Patent ID: 8571640

Claim:
A method of characterizing subsurface conditions in a tissue, comprising (a) providing a catheter that has a light source that emits light in selected wavenumbers within the range of mid-infrared (IR) spectrum; (b) emitting light in said selected wavenumbers within the range of mid-IR spectrum and directing the light in said selected wavenumbers within the range of mid-IR spectrum from the catheter to an area of tissue at a subsurface location at or below the tunica intima of a blood vessel of a subject; (c) collecting light reflected from the subsurface location and generating a reflectance spectra; and (d) comparing said reflectance spectra to a reference spectra of normal tissue, whereby a subsurface location having an increased number of absorbance peaks at said selected wavenumbers indicates a subsurface tissue inside said blood vessel containing a physiological marker for atherosclerosis, wherein the comparing step comprises that increased numbers of absorbance peaks at said selected wavenumbers are within at least one range of mid-infrared wavenumbers selected from the group of: about 3800-3000 cm −1 , about 3500-3000 cm −1 , and about 3020-3000 cm −1 .