Spectral Coloring

Spectral coloring is a phenomenon that becomes relevant when studying light of different “colors” (wavelengths) propagating through tissue. It is expected that light gets attenuated as it reaches further into the tissue. However, since the absorbing species in the tissue interact with different wavelengths, the spectrum of light that remains to be absorbed at deeper layers will change shape and thereby produce different absorption spectra. This particularly becomes an issue with photoacoustic imaging that is capable of spatially resolving absorption spectra several cm into tissue. Finding a way to correct for such undesired spectral changes becomes necessary to overcome in order to extract reliable spectral information at tissue depths that PAI are capable of measuring at.

The Figure demonstrates how an incoming fluence spectrum may change at different depths after experiencing absorption in tissue.