SELECTING SOURCE LOCATIONS IN MULTIFIBER INTERSTITIAL LASER PHOTOCOAGULATION

A theoretical basis and practical algorithm are described for selectin g optimal fiber source locations in multifiber interstitial laser phot ocoagulation (ILP). By analyzing the shape of overlapping coagulation patterns, the optimal separation of adjacent point heat sources inside a flat target volume boundary is shown to be d = 2 square-root 2r(c) , where r(c) is the coagulation radius of a single source. Against a c urved boundary, the algorithm specifies how d should be altered. To a ssess the validity of the theory, ILP was conducted in bovine muscle b y delivering 1064 nm laser energy through two or four plane-cut optica l fibers simultaneously. Delivered power, exposure duration, and sourc e separation were varied. The observed coagulation patterns matched th e theory-predicted patterns at delivered powers of 1.60W and 1.85W, bu t not at 2.40W. Also, the experiments indicate that reciprocity of del ivered power and exposure duration is invalid for ILP. (C) 1993 Wiley- Liss, Inc.