The inspection of parts of the human body with the help of optical instruments has been used in medical diagnosis for more than a century, but gained limited applications only. In recent years however extended knowledge of tissue optics in particular /10 (absorption coefficient), As (scattering coefficient) and g (anisotropy factor), and improved sensor technology offered new solutions to this problem.
J. Beuthan, J. Beuthan,
"IR-diaphanoscopy in medicine", Proc. SPIE 10311, Medical Optical Tomography: Functional Imaging and Monitoring, 103110H (5 August 1993); doi: 10.1117/12.2283762; https://doi.org/10.1117/12.2283762