Temperature modulation of the visible and near infrared absorption and scattering coefficients of human skin

We determine temperature effect on the absorption and reduced scattering coefficients $(μa$ and $μs′)$ of human forearm skin. Optical and thermal simulation data suggest that $μa$ and $μs′$ are determined within a temperature-controlled depth of ≈2 mm. Cutaneous $μs′$ change linearly with temperature. Change in $μa$ was complex and irreversible above body normal temperatures. Light penetration depth (δ) in skin increased on cooling, with considerable person-to-person variations. We attribute the effect of temperature on $μs′$ to change in refractive index mismatch, and its effect on $μa$ to perfusion changes. The reversible temperature effect on $μs′$ was maintained during more than 90 min. contact between skin and the measuring probe, where temperature was modulated between 38 and 22 °C for multiple cycles While temperature modulated $μs′$ instantaneously and reversibly, $μa$ exhibited slower response time and consistent drift. There was a statistically significant upward drift in $μa$ and a mostly downward drift in $μs′$ over the contact period. The drift in temperature-induced fractional change in $μs′$ was less statistically significant than the drift in $μs′.$$Δμs′$ values determined under temperature modulation conditions may have less nonspecific drift than $μs′$ which may have significance for noninvasive determination of analytes in human tissue. © 2003 Society of Photo-Optical Instrumentation Engineers.