Comparison of Broad vs Narrow Focal Width Lithotripter Fields

Area of Science:

• Biomedical Engineering
• Acoustic Lithotripsy

Background:

• Extracorporeal shock wave lithotripsy (ESWL) is a primary treatment for kidney stones.
• Optimizing lithotripter design is crucial for improving stone fragmentation and minimizing collateral tissue injury.

Purpose of the Study:

• To evaluate the effect of lithotripter focal width on stone fragmentation efficiency.
• To compare the performance of a narrow focal width versus a broad focal width lithotripter.

Main Methods:

• A modified HM3 lithotripter with a reduced -6 dB beam size (narrow focus) and increased peak pressure was used.
• In vitro fragmentation was assessed using BegoStone phantoms and in vivo fragmentation in a swine model.
• Fragmentation was evaluated at varying shock counts and radial distances from the lithotripter axis.

Main Results:

• The modified (narrow focus) reflector showed significantly higher stone fragmentation in vitro and in vivo compared to the original (broad focus) reflector at 2000 shocks (p ≤ 0.0016 and p ≤ 0.04, respectively).
• The narrow focus exhibited concentrated fragmentation power along the axis but rapidly diminished laterally.
• The broad focus demonstrated lower axial power but maintained significant fragmentation at greater radial distances.

Conclusions:

• A broad lithotripter beam size results in superior stone comminution compared to a narrow beam size under similar acoustic pulse energy.
• These results indicate that optimizing lithotripter beam width is key to enhancing fragmentation efficacy and potentially reducing tissue damage.