Interstitial Nd:YAG laser coagulation using simultaneous multiple fiber application with an optical beamsplitter: the importance of mutual fiber distance

In this study, the optimal combination of laser power and mutual fiber distance was assessed in order to take full advantage of simultaneous multiple fiber application in interstitial laser coagulation. For cylindrical diffusing fibers ((Theta) equals 600 micrometer, 2 cm diffusing length) were positioned in porcine liver tissue at a mutual distance of 1 - 4 cm. Nd:YAG laser light (lambda equals 1064 nm) of 4 - 7 W was guided through each fiber. By varying exposure time for the different power levels, energy applied was constant at 1800 J. The output of the four channels was measured with an output meter at various laser power levels with variation never exceeding 5%. After laser application the livers were sectioned and the zone of coagulation was measured in three directions; fusion between the coagulation zones surrounding the fibers was noted. Spherical lesions up to 5 cm (Theta) could be produced at the optimal settings of 7 W with a distance between the fibers of 2 cm. Mutual distances less than 2 cm resulted in smaller lesions with central carbonization and at larger distances no fusion between the four coagulative zones occurred.