Acoustic lens for shock wave lithotripsy and related methods

An acoustic lens for a shock wave lithotripter having a maximum pressure, said acoustic lens comprising:

• a first lens portion comprising a center portion of said acoustic lens, said first lens portion having a first concave geometry configured to produce a first shock wave from an acoustic shock wave pulse generated by an electromagnetic shock wave pulse generator and directing said first shock wave toward a target, said first shock wave comprising a first leading compressive component, a tensile component, and a second trailing compressive component;
• and
• a second lens portion comprising an outer rim portion of said acoustic lens, said second lens portion having a second concave geometry configured to produce a second shock wave from said acoustic shock wave pulse and directing said second shock wave toward said target, said second shock wave comprising a first leading compressive component, a tensile component, and a second trailing compressive component, said second lens portion comprising a groove formed in a surface of said outer rim portion that is offset relative to a surface of said first lens portion by a depth d such that transmission of said second shock wave through said second lens portion is delayed by a predetermined amount Δt relative to transmission of said first shock wave through said first lens portion;
• wherein said offset is selected based on a relationship between the predetermined amount Δt and the depth d, a speed of sound c0 in a coupling fluid with which the acoustic lens is to be used, and a speed of sound clens in a material from which the acoustic lens is composed:
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• wherein said tensile component of said second shock wave is superimposed with said second trailing compressive component of said first shock wave to produce a modified waveform comprising a second trailing compressive component having a reduced magnitude relative to a second trailing compressive component of said acoustic shock wave pulse;
• wherein said predetermined amount Δt is between 0.1 and less than 10 microseconds;
• wherein the depth d is between 5 mm and 25 mm;
• wherein said first lens portion comprises between 50% and 75% of a total transmissive or reflective area of said acoustic lens;
• and
• wherein said maximum pressure is in the range from 5 to 200 MPa.