Laser diode optical transducer assembly for non-invasive spectrophotometric blood oxygenation monitoring

• US 7,047,054 B2
• Filed: 09/14/2001
• Issued: 05/16/2006
• Est. Priority Date: 03/12/1999
• Status: Expired due to Fees

• Current Assignee: Cas Medical Systems Incorporated (Edwards Lifesciences Corporation)
• Original Assignee: Cas Medical Systems Incorporated (Edwards Lifesciences Corporation)
• Inventors: Benni, Paul
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US09/951,221
• Publication Number:
  US 20020016536A1
• Time in Patent Office: 1,705 Days
• Field of Search: 600322-328, 600/344, 600/310
• US Class Current: 600/323
• CPC Class Codes: A61B 2560/0242 adapted to measure environmental factors, e.g. temperature, pollution
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/14553 specially adapted for cerebral tissue
• CPC Class Codes: A61B 5/6814 Head

Abstract

A non-invasive near infrared spectrophotometric monitoring transducer assembly includes a housing member, which is adhered directly on a patient'"'"'s skin. The housing member contains a prism coupled to a flexible and lightweight single core optical light guide, which provides a means of transferring narrow spectral bandwidth light from multiple distant laser diodes of different wavelengths by use of a multi-fiber optic light combining assembly. Different wavelengths are needed to monitor the level of blood oxygenation in the patient. The assembly also contains a planar light guide mounted on the prism located in the housing member, which light guide contacts the patient'"'"'s skin when the housing member is adhered to the patient'"'"'s skin. The light guide controls the spacing between the prism and the patient'"'"'s skin, and therefore controls the intensity of the area on the patient'"'"'s skin which is illuminated by the laser light. The housing member contains a photodiode assembly, which detects the infrared light at a second location on the skin to determine light absorption. The photodiode assembly is preferably shielded from ambient electromagnetic interference (EMI) by an optically transparent EMI attenuating window. This rigid window placed over the photodiode also provides a planar interface between the assembly and the skin, improving optical coupling and stability as well as reducing the capacitive coupling between skin and the photodiode resulting in further EMI attenuation. The housing may be associated with a disposable sterile hydrogel coated adhesive envelope, or pad, which when applied to the patient'"'"'s skin will adhere the housing to the patient'"'"'s skin. The transducer assembly will thus be reusable, and skin-contacting part of the device, i.e., the envelope or pad can be discarded after a single use. The assembly also includes a laser safety interlock means, which is operable to turn off the laser light output in the event that the assembly accidentally becomes detached from the patient'"'"'s skin.

Claims

1. A near infrared spectrophotometric (NIRS) monitoring assembly for noninvasive monitoring of blood oxygenation levels in a subject'"'"'s body, said assembly comprising:

a) at least one flexible housing having a window and which can be attached directly to a subject'"'"'s body;

b) a plurality of laser light sources which are operatively associated with said housing, each of said light sources being operative to emit a near infrared light signal of a different wavelength, which light signals are transmitted through said housing window;

c) a photodiode assembly which can be attached directly to the subject'"'"'s body and which is operably connected to said light sources, said photodiode assembly being operative to measure light intensity values emanating from light emitted by said light sources and passing through the subject'"'"'s body; and

d) a laser safety interlock system designed to disable laser operation in case of assembly dislodgment from the patient'"'"'s body, said safety interlock comprising;

I) means for monitoring ambient light and emitted laser light; and

II) means for processing signals received by said photodiode assembly so as to determine secure assembly attachment to the subject'"'"'s body;

i) by monitoring ambient light conditions and disabling laser operation when ambient light levels are greater than a predetermined level;

ii) by monitoring laser output and disabling laser operation when laser output is outside of a predetermined range; and

iii) by monitoring changes in detected laser output over a predetermined measuring period and disabling laser operation if changes in laser output are above or below predetermined levels during a predetermined measuring period.

2. The assembly of claim 1, wherein said laser safety interlock system includes a laser start up sequence upon initial attachment of said assembly to the subject'"'"'s body to determine secure assembly attachment, wherein the ambient light level is monitored and verified to be below a predetermined level prior to allowing laser operation to begin.

3. A near infrared spectrophotometric (NIRS) monitoring assembly for noninvasive monitoring of blood oxygenation levels in a subject'"'"'s body, said assembly comprising:

a) at least one flexible housing having a window which housing can be attached directly to a subject'"'"'s body;

b) a plurality of light sources which are operably associated with said housing, each of said light sources being operable to emit a near infrared light signal of a different wavelength, which light signals are transmitted through said housing window;

c) a photodiode assembly which can be attached directly to the subject'"'"'s body and which is operatively connected to said light sources, said photodiode assembly being operative to measure light intensity values emanating from light emitted by said light sources and passing through the subject'"'"'s body; and

d) a processor which controls actuation of said light sources and which processes light intensity signals from said photodiode assembly; and

e) a connector housing assembly interposed between said processor and said light sources and photodiode assembly, said connector housing assembly including light source power driver controls connected to said processor and connected to said light sources, and an encoding calibration mechanism connected to said processor for supplying essential NIRS operating calibrating information to said processor whereby the following information is encoded;

i) light sources-to-photodiode assembly separation distance;

ii) light source wavelengths; and

iii) coefficients relating to change in light source wavelengths over temperature changes.

4. The assembly of claim 3 wherein coefficients indicating the relationship of laser diode automatic power control feedback, monitor current, and corresponding laser output power output are encoded in said calibration mechanism.

5. The assembly of claim 4 further comprising additional encoded coefficients in said calibration mechanism which indicate types of NIRS monitoring assemblies which are specifically intended to be used on different particular types of biological tissue, on different particular subject body parts, or on particular subject species.

6. The assembly of claim 5 wherein the calibration parameters are encoded by the use of encoding devices selected from the group consisting of:

resistors of predetermined values;

programmable read only memory devices;

bar codes; and

combinations thereof.

7. A near infrared spectrophotometric (NIRS) monitoring assembly for noninvasive monitoring of blood oxygenation levels in a subject'"'"'s brain, said assembly comprising:

a) a flexible housing which can be attached directly to a subject'"'"'s head, said housing having a first part which traverses the subject'"'"'s forehead;

b) a plurality of light sources which are operatively associated with said first part of said housing, each of said light sources being operative to emit near infrared light signals of different wavelengths, which light signals are transmitted through a window in said housing;

c) a photodiode assembly which is operatively associated with said first part of said housing and with said light sources, said photodiode assembly having a light sensitive surface and being operative to measure light intensity values emanating from light emitted by said light sources and passing through the subject'"'"'s brain;

d) a fiber optic guide assembly connected to said light sources;

e) an electrical signal-transmitting cable assembly connected to said photodiode assembly for transmitting electrical signals therefrom, said fiber optic guide assembly and said electrical signal-transmitting cable assembly being oriented relative to said housing so that both said fiber optic guide assembly and said cable assembly pass over the subject'"'"'s crown when said housing is attached to the subject'"'"'s forehead;

f) an ambient electromagnetic interference (EMI) shield surrounding said photodiode assembly, said EMI shield including an electrically conductive optically transparent material electrically interfaced to an electrically conductive capsule which covers all surfaces of said photodiode assembly which are not covered by said electrically conductive optically transparent material, said electrically conductive optically transparent material and said capsule allowing measurement of light intensity values emitted by said light sources while preventing ambient EMI from influencing operation of said NIRS monitoring assembly; and

g) a transparent rigid optical spacer of predetermined thickness, placed over said electrically conductive optically transparent material, interposed between said photodiode assembly and a surface of the NIRS monitoring assembly that abuts the subject'"'"'s skin when the assembly is attached to the subject'"'"'s head, said spacer being operative to further attenuate EMI from influencing operation of said NIRS monitoring assembly, by reducing the capacitive coupling between the photodiode light sensitive surface and the subject'"'"'s head.

8. A near infrared spectrophotometric (NIRS) monitoring assembly for noninvasive monitoring of blood oxygenation levels in a subject'"'"'s brain, said assembly comprising:

a) a flexible housing which can be attached directly to a subject'"'"'s head, said housing having a first part which traverses the subject'"'"'s forehead;

b) a plurality of light sources which are operatively associated with said first leg part of said housing, each of said light sources being operative to emit near infrared light signals of different wavelengths, which light signals are transmitted through a window in said housing;

c) a photodiode assembly which is operatively associated with said first leg part of said housing and with said light sources, said photodiode assembly having a light sensitive surface and being operative to measure light intensity values emanating from light emitted by said light sources and passing through the subject'"'"'s brain;

d) a fiber optic guide assembly connected to said light sources; and

e) an electrical signal-transmitting cable assembly connected to said photodiode assembly for transmitting electrical signals therefrom, said fiber optic guide assembly and said electrical signal-transmitting cable assembly being oriented relative to said housing so that both said fiber optic guide assembly and said cable assembly pass over the subject'"'"'s crown when said housing is attached to the subject'"'"'s forehead; and

f) a laser safety interlock system designed to disable laser operation in case of assembly dislodgment from the patient'"'"'s head, said safety interlock system comprising means for monitoring;

I) ambient light;

II) emitted laser light;

III) output by said photodiode assembly; and

IV) processing signals received by said photodiode assembly;

so as to determine secure assembly attachment to the subject'"'"'s head and

i) disabling laser operation when ambient light levels are greater than a predetermined level;

ii) disabling laser operation when laser output is outside of a predetermined range; and

iii) disabling laser operation if changes in laser output are above or below predetermined levels during a predetermined measuring period.