A lumped-element thermal model for understanding the selective photothermolysis of sebaceous glands

Traditional thermal modeling techniques for understanding the photothermal treatment of skin, such as finite element methods for solving the heat equation, are complex, expensive, and time-consuming. We present a much simpler, but equally accurate approach using a lumped-element circuit model. This approach, in which discrete circuit elements represent thermal properties of the skin along with various heating and cooling elements, yields good physical insight into the spatial and temporal heat transfer. Free, off-the-shelf circuit analysis tools lend themselves well to this application, enabling rapid parametric analysis of different treatment conditions. In particular, the SPICE (Simulation Program with Integrated Circuit Emphasis) circuit simulator, which was originally developed in the 1960s, is a computationally fast and robust tool for time-domain circuit analysis. It has numerous built-in circuit elements available that make the modeling of pulsed laser heating and modulated surface cooling easy. Additionally, custom scripts may be used to auto-generate the text-based circuit descriptions that SPICE uses as its input. Following a description of the model, we present results of simulating the selective laser heating of sebaceous glands, comparing the circuit model results with those from COMSOL^® finite-element models and with experimental, time-resolved, surface temperature measurements recorded with the Accure Acne, Inc. 1726nm acne laser system.