Dr. Burns reported findings from an ex vivo study conducted in porcine skin that evaluated laser tunnel dimensions and the safety margin against end-hits causing skin burns associated with the use of a hot tip that had no light transmission, and three optical tips emitting lipid-selective (924 nm) or water-selective (975 nm and 1,470 nm) light. The relative tissue effects of the 924 nm and 975 nm wavelengths were also investigated in an in vivo study involving patients undergoing abdominoplasty. In both studies, the methods were designed to mimic clinical use of LAL in which the treatment tips were inserted into the subcutaneous fat and through the skin.
STUDY RESULTS The results of the ex vivo study showed that the 924 nm optical tip had an improved margin of safety near the dermis and produced more efficient fat lipolysis than tips emitting the water-selective wavelengths. Compared with the hot tip, the optical-tip treatments afforded more efficient heat delivery and more uniform heating with reduced char formation.In the in vivo study, the coagulation profiles were much less uniform than in the ex vivo study, although Dr. Burns notes the difference may be due in part to the difficulty in achieving standardized conditions — particularly the rate of tip passage — in vivo. While further in vivo study is needed, the findings indicate that the heat propagated along the fibrous septae, he says.
"After Rox Anderson, M.D., and colleagues first reported the feasibility of selective photothermal targeting of lipid tissue based on wavelength selection (Anderson RR, et al. Lasers Surg Med. 2006;38(10):913-919), there has been continuing debate about whether laser tunnel formation in fat is wavelength-dependent or occurs through volumetric heating, as well as regarding the importance of wavelength in LAL safety," says Dr. Burns, a plastic surgeon in private practice, Dallas Plastic Surgery Institute, Dallas. "Even Dr. Anderson has remained skeptical about the mechanism of laser lipolysis, as his experiments were performed with external light delivery.