Femtosecond laser lithotripsy: feasibility and ablation mechanism

• Published in: Journal of Biomedical Optics Vol. 15; no. 2; p. 028001
• Main Authors: Qiu, Jinze, Teichman, Joel M, Wang, Tianyi, Neev, Joseph, Glickman, Randolph D, Chan, Kin Foong, Milner, Thomas E
• Format: Journal Article
• Language: English
• Published: United States 01.03.2010
• Subjects: Ablation; Calculi; Computer-Aided Design; Craters; Equipment Design; Equipment Failure Analysis; Feasibility Studies; Lasers; Lithotripsy; Lithotripsy, Laser - instrumentation; Magnesium; Reproducibility of Results; Sensitivity and Specificity; Shock waves; Stone
• ISSN: 1083-3668; 1560-2281
• DOI: 10.1117/1.3368998

Light emitted from a femtosecond laser is capable of plasma-induced ablation of various materials. We tested the feasibility of utilizing femtosecond-pulsed laser radiation ( =800 nm, 140 fs, 0.9 mJ/pulse) for ablation of urinary calculi. Ablation craters were observed in human calculi of greater than 90% calcium oxalate monohydrate (COM), cystine (CYST), or magnesium ammonium phosphate hexahydrate (MAPH). Largest crater volumes were achieved on CYST stones, among the most difficult stones to fragment using Holmium:YAG (Ho:YAG) lithotripsy. Diameter of debris was characterized using optical microscopy and found to be less than 20 m, substantially smaller than that produced by long-pulsed Ho:YAG ablation. Stone retropulsion, monitored by a high-speed camera system with a spatial resolution of 15 m, was negligible for stones with mass as small as 0.06 g. Peak shock wave pressures were less than 2 bars, measured by a polyvinylidene fluoride (PVDF) needle hydrophone. Ablation dynamics were visualized and characterized with pump-probe imaging and fast flash photography and correlated to shock wave pressures. Because femtosecond-pulsed laser ablates urinary calculi of soft and hard compositions, with micron-sized debris, negligible stone retropulsion, and small shock wave pressures, we conclude that the approach is a promising candidate technique for lithotripsy.