A lock-in thermal imaging setup for dermatological applications.

Abstract

Lock-in thermal imaging is a thermographic method that is widely used in the nondestructive testing of materials. The technique allows detecting under the sample surface, small variations of the thermophysical properties in a noninvasive and noncontact manner. Surprisingly, this method has, to our knowledge, never been used in dermatology although it is particularly suited. We present in this article the first lock-in thermal imaging setup dedicated to dermatological applications. The apparatus uses a temperature-modulated airflow to periodically stimulate the skin surface. The infrared images recorded by a high sensitive camera are demodulated according to the digital lock-in principle to compute a phase and amplitude image. First results obtained on benign skin lesions are presented. The images allow to detect small variations of the tissue thermophysical properties like for example, perfusion variations. Lock-in thermal imaging has the ability to reject disturbing thermal signals coming from subcutaneous tissues. The localization of the lesions is more accurate due the suppression of the lateral heat spreading. Lock-in thermal imaging is a promising method for the detection of lesions exhibiting modified thermophysical properties compared to the surrounding healthy skin.