Examination of biological tissue using frequency domain spectroscopy

A phase modulation spectroscopic system for examination of biological tissue of a subject, the scattering and absorptive properties of the examined tissue being determined by photons migrating between an optical input port and an optical detection port of said system, said system comprising:

• an optical input port located at a first location to introduce light to biological tissue;
• an optical detection port located at a second location at the tissue spaced apart from said input port;
• an oscillator, connected to a driver, that generates a carrier waveform of a selected frequency compatible with time delay of photon migration from said input port to said detection port;
• a light source, connected to said input port and connected to receive from said oscillator or said driver said carrier waveform, said light source generates over time optical radiation of a selected wavelength that is intensity modulated at said frequency and introduces said optical radiation to the tissue at said input port;
• an optical detector, connected to said detection port, said detector detects over time scattered photons of the introduced radiation that has migrated in said tissue of the subject between said input and detection ports and produces a detector signal;
• a phase splitter connected to receive said carrier waveform from said oscillator or said driver and produce first and second reference phase signals of predefined substantially different phases;
• first and second double balanced mixers connected to receive over time from said phase splitter said first and second reference phase signals, respectively, and connected to receive from said detector said detector signal and produce therefrom a real output signal and an imaginary output signal, respectively;
• and
• a signal processor connected to said double balanced mixers, said processor receives said real output signal and said imaginary output signal and determines therefrom a selected characteristic related to scattering or absorptive properties of said biological tissue.