Photosensor with multiple light sources

A sensor instrument for use in measuring parameters of body tissue, which comprises:

• a sensor head having a face for contact with the skin of a patient;
• a sensor carried on said head for detecting light striking a portion of said face;
• light sources positioned to pass said light to said face through said tissue, said light sources being of differing distances from said light sensor, a first group of said light sources of differing distances emitting light of one frequency and a second group of said light sources of differing distances emitting light of another frequency;
• a timing circuit for causing sequential illumination and shutting off of said light sources;
• a circuit for modulating an intensity of said light sources to provide amplitude modulated light signals at a first frequency;
• circuitry for providing a second signal coherent with said amplitude modulated light signals, at a second frequency, to the light sensor;
• circuitry for modulating the gain of, or for multiplying the output of, the light sensor by said second signal, said second frequency being different from said first frequency:
• electronics for deriving a resultant signal from said light sensor while receiving said modulated light signals, said resultant signal being at a frequency of the difference between the first and second frequencies;
• and
• a processor for receiving said resultant signal and determining at least two of phase shift, DC, and AC components of said light signals which pass sequentially from said light sources through the tissue to said light sensor, said processor also being for computing the slopes of said at least two of said phase shift, DC, and AC components provided by signals from said plurality of light sources of differing distances.

A sensor instrument for use in photometrically determining parameters of a highly scattering medium, which comprises:

• a sensor head having a face for contact with said medium;
• a sensor carried on said head for detecting light striking a portion of said face;
• at least one group of light sources positioned to pass said light to said face through said medium, said light sources being of differing distances from said light sensor;
• and wherein all sources in each of said at least one group of sources emit light of substantially the same wavelength;
• a timing circuit for causing sequential illumination and shutting off of said light sources;
• a circuit for modulating an intensity of said illuminated light sources to provide amplitude modulated light signals at a first frequency;
• electronics for providing frequency domain spectroscopy electronic processing of signals received by said sensor to provide a resultant signal which is a function of the modulated light signals received by said sensor;
• and
• a processor for receiving said resultant signal and determining at least two of phase shift, DC, and AC components of said light signals which pass sequentially from said light sources through said highly scattering media to said light sensor.

A sensor instrument for use in determining at least one of the scattering coefficient and absorption coefficient of a highly scattering medium, which comprises:

• a sensor head having a face for contact with the medium;
• a sensor carried on said head for detecting light striking a portion of said face;
• at least one group of light sources positioned to pass light to said face through said medium, said light sources being of differing distances from said light sensor and wherein all sources in each of said at lest one group of sources emit light of substantially the same wavelength;
• a timing circuit for causing sequential illumination and shutting off of said light sources;
• and electronics to compute at least two of phase shift, DC, and AC components of light from said light sources which has passed sequentially from said light sources through the medium to said light sensor, and to compute at least one of the scattering and absorption coefficients for said light sources.

A sensor instrument for use in measuring parameters of a highly scattering medium, which comprises:

• a sensor head having a face for contact with the medium;
• a sensor carried on said head for detecting light striking a portion of said face:
• at least one group of light sources positioned to pass said light to said face through said medium, said light sources being of differing distances from said light sensor, and wherein all sources in each of said at least one group of sources emit light of substantially the same wavelength;
• a timing circuit for causing sequential illumination and shutting off of said light sources;
• a circuit for modulating an intensity of said light sources to provide amplitude modulated light signals at a first frequency;
• circuitry for providing a second signal coherent with said amplitude modulated light signals, at a second frequency, to the light sensor;
• circuitry for modulating the gain of, or for multiplying the output of, said light sensor by said second signal, said second frequency being different from said first frequency;
• and
• electronics for deriving a resultant signal from said light sensor while receiving said modulated light signals, said resultant signal being at a frequency of the difference between the first and second frequencies, and electronics to compute at least two of phase shift, DC, and AC components of said resultant signals carrying information about the medium which is sequentially traversed through by the light signals emitted by said light sources, said electronics also being for computing at least one of a scattering coefficient and an absorption coefficient from said at least two of phase shift, DC, and AC components.