The article aims first to present a new study on the thermal regulatory response of the human skin surface while
exposed to a cold environment. Our work has shown that when a cold stress is applied to the left hand, thermal
infrared imaging (MWIR spectral band: 3-5 μm) allows a clear observation of a temperature rise on the right
hand. Moreover, a frequency analysis was also carried out upon selected vein pixels of the images monitored
during the same cold stress experiment. The objective was to identify the specific frequencies that could be
linked to some physiological mechanisms of the human body. This kind of study could be very useful for the
characterization of possible thermo-physiological pathologies. Besides thermoregulation, we also present in this
article some results on the extraction of the hand vein pattern. Firstly, we show some vein extraction results
obtained after image processing of the thermal images recorded in the thermal band (MWIR), then we compare
this vein pattern to the signature obtained with a camera operating in the NIR spectral band (0.85-1.7 μm).
This method could be used as a complementary means for finger print signatures in biometrics.
An imaging technique of the hand vein tree is presented in this paper. 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 approximately 0.03 Hz and a pressure range between 100 and 140 mmHg, according to the diastolic and systolic blood pressure, are used as stimulation. Then, dorsal hand amplitude and phase 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 and phase images by using a Fast Fourier Transform image processing technique. This work could be used for vein localization for perfusion or for the early diagnosis of vein diseases such as primitive varicose and deep vein thrombosis (DVT). A hand vein signature database for identification purposes is also possible.