Plasma-mediated tissue ablation with nanosecond laser pulses in the spectral region from ultraviolet to near-infrared: In-vitro study with porcine myocardium tissue

With a Q-switched Nd:YAG laser (the fundamental band and its harmonics), ablation characteristics have been investigated in vitro for porcine myocardium tissue. At a constant laser intensity of ∼ 2.0 GW/cm², the laser pulses irradiated the tissue and the depth of the ablation hole formed was measured. After the laser irradiation, the tissue was histologically analyzed with an optical microscope and a polarization optical microscope to evaluate the laser-induced damage in the tissue. It was found that the ablation rate for a 1064-nm laser irradiation was comparably high to that for a 355-nm laser irradiation, and the ablation efficiency was lower for a 266-nm laser irradiation than for a 355-nm laser irradiation. During the ablation, strong plasma formation was observed for 266 nm and 1064 nm, while the laser-induced optical emission was dominated by fluorescence for 355 nm. The histology showed that the thermal damage thickness decreased with decreasing the wavelength for 266, 355, and 532 nm, but for 1064 nm thermal damage was very limited although a certain extent of mechanical damage was observed. Based on these experimental results, the ablation mechanism for each laser wavelength and the optimum laser wavelength for the TMLR (transmyocardial laser revascularization) are discussed.