Spectral moment invariant analysis of disorder in polarization-modulated second-harmonic-generation images obtained from collagen assemblies.

Spectral moment invariants (SMIs) are applied, for what we believe to be the first time, to second-harmonic-generation data obtained from biological samples. This method can be used to identify the presence of structural abnormalities in collagenous tissues and also to quantify the extent of the abnormality through analysis of textural deterioration. SMIs are not affected by potentially confounding factors, such as the structural heterogeneity in biological subjects, variability in scan conditions, and differences in scanning techniques. In the present study, SMI analysis of polarization-modulated second-harmonic-generation scans is shown to be capable of discriminating between normal and damaged intervertebral disks obtained from an in vivo mouse model of disk injury. Preliminary evidence suggests that the values obtained with the discriminant function may be correlated with the degree of damage.