Time-Evolution of Tissue Photoablation by MID Infrared Lasers

The Holmium (2.13um) and Erbium(2.94um) lasers emit high energy pulses at wavelengths that are strongly absorbed by water. The phase change of the water contained in biological tissues induces a fast vapor expansion which results in tissue fragmentation and removal. A time-resolved video imaging technoque was set up to study the evolution of the photoablation induced bythe laser pulse. Images were taken of bovine artery samples and rabbit eyes, irradiated with free running and Q-switch laser pulses. Both Holmium and Erbium lasers are quite effective in tissue ablation. However, the images revealed that a mechanical stress develops hundreds of microseconds following the laser pulse.THe extent of this side effect depends on the tissue strength and the laser pulse parameters.