Christian Bohris

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.

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.

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.