First in vivo spectral characterization of breast up to 1300 nm

Spectral measurements were performed from 900 to 1300 nm, using a fully automated set-up for time domain optical spectroscopy. Spectrally selected picosecond pulses emitted from a supercontinuum fiber source were used for illumination. The detection of re-emitted pulses was achieved using a photomultiplier tube with InP/InGaAsP photocathode, followed by a PC board for time-correlated single photon counting. To allow the estimate of tissue composition at long wavelengths, the optical characterization of collagen type I powder was extended up to 1300 nm. A marked absorption peak was detected around 1200 nm, which could prove useful for collagen quantification from in vivo optical data. In vivo spectral measurements of breast tissue were performed for the first time from 900 to 1300 nm in reflectance geometry. The sensitivity of the detector was very low above 1200 nm, still it allowed us to reveal a long-wavelength range (1000-1300 nm) potentially interesting for applications. A dominant absorption peak is present around 1200 nm. All major tissue constituents (i.e., water, lipid, and collagen) contribute to it. Thus, it is potentially interesting for the assessment of tissue composition, but it might cause exceeding attenuation in some practical cases. However, slightly shorter wavelengths (i.e. 1100-1150 nm) corresponding to the raising edge of the peak, might allow an accurate estimate of tissue composition, with the advantage of much lower attenuation. © 2011 SPIE.