ABSTRACT
Therefore, visual inspection can only be used for surface
inspection. Penetration depth is usually defined as the
depth where 64% of the incident light is absorbed. (For
non-scattering media, the penetration depth can be calcu-
lated as 1/ma, where ma is the absorption coefficient (in cm-1 ). For highly scattering media, the penetration depth
can be estimated as 1= ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 3maðm0s þ maÞ
p , where m0s is the
reduced scattering coefficient (in cm-1).) The absorption
properties of biological tissue are wavelength dependent.
Studies have indicated that NIR light (700-1500 nm)
experiences minimal absorption in tissue. This region of
optical wavelengths provides a “window” for optical light
to probe into deep tissues. Optical imaging is a promising
technique that utilizes NIR to acquire images of the inter-
nal human body.
