SKIN REFLECTANCE: HOW LONG THE PHOTONS TRAVEL UNTIL REMISSION
Janis Spigulis, Vanesa Lukinsone, Anna Maslobojeva, Uldis Rubins, Maris Kuzminskis
Biophotonics Laboratory, Institute of Atomic Physics and Spectroscopy, University of Latvia, Riga
Abstract
Values of the skin-remitted photon path lengths at partricular wavelengths and input-output distances are important for several clinical applications including reflection pulse oximetry and skin chromophore mapping.The remitted photon path lengths in human skin can be estimated by modelling; however, there are very few experimental data available to validate the simulations. Models mostly consider distribution of pathlengths for all photons independently of their travel directions and interactions within the tissue. One can expect that the mean path length of the survived skin-remitted photons should be longer than that related to all photons launched in the tissue(were a certain amount of them is absorbed). Systematic experimental studies on spectral and spatial dependencies of the skin-remitted photons are needed to quantitatively answer this question.
This study exploited the photon time of flight method where picosecond laser pulses at seven wavelength bands (FWHM = 10 nm)in the spectral range 560-800 nm were launched into in-vivo forearm skin of 10 volunteers via an optical fiber. The pulses of back-scattered light were detected via another optical fiber placed at variable distance (1, 8, 12, 16 or 20 mm) from the input fiber, with subsequent analysis of their shapes for all 35 spectral-spatial combinations. Using a deconvolution algorithm, the distribution functions of remitted photon arrival times after infinitely narrow input pulse were calculated and transformed into distributions of skin-remitted photon path lengths.
Nearly linear dependences of the remitted photon mean path length on inter-fiber distance were obtained for all wavelength bands, while the spectral dependences at fixed inter-fiber distances showed more complicated character, most probably due to absorption of the dermal hemoglobin.
Speaker
Janis Spigulis
Biophotonics Laboratory, Institute of Atomic Physics and Spectroscopy, University of Latvia
Riga
Discussion
Ask question
