A method for noninvasively determining deep tissue temperature comprises measuring data relating to spectral shifts of chromophore absorption in tissue using broadband diffuse optical spectroscopy and generating a temperature reading corresponding to the spectral shift of an absorption peak of the chromophore. A bound water correction is made to the spectral shift. A frequency domain measurement at multiple wavelengths is made to determine the absolute absorption and scattering values between 600 and 1050 nm. The measurement of an absolute absorption comprises measuring an absolute absorption coefficient of selected tissue and further comprising deducing concentrations of tissue composition including lipids, deducing information related to heterogeneity and integrity of tissue matrix, and deducing temperature heterogeneity related to vulnerable plaque in vascular tissue. The measurement comprises making a measurement in the range of 600-1100 nm to interrogate a vessel wall in the presence of blood.