Device for and method of carrying out optical measurements in turbid media

A method of measuring biological tissue by irradiating the tissue with light from at least one light source comprising the following steps:

• a) controlling the at least one light source so as to generate frequency-modulated light irradiating the tissue with a substantially constant intensity but with a frequency which varies cyclically versus time in a frequency band of light frequencies;
• b) determining the amplitude and phase of intensity modulation appearing in light exiting the tissue with frequencies in a part of the frequency band, which intensity modulation in said part of the frequency band is at the same frequency as said cyclical variation;
• and
• c) determining parameters of the tissue from the amplitude and phase determined in step b.

A method of determining inhomogeneities in biological tissue by irradiating the tissue with light from a plurality of light sources comprising the following steps:

• a) controlling a first sub-group of light sources so as to generate from each, with a first substantially constant intensity, frequency-modulated light which varies in frequency versus time in accordance with a first cyclical variation in a frequency band of light frequencies, and a second sub-group of light sources so as to generate from each, with a second substantially constant intensity, frequency-modulated light which varies in frequency versus time in accordance with a second cyclical variation in the frequency band which is at the same frequency as, and in phase opposition with, said first cyclical variation;
• b) determining, in a position, an amplitude and a phase of a first intensity modulation of the light with light frequencies in a first part of the frequency band and determining an amplitude and a phase of a second intensity modulation of the light with light frequencies in a second part of the frequency band, which first and second intensity modulations are at the same frequency as said first and second cyclical variations;
• c) determining a position of an extremum of at least one of the first modulation and the second modulation;
• and
• d) comparing the positions found with the positions obtained from a previously executed reference measurement.