INFRARED THERMOMETER Field of the Invention The invention is directed to the field of diagnostic instruments and more particularly to a diagnostic instrument which is suitable for use with the ear or other medical/industrial target in order to accurately determine a temperature or a temperature profile.
Background of the Invention Medical diagnostic instruments such as infrared (IR) ear thermometers have traditionally been inaccurate as compared, for example, to thermistor type or mercury thermometers. This inaccuracy is due in large part to the large interrogation area found in the ear canal. This area includes not only the tympanic membrane (TM), but the ear canal walls as well. At present, there is not an adequate method of alerting the user when the instrument is not properly aligned with the TM. Similarly, the presence of foreign matter, such as ear wax, can block a direct line of sight to the TM and seriously affect the results indicated by the instrument. In addition, the narrowness of the ear canal, sometimes having large curves, also tends to prevent a suitable line of sight to the TM.
A basic assumption made in known IR thermometers is that the TM is within an interrogated area and that the TM subtends a specific portion of this interrogated area.
Therefore, the manufacturers of these instruments will add a compensation factor arithmetically to the reading of the thermometer to make up for the fact that the device is reading the ear canal wall in addition to the TM. These devices are particularly inaccurate when the ear canal has been cooled, e. g., immediately after a patient has come indoors from the cold outdoors.
Recently, data have become available which demonstrate that the temperature of the TM in the lower anterior quadrant thereof is largely independent of ambient and skin temperature due to its interconnection with the hypothalamus. This temperature is highly representative of the body"core"temperature. The remainder of the TM is not necessarily at the same temperature. It is therefore quite desirable to measure this"hottest"spot in order to realize a more accurate reading.
Another issue to consider in the use of IR thermometers is how to deal with the IR radiation originating from the ear tip housing. Radiation from the tip housing combines with that of the target, such that temperature variations of the housing can affect the temperature reading from the sensor.
A known method of avoiding this problem is to keep the temperature of the housing isothermal and at a known level, as described in U. S. Patent No. 4,759,324. In actual practice, however, this is difficult to accomplish, in part because the ear tip is relatively long, leading to axial temperature gradients. In addition, the geometry of the ear canal is such that little radial room is available for insulation, resulting in heat transfer to and from the ear tip housing by the environment.
Summary of the Invention It is a primary object of the present invention to improve the accuracy of medical diagnostic instruments.
It is a further primary object of the present invention to provide a medical diagnostic instrument which is capable of determining the hottest temperature of a medical target.
It is yet a further primary object of the present invention to provide a medical diagnostic instrument capable of determining body core temperature of a patient.
It is still another primary object of the present invention to provide a medical diagnostic instrument which is capable of estimating temperature of a target area if a portion thereof cannot be viewed directly; for example, if a portion of the target area is somehow obstructed.
It is still another object of the present invention to provide a means for negating or minimizing the effects of temperature changes in an ear thermometer on system response.
Therefore, and according to a preferred aspect of the invention, there is provided a temperature measuring apparatus for interrogating a medical target area, the apparatus comprising at least one infrared sensor capable of providing an output signal indicative of temperature of a portion of a medical target area, and processing means for processing output signals from the at least one infrared sensor. The processing means includes means for determining temperature based on the output signals of the at least one sensor. The apparatus also includes a movable mirror aligned with the at least one infrared sensor and focusing
optics for focusing an optical image of a portion of the medical target area captured by the movable mirror onto the sensor, such that the entire target area can be scanned by the mirror.
The apparatus preferably includes means for displaying at least one output signal of the at least one infrared sensor and more preferably for displaying the maximum temperature detected by the at least one infrared sensor. Alternately, the display means can display all output signals, such as ranges, in a predetermined format, one example of which is false colors.
The apparatus can also include means for calibrating the at least one infrared sensor, which can, for example, include a small target having a known temperature and emissivity that is disposed in the path of the at least one infrared sensor. Preferably, the target can be moved selectively into and out of the optical path to the at least one infrared sensor.
According to another version, at least one optical element is aligned with the known target, wherein at least one of the at least one optical element and known target are movable relative to each other.
Another means for calibrating includes a temperature measuring element disposed in relation to the at least one infrared sensor and a supporting substrate in which the temperature measuring element is capable of measuring a reference temperature.
The apparatus can be used to examine a medical target area such as the tympanic membrane, the armpit, under the tongue, the colon, the rectum, the temple area or an in vivo portion of the skin.
The processing means includes means for determining the pulse of a patient based on transient variations in the output signals of portions of a scanned temperature profile.
The processing means further includes means for estimating the hottest temperature of the medical target area if portions thereof are obstructed from the at least one infrared sensor.
Preferably, the estimating means estimates the hottest output signal from a scanned profile of output signals, the signal being extrapolated or interpolated therefrom. The apparatus can also provide an output signal to the user that the hottest temperature displayed is either not the hottest temperature of the medical target or is an estimated value.
The apparatus can also include directional guiding means for guiding a user to the portion of the medical target area having the hottest temperature. In addition, the display of the hottest temperature can be accompanied by audio, tactile, or light feedback.
The apparatus can also include means for thermally isolating the at least one sensor from input other than that of the medical target area, including an aperture stop in relation to the focusing optics and the at least one infrared sensor to allow only energy from the aperture stop and the medical target area to impinge on the at least one sensor. The aperture stop can be thermally connected to the substrate supporting the at least one infrared sensor such that the aperture stop and the substrate have substantially equivalent temperatures.
The apparatus includes means for measuring the temperature of the aperture stop, for example, by at least one infrared sensor.
According to another preferred aspect of the invention, there is disclosed a method for using an apparatus for accurately determining the temperature of a medical target, the apparatus including at least one infrared sensor and a movable mirror aligned with the target area and the at least one sensor. The method includes the steps of sequentially moving the mirror to receive an optical image of a portion of the target area and generating a temperature profile of the target area based on output signals from the at least one sensor of each portion of the target area.
The method also includes the step of outputting the signals representative of the temperatures of portions of the medical target, such as by displaying the value of selected individual output signals or the generated temperature profile, including the hottest temperature.
The method further includes the step of estimating the hottest temperature of the medical target (ear, colon, in vivo portion of skin, etc.) if portions of the medical target are obstructed from the sensor and displaying the estimated hottest temperature.
The method further includes the step of calibrating the sensor, such as by aiming the sensor at a target having a known temperature and emissivity.
The method further includes the step of thermally isolating the sensor from thermal input other than that from the medical target, such as by installing an aperture stop relative to the sensor which is configured to allow only energy from the medical target and the aperture stop to impinge on the sensor. Preferably, a substrate supports the sensor with the substrate and the aperture stop are thermally connected to the substrate such that the aperture stop and the substrate have substantially equivalent temperatures. Alternately, the method includes the
step of measuring the temperature of the aperture stop and incorporating the measured temperature during the processing step.
The method further includes an indicating step including the step of directionally guiding the user until the hottest temperature of the medical target has been identified.
According to yet another preferred aspect of the present invention, there is provided an ear thermometer including at least one infrared sensor capable of providing an output signal indicative of a portion of a target area, processing means for processing output signals from the at least one sensor, the processing means including means for determining body core temperature based on the output signal, a movable mirror aligned with the at least one infrared sensor and focusing optics for focusing an optical image of at least a portion of the target area captured by the movable mirror onto the at least one sensor, wherein the entire target area can be scanned by the mirror.
An advantage of the present invention is that a target can be interrogated more accurately without transient thermal effects typically found in the vicinity of a medical target such as the ear canal.
Another advantage provided by the present invention is that the presence of inflammations, abscesses, ear wax, and other obstructions can be quickly identified and compensated for so as to more accurately estimate the hottest temperature of a defined target area.
These and other objects, features and advantages will become apparent from the following Detailed Description which should be read in conjunction with the accompanying drawings.
Brief Description of the Drawings Fig. 1 is a partial perspective view of a diagnostic instrument system in accordance with a preferred embodiment of the present invention; Fig. 2 (a) is a partially exploded top perspective view of the diagnostic instrument depicted in Fig. 1; Fig. 2 (b) is an exploded rear perspective view of a diagnostic instrument similar to that depicted in Fig. 2 (a); Fig. 3 is a side sectioned view of the instrument of Figs. 1-2 (b); Fig. 4 is a top sectioned view of the instrument of Figs. 1-3; Fig. 5 is a partial ray trace diagram of the optical portion of the instrument of Fig. 1, including a thermal baffle according to a first embodiment of the present invention; Fig. 6 is a partial ray trace diagram of the optical portion of the instrument of Fig. 1, including a thermal baffle according to a second embodiment of the present invention and further including calibration means for the instrument; Fig. 7 depicts a typical output display indicating portion of a temperature profile according to the diagnostic instrument system of Fig. 1; Fig. 8 is a display output indicating regions of various temperatures of a predetermined target area; Fig. 9 depicts a digital temperature display for the instrument of Fig. 1 ; Fig. 10 is an enlarged front view of the thermal sensor array of the instrument of Fig.
1; Fig. 11 depicts a view of a target area including an occluded portion; Fig. 12 depicts a relative plot of temperature for the target area of Fig. 11; Fig. 13 depicts a predicted plot of temperature for the target area of Fig. 11 ; Fig. 14 depicts another predicted plot of temperature for the target area of Fig. 11 ; Fig. 15 illustrates a display portion for the diagnostic instrument made in accordance with a preferred aspect of the invention; Fig. 16 illustrates the display portion of Fig. 15 indicating the centering of the hottest temperature value; Fig. 17 illustrates a partial plan view of an instrument having a fixed thermal sensor used in conjunction with a scanning mirror assembly;
Fig. 18 illustrates an enlarged view of the thermal sensor and scanning mirror of Fig.
17 ; Fig. 19 illustrates an alternate embodiment of a movable thermal element; Fig. 20 is a side diagrammatic partial view of a diagnostic instrument having a movable optics assembly and Fig. 21 illustrates a predicted plot of temperature using an interpolation technique.
Detailed Description The following description relates to certain embodiments of a medical diagnostic instrument system used in conjunction with an otological medical device and particularly for measuring the body core temperature of a patient through interrogation of the tympanic membrane. It will be readily apparent from the following discussion, however, that the concepts detailed herein will find similar application in measuring other medical targets, such as under the armpit, under the tongue, the colon, portions of the skin for skin disorders, tumors, etc, as well as other anatomical areas of interest.
In addition, the concepts described herein can further be employed in devices intended for interrogating certain industrial targets. Finally, it should be pointed out that certain terms, such as"upper","lower","front","back","distally',"proximally"and the like, are used frequently throughout the discussion. These terms, however, are merely provided to provide a frame of reference for use with the accompanying drawings and are not intended to specifically limit the inventive concepts described herein.
Referring to Fig. 1, there is depicted an instrument system 20 in accordance with a preferred embodiment of the present invention. A portable examination or diagnostic instrument 24 includes a tethered electrical/video signal connection 26 with a video monitor 28 or other video peripheral device (not shown), although alternately a wireless connection through RF, IRdA or other means, shown figuratively as 32, can also be employed.
Referring to Figs. 1-2 (b), the portable examination instrument 24 includes an instrument head 36 which is attached, releasably or otherwise, to the top of a hand-grippable battery handle 40. The instrument head 36 is shown nearly identically in Figs. 2 (a) and 2 (b), except as noted specifically herein, though the hand-grippable handle 40A shown in Fig. 2 (b) is a variation. Similar variations for use with the instant instrument head 36 are contemplated
within the scope of the present invention. For example, and rather than using a video monitor, the instrument head could include a portable integral display.
Referring to the exploded views of Figs. 2 (a) and 2 (b), the instrument head 36 includes a detector assembly 42 and an optical assembly 70 which are each disposed within the confines of a housing 50. The housing 50 is attached to the hand-grippable handle 40, 40A, by conventional means. For example and as shown in Fig. 2 (b), threaded fasteners 53, can be used to secure the handle 40A to the rear side of the housing 50 using threaded holes 52.
The detector assembly 42 includes an IR element or sensor array 44 having a plurality of miniature infrared sensors 45, Fig. 10, such as the bolometer array manufactured by TI/Raytheon, which are mounted onto a supporting body 48. According to the present invention, a two dimensional 16 x 16 element array is defined, though the parameters thereof can easily be varied depending on the application. Furthermore, a single element or a one dimensional array can also be utilized based on the inventive concepts of the present invention. An enlarged view of an IR sensor array 44 in accordance with the present invention is depicted in Fig. 10. Each of the individual elements 45 comprising the sensor array 44 senses infrared radiation of a portion of a target area, akin to individual pixels of an electronic imager, such as a CCD, and produces an output signal which can be processed through suitable electronics to provide temperature of that sensed portion.
Referring to Figs. 2 (a)-Fig. 4, the optical assembly 70 includes a conically shaped aperture stop 60, which overlays the miniature IR sensor array 44, as well as an objective lens 61 and a relay lens 63 which focus incoming IR light onto the IR sensor array 44 of the detector assembly 42. The aperture stop 60 is mounted by conventional means such as threaded fasteners 65 (Fig. 2b) onto the supporting body 48. The aperture stop 60 includes a central through opening 64 which provides optical access to the IR sensor array 44.
Preferably, the aperture stop 60 is aligned with the IR sensor array 44 and is attached onto the supporting body 48 using fasteners 65 inserted through the holes 66.
Still referring to Figs. 2 (a)-4, the housing 50 includes a substantially frusto-conical insertion portion 78 which is sized to receive a speculum (not shown) and which can be placed up to a predetermined distance into the ear canal of a patient (not shown) such as through the use of a locator 58. The lenses 61,63 combine to focus incoming optical energy
onto the miniature IR sensor array 44. The objective lens 61 is disposed at the distal end of the frusto-conical insertion portion 78 of the housing 50 while the relay lens 63 is placed adjacent the aperture stop 60. The housing 50 is attached to the handle 40,40A by screws 53 that thread into the proximal end of the housing at threaded holes 52, Fig. 2 (b).
Moreover, the objective lens 61 being placed at the distal tip opening of the insertion portion 78 permits a wide field of view in order to"see"the tympanic membrane and to avoid hair, ear wax, and a significant bending portion of the ear canal. The locator 58 is positioned and shaped to allow the distal end of the insertion portion 78 to be repeatably positioned a predetermined distance within the ear canal, but without contacting the tympanic membrane.
The relay lens 63 permits the detector assembly 42 to be positioned within the instrument head 36 wherein the image obtained by the objective lens 61 can be focused thereupon.
The locator 58 provides repeatability and consistency with regard to alignment, depth of field, and orientation of a thermally imaged target area. This provides an additional advantage. For example, a thermal image can therefore be superimposed or have superimposed thereupon, a corresponding digital image of the target area captured by an electronic otoscope (not shown). The image could otherwise be in the form of any other optical data; for example, a spectroscopic or other image of a target area could also be superimposed onto the thermal image using the locator to utilize the same field of view using multiple instruments for obtaining each image or using a single imaging instrument with multiple imaging (thermal, optical, etc.) systems.
The above optical assembly 70 can be adjusted using a focusing screw 57 inserted through opening 68 in the housing 50 and threaded into the supporting body at hole 51. A focus spring 62 provides a biasing force to permit adjustment of the assembly containing the supporting body 48 and aperture stop 60 relative to the housing 50. During adjustment, supporting body 48 slides on pins 47, Figs. 2 (b) and 4, extending from the interior of the insertion portion 78.
Referring to Figs. 3,4, and 6, the aperture stop 60 further limits the amount of energy passing through the optical subassembly 70 from a target area 100 to the IR sensor array 44.
An alternate aperture stop 104 is illustrated in Fig. 5, the aperture stop being thermally linked directly to the supporting body 48 of the detector assembly 42, to provide the same
temperature of the aperture stop as that of supporting body 48 and IR thermal array 44 given that the aperture stop also emits energy which is detected by the IR sensor array 44.
Referring to Figs. 5 and 6, the aperture stops 60,104, as used in conjunction with the optical subassembly 70, provide the following benefits. As noted, the small diameter objective lens 61 can be positioned at the distal end of the insertion portion 78 to bypass hair, ear wax, and significant bending of the ear canal and to provide a relatively wide field of view of the target area. Furthermore, the provision of an aperture stop for the energy focused on the detector assembly 42 by the relay lens 63, insures that the representative pixels of the sensor array 44 see energy emanating only from the target 100, the aperture stop 60,104, and the relay lens 63. The relay lens 63 emits a negligible amount of energy as compared to the target 100 and the aperture stop 60,104. The effect of the aperture stop 104, Fig. 5, is negligible in relation to the signals received by the sensor array 44 in calculating the temperature of the interrogated target area 100. The energy of the aperture stop 60, Fig. 6, can be accounted for by subtraction as part of calibration of the sensor array 44, such as described herein.
Referring to Fig. 6, a movable target 84, such as a diode or other form of calibration element, having a known temperature and emissivity is movably disposed in relation to the optical path 54 to the detector assembly 42 in order to initially calibrate the miniature IR sensor array 44. Alternately, an optical element 98 could be aligned with the target 84 such that either the target 84 and/or the optical element 98"moves"the target into and out of the optical path 54 to the IR sensor array 44.
Referring to Fig. 10, and in lieu of the target 84, Fig. 6, a temperature measuring element 99, such as a thermocouple or thermistor, can be disposed on the supporting body 48 of the detector assembly 42, the element 99 being capable of measuring the reference temperature of the supporting body 48 to permit calibration of the array 44. Alternatively, and still referring to Fig. 10, one of the pixels 101 of the array can be"blinded"to incoming energy from the target to achieve a similar effect. It should be further noted in passing that a temperature measuring element, such as described above, could otherwise be disposed (e. g., on the aperture stop 60, Fig. 6).
Referring to Figs. 7-9, the display output of the IR sensor array 44 can be demonstrated to cover various forms. In a first version shown in Fig. 7, the display output
can take the form of a matrix or grid 106 having individual numeric processed temperature values 108. The displayed temperatures 108 can cover a portion of the grid 106, indicating only those temperature values exceeding a specific threshold temperature, as shown, or all of the sensor processed output values can be displayed.
According to Fig. 8, the display output 110 can be arranged into a predetermined format. For example and as shown, output signals of the individual sensors can be segregated' into different visually perceivable forms, such as textures or false colors, such as first, second, third, and fourth ranges 112,114,116,118, respectively, leading the user to identify a"hot" spot 122. It should be readily apparent that literally any visually perceivable form could be utilized in order to provide contrasts between ranges of temperatures as detected by the IR sensor array 44.
Alternately and in lieu of providing a field of view as shown in Figs. 7 and 8, a simplified display output 126 can include merely the hottest temperature in the field of view as a single temperature value, 130, such as shown in Fig. 9. It will be readily apparent that other forms of representation can be contemplated by one of sufficient skill in the field.
There may be situations, as described herein below, in which the displayed temperature is not the hottest temperature of the target area. In those instances, the display output 126 can also include an indicator 134 which informs the user that the displayed temperature 130 is estimated.
The detection of the hottest temperature of a medical target area, such as the ear, indicates body core temperature given that the arteries in the tympanic membrane are closely tied to the hypothalamus, the temperature regulator of the human body. Identification of body core temperature as described herein through the use of an IR sensor array provides an improvement in accuracy and reliability in the field of thermometry. In addition, and based on an adequately high signal to noise ratio, the pulse rate of the patient can also be determined due to flow of hot blood into the arteries. The transient effect can be included in each of the above display representations or separately to indicate this value.
As alluded to above, it is possible that the hottest temperature might not be directly discernible based on either the presence of an obstruction or that the hottest temperature of the target area is not in the immediate field of view of the IR sensor array 44. For example, and as shown in Fig. 11, it is possible that a portion 129 of an overall target area 120 (in this
case a portion of the tympanic membrane 121) is obstructed, as denoted by phantom line 124, such as by ear wax, an abscess, ear canal wall etc., which blocks the hottest spot 128 (that is the spot having the highest temperature) from view.
Referring to Figs. 11-14, a methodology of estimating a hottest temperature is illustrated pictorially. The processing electronics provided in the detector assembly 42, Fig.
3, includes a microprocessor (not shown) having sufficient memory for storing the calibrated values of the output signals of each of the IR sensors 45, Fig. 10, of the IR sensor array 44, Fig. 3.
Due to the presence of the obstruction shown in Fig. 11, a corresponding temperature profile 132 would be detected by the present sensor array. In actuality, however, the obstructed portion of the temperature profile 132 would be correctly represented by the profile depicted as 136 including the hottest spot, depicted as 128 in Fig. 11, and indicated as 140 in Fig. 12, if the obstruction did not exist.
Referring to Fig. 13, a predetermined number of points 144,145,146 along the profile 132 are processed due to the increase in temperature. A highest point is then extrapolated by curve fitting through the points 144,145,146 to determine an estimated hottest spot 140a, Fig. 14 through fitted curve 136a, Fig. 14.
Referring to Fig. 21, a hottest temperature of a target area can also be interpolated through curve fitting, for example, if the hottest spot is"between"pixels of the sensor array 44, Fig. 10, such as fitting an appropriate curve or temperature profile 157 through a number of predetermined temperature points 152 and interpolating an estimated hottest temperature 158.
Referring to Figs. 15 and 16, and as noted, it is also possible that the hottest temperature is not within the field of view of the instrument. According to a preferred embodiment of the invention, the instrument includes an indicator 150 connected in relation to the processing electronics of the device, the indicator having a set of directional guides 154 arranged in 90 degree intervals about a center guide 156. It should be readily apparent that the above description is exemplary as any varied number of directional guides can be suitably placed along a periphery. As the instrument is used, the hottest temperature in the field of view of the IR sensor array is determined and the locale of the hottest temperature is indicated by a corresponding directional guide 154. The guide 154 aids the user in adjusting the field
of view of the instrument by moving the instrument in the direction indicated by the indicator 150. As the instrument is adjusted by the user, the directional guide 154 will shift until the hottest temperature value is eventually located in the center guide 156, as shown in Fig. 16, thereby indicating that the hottest temperature value has been centered in the field of view.
During the adjustment, it is possible that a new hottest temperature will be located, the value of this temperature being stored into memory and compared using the processing electronics during use as the field of view is changed. Alternately, and rather than using multiple LEDs as shown in Figs. 15 and 16, a single LED could be provided. In this instance, the LED could provide the user with a visual indication when the hottest temperature has been detected by the microprocessor.
Alternately, other indicating means could be employed to notify the user that the hottest temperature of a target area has been located or identified, such as, for example, an audio signal or tactile feedback, such as a vibrational signal.
Referring to Figs. 17-19, alternate techniques are herein described in lieu of using a two dimensional IR sensor array. That is, alternately, an examination instrument 160 can utilize a single sensor or one dimensional IR sensor array 166 in conjunction with a movable mirror 170 to scan the target area of interest, as defined by 176 in two dimensions. The mirror 170 is retained within an instrument housing 164 and is made rotatable, for example, as supported within a frame 180 having rotatable sections 184,188 to provide rotation as indicated by arrows 189 about respective axes 187 to define a scan field 190 of the target area. An alternate micro-machined sensor support 192, in this case for a single IR sensor 166, is illustrated in Fig. 19, the support being translatable along orthogonal axes 196,198. In this case mirror 170, Fig. 17, is stationary and the single IR sensor 166 translates in the two orthogonal directions to capture each portion of field 190. As in the preceding, the sensor 166 can be calibrated using a movable or dedicated reference temperature element (not shown), or the other methods described in the preceding embodiment.
Finally, referring to Fig. 20, a further embodiment partially depicts an apparatus 200 including a single IR sensor 202 disposed within a housing 203. The sensor 202 or linear (one-dimensional) sensor array can be translated along orthogonal directions 208, 210 with respect to a target area 212 through a lens or aperture 204. The aperture 204 or lens can
alternately be moved (i. e. translated) in a similar manner to effectively scan a thermal image of the target area 212.
Though the above invention has been described in terms of certain embodiments, it will be appreciated that variations and modifications are possible within the scope of the invention as claimed herein, including use for various medical and industrial targets capable of being thermally imaged. For example, a similar IR sensor array assembly could be incorporated into an endoscope or laparoscope in order to examine a polyp or the appendix.
Likewise, a sensor assembly as described could also be included in a borescope for examining the interior of an industrial target, such as the interior of an aircraft engine.