|Approach: The human body temperature is about 36.85°C (310 K); as a consequence the thermal radiation is mainly located in the far infrared. Infrared imaging captures, in a non-harmful way, a part of this emitted natural energy.
Using the natural human circulatory system and a controlled armband pressure around the arm, a Lock-in Thermography technique with an internal excitation is carried out. Since the stimulation frequency is inversely proportional to the inspection depth, the subcutaneous layer requires the use of a very slow frequency. Thus, a sawtooth waveform is preferred to minimize the duration of the pressure applied to the armband during the experiment. A frequency of 0.03 Hz and a pressure range between 20 and 140 mmHg, according to the diastolic and systolic blood pressure, are used as stimulation. Then, dorsal hand amplitude images are obtained with IR_view (Klein, 1999), a tool specifically designed to analyze infrared images.
The hand vein structure is thermally mapped by an infrared camera operating in the middle wavelength infrared range (MWIR) at room temperature. Parasitic frequencies are avoided by keeping the hand fixed. The resulting images show a gradient of temperature between surrounding tissues and the back-of-hand veins. The vascular signature segmentation is extracted from the amplitude images by using a Fast Fourier Transform image processing technique. A Principal Component Thermography technique is used to reduce the data dimension and, consequently, filter the images. Ther thermoregulation of the upper body is studied during the experiment.