Sensor, apparatus and method for non-invasively monitoring blood characteristics of a subject

• US 8,694,067 B2
• Filed: 02/15/2011
• Issued: 04/08/2014
• Est. Priority Date: 02/15/2011
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Huiku, Matti
• Primary Examiner(s): Winakur, Eric
• Assistant Examiner(s): Fardanesh, Marjan
• Application Number:
  US13/027,544
• Publication Number:
  US 20120209095A1
• Time in Patent Office: 1,148 Days
• Field of Search: 600309-344
• US Class Current: 600/322
• CPC Class Codes: A61B 5/14551 for measuring blood gases

Abstract

A sensor, apparatus and method for non-invasively monitoring blood characteristics of a subject are disclosed. The sensor comprises an emitter unit configured to emit radiation through the tissue of the subject at a plurality of measurement wavelengths and a detector unit that comprises photo detectors. To achieve a simple sensor assembly, the photo detectors are together adapted to receive the radiation at the plurality of wavelengths and to produce in-vivo measurement signals corresponding to the plurality of measurement wavelengths, the in-vivo measurement signals being indicative of absorption caused by blood of the subject. Furthermore, the photo detectors are mounted so that optical paths from the emitter unit to the photo detectors are different, and the plurality of wavelengths are divided between the photo detectors so that two spectrally adjacent photo detectors have at least one common wavelength. The apparatus comprises a path normalization unit configured to normalize the in-vivo measurement signals to an optical path specific to one of the photo detectors.

Claims

1. A sensor for determining blood characteristics of a subject, the sensor being attachable to the subject and comprising:

an emitter unit configured to emit radiation through the tissue of the subject at a plurality of measurement wavelengths;

a detector unit comprising at least a first photo detector and at least a second photo detector that are together adapted to receive the radiation at the plurality of wavelengths and to produce in-vivo measurement signals corresponding to the plurality of measurement wavelengths, the in-vivo measurement signals being indicative of absorption caused by blood of the subject, wherein the first and second photo detectors are mounted so that the optical paths from the emitter unit to the first photo detectors is different from the optical path from the emitter unit to the second photo detector and wherein the first photo detector detects a first subset of the plurality of wavelengths and the second photo detector detects a second subset of the plurality of wavelengths such that the plurality of wavelengths are divided between the first and second photo detectors, wherein the first and second subsets include at least one common wavelength; and

a path normalization unit configured to normalize the in-vivo measurement signals to one of the optical paths specific to either the first or second photo detector.

2. The sensor according to claim 1, wherein the photo detectors are mounted side by side in the sensor.

3. The sensor according to claim 2, wherein the photo detectors are arranged in an array configuration.

4. The sensor according to claim 2, wherein the photo detectors are arranged in a matrix configuration.

5. The sensor according to claim 1, wherein the first and second photo detectors have an overlapping spectral responsivity range from approximately 800 nm to approximately 1000 nm, and wherein the at least one common wavelength comprises one wavelength located within the overlapping spectral responsivity range.

6. The sensor according to claim 1, wherein the sensor comprises a silicon photodiode and an InGaAs photodiode.

7. An apparatus for determining blood characteristics of a subject, the apparatus comprising:

an interface unit configured to receive in-vivo measurement signals from at least a first photo detector and a second photo detector, wherein the in-vivo measurement signals are indicative of absorption caused by blood of a subject and wherein the first photo detector is adapted to receive optical signals from a first optical path specific to the first detector and the second photo detector is adapted to receive optical signals from a second optical path specific to the second detector; and

a path normalization unit configured to normalize the in-vivo measurement signals received from the first and second photo detectors to the optical path specific to either one of the first and second photo detectors based on a measurement at a common wavelength.

8. The apparatus according to claim 7, wherein the path normalization unit is configured to

derive modulation signals from the in-vivo measurement signals, wherein each modulation signal represents a ratio of AC and DC signal components at a specific wavelength;

determine a ratio of two modulation signals obtained at the common wavelength detected by both the first and second photo detectors;

select a set of modulation signals; and

multiply the selected modulation signals by the ratio.

9. The apparatus according to claim 7, further comprising a sensor unit attachable to the subject, the sensor unit comprising:

an emitter unit configured to emit radiation through the tissue of the subject at a plurality of measurement wavelengths; and

a detector unit comprising the first and second photo detectors, wherein the photo detectors are together adapted to receive the radiation at the plurality of wavelengths and to produce the in-vivo measurement signals, wherein the first and second photo detectors are mounted so that the first and second optical paths from the emitter unit to the photo detectors are different and wherein the plurality of wavelengths are divided between the photo detectors so that two spectrally adjacent photo detectors have at least one common wavelength.

10. A method for monitoring blood characteristics of a subject, the method comprising:

mounting multiple photo detectors in a sensor arrangement so that optical paths from an emitter unit to the photo detectors are different;

providing the emitter unit with a plurality of measurement wavelengths;

acquiring in-vivo measurement signals at the plurality of measurement wavelengths, the in-vivo measurement signals being indicative of absorption caused by blood of a subject;

determining a path normalization coefficient based on different in-vivo measurement signals obtained respectively from different photo detectors at a wavelength common to the different photo detectors;

applying the path normalization coefficient to selected in-vivo measurement signals, thereby to obtain path normalized in-vivo measurement signals; and

employing the path normalized in-vivo measurement signals for determining blood characteristics of the subject.

11. The method according to claim 10, wherein

the determining includes deriving in-vivo modulation signals from the in-vivo measurement signals, wherein each in-vivo modulation signal represents a ratio of AC and DC signal components at a specific wavelength;

the applying includes applying the path normalization coefficient to selected in-vivo modulation signals, thereby to obtain path normalized in-vivo modulation signals; and

the employing includes employing the path normalized in-vivo modulation signals for determining the blood characteristics.