Method and apparatus for noninvasive measurement of blood glucose by photoacoustics

• US 5,941,821 A
• Filed: 11/25/1997
• Issued: 08/24/1999
• Est. Priority Date: 11/25/1997
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Chou, Mau-Song
• Primary Examiner(s): Nasser, Robert L.
• Assistant Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US08/978,317
• Time in Patent Office: 637 Days
• Field of Search: 600/310, 600/316, 600/322, 600/473, 600/476, 374/45, 73/24.01
• US Class Current: 600/316
• CPC Class Codes: A61B 5/0095 by applying light and detecting acoustic waves, i.e. photoacoustic measurements
• 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: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids

Abstract

A method and apparatus for noninvasively measuring blood glucose levels provides an indirect, reagentless, differential, photoacoustic technique which responds to absorption in a thin surface layer. An excitation source provides electromagnetic energy which is utilized to irradiate the tissue, such as skin. The output of the radiation of the excitation source at the desired wavelength is coupled through a transmission device, such as a fiber optic bundle, which irradiates the electromagnetic energy onto the body surface. Upon irradiation, acoustic energy is generated by the absorption of the electromagnetic energy in a relatively thin layer of the sample to be measured, characterized by a heat-diffusing length. The acoustic energy is detected by the probe which includes a measuring cell, reference cell, window and differential microphone. Absorption of the light beam results in periodic heating of the tissue, at and near the tissue surface. The air in contact with the tissue surface in the measuring cell is in turn heated, and produces an acoustic emission in the measuring cell. This acoustic emission is detected with the differential microphone, one end of which is positioned in the measuring cell and the other end of which is positioned in the reference cell. A processor determines the concentration of the substance based upon the detected acoustic signal.

Claims

1. An apparatus for determining a concentration of a component in a first medium, comprising;

a source for irradiating a portion of said first medium by heat-diffusion to generate acoustic energy propagating in a second medium over a surface of said first medium in response to said irradiation;

a detector for detecting said acoustic energy and providing an acoustic signal in response to said acoustic energy, said detector comprising a differential microphone for converting said acoustic energy to said acoustic signal disposed externally of said first medium and in contact relation with said second medium for detecting said acoustic energy; and

a processor for determining the concentration of said component in response to said acoustic signal and characteristics of said component.

2. The apparatus claimed in claim 1, wherein said detector for detecting said acoustic energy and providing an acoustic signal in response to said acoustic energy, further comprises:

a first cell adapted to be disposed in contact relation with said irradiated portion of said first medium and connected to said differential microphone; and

a second cell adapted to be disposed in contact relation with said first medium, adjacent to said irradiated portion, and connected to said differential microphone,

wherein said acoustic energy is generated in said first cell due to affect of irradiation on said first medium.

3. A method for determining a concentration of a component in a first medium, comprising the steps of:

irradiating a portion of said first medium by heat-diffusion to generate acoustic energy propagating in a second medium over a surface of said first medium in response to said irradiation;

detecting said acoustic energy and providing an acoustic signal in response to said acoustic energy by converting said acoustic energy to said acoustic signal utilizing a device disposed externally of said first medium and in contact relation with said second medium for detecting said acoustic energy and differentiating said acoustic signal from background signals; and

determining the concentration of said component in response to said acoustic signal and characteristics of said component.

4. The method claimed in claim 3, wherein said step of detecting said acoustic energy and providing an acoustic signal in response to said acoustic energy, further comprises the steps of:

determining a first acoustic response in a first cell disposed in contact relation with said irradiated portion of said first medium;

determining a second acoustic response in a second cell disposed in contact relation with said first medium, adjacent to said irradiated portion; and

differentiating said first and second acoustic responses to generate said acoustic signal.

5. An apparatus for measuring a concentration of an analyte in a first medium, comprising:

means for providing electromagnetic energy at wavelengths corresponding to the absorption characteristics of said analyte to excite a portion of said first medium by heat-diffusion to generate acoustic energy propagating in a second medium in response to said excitation;

means for detecting said acoustic energy and providing an acoustic signal in response to said acoustic energy, comprising;

a differential microphone;

a first cell adapted to be disposed in contact relation with said irradiated portion of said first medium and connected to said differential microphone; and

a second cell adapted to be disposed in contact relation with said first medium, adjacent to said irradiated portion, and connected to said differential microphone,

wherein said acoustic energy is generated in said first cell due to expansion and contraction of said second medium in response to said electromagnetic energy; and

means for determining said concentration in response to said acoustic signal and absorption spectrum of said analyte.

6. The apparatus claimed in claim 5, wherein said means for determining said concentration in response to said acoustic signal and absorption spectrum of said analyte, further comprises:

means for generating a photoacoustic spectrum of said analyte.

7. A method for measuring a concentration of an analyte in a first medium, comprising the steps of:

providing electromagnetic energy at wavelengths corresponding to the absorbing characteristics of said analyte to excite a portion of said first medium by heat-diffusion to generate acoustic energy propagating in a second medium in response to said excitation;

detecting said acoustic energy and providing an acoustic signal in response to said acoustic energy, comprising the steps of;

generating a first acoustic response in a first cell disposed in contact relation with said irradiated portion of said first medium and connected to said differential microphone;

generating a second acoustic response in a second cell disposed in contact relation with said first medium, adjacent to said irradiated portion, and connected to said differential microphone; and

applying said first and second acoustic responses to a differential microphone to generate said acoustic signal; and

determining said concentration in response to said acoustic signal and absorption spectrum of said analyte.

8. An apparatus for determining a concentration of glucose in a body part, comprising;

a source for irradiating a portion of said body part by heat-diffusion to generate acoustic energy propagating in air over a surface of said body part in response to said irradiation;

a detector for detecting said acoustic energy and providing an acoustic signal in response to said acoustic energy, said detector comprising a differential microphone for converting said acoustic energy to said acoustic signal disposed externally of said body part and in contact relation with said air for detecting said acoustic energy; and

a processor for determining the concentration of said glucose in response to said acoustic signal and characteristics of said glucose.

9. The apparatus claimed in claim 8, wherein said detector for detecting said acoustic energy and providing an acoustic signal in response to said acoustic energy, further comprises:

a first cell adapted to be disposed in contact relation with said irradiated portion of said body part and connected to said differential microphone; and

a second cell adapted to be disposed in contact relation with said body part, adjacent to said irradiated portion, and connected to said differential microphone,

wherein said acoustic energy is generated in said first cell due to affect of irradiation on said body part.

10. A method for determining a concentration of glucose in a body part, comprising the steps of:

irradiating a portion of said body part by heat-diffusion to generate acoustic energy propagating in air over a surface of said body part in response to said irradiation;

detecting said acoustic energy and providing an acoustic signal in response to said acoustic energy by converting said acoustic energy to said acoustic signal utilizing a device disposed externally of said body part and in contact relation with said air for detecting said acoustic energy and differentiating said acoustic signal from background signals; and

determining the concentration of said glucose in response to said acoustic signal and characteristics of said glucose.

11. The method claimed in claim 10, wherein said step of detecting said acoustic energy and providing an acoustic signal in response to said acoustic energy, further comprises the steps of:

determining a first acoustic response in a first cell adapted to be disposed in contract relation with said irradiated portion of said body part;

determining a second acoustic response in a second cell adapted to be disposed in contact relation with said body part, adjacent to said irradiated portion; and

differentiating said first and second acoustic responses to generate said acoustic signal.