In vitro Erbium:YAG laser lithotripsy

The potential application of an Erbium:YAG (Er:YAG) laser (Q(0) = 50 mJ/pulse; tau(p) = 275 mu s; rep. rate = 2, 10 Hz) with a sapphire delivery fiber for intracorporeal laser lithotripsy was explored. Preliminary measurements on calculus mass-loss and fragmentation efficiency were conducted and results were compared with that of Ho:YAG laser lithotripsy. Laser induced bubble and lithotripsy dynamics were investigated to assess the mechanism(s) involved in the fragmentation process. Results showed that the fragmentation efficiency (mass-loss/H-0 - g.mu m(2)/J) in Er:YAG laser lithotripsy was about 2.4 times that of Ho:YAG laser lithotripsy (used: Q(0) = 500 mJ/pulse; tau(p)= 250 mu s; rep, rate = 10 Hz). Acoustic transients were found to have minimal effect during Er:YAG laser lithotripsy. Schlieren flash images suggested a predominantly photothermal mechanism due to direct laser energy absorption, which resulted in recrystallization and plume formation. These events indicated melting and chemical decomposition of the calculus composition. Another observation led to the possibility of a plasma-mediated photothermal mechanism. The 'Moses effect' facilitating pulsed mid-infrared laser delivery appeared more efficient for the Er:YAG laser than for the Ho:YAG laser. With the sapphire fiber, experimental results suggested the potential of an improved treatment modality by the Er:YAG laser for intracorporeal laser lithotripsy.