WO2007061977A2

WO2007061977A2 - Mri compatible wireless tympanic ear thermometer

Info

Publication number: WO2007061977A2
Application number: PCT/US2006/044947
Authority: WO
Inventors: Stephen Douglas Fisher; Jorgen Kilden-Pedersen; David Molyneaux; Dennis Hosler; Arthur R. Weeks, Jr.
Original assignee: Invivo Corporation
Priority date: 2005-11-18
Filing date: 2006-11-17
Publication date: 2007-05-31
Also published as: WO2007061977A3

Abstract

A portable, wireless patient monitor may be placed with the patient in the bore of an MRI machine eliminating the need for separate cabling between the MRI machine and an external monitoring unit. In one embodiment, the patient monitor may be attached to the patient's shoulder by a harness or the like which may also serve to corral leads between the patient monitor and the patient.

Description

MRI COMPATIBLE WIRELESS TYMPANIC EAR THERMOMETER

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U. S. provisional application 60/737,917, filed November 18, 2005 and is a continuation-in-part on U. S. Application 11/075,620, filed March 9, 2005.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to electronic patient monitors, and in particular, to a wireless patient temperature sensor suitable for use in the severe electromagnetic environment of a magnetic resonance imaging (MRI) machine. [0003] Magnetic resonance imaging (MRI) allows images to be created of soft tissue from faint electrical resonance signals (NMR signals) emitted by nuclei of the tissue. The resonance signals are generated when the tissue is subjected to a polarizing magnetic field and excited by a radio frequency pulse.

[0004] The quality of the MRI imaging is in part dependent on the quality of the polarizing magnetic field, which must be strong and extremely homogenous. Ferromagnetic materials are normally excluded from the MRI environment to prevent unwanted forces of magnetic attraction on these materials and distortion of the homogenous magnetic field by these materials. Switched magnetic gradients and radio frequency transmissions used in the MRI process make it a difficult environment for the operation of other types of electrical equipment.

[0005] A patient undergoing an MRI "scan" may be received within a relatively narrow bore or cavity in the MRI magnet. During this time, the patient may be remotely monitored to determine, for example, heart beat, respiration, temperature, and blood oxygen.

[0006] A typical remote temperature sensor, allowing in-bore determination of patient temperature, provides a patient thermometer linked by cables to a monitoring unit outside the bore. [0007] Long runs of electrical cables can be a problem in the magnetic environment because of high currents that may be induced on these cables. Accordingly, optical fibers may be used instead. These optical cables have a number of drawbacks. First, they are expensive and fragile, having a tendency to break during normal use. Long fibers can be cumbersome and interfere with access to the patient and free movement of personnel about the magnet itself. Attaching the thermometer to a cable restricts motion of the patient and can be uncomfortable for the patient. In addition, contact thermistor types of thermometers require precautions to prevent indirect currents from burning a patient.

SUMMARY OF THE INVENTION

[0008] The present invention provides a wireless, in-bore tympanic temperature sensor that provides radio connection with a remote station. By observing the temperature of the eardrum, a reliable core temperature reading may be obtained while the patient is otherwise inaccessible in the bore of the MRI machine. The temperature sensor is shielded with a Faraday shield designed to allow the thermometer to be scanned in the magnet bore without damages, vibration and interference when the thermometer is wholly supported on the ear using an ear clip or the like and powered by a self- contained nonmagnetic battery. Advanced radio techniques prevent interference between the MRI machine and the wireless transmission of data, which may be sent to a station in the magnet room that may also receive signals from other independent physiological monitors.

[0009] Specifically, the present invention provides a wireless tympanic ear thermometer for use in a magnetic resonance imaging machine, the tympanic ear thermometer including an optical temperature sensor for non-contact measurement of tympanic temperature and a support housing holding the optical temperature sensor and supporting the optical temperature sensor on a patient's head directed into an ear canal. A Faraday shield surrounds the temperature sensor and provides a visible light aperture permitting infrared radiation to be received by the optical temperature sensor. [0010] It is thus another aspect of at least one embodiment of the invention to allow convenient monitoring of a patient's temperature during an MRJ scan.

[0011] The ear thermometer may further include a wireless transmitter communicating with the optical temperature sensor for transmitting temperature information from the temperature sensor to a remote source.

[0012] It is thus another aspect of at least one embodiment of the invention to provide a cable free system that does not interfere with movement of the patient.

[0013] The wireless transmitter may be within the housing and may communicate with an antenna supported within the housing and outside the Faraday shield to provide a thermometer that is wholly self-contained without the need for attachment to a separate transmitter element.

[0014] The wireless transmitter may communicates with an antenna outside the

Faraday shield using a portion of a printed circuit board having an internal conductive trance surrounded by outer cladding of the printed circuit board.

[0015] It is thus another aspect of at least one embodiment of the invention to provide a simple method of wireless communication from a device that is fully shielded.

[0016] The housing includes an ear clip supporting the housing on the patient's external ear.

[0017] It is thus another aspect of at least one embodiment of the invention to provide an ear thermometer that may be quickly and easily attached to a patient undergoing an

MRI scan.

[0018] The wireless transmitter may be a transceiver receiving programming data from the ear thermometer.

[0019] It is thus another aspect of at least one embodiment of the invention to provide a two directional communication path allowing configuration of the ear thermometer from a more substantial base station.

[0020] The wireless tympanic ear thermometer may use a non-ferromagnetic battery, such as a polymer battery communicating with the wireless transmitter and also supported within the housing. [0021] It is thus another aspect of at least one embodiment of the invention to create a wholly wireless unit that is compatible with the MRI environment

[0022] The Faraday shield may comprise separate sections joined by eddy-current- blocking elements selected from the group consisting of capacitors and resistors.

[0023] It is thus another aspect of at least one embodiment of the invention to minimize eddy-current-induced vibration such as may be a source of discomfort to the patient and/or may dislodge or misalign the ear thermometer.

[0024] The thermometer may include a base station communicating with the wireless ear thermometer wherein the wireless transmitter communicates with the base station by using diverse multiple radio channels between the thermometer and the base station such as may be polarization or spatially diverse.

[0025] It is thus another aspect of at least one embodiment of the invention to provide a wireless system that can operate in the difficult environment of an MRI machine.

[0026] These particular aspects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Fig. 1 is a simplified, perspective view of an MRI system showing the MRI magnet and the location of an in-bore tympanic thermometer and an out-of-bore base station;

[0028] Fig. 2 is a perspective view of the tympanic thermometer of the present invention communicating with a remote display screen;

[0029] Fig. 3 is a simplified block diagram of the major components of the temperature probe; and

[0030] Fig. 4 is a detailed view of a cross-section of the internal circuit card holding the components of Fig. 3 showing an extension that may pass though the housing to attach to an external antenna. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0031] Referring now to Fig. 1, an MRI magnet room 10 containing an MRI magnet 14 may have shielded walls 12 blocking and reflecting radio waves. The MRI magnet 14 may have a central bore 16 for receiving a patient 18 supported on a patient table 19. As used henceforth, bore shall refer generally to the imaging volume of an MRI machine and should be considered to include the patient area between pole faces of open frame MRI systems.

[0032] During the MRI scan, the patient 18 is held within the bore 16 and may be monitored via wireless ear thermometer 20 attached to the patient 18 or patient table 19 and within the bore 16 during the scan. The ear thermometer 20 transmits via radio waves 22 the patient's temperature and status data (as will be described) to base station 24 outside the bore 16 useable by personnel within the magnet room 10. The base station 24 typically will include controls 26 and a display 28 providing an interface for the operator, and may be usefully attached to an IV pole 30. The IV pole 30 may have hooks 32 for holding IV bags (not shown) and a rolling, weighted base 34 that may be freely positioned as appropriate without the concern for wires between the ear thermometer 20 and base station 24.

[0033] Referring now to Figs. 1 and 2, the ear thermometer 20 may include a housing 35 of an insulating and cleanable non- ferromagnetic material such as plastic preferably incorporating a Faraday cage electromagnetic interference shield. In a first embodiment, the housing 35 is sized to be supported by the patient's ear 42 by means of an ear cone 36 formed integrally with the housing 35 that may be inserted within the ear canal 39 of the patient 18. The ear cone 36 may be covered by a disposable, sterile, and thermally transparent shield 38.

[0034] The housing 35 may be supported on the patient 18 by means of an ear clip 40 forming part of the housing 35 fitting behind the ear 42 so as to further stabilize the housing 35 with respect to the ear 42. In an alternative embodiment, the ear clip 40 may be replaced by a headphone-type ear cup that may provide an opportunity for sound dampening for both ears against the ambient noise of the MRI machine by providing dual ear cups (not shown) per conventional headphones. [0035] The ear cone 36 may terminate within the ear at a clear infrared transparent window 43 behind which may be positioned a thermopile 44 fitting within a tubular portion of the Faraday shield 37, which by virtue of its length and opening into the ear canal 39 prevents significant ingress of radio frequency interference into the circuitry of the ear thermometer 20. Alternatively or in addition, a fine metal screen (not shown) electrically attached to the Faraday shield 37 may cover the light receiving portion of the thermopile 44 allowing the passage of short wavelengths of light, but blocking most radio frequency energy.

[0036] The Faraday shield 37 maybe composed of separate conductive elements providing radio frequency shielding for different portions of the housing 35 and insulated from each other with respect to direct currents, yet joined by resistors or capacitors 86 at the corner edges of the box to allow the passage of a radio frequency current. The effect of these capacitors is to block the flow of lower frequency eddy currents induced by the magnetic gradients such as can vibrate the ear thermometer 20 when it is positioned on the patient 18.

[0037] The thermopile 44 may be of conventional design but with all ferromagnetic elements replaced with ceramic components. The thermopile 44 communicates with a signal amplifier 47 which may provide an input to a single chip microcontroller and transceiver 48, for example, the nRF2401 A or nRF24El integrated circuits manufactured by Nordic Semiconductors of Norway.

[0038] The microcontroller and transceiver 48 may transmit on antenna 50, for example, being a microstrip antenna located outside of the Faraday shield 37, but within the housing 35. Referring to Fig. 4, passage of transmitted and received radio waves 22 from the base station 24 between the shielded transceiver 48 and the antenna 50 may be through a small aperture 62 in the Faraday shield 37 that allows a tongue 64 of a printed circuit board 59 holding the transceiver 48 to extend from within the Faraday shield 37 to outside of the Faraday shield 37. The printed circuit board 59 includes outer conductive layers 66 that may be held at ground potential, and which are separated by the insulating dielectric of the printed circuit board material itself 68 (e.g. epoxy-glass) around a central interior trace 70 on which radio frequency signals may be provided to the antenna 50. The antenna 50 connects to this interior trace 70 through a plated- through hole 72 joining to the interior trace 70 and providing exposed pads on at least one side of the tongue 64.

[0039] The housing 35, as supported on the ear 42, may provide for a clear transmission path for radio waves 22 forwarded to a base station 24 from the antenna 50 positioned near the ear to thereby provide a remote display 28 of the patient's temperature.

[0040] A polymer battery such as a lithium polymer (LiPo) rechargeable battery 74 may provide power to the signal amplifier 47 and the microcontroller and transceiver 48 and has recharging studs 75 located at the edge of the housing 35 for fitting into a recharging unit (not shown). Alternatively, a ferrous-metal- free super capacitor may be used for this purpose. The battery 74 may be held in a "hot box" isolated from the transceiver 48 both by the Faraday shield 37 and having a cover 76 fitting over the battery 74 holding a portion of a conductive shield electrically connected to the Faraday shield 37. The direct current leads from the battery passing through the Faraday shield 37 with feed through capacitors forming part of a low pass filter possibly with corresponding series inductive elements.

[0041] Referring still to Fig. 3, the transceiver 48 may communicate with a light emitting diode 80, in this case a bi-colored LED, which may display operating information according to the following states:

[0042] The LED 80 may thus distinguish between signal failures caused by improper engagement of the ear thermometer 20 in the ear canal 39 or the associated processing circuitry of the signal amplifier 47 or transceiver 48 and communication failures caused by environmental problems or failure of the transceiver 48, preventing wireless communication. The LED 80 may alternatively or in addition, using different codes and colors, provide additional indications such as low battery, device over-heating, test information and the like.

[0043] Ideally the LED 80 has a lens that protrudes from the housing 35 of the ear thermometer 20 so that it can be viewed by an operator sighting along the bore 16 from a variety of attitudes. Particularly when radio communication has not been established, the LED 80 can provide important information, or may provide a redundant source of critical information even when radio communication has been established. Importantly, the LED 80 may be used during preparation of the patient 18 outside of the bore 16, even in the absence of the base station 24, for example, in the patient's hospital room. [0044] Referring still to Fig. 3, the base station 24 contains two transceivers connected to two antennas: antennas 84 and 87 providing the spatial and/or polarization diversity using the techniques described in copending U. S. Application 11/075620 filed March 9, 2005, assigned to the same assignee as the present invention and hereby incorporated by reference. The multiple antennas 84 and 87 allow the transceivers to provide beam- forming to the antenna 50 or otherwise select between two transmission channels to avoid interference from the MRI machine.

[0045] A method of ensuring that ear thermometers 20 (and associated patients) are properly identified to a particular base station 24 or communication channel, or data window on display 28, is described in copending U.S. application 10/066,549 filed February 5, 2002, entitled: System and Method for Using Multiple Medical Monitors, assigned to the same assignee as the present invention and hereby incorporated by reference.

[0046] The present invention contemplates that the ear thermometer 20 may be used for setup of the patient 18 without the need for a base station 24, for example, in the patient's room before the patient 18 is transported to the magnet room 10 or as a portable patient monitor that may be used for short periods of time in the patient room or during transportation of the patient 18. The ear thermometer 20 may further receive signals from the base station 24 for programming the ear thermometer 20, for example, for software upgrades or to activate or deactivate the ear thermometer 20 or change its sampling rate.

[0047] Techniques for transmitting wirelessly in the MRI environment and for providing necessary shielding and other features are described in co-pending U.S. application 11/075,620 filed March 9, 2005, assigned to the same assignee as the present invention and hereby incorporated by reference. [0048] It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.

Claims

CLAIMSWhat we claim is:

1. A wireless tympanic ear thermometer for use in a magnetic resonance imaging machine comprising: an optical temperature sensor for non-contact measurement of tympanic temperature; support housing holding the optical temperature sensor and supporting the optical temperature sensor on a patient's head directed into an ear canal; a Faraday shield surrounding the temperature sensor and providing a visible light aperture peπnitting infrared radiation to be received by the optical temperature sensor.

2. The wireless tympanic ear thermometer of claim 1 further including a wireless transmitter communicating with the optical temperature sensor for transmitting temperature information from the temperature sensor to a remote source.

3. The wireless tympanic ear thermometer of claim 2 wherein the wireless transmitter communicates with an antenna supported within the housing and outside the Faraday shield.

4. The wireless tympanic ear thermometer of claim 2 wherein the wireless transmitter communicates with an antenna outside the Faraday shield using a portion of a printed circuit board having an internal conductive trance surrounded by outer cladding of the printed circuit board.

5. The wireless tympanic ear thermometer of claim 1 wherein the housing includes an ear clip supporting the housing on the patient's external ear.

6. The wireless tympanic ear thermometer of claim 1 wherein the wireless transmitter is a transceiver receiving programming data from the ear thermometer.

7. The wireless tympanic ear thermometer of claim 1 further including a non- ferromagnetic battery communicating with the wireless transmitter and also supported within the housing.

8. The electronic patient monitor of claim 7 wherein the battery is a polymer battery.

9. The electronic patient monitor of claim 1 wherein the Faraday shield comprises separate sections joined by eddy-current-blocking elements selected from the group consisting of capacitors and resistors.

10. The wireless tympanic ear thermometer of claim 1 further including a base station communicating with the wireless ear thermometer wherein the wireless transmitter communicates with the base station by using diverse multiple radio channels between the thermometer and the base station.

11. The wireless tympanic ear thermometer of claim 10 wherein the channels are polarization diverse.

12. The wireless tympanic ear thermometer of claim 10 wherein the channels are spatially diverse.