STUDY ON FOCUSING OF UNDERWATER SHOCK WAVES FOR EXTRACORPOREAL STONE DISINTEGRATION

Focusing of underwater shock waves was studied for the purpose of its application to extracorporeal stone disintegration. Shock waves were observed by a holographic interferometry using a holographic ruby laser (single or double exposure). The focusing was conducted with pseudoellipsoidal reflector.<br>Two focusing methods were studied. One involved placing the lead azide pellet at the distal focus (E₁) with an object placed at the proximal focus (E₂) from the reflector (A-method). The other method (B-method) was vice versa. The lead azide pellet (4-10mg) was exploded by radiating with a Q-switched ruby laser beam. The extracted human calculi (mixed calculus of calcium-oxalate and calcium phosphate) of 8mm in diameter and model calculi (activated alumina) of 6mm in diameter were easily disintegrated by both methods in one explosion. The pressure profile of the shock wave was composed of a single spike with almost vertical onset and a gradual decrease. It half time was approximately 2.0μsec (3mm in width). The ideal focusing condition was obtained in the A-method, and pressure obtained at the focus in the A-method was 880 bar in the lead azide pellet of 4mg. In the B-method, the explosion product gas bubbles inside the reflector prevented the ideal focusing, however, the maximum pressure evaluated at the focus attained 13Kbar with a lead azide pellet of 10mg. An experiment on the transmission of shock waves through a biological tissue was also performed, in which pig fatty tissue of 20mm in thickness was interpolated between the reflector and the disintegrating object. It was shown that the transmission of shock waves did not affect the shock wave focusing and the object was disintegrated in one explosion.<br>The results indicate that the explosive materials seem to be applicable in the extracorporeal stone disintegration. Further investigation for the safety of this method is conducting now in animal experiments.