1. A spectrophotometer for biological tissue examination, comprising: a support structure adapted to be mounted on a subject including an optical input port located at a first location to introduce light to biological tissue of the subject; an optical detection port located at a second location on said support structure spaced apart from said input port; and a barrier constructed and positioned to absorb photons directly propagating from said input port to said detection port; an oscillator, including oscillator electronics, that generates a carrier waveform of a selected frequency comparable to an average migration time of photons scattered in tissue on paths from said optical input port to said optical detection port, said frequency being above 10 MHz; a light source mounted on said support structure and connected to and receiving said carrier waveform from said oscillator, said light source generates light of a selected wavelength that is intensity modulated at said frequency and is introduced to the tissue of the subject at said input port; a photodiode detector mounted on said support structure and connected to said detection port, said photodiode detector detects scattered light of said wavelength that has migrated in examined tissue of the subject between said input and detection ports; a phase detector, including phase detector electronics, connected to receive signals from said oscillator and said diode detector, said phase detector measures a phase shift between said introduced light and said detected light that has migrated in the examined tissue over photon migration paths from said input port to said detection port; and a processor connected to receive said phase shift from said phase detector, said processor determines, based on said measured phase shift, a physiological property of the examined tissue dependent on tissue scattering and absorptive properties.