Photosensor with multiple light sources

• US 5,772,587 A
• Filed: 11/29/1995
• Issued: 06/30/1998
• Est. Priority Date: 12/16/1993
• Status: Expired due to Term

• Current Assignee: Board of Trustees of The University of Illinois, ISS
• Original Assignee: Board of Trustees of The University of Illinois, ISS
• Inventors: Fantini, Sergio, Gratton, Enrico, Franceschini, Maria Angela, Barbieri, Beniamino, Mantulin, William
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US08/564,439
• Time in Patent Office: 944 Days
• Field of Search: 126/633-4, 126/664-6, 356/41
• US Class Current: 600/310
• CPC Class Codes: A61B 2562/0233 Special features of optical sensors or probes classified in A61B5/00
• CPC Class Codes: A61B 2562/046 in a matrix array
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/6824 Arm or wrist
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427
• CPC Class Codes: G01N 21/49 within a body or fluid

Abstract

The quantitative determination of various materials in highly scattering media such as living tissue may be determined in an external, photometric manner by the use of a plurality of light sources positioned at differing distances from a sensor. The light from said sources is amplitude modulated, and, in accordance with conventional frequency domain fluorometry or phosphorimetry techniques, the gain of the sensor is modulated at a frequency different from the frequency of the light modulation. Data may be acquired from each of the light sources at differing distances at a frequency which is the difference between the two frequencies described above. From these sets of data from each individual light source, curves may be constructed, and the slopes used to quantitatively determine the amount of certain materials present, for example glucose, oxyhemoglobin and deoxyhemoglobin in living tissue.

Claims

1. The method of determining parameters of a highly scattering medium, which comprises:

passing a group of modulated beams of light of the same wavelength through differing distances of said medium, said beams of light being modulated at a first frequency;

detecting said beams of light which traverse said medium using at least one light sensor modulated at a second frequency that is different from said first frequency but phase-coherent with said modulated light;

deriving at a third frequency resultant signals from said light beams detected at said second frequency, said third frequency being the difference between said first frequency and said second frequency;

determining data comprising at least two of phase shift, DC and AC components of said light; and

determining a parameter of said medium from said data.

2. The method of claim 1 in which the parameter determined comprises at least one of an absorption coefficient and a scattering coefficient of said medium.

3. The method of claim 1 comprising the step of determining slopes of at least two of said phase shift, DC, and AC components detected from the resultant signals derived from said light beams of differing distances, and determining at least one of an absorption coefficient and a scattering coefficient of said medium from said slopes.

4. The method of claim 3 comprising the step of determining an absolute concentration in said medium of at least one form of hemoglobin from said absorption coefficient.

5. The method of claim 3 comprising the step of determining a relative concentration of glucose in said medium from said scattering coefficient.

6. The method of claim 1, performed with at least two groups of light beams, each group comprising light of a wavelength which is different from the wavelength of the other group.

7. The method of claim 6 in which each of said wavelengths is at an absorption frequency of one different material of pair of materials in said scattering medium, each of said wavelengths being substantially transparent to the other of said pair of materials.

8. The method of claim 1 in which said highly scattering medium is living tissue.

9. The method of claim 1 in which the wavelength of said light is about 650 mn to about 1000 nm, the intensity of light from said light sources being amplitude modulated at said first frequency of 10-500 mhz, and the second frequency differs from said first frequency by about 10 hz-100 khz.

10. The method of claim 1 which is free of a step of comparing said beams of light which traverse said medium with beams of said light as emitted prior to traversing said medium.

11. The method of sample analysis which comprises:

sequentially illuminating and shutting off a plurality of light sources which are spaced at different distances from a light sensor to provide differing pathlengths through said sample while modulating the intensity of light from said light sources at a first frequency, while also passing said modulated light through a highly scattering sample for testing and then to said sensor;

providing a signal coherent with said modulated light at a second frequency to said light sensor;

modulating the gain of, or multiplying the output of, said light sensor by said coherent signal, said second frequency being different from said first frequency; and

deriving resultant signals from the sensor while sequentially receiving said modulated light from said plurality of light sources, said resultant signals being at a frequency of the difference between the first and second frequencies; and

determining at least two of phase shift, DC and AC components of said modulated light as sensed by the sensor, compared with the modulated light as originally emitted by the light sources.

12. The method of claim 11 in which each of said plurality of light sources is sequentially illuminated for a length of time that is an exact multiple of a wave period having a frequency which comprises the difference between said first and second frequencies.

13. The method of claim 12 in which information sensed by said light sensor from each light source is summed and averaged from about 8 to about 800 times to obtain an intensified average of the photometric information received from each light source.

14. The method of claim 12 in which a first group of said light sources emits light at a first wavelength and a second group of said light sources emits light at a second, different wavelength.

15. The method of determining an absolute concentration of at least one form of hemoglobin in a highly scattering medium, which comprises:

passing a group of modulated beams of light through differing distances of said medium, said beams of light being modulated at a first frequency;

detecting said beams of light which traverse said medium using at least one light sensor modulated at a second frequency that is different from said first frequency but phase-coherent with said modulated light;

deriving at a third frequency resultant signals from said light beam detected at said second frequency, said third frequency being the difference between said first frequency and said second frequency;

determining data comprising at least two of phase shift, DC, and AC components of said light;

determining the slopes of said at least two of the phase-shift, DC and AC components computed from the resultant signals;

determining the absorption coefficient of said medium from said slopes; and

determining said concentration of at least one form of hemoglobin from said absorption coefficient.

16. The method of claim 15 which is performed with at least two groups of light beams, each group comprising light of a wavelength which is different from the wavelength of the other group, one of said wavelength being at an absorption frequency of oxyhemoglobin, and the other of said wavelengths being at an absorption frequency of deoxyhemoglobin, each of said wavelengths being substantially transparent to the other of said oxyhemoglobin and deoxyhemoglobin.

17. The method of claim 16 in which said highly scattering medium is living tissue.

18. The method of determining the relative concentration of a material in a highly scattering medium, which comprises:

passing a group of modulated beams of light through differing distances of said medium, said beams of light being modulated at a first frequency;

detecting said beams of light which traverse said medium using a light sensor modulated at a second frequency that is different from first frequency but phase-coherent with said modulated light;

deriving at a third frequency resultant signals from said light beams detected at said second frequency, said third frequency being the difference between said first frequency and said second frequency;

determining data comprising at least two of phase shift, DC, and AC components of said light;

determining the slopes at least two of said phase shift, DC and AC components detected from the resultant signals;

determining the scattering coefficient of said medium from said slopes; and

determining the relative concentration of said medium as a function of said scattering coefficient.

19. The method of claim 18 in which said highly scattering medium is living tissue.

20. The method of claim 19 in which said material is glucose.

21. The method of claim 18 in which at least a plurality of said modulated beams of light are of the same wavelength.