Gallstone movement during lithotripsy: mechanisms and effects on fragmentation

Area of Science:

• Biomedical Engineering
• Medical Physics
• Gastroenterology

Background:

• Gallstone fragmentation via lithotripsy is a key treatment.
• Understanding the physical mechanisms of gallstone movement during lithotripsy is crucial for optimizing treatment efficacy.
• In vitro studies are essential for dissecting the complex interactions between shock waves, gallstones, and surrounding fluid dynamics.

Purpose of the Study:

• To investigate the mechanisms responsible for gallstone and fragment movement during shock wave lithotripsy.
• To determine how varying degrees of gallstone movement influence fragmentation efficiency in vitro.
• To elucidate the roles of radiation force and fluid streaming in gallstone lithotripsy.

Main Methods:

• Experiments were conducted using four custom-designed phantoms to control gallstone movement during shock wave application.
• Gallstone fragmentation was assessed under conditions of decreasing movement and varying surrounding fluid volumes.
• The influence of stone displacement and fragment return to the lithotripter's focus was analyzed.

Main Results:

• Shock waves caused initial gallstone displacement, but fluid streaming returned stones and fragments to the focus in small fluid volumes.
• Streaming movements were ineffective in large fluid volumes, hindering fragment return.
• Restraining gallstone movement did not improve fragmentation outcomes; complete immobilization offered no benefit.

Conclusions:

• Radiation force and surrounding liquid streaming are primary drivers of gallstone and fragment movement during lithotripsy.
• Smaller fluid volumes enhance lithotripsy effectiveness by facilitating fragment recirculation to the shock wave focus.
• Impeding stone rotation by total immobilization may reduce lithotripsy efficacy, suggesting a need for controlled movement.