From the paper “The Physiological Basis for Clinical Thermography and the Detection of Infrared Radiation from the Human Body.” By Peter Leando (Ref 11) I quote; “The emissivity of human skin is almost 100% (close to black body emissivity) so the human subject is an ideal subject for thermographic imaging.

All thermographic images (thermograms) of the human body depend on the sympathetic control of skin blood-flow.  Only the dermal blood flow changes explain the heat seen on the surface of the body. The heat of a muscle, a joint or a bone is not conducted to the dermal tissues and cannot influence the dermal temperature recorded by thermography. Conduction of heat from the deeper portions of the body to the surface does not occur or create changes in the surface temperature. 
The major basis of clinical thermography is the correlation of temperature recordings with various conditions from diseqase and injury as it relates to autonomic function.”

Digital Infrared Thermal Imaging (DITI) is the only medically recognized method available to indicate pain location originating from vascular, muscular or skeletal systems. Currently recognized by both the FDA and the TGA. It is a non-invasive clinical imaging procedure for detecting and monitoring a number of diseases and physical injuries, by showing the thermal abnormalities present in the body. X-ray, C.T. Ultrasound and M.R.I. etc are all tests of “anatomy” that measure the structures of your body. DITI shows physiological change and metabolic processes using colour to visually represent these changes.

It is used as an aid for diagnosis and prognosis, as well as monitoring therapy progress, for conditions and injuries, including back injuries, arthritis, headache, nerve damage, unexplained pain, Fibromyalgia, RSD, Dental and TMJ, Artery inflammation, vascular disease, breast disease, carpal tunnel syndrome, disc disease inflammatory pain, skin cancer, referred pain syndrome, pain/strain, whiplash and digestive disorders.