Fig. 1

Schematic representation of the relationship between collagen structure and the forward-to-backward (F/B) Second Harmonic Generation (SHG) ratio. This figure illustrates how the F/B SHG ratio, obtained through SHG microscopy, reflects the microstructural properties of collagen fibers. On the left, a high F/B SHG ratio, indicative of normal tissue, is associated with well-organized collagen fibrils forming thick, intact fibers. In contrast, on the right, a low F/B SHG ratio, characteristic of pathologic tissue, suggests smaller fibril diameters, decreased order in interfibrillar packing, and increased fiber segmentation. The center panel depicts the SHG microscopy process, where a laser beam interacts with collagen, generating forward and backward SHG signals. The ratio of these signals provides insights into the collagen’s microstructural organization, which is altered in disease states