Time-domain broadband near infrared spectroscopy of the female breast: a focused review from basic principles to future perspectives

A review of near infrared (NIR) spectroscopy of the female breast performed using time domain broadband systems is presented, summarising the key studies performed at Politecnico di Milano. The time domain approach, based on pulsed tunable lasers and single-photon detection, makes it possible to uncouple absorption from scattering contributions and to derive tissue optical properties in vivo non-invasively. The basic tissue absorbers in the 600-1100 nm range are discussed, together with the interpretation of the scattering spectra. Inter- and intra-subject variations in breast optical properties are addressed based on in vivo measurements on different women and on the same subject as a function of the menstrual cycle phase and of the measurement geometry. Results demonstrate that a specific breast type can be identified for each woman, ultimately related to the water, lipid and collagen content and to the scattering properties. As an example of the application of spectroscopy-derived information, we discuss the non-invasive optical detection of breast density as an important risk factor for breast cancer, envisaging an attractive contribution of NIR spectroscopy to the fight against breast cancer on both a medical diagnostics and research level.