The role of laser tunnels in laser-assisted lipolysis.

Background And Objectives: Laser-assisted lipolysis (LAL) devices are used as adjuncts to liposuction that create laser tunnels to heat the adipose and connective tissue. Available systems vary significantly across choice of wavelengths, power delivery, and tip design. Rationale are developed for optimum laser parameters evaluated with physical principles and in controlled ex vivo tests.

Study Design/materials And Methods: A computer model for radiation propagation, thermal conduction and coagulation was developed to study laser tunnels formed in human adipose tissue. An ex vivo study with porcine tissue compared laser tunnels created by a device that operates in short-pulse mode with a 0.6 mm diameter fiber emitting lipid non-selective laser wavelengths to a device that operates in continuous-wave (CW) mode with a 1.5 mm diameter fiber emitting lipid- and water-selective laser wavelengths.

Results: Photothermolytic heating is the optimum mechanism to control delivery of heat to the tissue. Fiber tip surface power density can be optimized for ease of penetration and good volumetric heating while avoiding extremely high peak temperatures. CW rather than pulsed laser emission also minimizes peak temperature rise that can interfere with tunnel formation. Lipid- or water-selective laser wavelengths with low absorption yield lower peak temperatures and more uniform volume heating, while lipid-selective wavelengths offer greater safety near the dermis. Ex vivo histology demonstrated greater volumetric heating with the CW, lipid-selective device at similar power settings.

Conclusion: Wavelength, power delivery, and tip design are based on physical principles and together with treatment technique laser tunnel dimensions can be optimized as confirmed in ex vivo histology. The resulting thermal zones provide ease of penetration through adipose tissue and enable treatment uniformity. Based upon principles of fractional skin treatment the thermal zones induce healing responses in adipose tissue with potential to enhance clinical efficacy.