Quantitative discrimination between endogenous SHG sources in mammalian tissue, based on their polarization response

In this study, the second harmonic generation (SHG) response to polarization and subsequent data analysis is used to discriminate, in the same image, different SHG source architectures with pixel resolution. This is demonstrated in a mammalian tissue containing both skeletal muscle and fibrilar collagen. The SHG intensity variation with the input polarization (PSHG) is fitted pixel by pixel in the image using an algorithm based on a generalized biophysical model. The analysis provides the effective orientation, θe, of the different SHG active structures (harmonophores) at every pixel. This results in a new image in which collagen and muscle are clearly differentiated. In order to quantify the SHG response, the distribution of θe for every harmonophore is obtained. We found that for collagen, the distribution was centered at θe = 42.7° with a full width at half maximum of ∆θ = 5.9° while for muscle θe = 65.3°, with ∆θ = 7.7°. By comparing these distributions, a quantitative measurement of the discrimination procedure is provided.This work is supported by the Generalitat de Catalunya and by the Spanish government grant TEC2006-12654 SICO. Authors also acknowledge The Centre for Innovacio i Desenvolupament Empresarial-CIDEM (RDITSCON07-1-0006), Grupo Ferrer and the European Regional Development Fund. This research has been partially supported by Fundació Cellex Barcelona.Peer reviewe