for error estimation. RESULTS AND DISCUSSION: In the model stone tests, the number of shock waves required for complete fragmentation doubled if the stone was about 7.5 to 10 mm off focus in lateral direction. In the clinical trial, the stone positions obtained from an inline and an external transducer coincided within a 5 mm range of tolerance, but that approach suffered from some practical difficulties, resulting in measurement imprecision. The sound path analysis showed that the lengths through fatty tissue were too short to result in significant image distortion. The body mass index (20-31 kg/m(2)) was representative, except for very obese patients. Additional confirmation of correct stone positioning could be achieved quite easily by looking for pixel movement in the B-mode image or employing Doppler hit/miss monitoring. CONCLUSION: Within the study group, no image distortion caused by fatty tissue that could be clinically relevant for SWL was observed.

Impact of microbubbles on shock wave-mediated DNA uptake in cells in vitro.

Gas-filled microbubbles have been successfully used as gene delivery reagents in combination with diagnostic ultrasound. Although shock wave exposure has been shown to transfect cells with naked DNA in vitro, it has not been tested whether the addition of microbubbles would augment DNA uptake under those conditions. Therefore, the aim of this study was to test the impact of microbubbles on transgene expression in vitro under shock wave exposure conditions. HEK 293 cells were treated with 60 or 120 pulses of shock waves at varying energy levels. Cells were mixed with either 100 microg/mL luciferase expressing plasmid DNA or with microbubbles that were produced with the same amount of this DNA. Cell death was evaluated after 1 h and transgene expression, after 24 h. In the presence of microbubbles, transgene expression was significantly higher (as much as 29-fold) relative to that obtained without microbubbles. Cells exposed to 120 pulses demonstrated higher transgene expression (as high as 2.7-fold) compared with cells exposed to 60 pulses. The use of microbubbles resulted in greater cell death, varying from 26% (low energy) to 78% (high energy). In conclusion, DNA-loaded microbubbles can significantly increase shock wave mediated gene transfer. However, this effect is associated with increased levels of cell destruction.

A new integrated ultrasound system for shockwave lithotripsy.

BACKGROUND AND PURPOSE: Inline ultrasound monitoring requires good image quality for accurate stone localization, as well as low shockwave shadowing and a robust transducer. In general, conventional transducers designed for another purpose, such as abdominal scanning, are employed. The distance between the transducer and the SWL focus can be varied by a mechanical drive. The drawback is reduced fragmentation at short distances and poor imaging at long distances. This paper introduces a new approach using a specially designed transducer without a mechanical drive. MATERIALS AND METHODS: A transducer prototype with optimized beam focusing (B-K Medical, Herlev, Denmark) was integrated into a modified Compact Delta II therapy head (Dornier MedTech, Wessling, Germany). Image quality was tested at two clinical sites, where 40 kidney and 14 ureteral stones were treated. The shockwave was characterized by model stone tests and fiberoptic hydrophone measurements. RESULTS: Both kidney and ureteral stone treatments could be monitored reliably. Despite the long distance to the SWL focus, the transducer could be operated with relatively high frequencies (3.5-6 MHz), so that high image resolution was obtained. Model stone tests yielded the same fragmentation as the standard Compact Delta II without a transducer. CONCLUSIONS: This study shows that the concept of an integrated transducer distant from the shockwave focus is feasible. Transducer elevation, which is accompanied by shockwave shadowing and early transducer failure, is avoided by employing a dedicated transducer design.

Hit/Miss monitoring of ESWL by spectral Doppler ultrasound.

The objective of this study was to investigate spectral Doppler ultrasound (US) for monitoring extracorporeal shock-wave lithotripsy (ESWL). In vitro experiments with model stones showed that Doppler spectra acquired after a shock wave hit result in a high peak followed by a decaying signal. The duration of decay was dependent on shock-wave energy, stone size, gas content of the water and the level of disintegration. It typically ranged from 30 ms to 150 ms. It was found, by comparison with optical high-speed imaging and US B-scan imaging, that the signal originated from fragments released by the stone and cavitation. If the monitored volume contained no target, the signal duration was significantly shorter. By this means, hits were reliably distinguished from misses. The results of clinical treatments were highly consistent with those of in vitro experiments. Therefore, spectral Doppler US is an excellent tool for hit/miss monitoring in ESWL.