DEPENDENCE OF LASER PHOTOCOAGULATION ON INTERSTITIAL DELIVERY PARAMETERS

Photocoagulation was performed ex vivo between tissue slabs by deliver ing continuous-wave laser energy from an optical fiber either directly , or by depositing the energy into a 2.4 mm diameter steel sphere at t he fiber tip. The dependence of photocoagulation lesions on the follow ing variables was assessed: (1) energy source: Nd:YAG-532 nm, 1,064 nm +/- steel sphere, (2) tissue type: porcine muscle (light), bovine mus cle (dark), (3) delivered pourer: P = 1.5-3.0 W (porcine), 1.0-2.5 W ( bovine), (4) exposure duration: T = 300-1500 s. The resulting cross-se ctional photocoagulation lesions are summarized as follows: 532 nm: el ongated; central charring in all cases; 1,064 nm: circular; central ch arring only in bovine for P greater than or equal to 2.0 W, T greater than or equal to 500 s; sphere: circular; central charring in bovine f or P greater than or equal to 1.5 W and porcine for P greater than or equal to 2.0 W. These experiments suggest photocoagulation lesion size decreases as optical penetration increases. The results indicate that interstitial laser photocoagulation lesions > 10 mm diameter can be m ade without charring in both lightly and heavily pigmented tissues ex vivo by delivering 1,064 nm laser energy at sufficiently low power for at least 1,000 s from well-polished optical fibers. (C) 1994 Wiley-Li ss, Inc.