ABSTRACT
Absorption of light can also attenuate the signal, both in the visible wavelengths as well as in the NIR when light is transmitted through thick tissues. In the NIR regime, the absorption coe–cient is about two orders of magnitude lower than its scattering counterpart whereas in the visible regime the two are more comparable (see Figure 20.1). Hence, light can travel through several centimeters of tissue and still have enough intensity to be detected; thus, its spectrum (which is altered by absorption and scatter) can be used for breast imaging. ™e absorption coe–cient, μa, represents the inverse of the mean free distance for exponential attenuation, estimated in the absence of scatter. Several tissue molecular components contribute signiœcantly to light absorption in the NIR region including oxyand deoxy-hemoglobin, water, and lipids. At each wavelength these individual chromophores contribute linearly to the total
20.3 NIR Systems for Whole Breast Tomography ...................................................................... 256 NIR for Diagnostic and ™erapeutic Breast Monitoring
20.7 Conclusions.............................................................................................................................. 264 References ............................................................................................................................................ 264
absorption coe–cient, weighted by their respective concentrations and molar extinction coe–cients.
