Pulsed versus continuous wave Nd-YAG laser-induced necrosis: Comparison in the rat liver in vivo

It is assumed that a pulsed Nd-YAG laser will avoid heat diffusion in tissue and thus produce more predictable and less deep lesions. The aim of this study was to compare lesions induced in an homogeneous tissue by the pulsed wave (PW) and the continuous wave (CW) modes of the Nd-YAG laser. Single laser shots were delivered to the liver surface of anaesthetized rats after laparotomy, in vivo. In experiment 1, the quartz fibre was handled close to the liver surface. Energies of 10, 20, 40 J were applied. In experiment 2, the quartz fibre was fixed at a distance from the liver and the laser beam was focused through a handpiece, to obtain a spot of 3 mm in diameter at the liver surface. Energies of 20, 40, 80 J were applied. In both studies, four or five shots were performed for each parameter with each laser mode. After excision of the liver, the maximal depth and width of the crater, the necrotic area and the total affected tissue were measured for each lesion. In experiment 1, there was no difference in any dimension of lesion between the two modes. In experiment 2, the only statistical difference was observed at the fluence of 566 J cm^–2 where the necrotic area as well as the total lesion were deeper with the pulsed mode. This difference was not observed for the crater. In this experimental model depths and widths of the different layers of the lesion induced by the PW mode were comparable to those obtained with the CW mode. This PW mode of Nd-YAG laser does not prevent heat diffusion in tissue.