Pseudo-color thermographic image of forearms when fingers have been immersed in paraffin at 50 degrees C for 10 to 15 minutes. Heat from the paraffin has warmed the blood in the veins, which shows up as warm patterns (red colors) on the skin surface. This "warm challenge" and an analogous "cold challenge" can be used to diagnose vascular and/or peripheral vascular control abnormalities.

The original thermal image data have been filtered with a 1-D median filter in the horizontal direction (window width=5) and a 3-wide triangular filter in the vertical direction to reduce noise effects.

From the award-winning dissertation of Dr. Eric K.Y. Chan, August 1991