Sources of absorption and scattering contrast for near-infrared optical mammography

Rationale and Objectives. Near-infrared (NIR) diffuse optical spectroscopy and imaging may enhance existing technologies for breast cancer screening, diagnosis, and treatment, NIR techniques are based on sensitive, quantitati ve measurements of functional contrast between healthy and diseased tissue. In this study, the authors quantified the origins of this contrast in heal thy breasts. Materials and Methods. A seven-wavelength frequency-domain photon migration probe was used to perform noninvasive NIR measurements in the breasts of 2 8 healthy women, both pre- and postmenopausal, aged 18-64 years. A diffusiv e model of light transport quantified oxygenated and deoxygenated hemoglobi n, water, and lipid by their absorption signatures. Changes in the measured light-scattering spectra were quantified by means of a "scatter power" par ameter. Results. Substantial quantitative differences were observed in both absorpt ion and scattering spectra of breast as a function of subject age. These ph ysiologic changes were consistent with long-term hormone-dependent transfor mations that occur in breast. Instrument response was not adversely affecte d by subject age or menopausal status. Conclusion. These measurements provide new insight into endogenous optical absorption and scattering contrast mechanisms and have important implicatio ns for the development of optical mammography. NIR spectroscopy yields quan titative functional information that cannot be obtained with other noninvas ive radiologic techniques.