Advanced acoustic field measurements of shock wave lithotripters

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DESCRIPTION (provided by applicant): The goal of this project is to measure the instantaneous acoustic field of shock wave lithotripters (SWL) using a linear hydrophone array. All previous measurements of SWL acoustic fields have been performed with single-element hydrophones which are only effective if the sound field does not vary from shock to shock. Specifically, we propose to 1) fabricate linear hydrophone arrays based on techniques developed for high-frequency imaging arrays, 2) characterize the arrays electrically and acoustically, 3) drive the arrays to failure to determine durability, and 4) test the arrays in SWL devices to improve the understanding of the instantaneous acoustic field. The proposed measurements would represent the first instantaneous "snapshot" of an SWL acoustic field and would have broad implications for lithotripter device design, theoretical models of stone fragmentation, device calibration, and patient management. SWL has been employed for nearly 25 years to non-invasively treat kidney stones and is utilized in H 50% of the treatments when medical intervention is required. According to the National Institute of Diabetes and Digestive and Kidney Diseases, 5.2% of adults aged 20 to 74 have had kidney stones and H 171,000 adults require a hospital stay each year to undergo treatment of "calculus of kidney and ureters." Even though "improved" SWL systems have come to market, the original Dornier HM3 is still considered the gold standard in treatment. However, the acoustic field of the HM3, when measured at a single point, varies by as much as 50%. This variation is thought to improve stone fragmentation but it also increases the likelihood of trauma to the surrounding kidney tissue. The proposed linear hydrophone array will be fabricated at RRI by Dr. Ketterling. The initial array design will have 20 elements and span 18 mm. After validating the basic operation of the array at RRI, additional arrays will be fabricated and sent to Dr. Cleveland at Boston University and Dr. Bailey at the University of Washington. The arrays will then be employed to make the first instantaneous acoustic field measurements of the three major classes of SWL systems: electrohydraulic, electromagnetic, and piezoelectric lithotripters. The measurements will yield important information about the dimensions and peak pressure location of the instantaneous acoustic field, the effect on the acoustic field of different reflectors, and the performance of new versus old electrodes. A successful outcome of this project will, ultimately, help improve clinical efficacy through more efficient stone fragmentation and improve clinical safety by reducing tissue damage. PUBLIC HEALTH RELEVANCE: The ultimate goal of this work is to improve the efficacy of shock wave lithotripsy (SWL) treatment of kidney stones by more efficiently fragmenting the stones while exposing the surrounding kidney tissue to minimal trauma. The proposed measurements would represent the first instantaneous acoustic field measurements of SWL systems and would provide valuable information that could be used to improve lithotripter devices, theoretical models of stone fragmentation, device calibration, and patient management.