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

• US 20020016536A1
• Filed: 09/14/2001
• Published: 02/07/2002
• Est. Priority Date: 03/12/1999
• Status: Active Grant

• Current Assignee: Cas Medical Systems Incorporated (Edwards Lifesciences Corporation)
• Original Assignee: Cas Medical Systems Incorporated (Edwards Lifesciences Corporation)
• Inventors: Benni, Paul
• Granted Patent: US 7,047,054 B2
• Time in Patent Office: Days
• 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 non-invasive monitoring of blood oxygenation levels in a subject'"'"'s body, said assembly comprising:

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

b) a plurality of light sources which are operatively associated with 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 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 having a light sensitive surface and being operative to measure light intensity values derived from light emitted by said light sources and passing through the subject'"'"'s body;

d) an ambient electromagnetic interference (EMI) shield surrounding said photodiode assembly, said EMI shield including a 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

e) a 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 body, said spacer being operative to further attenuate EMI from influencing operation of said NIRS monitoring assembly, by reducing capacitive coupling between the photodiode light sensitive surface and the subject'"'"'s body.

2. The assembly of claim 1 wherein said electrically conductive optically transparent material is a conductive wire mesh screen.

3. The assembly of claim 1 wherein said electrically conductive optically transparent material is a thin film or coating.

4. The assembly of claim 3 whereby said electrically conductive optically transparent thin film or coating is applied onto the photodiode light sensitive surface.

5. The assembly of claim 3 whereby said electrically conductive optically transparent thin film or coating is applied onto the side of said optical spacer abutting the photodiode light sensitive surface.

6. A near infrared spectrophotometric (NIRS) monitoring assembly for non-invasive 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 subjects body;

b) a plurality of light sources which are operatively associated with said housing, each of said light sources being operative to emit near infrared light signals of different wavelengths, 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 operable to measure light intensity values emanating from light emitted by said light sources and passing through the subject'"'"'s body; and

d) a light combining assembly, allowing for said different wavelength light sources to transmit light into a single core output fiber optic, whereas said single core output fiber optic transmits light signals through said housing window, with said light combining apparatus having the following components;

i) an input fiber optic bundle of a given diameter, consisting of a plurality of single core fiber optics whereby each individual single core fiber optic is operably connected to each different light source; and

ii) a focusing means to direct light from said larger diameter input fiber optic bundle to said smaller diameter output fiber optic.

7. The assembly of claim 6 wherein said single core output fiber optic is a multimode type, with a diameter less than said input fiber bundle thereby resulting in reduced weight and increased flexibility when compared to said input fiber bundle.

8. The assembly of claim 6 wherein said focusing means is a pair of lenses.

9. The assembly of claim 8 wherein said lenses are ball lenses that have different optical characteristics, wherein the second ball lens is abutting to and is optically aligned with said output fiber optic and wherein said second ball lens has a higher refractive index compared to the first ball lens so as to focus light onto said smaller diameter output fiber optic, with said first ball lens being optically aligned with said second ball lens as well as optically aligned with said input fiber bundle on a common axis.

10. The assembly of claim 6 wherein said input fiber optic bundle consists of individual multimode type fiber optics.

11. A near infrared spectrophotometric (NIRS) monitoring assembly for non-invasive 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 dislodgement 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.

12. The assembly of claim 11, 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.

14. The assembly of claim 13 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.

15. The assembly of claim 14 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.

16. The assembly of claim 15 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.

18. The assembly of claim 17 further comprising an ambient electromagnetic interference (EMI) shield surrounding said photodiode assembly, said EMI shield including a 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.

19. The assembly of claim 18 further comprising a 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.

20. The assembly of claim 17 further comprising a laser safety interlock system designed to disable laser operation in case of assembly dislodgement from the patient'"'"'s head, said safety interlock 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.

13. A near infrared spectrophotometric (NIRS) monitoring assembly for non-invasive 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.

17. A near infrared spectrophotometric (NIRS) monitoring assembly for non-invasive 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 leg which traverses the subject'"'"'s forehead and a second leg which is normal to said first leg and passes over the crown of the subject'"'"'s head when the housing is attached to the subject'"'"'s head;

b) a plurality of light sources which are operatively associated with said first leg 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 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 operatively associated with said second leg of said housing; and

e) and electrical signal-transmitting cable assembly connected to said photodiode assembly for transmitting electrical signals therefrom, said cable being operatively associated with said second leg of said housing, whereby both said fiber optic guide assembly and said cable pass over the subject'"'"'s crown when said housing is attached to the subject'"'"'s head.