Deep cooling characteristics of multi-pulsed cryogen spray: A new technology to assist laser lipolysis

Obesity is a fast growing health problem that may induce severe chronic diseases. Laser lipolysis, as an effective noninvasive treatment, has great potential. Multi-pulsed cryogen spray (MCS) can be used to improve therapeutic effect, particularly by protecting epidermis and dermis from thermal damage caused by the competitive absorption of laser energy between dermal water and subcutaneous fat. Epoxy resin was employed as skin phantom, and surface heat transfer characteristics exposed in deep cooling by continuous and multi-pulsed cryogen spray were investigated by R134a. Findings indicate that MCS is more suitable for laser lipolysis than continuous spray given the deeper cooling depth and better cooling efficiency due to the dispersion of the accumulated liquid film that hinders surface heat transfer. Spatial heat transfer has a large inhomogeneity with short pulse duration and more homogeneity distribution with long pulse duration. The optimal duty cycle of 0.039 obtained good cooling effect without frostbite given the same pulse durations (Δt_p) and number of pulses (n_p). The MCS with parametric settings of Δt_p = .10 ms, Δt_d (pulse delay) ≥ 1500 ms, n_p ≤ 10 and Δt_p = .30 ms, Δt_d ≥ 3000 ms, n_p ≤ 6 can be used as reference for clinical treatment given their good cooling effect on 2-mm deep dermis without frostbites.