Size and location of defects at the coupling interface affect lithotripter performance.

Area of Science:

• Biomedical Engineering
• Acoustics
• Urology

Background:

• Air pockets at the lithotripsy coupling interface impede shock wave energy transmission.
• Ineffective coupling reduces the efficacy of shock wave lithotripsy (SWL).

Purpose of the Study:

• To investigate how coupling defect size and location affect SWL shock wave properties.
• To determine the impact of coupling defects on stone breakage efficacy.

Main Methods:

• Simulated coupling defects in a test system using a Dornier Compact-S lithotripter.
• Measured acoustic pressures and focal zone dimensions using a fiber-optic probe hydrophone.
• Assessed stone breakage using gypsum model stones under various coupling conditions.

Main Results:

• Stone breakage decreased proportionally to the defect area; an 18% central defect reduced breakage by ~30%.
• Central defects narrowed the lithotripter's focal width by ~30% and disrupted acoustic field symmetry.
• Defect location influenced impact, with central defects causing greater reductions in stone breakage and energy density.

Conclusions:

• Coupling defects not only block energy but also alter shock wave properties crucial for stone breakage.
• The size and location of defects significantly impact SWL effectiveness, with central defects being most detrimental.
• Eliminating air pockets at the coupling interface is critical for optimal SWL treatment outcomes.