Accurate, real-time skin temperature monitoring and control using a compact thermal imaging camera for the laser treatment of acne vulgaris

We describe a 1726nm laser system for treating inflammatory acne, key to which is a real-time skin temperature monitoring subsystem. This capability allows us to use a closed-loop, “treat-to-temperature” approach rather than the conventional “treat-to-power” (or fluence) approach used in most dermatological lasers. The goal of our acne treatment is to raise sebaceous gland (SG) temperature high enough to damage the gland while sparing the surrounding dermal tissue. Unfortunately, even at 1726nm, where there is a small window of selectivity between sebum and water, the contrast in absorption coefficient is small, ~2:1. The result is that the target temperature window for safe and efficacious acne treatment is also small, approximately 5°C at the skin surface. The open-loop, treat-to-power approach, wherein the clinician selects a suggested good laser power or fluence, does not work well for acne as the variability in skin response, as well as variability in system heating and cooling, results in treatment temperature variations of 6 to 8°C or more. Additionally, there is no consistent clinical endpoint to indicate to the clinician that the treatment was safe and effective. To overcome this challenge, we employ a compact thermal imaging camera into the treatment handpiece to enable the accurate, real-time measurement of skin temperature. Real-time temperature feedback allows software to control laser power to reach a target skin surface treatment temperature while ensuring that the epidermal and dermal tissues do not overheat. Our thermal camera monitors the entire treatment area by sensing thermal radiation in the 7 to 14 micron band at 60 frames per second . To ensure measurement accuracy, which is key, we added a temperature-controlled reference source in the field-of-view of the camera. As an added safety feature, these measurements allow software to detect skin over-heating or over-cooling conditions and stops the treatment and shuts off the laser and/or air cooling, if needed.