Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-09-29
2001-08-07
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S200000
Reexamination Certificate
active
06272375
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to an infrared thermometer, and, more particularly, to an infrared medical thermometer that receives infrared emission from the tympanic membrane via a narrow fiber optic cable with a radially varying index or refraction, thereby measuring core body temperature.
The core body temperature of a person or of a warm blooded animal reflects the state of his, her, or its health. Fevers of 1° C.-2° C. above normal are the body's normal response to infection. Higher temperatures, as in heat stroke or severe infection, can be rapidly fatal. Thus, measurement of core body temperature is an important medical diagnostic tool, particularly with patients, such as animals and young children, who cannot describe their symptoms verbally. The tragic consequences of misdiagnosing potentially fatal human diseases are obvious. Ignorance of dangerously elevated temperatures in valuable animals may have severe economic consequences, for example if the animals are race horses which have not been acclimated to hot and humid climates.
The classical way to measure core body temperature is by using a rectal thermometer. This requires more cooperation from the patient than often may be forthcoming. Some adult humans and many animals may regard the insertion of foreign body in their rectums as an invasion of their privacy. In a clinic or hospital setting, routine use of a rectal thermometer invites the risk of transferring infection body fluids among patients if proper hygienic precautions are not taken. Thus, it would be highly advantageous to have a non-contact method of measuring core body temperature.
More localized temperature measurements may be diagnostic of localized infections, particularly infections of the middle ear. It is important to know which, if either, of a patient's two ears is infected, particularly if the therapy is to include myringotomy, which includes piercing the tympanic membrane and draining the fluid to from the middle ear. Being able to clearly distinguish which of a patient's two tympanic membranes is hotter would make this diagnosis much easier, especially if the patient is too young to describe his or her symptoms verbally.
One promising non-contact method of measuring temperature is infrared thermometry. All material bodies emit electromagnetic radiation. The emission spectrum is described by Plank's law. Bodies at temperatures near ordinary room temperature have emission spectra that peak in the mid-infrared, at wavelengths around 10 microns. By the Stefan-Boltzmann law, the intensity of emission is proportional to the fourth power of the temperature. Thus, the temperature of an object can be measured by measuring its infrared emission, using any one of many sensors known to the art, such as thermopiles, pyroelectric sensors, bolometers, or active infrared sensors. Several such devices have been patented, for example, by Fraden (U.S. Pat. No. 5,368,038), Seacord et al. (U.S. Pat. No. 5,167,235), and Pompei (U.S. Pat. No. 5,445,158). These three patents are incorporated by reference for all purposes as if fully set forth herein. In these devices, infrared radiation from both the tympanic membrane and the walls of the ear canal are transmitted by a waveguide to an infrared sensor. These devices provide means for convenient non-contact body temperature measurement. However, they sense infrared radiation emitted both by the tympanic membrane and by the generally cooler ear canal. Therefore, they do not measure the true core body temperature, and do not have sufficient resolution to distinguish infected ears from uninfected ears. Pompei recognizes this problem, and advocates scanning the tympanic membrane, on the unverifiable assumption that the highest temperature thus measured is the true core body temperature.
There is thus a widely recognized need for, and it would be highly advantageous to have, a medical thermometer capable of non-contact measurement of core body temperature via measurement of tympanic membrane temperature alone, without interference by infrared emissions from the surrounding ear canal.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an otoscope for measuring the temperature of a tympanic membrane on the basis of mid-infrared radiation emitted by the tympanic membrane, including: (a) a waveguide for conducting the mid-infrared radiation from the tympanic membrane, the waveguide having: (i) a distal end for receiving the mid-infrared radiation from the tympanic membrane, and (ii) a proximal end; (b) an optical mechanism for simultaneously observing the distal end of the waveguide and the tympanic membrane to determine a distance of the distal end of the waveguide from the tympanic membrane; (c) a positioning mechanism for positioning the distal end of the waveguide at a desired distance from the tympanic membrane; and (d) a radiometer optically coupled to the proximal end of the waveguide, the radiometer including a mid-range infrared sensor.
Our improvement in infrared thermometry is an extension of teaching of Seacord et al. They disclose the use of a fiber optic cable to conduct infrared radiation from the target to the infrared sensor. Their fiber optic cable is a bundle of many thin fibers. The fiber optic cable of the present invention is a single fiber with particularly advantageous physical and chemical properties.
In preferred embodiments of the present invention, the cable is made of crystalline silver halides, preferably a mixture of silver chloride and silver bromide, as described below. The cable is transparent to mid-range infrared radiation of wavelengths between 3 microns and 25, microns with a transmission less than 0.2 dB/meter at 10.6 microns. This low transmission loss means that, unlike Seacord et al.'s fiber bundle, the single fiber cable of the present invention transmits useable levels of infrared radiation over distances as great as 10 meters. Thus, the cable can extend outside the housing of the thermometer itself, and can be positioned within a few (1 to 5) millimeters of a confined target such as the human tympanic membrane. The cable can be fabricated with a diameter as small as 0.5 millimeters, thus being able to resolve the temperature of targets, such as the human tympanic membrane, whose size is on the order of several millimeters, without interference from infrared emission from other nearby bodies. The field of view of the optical fiber can be narrowed further by properly adjusting the radially decreasing index of refraction. A smaller field of view increases the spatial resolution of the measurement, because the fiber “sees” a smaller area of the target. The cable is flexible, insoluble in water, and stable with respect to decomposition by light. Unlike hollow waveguides, whose transmission and field of view are strongly dependent on their radii of curvature, the cable can be curved to relatively small radii curvature without losing its advantages, because its transmission and field of view are practically independent of the radii of curvature. Unlike optical fibers made from other media transparent to mid-range infrared radiation, such as chalcogenide glasses and fluoride glasses, the cable is nontoxic and nonhygroscopic, which are very desirable properties in medical applications.
To make it easier to position the distal end of the cable near a small target, preferred embodiments of the present invention incorporate further means for observing the relative positions of the distal end and the target, and for moving the distal end relative to the target. In a preferred embodiment of the present invention intended for medical use, the distal end of the cable is movably inserted into the speculum of a conventional otoscope, so that a physician can look through the otoscope at the patient's ear canal and position the distal end of the cable within a few millimeters of a patient's tympanic membrane without rupturing the membrane.
It is to be understood that the preferred embodiments of the pr
Derow Ari
Eyal Ophir
Katzir Abraham
Friedman Mark M.
Lateef Marvin M.
Shaw Shawna J
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