Fracture mechanics model of stone comminution in ESWL and implications for tissue damage

• Published in: Physics in medicine & biology Vol. 45; no. 7; pp. 1923 - 1940
• Main Authors: Lokhandwalla, Murtuza, Sturtevant, Bradford
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.07.2000; Institute of Physics
• Subjects: Biological and medical sciences; Calcium Oxalate; Humans; Kidney - pathology; Kidney Calculi - therapy; Lithotripsy - methods; Medical sciences; Models, Biological; Models, Statistical; Nephrology. Urinary tract diseases; Time Factors; Urinary lithiasis; Water; Kidney disease; Urinary system disease; Mechanical model; Instrumentation therapy; Physical properties; Shock wave; Kidney; Urinary stone; Fragmentation; Extracorporeal irradiation; Tissue; Focusing; Lithotripsy; Lithiasis; Mechanism of action
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/45/7/316

Focused shock waves administered during extracorporeal shock-wave lithotripsy (ESWL) cause stone fragmentation. The process of stone fragmentation is described in terms of a dynamic fracture process. As is characteristic of all brittle materials, fragmentation requires nucleation, growth and coalescence of flaws, caused by a tensile or shear stress. The mechanisms, operative in the stone, inducing these stresses have been identified as spall and compression-induced tensile microcracks, nucleating at pre-existing flaws. These mechanisms are driven by the lithotripter-generated shock wave and possibly also by cavitation effects in the surrounding fluid. In this paper, the spall mechanism has been analysed, using a cohesive-zone model for the material. The influence of shock wave parameters, and physical properties of stone, on stone comminution is described. The analysis suggests a potential means to exploit the difference between the stone and tissue physical properties, so as to make stone comminution more effective, without increasing tissue damage.