Breast monitoring by time-resolved diffuse optical imaging

The aim of this chapter is to provide an overview on the applications of time-domain diffuse optics to the assessment of breast physiology and pathology. A number of different implementations to optical mammography have been evaluated ranging from lesion detection and characterisation using endogenous or exogenous contrast, to breast density assessment as strong cancer risk factor, and to monitoring during neoadjuvant chemotherapy. The time-domain approach is the common factor of all these applications, which permits to uncouple absorption from scattering contributions and to derive tissue optical properties in vivo. The Time-Correlated Single-Photon Counting (TCSPC) is the measurement technique of choice to acquire fast and weak optical signals at the picosecond time scale. For what concerns the time-resolved optical mammography with endogenous contrast, results obtained within the European project Optimamm are reported. The aim of the clinical trial was to understand the detection breast tumor capability of the developed multi-wavelength time-domain scanning systems operating in transmittance geometry on compressed breast. Results of the Berlin and Milan groups, have shown a similar detection rates for malignant breast lesions, with a high contrast at short wavelengths due to the presence of high blood volume. Regarding the optical mammography with exogenous contrast agent, a time domain optical mammography with Indocyanine Green (ICG) including also fluorescence measurements is presented. Results have shown a good sensitivity of the fluorescent optical mammography in detecting tumor. A good discrimination between healthy and tumor tissue was achieved. Concerning the optical mammography for therapy monitoring, a time-domain optical tomography system and very preliminary results were presented, showing good results on monitoring tumor response to chemotherapy using this approach. The other application presented in this chapter is based on the use of a multi-wavelength time-domain optical mammography for the assessment of breast density since it is a recognized independent risk factor for the development of breast cancer. A good correlation between optical data and mammographic breast density (provided by X-ray mammograms) was obtained, showing an increase of water and collagen in subjects with high breast density as expected from the physiological point of view and demonstrating the capability of the time-domain system to identify subjects with a high risk to develop breast cancer.