Functional assessment of hand vasculature using infrared and laser speckle imaging

To assess vascular responses of the human hand to inspiratory gasps and hand cooling, two imaging "remote sensing" instruments were utilized: 1) a high-resolution infrared (IR) imaging camera and 2) a full-field laser perfusion imager (FLPI). Data analysis was performed on the data sets collected simultaneously from both instruments. A non-localized drop of both FLPI and IR signals was observed at ∼0.5-2.0 min after gasp onset. Spontaneous oscillations, much below the human cardiac and respiratory frequencies, were observed with both imagers. The dominant oscillations for both imaging modalities centered around 0.01Hz. Spectral frequencies, their power, and the duration of temperature oscillations (bursts) for different hand areas changed in time and were spatially heterogeneous. The highest spatial correlation between the two data sets was found between the mean IR derivative image and the mean original FLPI image for the baseline conditions. Heterogeneous images of the human hand were consistently detected non-invasively by both instruments. After cooling, a temperature elevation of ∼0.5°C was seen as a spotted pattern mainly in the thenar and hypothenar areas. A generalized increase in perfusion over the same areas was observed in FLPI images. Both IR and FLPI imagers sensitively identify vasoconstrictor responses induced by inspiratory gasp and hand cooling maneuvers. The specificity to physiological changes and high imaging rate for both instruments, coupled with the current ease of use of optical cameras in clinical settings, make the described combination of two instruments an ideal imaging approach to studying the dynamics of thermal and perfusion heterogeneity in human skin.