Evaluation of tissue thermal effects from 1064/1320-nm laser-assisted lipolysis and its clinical implications

Abstract

Liposuction is a standard for removing fat. Recently developed, laser lipolysis can be used to simultaneously remove unwanted fat and tighten skin. Laser lipolysis is accomplished with single or multiple sequential wavelengths. Development of an optimal method requires detailed understanding of tissue heating for the wavelengths employed. This study systematically evaluates tissue heating for superficial and deep laser lipolysis using three approaches, and correlates temperature rise with histology changes, defining appropriate system parameters. Two individuals scheduled for abdominoplasty had laser testing on healthy abdominal skin scheduled for excision. Each treatment was applied to 3×3 cm squares with various laser parameters. Treatment was conducted in the fatty layer for lipolysis and subdermally for skin tightening. Individual squares were treated with SmartLipo (Cynosure, Inc. Westford, MA, USA) using 1064 nm, 1320 nm, or MultiPlex (1064 nm/1320 nm) with laser doses of 8.3 to 333 J/cm2. Exposures were applied at 3–5 mm or ∼20 mm depth below the skin surface. Skin temperatures at the surface and at depths of 5 mm to 37 mm were recorded immediately post-treatment for each exposure. Treated tissue was excised and evaluated for thermal injury using H&E and transmission polarization microscopy. Histology was correlated to tissue temperature to determine appropriate treatment limits. Superficial treatment with surface temperatures exceeding 47°C (50°C and 55°C at 5 mm depth) typically caused epidermal and dermal injury, with blistering above 58°C. Below this threshold, focal collagen change and dermal inflammatory response were found in many samples without epidermal injury. These acute thermal effects may link to skin tightening during the healing process. Deep treatments, at up to 133 J/cm2, exhibited minimal temperature rise and induced thermal effects in vessels and ligaments. Higher laser doses were associated with a significant temperature increase. In conclusion, superficial subdermal heating (within approximately 5 mm of the surface) during laser lipolysis should limit skin surface temperature to 42°C. The laser dose per surface temperature rise in treatments are 4.5 J/cm2/°C for 1320 nm, 6 J/cm2/°C for MultiPlex and 7.5 J/cm2/°C for 1064 nm. Clinical studies should be performed to validate these results.