Effect of the Body Wall on Lithotripter Shock Waves

Abstract

Purpose: Determine the influence of passage through the body wall on the properties of lithotripter shock waves (SWs) and the characteristics of the acoustic field of an electromagnetic lithotripter. Methods: Full-thickness ex vivo segments of pig abdominal wall were secured against the acoustic window of a test tank coupled to the lithotripter. A fiber-optic probe hydrophone was used to measure SW pressures, determine shock rise time, and map the acoustic field in the focal plane. Results: Peak positive pressure on axis was attenuated roughly proportional to tissue thickness-approximately 6% per cm. Irregularities in the tissue path affected the symmetry of SW focusing, shifting the maximum peak positive pressure laterally by as much as *2 mm. Within the time resolution of the hydrophone (7-15 ns), shock rise time was unchanged, measuring *17-21 ns with and without tissue present. Mapping of the field showed no effect of the body wall on focal width, regardless of thickness of the body wall. Conclusions: Passage through the body wall has minimal effect on the characteristics of lithotripter SWs. Other than reducing pulse amplitude and having the potential to affect the symmetry of the focused wave, the body wall has little influence on the acoustic field. These findings help to validate laboratory assessment of lithotripter acoustic field and suggest that the properties of SWs in the body are much the same as have been measured in vitro.

The effect of renal cortical thickness on the treatment outcomes of kidney stones treated with shockwave lithotripsy

“…Second, a thinner KT resulted in a poorer treatment outcome. This observation differed particularly from those of other studies, most of which showed that a greater tissue thickness/SSD resulted in a poorer treatment result [ 12 , 13 ]. We postulated that these two findings were due to an effect of renal cortical scarring on SW transmission.…”

“…In the clinical study by Hammad and Balakrishnan [ 16 ], KT and MT were combined for the analysis, and the effect of KT on the efficacy of SWL might therefore not be demonstrated. For the other in vivo and in vitro studies, the degree of renal cortical scarring in relatively young pigs compared with that in our study patients, who had a mean age of 50 years, might have hampered the demonstration of an effect of the renal cortex on SW transmission [ 12 , 13 , 15 ]. This difference in the composition of tissues may explain the inconsistent effects of SSD reported in different studies.…”

“…Among the various stone parameters, skin-to-stone distance (SSD) is another factor that might be able to predict the results of treatment, although its role in the prediction of treatment outcomes is still controversial [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ]. Because the shock wave (SW) path passes through various tissues with different compositions and densities, transmission of the SW along these different tissue planes may lead to energy loss and hence affect treatment outcome [ 12 , 13 ].…”