Subsurface and transcutaneous Raman spectroscopy and mapping using concentric illumination rings and collection with a circular fiber-optic array.

Different spatial separations between an illumination ring and a bundle of 50 collection fibers focused to collect light in the center of the ring were used to investigate the recovery of subsurface Raman spectra. The depth of Raman signal recovery and the preservation of spatial information in the recovered signal were investigated using polymer blocks stacked in different geometries. The illumination rings were then combined into a single data set to increase variation in the signal. Multivariate data analysis was used to recover the Raman spectra of the subsurface component. The Raman spectrum of a Delrin target was recoverable at depths up to 22.6 mm of overlying Teflon. Spatial information was lost at approximately 6.5 mm below the Teflon surface. The same protocols were used to recover canine bone spectra transcutaneously at depths up to 5 mm below the skin's surface. The recovered bone spectra were validated by exposed bone measurements.