Multi-wavelength frequency domain near-infrared cerebral oximeter

• US 6,438,399 B1
• Filed: 02/16/2000
• Issued: 08/20/2002
• Est. Priority Date: 02/16/1999
• Status: Expired due to Term

• Current Assignee: Children's Hospital of Philadelphia (Children's Hospital of Philadelphia Foundation)
• Original Assignee: Children's Hospital of Philadelphia (Children's Hospital of Philadelphia Foundation)
• Inventors: Kurth, Charles D.
• Primary Examiner(s): Winakur, Eric F.
• Assistant Examiner(s): Kremer, Matthew J
• Application Number:
  US09/504,693
• Time in Patent Office: 916 Days
• Field of Search: 600/309-311, 600/322-324, 600/326-328, 600/364, 356/39-42
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14553 specially adapted for cerebral tissue

Abstract

The present invention provides a frequency domain near infrared oximeter (fdNIRS) instrument and associated method of determining the oxygenation level of tissue. The tissue is irradiated by a near infrared light source whereby the incident light passing through the tissue is detected by a light detector. Specifically, light signals of a single frequency at at least three separate wavelengths are provided from the near infrared light source. The near infrared light signals are collected with the light detector and, the phase differences between the collected near infrared light signals and a reference near infrared light signal are determined. The fdNIRS oximeter utilizes frequency domain technology to monitor phase shifts relative to a reference signal to derive SO₂ through photon transport and Beer-Lambert equations.

Claims

1. A method of determining an oxygenation level of tissue comprising:

providing light signals of a single frequency at at least three separate wavelengths from a near infrared light source to the tissue;

collecting the light signals passing through the tissue with a light detector, the collected signals defining a first, a second and a third light signal; and

determining phase differences between the collected light signals defining said first, said second and said third light signal and a reference near infrared light signal and using phase differences to calculate the oxygenation level of the tissue.

2. The method of claim 1 wherein one of the at least three separate wavelengths is less than 800 nm.

3. The method of claim 2 wherein another one of the at least three separate wavelengths is more than 800 nm.

4. A method of determining oxygenation level of tissue comprising:

providing light signals of a single frequency at three separate wavelengths from a near infrared light source to the tissue;

collecting light signals passing through the tissue with a light detector, the collected signals defining a first, a second, and a third light signal having respective wavelengths λ

1, λ

2, and λ

3;

comparing the collected light signals with a reference near infrared signal;

determining a difference in phase between the first and third collected signals θ

(λ

1−

λ

3);

determining a difference in phase between the second and third collected signals θ

(λ

2−

λ

3) to define a phase difference ratio of θ

(λ

1−

λ

3)/θ

(λ

2−

λ

3); and

deriving the oxygenation level of the tissue from the phase difference ratio.

5. The method of claim 4 wherein the first light signal has a wavelength (λ

1) of less than 800 nm.

6. The method of claim 5 wherein the second light signal has a wavelength (λ

2) of less than 800 nm and greater than that of (λ

1).

7. The method of claim 6 wherein the third light signal has a wavelength (λ

3) of greater than 800 nm.