Theoretical considerations and experiments show that thermography at centimeter wavelengths offers an attractive penetration depth of more than one centimeter; however it is not well suited for remote imaging of the temperature of the human body because of its marginal spatial resolution and the required large distance between the receiver and the object. Millimeter wave thermography tests around 45 GHz show that a spatial resolution of a few millimeters and a temperature resolution of 0.1°K can be achieved. A penetration depth of several millimeters makes millimeter wave thermography more attractive for remote temperature sensing of deeper lying body tissues than infrared thermography.
Jochen Edrich, Jochen Edrich,
"Thermographic Imaging At Millimeter And Centimeter Wavelengths", Proc. SPIE 0070, Application of Optical Instrumentation in Medicine IV, (25 March 1976); doi: 10.1117/12.954628; https://doi.org/10.1117/12.954628