Experimental Biology 2010: Second Harmonic Generation And Its Clinical Utilization In Liver Fibrosis

Purpose of Study: Second Harmonic generation is a coherent imaging process where two lower energy photons are up-converted to one photon. Collagen is an extremely bright source of SHG. SHG microscopy is used as a tool for imaging collagen at the cellular level. Fibrosis with collagen deposition occurs as a response to liver injury. This study was performed to assess the utility of SHG in assessing fibrosis in liver disease.

Methods Used: H & E stained slides from liver biopsies of various stages were included. The slides were examined under the laser microscope using infrared wavelengths(800nm). Fluorescent and SHG microscopy were used consecutively to obtain images from each slide. The SHG images were analyzed using Image J software (NIH).

Summary of Results: SHG image of NASH with minimal fibrosis showed early collagen deposition surrounding the adipocytes(a). In mild liver fibrosis, collagen deposition is seen clearly around the central vein(b) and along the sinusoides(c). In advanced cirrhosis, dense collagen deposition was seen throughout the liver(d). SHG is able to quantify the amount of collagen using histogram analysis.

Conclusions: SHG has the capability in evaluating abnormal collagen deposition, with higher resolution and clarity than light microscopy. SHG has a role in detecting collagen in the earlier stages of liver disease. It does not require any additional staining or slide preparation. Future uses can include studying the progression/regression of fibrosis after treatment of viral hepatitis. Also reassessing the presence of collagen in cases of NASH in its early stages.