Thermally isolated probe

Abstract: The thermal isolation apparatus for the protruding probe (16) of a biomedical thermometer (10) includes an insulative air gap and a heat sink (20) disposed between the surface of the probe and the optical path through the probe. The heat sink surrounds the optical path, such as a waveguide (18), and acts to evenly distribute any heat along the entire length of the waveguide to avoid temperature variations. Additionally, the heat sink has sufficient mass for high heat capacity and may slow the progress of any heat from reaching or leaving the waveguide until after the measurement by the biomedical instrument has been completed. Disposed over the heat sink is a boot (24) which forms the closed air space between the heat sink and the outer probe surface. The air gap combined with the heat sink provide relative thermal isolation of the optical path through the probe and provide relative thermal isolation of the target anatomy from the temperature of the probe.

Description: Field of the Invention: This invention relates generally to a thermal isolation apparatus for biomedical instrumentation, and more particularly relates to thermally isolating a probe of a biomedical thermometer. Description of Related Art: Medical thermometers are useful in the diagnosis of many diseases. Infrared (IR) biomedical thermometers have been adapted for measuring temperature from the auditory canal and the tympanic membrane. Such thermometers typically have an optical path, for example a waveguide, connecting the tip of the probe to a thermal detector located in the body of the thermometer. Temperature stability of this optical path is desirable so that it does not add unknown thermal components and adversely affect the temperature measurement of the patient. Contact of the probe with the ear of the patient may cause a cooling or heating of the ear canal depending upon the relative temperature of the probe, it may also cause heat of the patient to be conducted through the probe and to the waveguide which may result in "hot spots" or temperature variations in the waveguide, and an inaccurate temperature measurement of the patient may result. While it is desirable that physical contact of the probe with the patient not occur, such contact is inevitable. The length of such contact and the point or points of the probe contacting the patient vary with each user of the probe and with the physical configuration of each patient. While probe covers may be used over the thermometer probe to prevent contamination of the probe, these covers typically do not provide substantial thermal isolation by themselves and in fact may, if the probe cover is substantially hotter or colder than the probe or the ear canal, themselves undesirably affect the thermal performance of the probe and the temperature of the ear canal. Problems associated with prior art probes include: temperature differences along the optical path ("hot spots") which impair the thermal performance of the thermometer, the temperature differences resulting from a lack of thermal isolation; potential damage to the waveguide caused by subjecting the probe tip to excessive shock; contamination of the waveguide by dirt or other debris via the probe's distal end; and the need to replenish gases within the waveguide tube when the window at the distal end is replaced. A discussion of pertinent temperature sensing devices follows. An infrared thermometer having a probe for receiving the infrared energy of a patient's ear is described in United States Patent No. 4,895,164 to Wood. The probe comprises a waveguide for communicating the thermal energy from the probe tip to a thermal detector. The waveguide is protected only by a replaceable speculum that may be inadequate to prevent damage to the waveguide if the probe tip is subjected to excessive shock, such as that which can occur if the thermometer were dropped on the probe tip. Moreover, the waveguide is not sealed at its distal end by anything besides the replaceable speculum, thus being subject to contamination by dirt or other debris when the speculum is not in place on the probe tip. A similar approach is shown in PCT Pub. WO-A-90 06090 which also discloses a probe having a waveguide with a heat sink in an infrared thermometer. The waveguide is filled with a gas such as Xenon, and is closed by a germanium window affixed to the distal end of the waveguide. This reference contains no disclosure or teaching of the window being replaceable. In fact, the reference states that the tube is "closed" by the window and that the tube holds Xenon gas. This arrangement is disadvantageous in that if the window becomes damaged, replacement of the window would not be easily accomplished. Replacement would require removing the damaged window, replenishing the Xenon gas, and mounting and sealing a new window. Thus, it would be desirable for an infrared biomedical probe to include an apparatus for thermally isolating the optical path of the probe from thermal energy which may be transferred to or from the probe by patient contact, by installing a new probe cover, and from other sources of heat or cold with which the probe may come into contact during use. The present invention addresses these needs and provides a solution to the other problems associated with prior art probes as discussed above. SUMMARY OF THE INVENTION Briefly, and in general terms, the invention provides an apparatus for thermally isolating the optical path through the probe of an infrared thermometer and for thermally isolating the exterior surface of the probe from the interior of the probe. A heat sink means is provided in thermal communication with the waveguide of the probe for minimizing the effects of extraneous thermal influences on the thermometer. The heat sink means is made of an excellent thermal conductor such as copper having a high thermal diffusivity and conductivity and has sufficient mass for high heat capacity. The thermal isolation apparatus also comprises a closed air gap provided between the heat sink of the probe and the outer surface of the probe. In one embodiment, an outer boot forms the outer surface of the probe and has an inner contour generally conforming to the outer surface of the heat sink. The boot is spaced apart from the heat sink over the entire length of the waveguide in the probe and forms a thermal isolation air gap between the waveguide and the boot. The combination of the air insulation with the heat sink provides relative thermal isolation of the probe's optical path and provides relative thermal isolation of the exterior of the boot. The present invention provides a hand-held biomedical apparatus adapted to communicate electromagnetic energy to an energy detector. The apparatus comprises a probe having an outer surface, a first optical opening facing the electromagnetic energy to be communicated, a second optical opening facing the energy detector, with the first optical opening and the second optical opening defining an optical path, a waveguide disposed in the optical path and extending between the first and second openings, and a heat sink in thermal contact with the waveguide. The apparatus is characterized in that the apparatus further comprises: an outer boot positioned over the heat sink and having an inside surface separated from the heat sink, the separation providing a closed layer of insulating air between the heat sink and the inside surface of the outer boot along the entire length of the waveguide in the probe; and the outer boot comprises a distal tip portion that is involuted to provide a portion of the closed layer of air insulation and to close the air space around the distal end of the probe. In an embodiment the biomedical apparatus is further characterized in that the apparatus comprises a removable window (22) formed of a rigid material that is transparent to said electromagnetic energy; wherein the outer boot is removable and is adapted to secure the removable window at a position internal to the boot and in place at said first optical opening such that when the boot is removed, the window may be removed. The apparatus may further be characterized in that the apparatus comprises a removable sleeve having an opening, said window adapted to fit within the opening of said sleeve and be held in position in the sleeve, wherein the removable outer boot is also adapted for retaining said sleeve at said first optical opening; and said sleeve and window being removable after the boot has been removed from the probe. The apparatus may be even further characterized in that the removable sleeve comprises a flange; the heat sink comprises an inset portion for slidable receiving the flange of the sleeve; and the removable outer boot contacts the flange of the sleeve to hold the sleeve and window in place at the first optical opening when the boot is in place and the sleeve and window are slidable removable from the heat sink when the boot is removed from the probe. The removable outer boot may be formed of a durable material and the involution of it may extend distally beyond the window to provide shock protection to the window. Other aspects and advantages of the invention will become apparent from the following detailed description, and the accompanying drawings, which illustrate by way of example the features of the invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front perspective view of a hand held biomedical thermometer which shows the protruding probe; FIG. 2 is a partial sectional view through the axis of the probe of the thermometer shown in FIG. 1; and FIG. 3 is an exploded view of the thermal isolation boot and the heat sink containing the waveguide portion of the probe of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As is shown in the exemplary drawings, the invention is embodied in a thermal isolation apparatus for a probe of a biomedical thermometer. The probe includes a waveguide which receives and channels infrared radiation to an infrared detector in the body of the thermometer. The thermal isolation apparatus isolates the waveguide and other optical path components from producing or receiving extraneous thermal influences which may arise during use. Referring now to FIGS. 1 and 2, a biomedical infrared thermometer 10 is shown for sensing the temperature of a patient. The body of the biomedical thermometer 11 houses an infrared radiation detector (not shown) and functional elements necessary for the detection of the temperature of the patient based upon the infrared radiation received by the thermometer from a body cavity such as the tympanic canal, or other portions of the patient's anatomy. The thermometer is preferably a hand held type including a handle 12, and an on-off trigger switch 14, so that the temperature readings may be quickly taken by the user by pointing the protruding probe 16 end at the target area of the patient from which a temperature reading is to be taken, such as the tympanic membrane. The probe 16 includes a waveguide portion 18, which is preferably formed of a highly thermally conductive material such as copper, although it may be formed of other good heat conductive and reflective or platable material such as aluminum, brass, stainless steel, or the like. Surrounding the waveguide 18 is a heat sink 20. The heat sink may be integral with the waveguide 18 or may be a supporting structure within which the waveguide is mounted. Preferably, the waveguide is formed by forming a channel through the heat sink and plating the channel with a substance which is highly reflective to infrared energy, such as gold. In another embodiment, the waveguide may be formed by inserting an intimately bonded sleeve of reflective material into the channel. The heat sink is in thermal communication with a heat sink 19 in the body 11 of the thermometer formed of a similar material. In the embodiment shown in FIG. 2, the waveguide is generally cylindrical in shape and extends axially through the heat sink 20 for communication of infrared energy from the temperature source to the infrared detector. In another embodiment, the waveguide is frustro-conically shaped with the larger opening at the distal end of the probe for direction at the patient. The smaller opening faces the IR detector in the body of the thermometer. This configuration resulted in more IR energy from the patient reaching the detector. In this embodiment, the waveguide opening at the distal end of the probe was selected to be a particular size based on the opening of the average ear. This size was larger than the size of the waveguide opening permitted by the particular detector used. Thus a frustro-conically shaped waveguide was used, although with other applications, a differently shaped waveguide may be more appropriate. Referring now to FIGS. 2 and 3, a window 22 is disposed at the end of the waveguide 18, and is mounted and protected in a transparent sleeve 23 placed over the distal tip of the waveguide 18 and the window 22. The window 22 may be formed of a glass-like material such as zinc selenide which is substantially transparent to infrared energy. Alternatively, the window could be made of polyethylene or other similar materials that are also substantially transparent to infrared energy. In the embodiment disclosed, the zinc selenide window passes the infrared energy while sealing the end of the waveguide from contamination. The sleeve 23 is preferably generally tubular and is made of a rugged material such as stainless steel to protect the window 22 and waveguide end. Additionally, the material is chosen to have a low thermal conductivity to provide additional insulation for these same two elements. In one embodiment, low thermal conductivity stainless steel was used. The sleeve 23 may also include a flange 32 at one end to fit snugly against a correspondingly inset portion of the heat sink 20. The sleeve 23 preferably includes a lip around the inside of the end of the sleeve away from the flange end 32 for retention of the window 22 during assembly, and a series of holes around the lip end of the sleeve through which adhesive may be applied to the edge of the window to permanently bond it in place in the sleeve 23. The window 22 and the sleeve 23 assembly can therefore be readily removed and replaced by sliding the sleeve 23 off the end of the waveguide 18. The heat sink 20 shown in FIGS. 2 and 3, is generally conically shaped so that it will fit inside the outer boot 24 as is discussed below. The heat sink 20 is used to insulate the waveguide 18 from extraneous heat sources and to avoid the generation of "hot spots" or temperature variations along the waveguide. As used herein, hot spots are areas of significantly different temperature from the average temperature of the waveguide. When the probe is used to measure the temperature of a patient, it may come into contact with the patient at a point or points on the probe. It is desirable that the heat of the patient received by the probe due to contact at this point or points, not be conducted to the waveguide or if it is, at least be conducted evenly around the waveguide so that hot spots are not formed. In order to resist the formation of hot spots, the heat sink 20 is formed of a material having high thermal conductivity and diffusivity. By using such a material, the heat conducted to the heat sink at this point or points will be evenly distributed throughout the heat sink and along the waveguide. Additionally, the mass of the heat sink 20 is selected to have a high heat capacity. Depending on its size, the heat sink may present such a large heat capacity to the heat or cold source, that before any temperature change can reach the waveguide, which is located at the center of the heat sink, the temperature measurement of the patient will have been completed. In the embodiment shown in the FIGS., the heat sink 20 was formed of copper. In addition to having high thermal conductivity, high thermal diffusivity and sufficient mass for high heat capacity, it provides an excellent surface on which to plate highly thermally conductive materials, such as gold, to form the waveguide 18. Another means of thermally isolating the probe includes forming a closed air space around the optical path. Mounted over the heat sink 20 of the probe is an outer boot 24 which contacts the heat sink 20 at the proximal base portion 26 of the boot, and contacts the sleeve 23 at the distal tip portion 28 of the boot. The outer boot may be approximately 2.54 mm (0.10 inch) thick and is preferably formed of a durable, hard plastic such as ABS, which is well known for its durability and thermal insulation properties and which can be plated with reflective materials. However, other materials may also be suitable. One or more tabs 27 are preferably provided for interfacing with corresponding slots (not shown) in the body 11 of the thermometer for securing the boot 24 to the thermometer. The inner surface of the boot between the proximal and distal areas of contact with the waveguide 18 is preferably spaced from the outer surface of the waveguide 18 by typically approximately 1.02 mm (0.04 inches) although the spacing can vary, depending on the amount of air desired. A chamber forming a closed air space or air gap 25 is thereby formed between the boot and the waveguide, providing a layer of insulative air around the probe to further protect the waveguide channel from transient temperature changes due to patient contact or other extraneous thermal sources and protecting the target from temperature change due to contact with the probe. The air gap preferably extends inside the boot 24 from the area where the proximal base portion 26 of the boot contacts the heat sink 20 to an area approximately where the distal tip portion 28 of the boot contacts the sleeve 23 over the distal tip of the probe. The distal tip 28 of the boot is preferably involuted to form an inwardly folded extension 29 which slips over the sleeve 23. This configuration holds the window and sleeve in position at the distal end of the waveguide 18. The air gap therefore extends forwardly between this inwardly folded extension 29 and the base portion 26 of the boot so that the air gap thermally isolates the entire length of the waveguide in the probe from thermal influences outside the boot. In considering the amount of thermal isolation required for the probe, at least three situations would typically be considered: 1) the patient could be hot relative to the temperature of the probe; 2) the patient could be cold relative to the temperature of the probe; and 3) the protective probe cover placed over the probe for hygienic and protective reasons could be either hot or cold relative to the probe temperature. In addition to the above three situations, two other factors are normally considered when determining the dimension of the air gap: 1) the amount of time the detector takes to complete its temperature measurement; and 2) the typical amount of time that the instrument operator will leave the probe in contact with the patient while taking the patient's temperature. In an embodiment of the invention, an air gap formed between the heat sink 20 and the inside surface of the outer boot 24 within the range 0.51 to 1.52 mm (0.020 to 0.060 in.) was found to be very effective in isolating the optical path in the probe from external temperature influences encountered in normal use. Thus the combination of a heat sink with high thermal diffusivity, high thermal conductivity, sufficient thermal mass for high heat capacity and a closed air space having low thermal diffusivity and conductivity results in relative thermal isolation. The heat sink and air gap thermally isolate the infrared optical path in the probe portion of the thermometer from extraneous thermal changes. Additionally, the combination of the two provide enough thermal protection such that a measurement may be completed prior to thermal influences reaching the waveguide.

Claims: A hand-held biomedical apparatus adapted to communicate electromagnetic energy to an energy detector, the apparatus comprising a probe (16) having an outer surface, a first optical opening facing the electromagnetic energy to be communicated, a second optical opening facing the energy detector, said first optical opening and said second optical opening defining an optical path, a waveguide (18) disposed in the optical path and extending between the first and second openings, a heat sink (20) in thermal contact with the waveguide (18), characterized in that: the apparatus further comprises an outer boot (24) positioned over the heat sink (20) and having an inside surface separated from the heat sink (20), the separation providing a closed layer of insulating air (25) between the heat sink (20) and the inside surface of the outer boot (24) along the entire length of the waveguide (18) in the probe (16); and the outer boot (24) comprises a distal tip portion (28) that is involuted to provide a portion of the closed layer of air insulation (25) and to close the air space around the distal end of the probe. The biomedical apparatus according to claim 1 further characterized in that the apparatus comprises a removable window (22) formed of a rigid material that is transparent to said electromagnetic energy; wherein the outer boot (24) is removable and is adapted to secure the removable window (22) at a position internal to the boot (24) and in place at said first optical opening such that when the boot (24) is removed, the window may be removed. The apparatus according to claim 2 further characterized in that: the apparatus comprises a removable sleeve (23) having an opening, said window (22) adapted to fit within the opening of said sleeve (23) and be held in position in the sleeve (23), wherein the removable outer boot (24) is also adapted for retaining said sleeve (23) at said first optical opening; and said sleeve (23) and window (22) being removable after the boot (24) has been removed from the probe (16). The apparatus according to claim 3 further characterized in that: the removable sleeve (23) comprises a flange (25); the heat sink (20) comprises an inset portion for slidably receiving the flange (25) of the sleeve (23); and the removable outer boot (24) contacts the flange (25) of the sleeve (23) to hold the sleeve (23) and window (22) in place at the first optical opening when the boot (24) is in place and the sleeve (23) and window (22) are slidably removable from the heat sink (20) when the boot (24) is removed from the probe (16). The apparatus of any preceding claim further characterized in that: the removable outer boot (24) is formed of a durable material; and the involution of the removable outer boot (24) extends distally beyond the window (22) to provide shock protection to the window (22).

Inventors: DEFRANK MICHAEL P, ROSATI ROBERT J, DEFRANK, MICHAEL P., ROSATI, ROBERT J.
Applicants: IVAC CORP, IVAC CORPORATION
Application year: 1991
Main classification: G01J5
IPC codes: G01J5, G01K13, A61B5