Laser-Based Mid-Infrared Reflectance Imaging of Biological Tissues

Mid-infrared (MIR) (3-12 um) spectral imaging is a power analytical tool, but difficult in the back-reflectance mode for in-vivo diagnostics. Feasibility of MIR back-reflectance imaging is demonstrated using MIR semiconductor lasers. Transmittance trhough 500-mum thick films of water and blood showed a capability to resolve more than 6-OD signal dynamic range. Reflectance scanning imaging through a 150-mum thick film of blood showed negligible scattering effect, indicating the feasibility of optical coherent imaging. The result of coherent imaging of palm leaf shows a MIR sub-surface image that would not be visible in white light. With two wavelengths, a similar result for a chicken skin subcutaneous tissue at different focal depths was obtained, showing blood vessels beneath a lipid layer. These results suggest that advanced multilaser wavelength systems in the fingerprint spectral region can be a useful tool for in-vivo spectral imaging in biomedical research and diagnostic applications.