Radiation detector suitable for tympanic temperature measurement

Claims

We claim:

1. A radiation detector comprising:

a thermopile mounted within a thermal mass and having a junction thermally coupled to the thermal mass;

a thermally conductive tube coupled to the thermal mass for guiding radiation to the thermopile from an external target; and

a thermal barrier surrounding the thermal mass and tube;

the outer thermal RC time constant for thermal conduction through the thermal barrier to the thermal mass and tube is at least two orders of magnitude greater than the inner thermal RC time constant for the temperature response of the cold junction to heat transferred to the tube and thermal mass through the thermal barrier.

2. A radiation detector as claimed in claim 1 wherein the outer RC time constant is at least three orders of magnitude greater than the inner RC time constant.

3. A radiation detector as claimed in claim 1 wherein the inner RC time constant is about 1/2 second or less.

4. A radiation detector as claimed in claim 1 comprising a continuous low thermal resistance path from the end of the tube to the junction of the thermopile.

5. A radiation detector as claimed in claim 1 wherein the thermopile is mounted within a low conductivity gaseous environment which extends through the length of the conductive tube.

6. A radiation detector as claimed in claim 1 wherein the thermopile is mounted to a film suspended within a ring, the ring being supported on electrically conductive pins extending through an adjacent ring to the side of the film on which the thermopile is mounted, the film being spaced from the adjacent ring, the rings and thermopile being surrounded by a low conductivity gaseous volume, the radiation detector further comprising the improvement wherein the space between the film and the adjacent ring through which the conductors extend is filled with thermally conductive material.

7. A radiation detector as claimed in claim 1 wherein:

the thermopile is mounted within a low conductivity gaseous volume within a can;

the thermal mass comprises an annular member which surrounds the can and a length of the tube adjacent to the can, the annular member being tapered about its outer periphery toward the tube, and a conductive plug positioned behind the can within the annular member, the can, tube, annular member and plug being bonded together by high thermal conductivity material; and

the thermal barrier comprises a sleeve spaced from the thermal mass and tube, the sleeve being tapered toward the end of the tube away from the can.

8. A radiation detector as claimed in claim 1 adapted to provide an indication of tympanic temperature.

9. In a thermopile assembly comprising a thermopile mounted to a film suspended within a ring, the ring being supported on electrically conductive pins extending through an adjacent ring to the side of the film on which the thermopile is mounted, the film being spaced from the adjacent ring, and the rings and thermopile being surrounded by a low conductivity gaseous volume, the improvement wherein the space between the film and the adjacent ring through which the conductors extend is filled with thermally conductive material.

10. A radiation detector comprising a thermopile mounted within a can and a waveguide tube of lesser internal diameter than the can and integral with the can, the tube having an airtight window at a distal end thereof and directing radiation which passes through the window to the thermopile, a gaseous environment having a thermal conductivity significantly lower than that of air being maintained about the thermopile within the can and through the length of the tube.

11. A tympanic temperature detector comprising:

a housing adapted to be held by hand;

an extension from the housing adapted to be inserted into an ear, the extension supporting a radiation sensor and having a window at the end thereof through which the sensor receives radiation from a tympanic membrane area;

a temperature display on the housing for displaying tympanic temperature;

battery powered electronics in the housing for converting radiation sensed by the sensor to temperature displayed by the display; and

a removable plastic sheet stretched over the end of the extension, the sheet having holes at opposite ends thereof which are secured to retaining members on the side of the extension to retain the sheet on the extension.

12. A tympanic temperature detector as claimed in claim 11 wherein the radiation sensor is a thermopile, the cold junction of which is allowed to follow ambient temperature.

13. A tympanic temperature detector as claimed in claim 12 wherein the radiation sensor is a thermopile mounted within a thermal mass in the extension and having a junction thermally coupled to the thermal mass, a thermally conductive tube is coupled to the thermal mass for guiding radiation to the thermopile from an external target and a thermal barrier surrounds the thermal mass and tube, the outer thermal RC time constant for thermal conduction through the thermal barrier to the thermal mass and tube is at least two orders of magnitude greater than the inner thermal RC time constant for the temperature response of the cold junction to heat transferred to the tube and thermal mass through the thermal barrier.

14. A tympanic temperature detector as claimed in claim 13 wherein the inner thermal RC time constant is about 1/2 second or less.

15. A tympanic temperature detector as claimed in claim 12 further comprising an airtight waveguide tube mounted in the extension integral with a can containing the thermopile, the tube guiding radiation from the window to the thermopile and being filled with a low conductivity gas.

16. A tympanic temperature detector as claimed in claim 12 wherein the thermopile is mounted to a film suspended within a ring, the ring being supported on electrically conductive pins extending through an adjacent ring to the side of the film on which the thermopile is mounted, the film being spaced from the adjacent ring, the rings and thermopile being surrounded by a low conductivity gaseous volume, the radiation detector further comprising the improvement wherein the space between the film and the adjacent ring through which the conductors extend is filled with thermally conductive material.

17. A tympanic temperature detector as claimed in claim 12 wherein:

the thermopile is mounted within a low conductivity gaseous volume within a can;

the thermal mass comprises an annular member which surrounds the can and a length of the tube adjacent to the can, the annular member being tapered about its outer periphery toward the tube, and a conductive plug positioned behind the can Within the annular member, the can, tube, annular member and plug being bonded together by high thermal conductivity material; and

the thermal barrier comprises a sleeve spaced from the thermal mass and tube, the sleeve being tapered toward the end of the tube away from the can.

18. A tympanic temperature detector as claimed in claim 11 which provides a display of tympanic temperature within five seconds of inserting the extension into the ear.

19. A tympanic temperature detector as claimed in claim 11 wherein the radiation sensor is a thermopile and the window is positioned at the end of a waveguide tube integral with a can surrounding the thermopile, a low conductivity gaseous environment surrounding the thermopile within the can and extending through the length of the conductive tube.

20. A tympanic temperature detector as claimed in claim 11 further comprising a tape of said removable plastic sheets, individual sheets being adapted to be torn from the tape to be stretched over the end of the extension.

21. A tympanic temperature detector as claimed in claim 11 wherein the extension extends about orthogonally from an intermediate extension which extends at an angle of about 15 degrees from an end of the housing, the extension being curved outwardly along its length from its distal end.

22. A tympanic temperature detector as claimed in claim 11 further comprising a processor for providing the temperature displayed on the housing as a function of the received radiation compensated by an indication of ambient temperature to provide a core temperature approximation.

23. A tympanic temperature detector comprising:

a housing adapted to be held by hand;

an extension from the housing adapted to be inserted into an ear, the extension supporting a radiation sensor and having a window at the end thereof through which the sensor receives radiation from a tympanic membrane area;

a temperature display on the housing for displaying tympanic temperature;

battery powered electronics in the housing for converting radiation sensed by the sensor to temperature displayed by the display, the electronics including a processor for providing the temperature displayed on the housing as a function of the received radiation compensated by an indication of ambient temperature to provide a core temperature approximation.

24. A tympanic temperature detector comprising:

a housing adapted to be held by hand;

an extension from the housing adapted to be inserted into an ear, the extension supporting a thermopile radiation sensor and having a window at the end thereof through which the sensor receives radiation from a tympanic membrane area;

a temperature display on the housing for displaying tympanic temperature;

battery powered electronics in the housing for converting radiation sensed by the sensor to temperature displayed by the display;

a removable plastic sheet stretched over the end of the extension; and

a thermal mass in the extension within which the thermopile is mounted, the thermopile having a junction thermally coupled to the thermal mass, and therein a thermally conductive tube is coupled to the thermal mass for guiding radiation to the thermopile from an external target, a thermal barrier surrounds the thermal mass and tube, and the outer thermal RC time constant for thermal conduction through the thermal barrier to the thermal mass and tube is at least two orders of magnitude greater than the inner thermal RC time constant for the temperature response of the cold junction to heat transferred to the tube and thermal mass through the thermal barrier.

25. A tympanic temperature detector as claimed in claim 24 wherein the inner thermal RC time constant is about 1/2 second or less.

26. A tympanic temperature detector comprising:

a housing adapted to be held by hand;

an extension from the housing adapted to be inserted into an ear, the extension supporting a radiation sensor and having a window at the end thereof through which the sensor receives radiation from a tympanic membrane area, the radiation sensor being a thermopile having a cold junction which is allowed to follow ambient temperature, the thermopile being mounted to a film suspended within a ring which is supported on electrically conductive pins extending through an adjacent ring to the side of the film on which the thermopile is mounted, the film being spaced from the adjacent ring and the rings and thermopile being surrounded by a low conductivity gaseous volume, the radiation detector further comprising the improvement wherein the space between the film and the adjacent ring through which the conductive pins extend is filled with thermally conductive material;

a temperature display on the housing for displaying tympanic temperature; and

battery powered electronics in the housing for converting radiation sensed by the sensor to temperature displayed by the display.

27. A tympanic temperature detector comprising:

a housing adapted to be held by a hand;

an extension from the housing adapted to be inserted into an ear, the extension supporting a radiation sensor and having a window at the end thereof through which the sensor receives radiation from a tympanic membrane area, and wherein the extension extends about orthogonally from an intermediate extension which extends at an angle of about 15 from an end of the housing, the extension being curved outwardly along its length from its distal end;

a temperature display on the housing displaying tympanic temperatures; and

battery powered electronics in the housing for converting radiation sensed by the sensor to temperature displayed by the display.

28. A radiation detector comprising:

a thermopile mounted within a thermal mass and having a junction thermally coupled to the thermal mass;

a thermally conductive tube coupled to the thermal mass for guiding radiation to the thermopile from an external target; and

a thermal barrier surrounding the thermal mass and tube;

an inner thermal RC time constant for the temperature response of the cold junction to heat transferred to the tube and thermal mass through the thermal barrier along being about 1/2 second or less.

The most common way of measuring a patient's temperature is by use of a sublingual thermometer, that is, one placed under the tongue. Such thermometers have suffered several disadvantages. Accuracy of a reading depends on the mouth remaining closed and the thermometer being properly positioned under the tongue. Drinking liquids or breathing through the mouth prior to taking a measurement can affect the reading. Further, the mouth is a source of mucous which presents a significant risk of cross-contamination. Also, the cost per reading of such instruments has typically been high.

One type of sublingual thermometer is the common mercury thermometer. Such thermometers have the disadvantage of taking a considerable amount of time to reach a steady state temperature in order to provide an accurate reading. Further, they are easily broken, require serialization, and are difficult to read.

As an alternative to the mercury thermometer, disposable liquid crystal thermometers are often favored. As a disposable item, the serialization requirement is eliminated, but the cost per reading is high.

To decrease the time required to obtain a patient's temperature, electronic thermometers have been developed. Such thermometers typically include a thermistor which may be positioned in a disposable cover. Although the thermometers do not reach a steady state temperature during their measurement time of 15 to 30 seconds, through electronic interpolation a steady state temperature may be estimated from the temperature readings throughout the 15 to 30 seconds. The thermometers are often cumbersome, and as with other sublingual thermometers the temperature readings may be unreliable in certain circumstances, especially when the probe is not precisely placed under the tongue.

Another electronic temperature device is a tympanic temperature measurement device. Such devices rely on a measurement of the temperature of the tympanic membrane area in the ear by detection of infrared radiation. The tympanic membrane area is often considered to be more representative of a patient's core temperature, and infrared temperature measurements using a thermopile are extremely rapid. Disposable sleeves may be placed over the radiation detector. A commercial tympanic temperature measurement device is illustrated in U.S. Pat. No. 4,602,642 to O'Hara et.al. As suggested in that patent, the infrared detection approach does present demands on the instrumentation to avoid inaccuracies due to ambient temperature and spurious heat flux to the thermopile.

SUMMARY OF THE INVENTION

The present invention relates to various features of a radiation detector which make the detector particularly suited to tympanic temperature measurements without certain deficiencies of prior tympanic temperature detectors. For example, the O'Hara et.al. system relies on heating of the radiation probe to a precise temperature to maintain calibration of the device during a test. As a result, the instrument is not usable where the ambient temperature exceeds that precise temperature. Also, to assure proper calibration for each test, the O'Hara et.al. system uses a light chopper-type of calibration unit having a target heated to approximately 98.degree. F. Before each test, the thermopile in the probe is calibrated as it views the chopper unit target. Once removed from the chopper, the temperature reading must be obtained promptly because the probe will cool after removal from the unit and thus introduce errors. This requirement for calibration in the chopper unit prior to each temperature reading imposes a rigid protocol on the user which is more cumbersome than that of electronic thermometers. Further, the requirement for heating the target and the probe adds bulk and weight to the system. The present . invention provides for a radiation detector which is at all times properly calibrated without heating of the thermopile and without a chopper calibration unit. As a result, the instrument is less cumbersome, uses less power and provides quicker readings without having to follow an extensive protocol.

In accordance with one aspect of the present invention, a thermopile is mounted within a thermal mass and has a junction thermally coupled to the thermal mass. A thermally conductive, reflective tube is coupled to the thermal mass for guiding radiation to the thermopile from an external target. A thermal barrier surrounds the thermal mass and tube. The temperature of the thermal mass, and thus of the thermopile cold junction, is allowed to float with ambient. A temperature measurement of the thermal mass is made to compensate the thermopile output.

Temperature differences between the tube and thermopile cold junction would lead to inaccurate readings. To avoid those differences, the large thermal mass minimizes temperature changes from heat which passes through the thermal barrier, and good conductivity within the mass increases conductance and minimizes temperature gradients. The outer thermal RC time constant for thermal conduction through the thermal barrier to the thermal mass and tube is at least two, and preferably at least three, orders of magnitude greater than the inner thermal RC time constant for the temperature response of the cold junction to heat transferred to the tube and thermal mass. For prompt readings, the inner RC time constant should be about 1/2 second or less.

Preferably, the thermopile is mounted to a film suspended within a ring. The ring is supported on electrically conductive pins extended through an adjacent ring to the side of the film on which the thermopile is mounted. The film is spaced from the adjacent ring, and the rings and thermopile are surrounded by a low conductivity gaseous volume. Preferably, the low conductivity gaseous volume extends through the length of the conductive tube. The space between the film and the adjacent ring through which the conductors extend is filled with thermally conductive material.

The thermopile may be mounted in a can which encloses the low conductivity gaseous volume. The thermal mass may comprise an annular member which surrounds the can and a length of the tube adjacent to the can. The annular member is tapered about its outer periphery toward the tube. A conductive plug is positioned behind the can within the annular member. The can, tube, annular member and plug are bonded together by high thermal conductivity material such as solder, epoxy, or powdered metal to obtain a continuous low resistance path from the end of the tube to the cold junction of the thermopile. Alternatively, the parts may be press fit together to provide the high conductance bond. The thermal barrier comprises a sleeve spaced from the thermal mass and tube. The sleeve is tapered toward the end of the tube away from the can.

Preferably, a probe extension which supports the radiation sensor extends from a housing which displays the tympanic temperature. This housing supports battery powered electronics for converting radiation sensed by the sensor to tympanic temperature displayed by the display. The entire instrument may be housed in a single hand-held package because a chopper calibration unit is not required. The small additional weight of the electronics in the hand-held unit is acceptable because readings can be made quickly. The readings can be made in less than five seconds, and preferably in less than two seconds.

Preferably, the probe extension extends about orthogonally from an intermediate extension which extends at an angle of about 15.degree. from an end of the housing. The surface of the extension curves outwardly along its length from its distal end following a curve similar to that of an otoscope. A sanitary cover in the form of a removable plastic sheet may be stretched over the end of the probe. The sheet may be retained on the probe by posts on the sides of the probe over which holes in the sheet are positioned.

Many of the sheets can be formed in a tape of transparent, flexible membrane segmented into individual covers by frangible lengths across the tape. The holes adapted to retain the sheet across the probe are formed to each side of each frangible length. Reinforcement tape may be positioned on the tape, and the frangible lengths may be formed as by perforations through the reinforcement tapes. In the present application, the membrane must be transparent to infrared radiation. The covers may be adapted to other measuring instruments by using membranes which are transparent, for example, to visual light, sound or the like. Polyethylene sheet is preferred for infrared measurements.

The electronics may include an optical signal detector for receiving a digital input, and an electrically erasable programmable read only memory (EEPROM). A processor is programmed to respond to input from the optical signal detector to store information in the EEPROM and to use the stored information to respond to radiation and to drive the display. The processor may also be programmed to operate in a communications mode in which it transfers information to an external optical signal detector by modulation of the display. Communications may be with an external computer through a boot which fits over the display during calibration.

The information stored in the EEPROM may include calibration information. It may also establish a range and incremental response of the display to sensed radiation and other information which characterizes the personality of a particular unit. For example, the information stored in the EEPROM may determine whether the display is in degrees Fahrenheit or degrees centigrade. That information may be controlled by a switch to which the processor responds. The system may include a sound source, and the stored information may determine the timing at which the sound source is activated. For example, the stored information may cause the display to be locked to a reading a predetermined time after the radiation detector is turned on, and the stored information may cause the sound source to be activated when the display is locked. Similarly, the stored information may cause the radiation detector to be turned off after a predetermined time and cause the sound source to be activated as the radiation detector is turned off. Alternatively, the stored information may cause the display to indicate the peak radiation sensed during a period of time and may cause the sound source to be activated when radiation sensed by the sensor approximates the peak.

The information stored in the EEPROM may cause a conversion from sensed tympanic temperature to a temperature which approximates oral and/or core temperature and which is displayed. The processor may also perform conversions based on linear approximations, and the stored information may establish the end points and slopes of the linear approximations. For example, a linear approximation may be used to determine ambient temperature from a thermistor output or to determine target temperature from a thermistor output and a thermopile output.

The electronics support a simple watchdog operation associated with the on switch to the unit. An active device is turned on by the switch to apply power to the electronics. A capacitor stores, for a limited time, a charge which holds the active device after release of the switch. The processor is programmed to periodically charge the capacitor after power is applied through the active device. Failure of the processor to follow a program routine results in discharge of the capacitor and turning off of the active device on the radiation detector. The switch may also be coupled directly to the processor so that the processor may respond to actuation of the switch after the radiation detector is turned on for other functions.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 illustrates a radiation detector for tympanic temperature measurements in accordance with the present invention.

FIG. 2A is an illustration of a disposable sheet for covering a probe of the detector of FIG. 1; FIG. 2B is an illustration of a tape of the disposable sheets of FIG. 2A; FIG. 2C is a perspective view of a carton containing a stack of the sheets formed by a z fold of the tape of FIG. 2B; and FIG. 2D is an illustration of a roll of such sheets.

FIG. 3A is a side illustration of the sheet of FIG. 2A pulled over the probe o