System for transcutaneous monitoring of intracranial pressure (ICP) using near infrared (NIR) telemetry

• US 20050187488A1
• Filed: 02/24/2005
• Published: 08/25/2005
• Est. Priority Date: 02/25/2004
• Status: Active Grant

• Current Assignee: Erich W. Wolf
• Original Assignee: Erich W. Wolf
• Inventors: Wolf, Erich W.
• Granted Patent: US 7,435,229 B2
• Time in Patent Office: Days
• US Class Current: 600/561
• CPC Class Codes: A61B 5/0017 transmitting optical signals transmission by light H04B10/00
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/0075 by spectroscopy, i.e. measuring spectra, e.g. Raman spectroscopy, infrared absorption spectroscopy A61B5/0071 takes precedence
• CPC Class Codes: A61B 5/0086 using infrared radiation
• CPC Class Codes: A61B 5/031 Intracranial pressure

Abstract

A system for measuring and converting to an observer intelligible form an internal physiological parameter of a medical patient. The invention allows transcutaneous telemetry of the measured information intracranial pressure via a system which includes a patient implanted sensor module and a processing and display module which is external of the patient and optically coupled to the sensor module via an external coupling module. A sensor within the implanted module transduces the measured information and a near infrared (NIR) emitter transmits this telemetry information when interrogated by the complementary external coupling module. Power for the sensor module is derived inductively through rectification of a transcutaneously-applied high-frequency alternating electromagnetic field which is generated by a power source within the external coupling module, in concept much like a conventional electrical transformer. A computer within the processing and display module calculates the parameter value from the NIR telemetry signal and represents this data either in numerical, graphical, or analog format.

Claims

1. A system for measuring and converting to an observer intelligible form an internal physiological parameter of a medical patient, comprising:

(a) a patient-implantable sensor module;

(b) a coupling module positionable externally of the patient; and

(c) a processing and display module for receiving the output from said coupling module and generating observer intelligible information indicative of said parameter;

(d) said implantable sensor module including (1) means for measuring the said physiological parameter and providing a digital signal indicative of the measurement;

(2) a source of NIR wavelength light;

(3) means for modulating the NIR radiation to reflect the said digital signal and thereby produce an NIR telemetry signal indicative of said measured parameter; and

(4) means to direct the said NIR telemetry signal through the patient'"'"'s tissues to a patient external point for coupling with said processing and display module;

(e) said coupling module including means for receiving the NIR telemetry signal which has transited said patient tissues and providing a corresponding electrical signal to said processing and display module; and

wherein

(f) said processing and display module includes means for converting said electrical signal from said coupling module to said observer intelligible form.

2. A system in accordance with claim 1 wherein said source of NIR wavelength light is a vertical cavity surface emitting laser (VCSEL).

3. A system in accordance with claim 1 wherein said external coupling module includes means for generating a high frequency alternating electromagnetic field for transcutaneous transmittal to said implantable sensor module;

and wherein said sensor module includes means for converting energy in said transmitted electromagnetic field to power for operating said sensor module.

4. A system in accordance with claim 3 wherein said sensor module is adapted for measuring pressure in a bodily fluid of said patient.

5. A system in accordance with claim 4, wherein said sensor module includes a chamber in communication with said bodily fluid, and a deformable diaphragm mounted in said chamber and being deformable as a function of the pressure of said fluid;

and means for converting the deformation state of said diaphragm to said digital signal indicative of the pressure being measured.

6. A system in accordance with claim 5, wherein said sensor module includes a puncture-resistant shield overlying said diaphragm.

7. A system in accordance with claim 5, wherein said diaphragm comprises a transducer crystal which exhibits a change in oscillation frequency as a function of its deformation.

8. A system in accordance with claim 7, wherein said crystal comprises quartz.

9. A system in accordance with claim 7, wherein said sensor module includes an NIR emitter and a monolithic circuit including means for modulating the output of said output emitter as a function of said pressure on said transducer crystal.

10. A system in accordance with claim 9, wherein the output of said NIR emitter is frequency modulated.

11. A system in accordance with claim 7, wherein said transducer crystal comprises an x-cut quartz crystal, means for resonating the said crystal at its fundamental frequency, and means for determining the said change in oscillation frequency and utilizing said change for said converting of said deformation state to said digital signal indicative of the pressure being measured.

12. A system in accordance with claim 11, wherein said transducer crystal is paired with a nominally identical reference crystal which is not in contact with said bodily fluid, the output signals from said transducer and reference signals respectively controlling a transducer oscillator and a reference oscillator;

means for detecting and measuring the difference in frequency between the two said oscillators; and

means for using the said difference frequency to compute the pressure applied to said transducer signal.

13. A system in accordance with claim 12, wherein said transducer crystal has a nominal oscillation frequency no higher than that of said reference crystal to ensure that said difference frequency is monotonic.

14. A system in accordance with claim 12, wherein said source of NIR radiation is a vertical cavity surface emitting laser (VCSEL);

and including means for turning the NIR source on and off at said difference frequency of said two oscillators.

15. A system in accordance with claim 1, wherein said physiological parameter measured is the intracranial pressure of said patient.

16. A system in accordance with claim 1, wherein said physiological parameter measured is the brain tissue oxygenation state of said patient;

and wherein said system includes a further NIR source disposed to transmit its NIR radiation through said brain tissue to be evaluated; and

an optical detector optically coupled to said further source for receiving the NIR radiation scattered by said brain tissue; and

means for converting the intensity value of said scattered light received by said detector to a further digital signal for transmission to the external module for display as observer intelligible information.

17. A system in accordance with claim 1, further including a narrow band-pass optical filter in the optical path of said NIR radiation between said sensor module and said coupling module to improve signal-to-noise ratio.

18. A system in accordance with claim 1 wherein said module external of said patient and a said module internal of said patient, respectively further include sending and receiving means for modulated NIR transmission of desired information from said external to a said internal module, thereby to enable two way communication between said external point and the local of said implant module.

22. A system in accordance with claim 8, wherein a metallic coaxial electrode pattern is deposited onto the crystal.

23. A system in accordance with claim 22, wherein the deposited metal is biocompatible and is lapped around the crystal edge to the side of the crystal non-adjacent the biofluid being sensed for said parameter;

electrical contacts with said electrode pattern being made at said side non-adjacent to said biofluid.

24. A system in accordance with claim 22, wherein said deposited pattern includes slots to minimize eddy currents.

19. A system for measuring and converting to an observer intelligible form an internal physiological parameter of a medical patient, comprising:

(a) a patient-implantable sensor for detecting and measuring said parameter;

(b) patient-implantable means connected to said sensor for converting the parameter measurement by said sensor to an NIR telemetry signal for transcutaneous transmission from said patient to

(c) coupling and display means positionable externally of the patient for receiving the NIR telemetry signal and generating observer intelligible information indicative of said parameter.

20. A system in accordance with claim 19 wherein said means (b) includes a source of NIR wavelength light;

and means for modulating the NIR light to produce an NIR telemetry signal indicative of said measured parameter.

21. A system in accordance with claim 20 wherein said source of NIR wavelength light is a vertical cavity surface emitting laser (VCSEL).