Comparison of thermography and laser Doppler imaging in the assessment of Raynaud's phenomenon.

The main objective of the study was to compare the techniques of thermographic and laser Doppler imaging in the assessment of digital blood flow. Thermography measures surface temperature; laser Doppler measures microciculatory flow. Seventeen healthy control subjects and 40 patients with Raynaud's phenomenon (7 primary, 33 secondary to systemic sclerosis) underwent a 20-min acclimatization period at 23 degrees C. Thermographic and then laser Doppler images were taken of the dorsal aspect of both hands, and the procedure was repeated at a room temperature of 30 degrees C. Three regions/values of interest from each hand were chosen for analysis: the dorsum of the hand, the tip of the middle finger, and the "gradient" between these. Thermographic and laser Doppler results correlated poorly. For example, correlations between techniques for the gradient value were as follows: left hand 23 degrees C, r = 0.61; right hand 23 degrees C, r = 0.64; left hand 30 degrees C, r = 0.47; right hand 30 degrees C, r = 0.48. One explanation for these findings is that laser Doppler imaging is more sensitive to blood flow changes and therefore more likely to show inhomogeneities than the highly damped temperature response. Therefore one technique cannot substitute for another.