Optical discrimination of type I and type III collagen through second order susceptibility imaging

Abstract Second order susceptibility (SOS) microscopy is used as a contrast mechanism for distinguishing type I and III collagen microstructure in tissues. We found that the SOS tensor elements for type III collagen are χ zzz /χ zxx  = 1.20 ± 0.14 and χ xzx /χ zxx  = 0.49 ± 0.15 which are different from the type I collagen values of χ zzz /χ zxx  = 1.44 ± 0.15 and χ xzx /χ zxx  = 0.58 ± 0.14. In addition, relative proportion of collagen type was determined by analyzing the histogram of SOS ratio. Through the use of a Gaussian mixture model, the ratio of collagen I and III was determined. We found that in rat skin, type III collagen is present in rat skin in an average ratio of 0.36 ± 0.07. This result shows that SOS microscopy can be applied to in vivo label-free studies to investigate the interaction of types I and III collagen molecules and related diseases.