Abstract

Comparison of Electromagnetic and Electrohydraulic Lithotripters

R.O.Cleveland, P.V.Chitnis (Department of Aerospace and Mechanical Engineering, Boston University, Boston, MA, USA); J.A.McAteer, J.C.Williams Jr. (Department of Anatomy, Indiana University School of Medicine, Indianapolis, IN, USA); R.Anglade, R.K.Babayan (Department of Urology, Boston Univeristy School of Medicine, Boston, MA, USA)

e-mail: robinc@bu.edu

Most clinical lithotripters are based on one of two shock wave generating principles: a spark gap (electrohydraulic) or a coil (electromagnetic). We compared the physical characteristics and stone breaking performance of an electrohydraulic lithotripter (EHL) and an electromagnetic lithotripter (EML). The pressure field was measured using a PVDF membrane hydrophone. The EML had a higher peak positive pressure than then EHL (115 MPa vs 45 MPa) and the EML waveform was more consistent. The -6 dB focal spot in the EML (25 mm long by 5 mm) was much smaller than that of the EHL (60 mm long by 10 mm). The fragmentation performance was determined by treating artificial kidney stones (cylinders, 7.5 mm long and 6.5 mm diameter, made from Ultracal-30 gypsum). After treatment stone remnants greater than 2 mm in diameter were dried and weighed. The EML was highly sensitive to position of the stone and displacement by more than 4 mm off-axis lead to a statistically significant decrease in fragmentation (p<0.03). The tighter focus of an EML may not be an advantage in the clinic as respiratory motion is typically greater than 20 mm occur. [Work partially supported by NIH through P01-DK 43881].

Section : 5