STUDY OF SHOCK WAVE PROPAGATION AND PHASED-ARRAY FOCUSING FOR LITHOTRIPSY

THIS PHASE I EFFORT WILL APPLY THEORETICAL METHODS BASED PRINCIPALLY ON CAGNIARD'S FORMALISM (PREVIOUSLY INCORPORATED BY US INTO OUR POWERFUL SWREF CODE), TO THE PROPAGATION AND FOCUSING, IN BOTH REFLECTIVE AND PHASED-ARRAY EQUIPMENT, OF SHOCK-WAVES PRODUCED BY UNDERWATER SPARKS. THE OBJECTIVE IS TO INVESTIGATE AND PROVIDE DESIGN DATA FOR LITHOTRIPSY EQUIPMENT IN WHICH FOCUSED SHOCK WAVES ARE USED TO DISINTEGRATE HUMAN KIDNEY STONES WITHOUT SURGICAL INTERVENTION. AREAS OF INTEREST NOT STUDIED BY PREVIOUS INVESTIGATORS WILL BE THE EFFECT OF EXTRA-FOCAL INCLUSIONS (E.G., PELVIC BONE) ON THE FOCUSING PROPERTIES OF REFLECTIVE AND PHASED ARRAYS, THE IMPORTANCE OR OTHERWISE ANOMALOUS EFFECTS SUCH AS PRODUCTION OF PSEUDO-RAYLEIGH WAVES, AND REVERBERATION EFFECTS IN STONES OF VARIOUS SIZES AND COMPOSITION; DEGRADATION OF SHOCK-PULSE RISE-TIMES WITH DISTANCE WILL ALSO BE INVESTIGATED. THE ADVANTAGES OF PHASED ARRAYS, EXPECTED TO BE INCREASED POWER-DENSITY, SHORT PROPAGATION DISTANCES AND FACILITY OF LOCALIZATION (THROUGH ELIMINATION OF THE LARGE WATER BATHS NOW NECESSARY), WILL BE EVALUATED. THE PHASING REQUIREMENTS AND THE ROLE OF FIRING-TIME JITTER WILL BE STUDIED BOTH THEORETICALLY AND BY A SIMPLE EXPERIMENT INVOLVING TWO INDEPENDENTLY-TRIGGERED SPARK GAPS. THE STUDY IS PLANNED TO ELUCIDATE FUNDAMENTAL PHENOMENA, AND NEITHER EQUIPMENT CONSTRUCTION NOR EXPERIMENTS IN LIVING TISSUES ARE CONTEMPLATED IN PHASE I.