Noninvasive Determination of Depth in Transmission Raman Spectroscopy in Turbid Media Based on Sample Differential Transmittance.

Here we propose a simple noninvasive approach to determine the depth of a buried object using transmission Raman spectroscopy. In accordance with theory, the photons arising from spectral peaks that are suitably separated will be subjected to different optical properties in the media through which they travel. These differences can impact the relative intensities of Raman peaks as a function of the transmission path length, thereby the depth of signal generation is inherently encoded in the spectra. In a proof-of-concept study, through only external calibrations, it was possible to accurately predict the depth of Polytetrafluoroethylene (PTFE) layer purely on the basis of relative intensity of two peaks in a predominantly absorbing solution Indian ink (0.1 μL/mL; RMSE 0.42 mm) and a scattering solution (RMSE 0.50 mm). This simple approach offers the possibility to noninvasively identify the depth of a buried object, such as breast calcifications, using simple transmission measurement geometries for the first time.