Non-invasive temperature measurement method and apparatus

Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor

Reexamination Certificate

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C600S475000

Reexamination Certificate

active

06220750

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to temperature measurement. More particularly, the invention relates to a method and apparatus for the accurate measurement of the core temperature of a body by sensing the temperature at points outside the body.
BACKGROUND OF THE INVENTION
Temperature measurements are widespread and essential in many fields of modern life, such as industry, science, medical care and many other basic human needs. A lot of processes in industry are temperature controlled or strongly affected by temperature. Therefore, accurate temperature measurements are required for carrying them out properly. The same requirements apply also in science, when experimentation and research often require temperature sensing. Human body temperature measurements are mandatory in many cases. Accurate measurement of human body temperature is carried out as a routine in hospitals and clinics and is generally required for medical care in view of its symptomatic significance.
Mercury thermometers are used frequently for measuring the temperature of the human body orally, in the axilla or rectally. However, in spite of the fact that such measurements are in themselves accurate, they often poorly reflect the inner temperature of the human body, since there is a substantial difference between said temperature and that of the sensed area and, further, the temperature that is read depends of the way the thermometer tip is held in the measurement. Another reason for inaccuracy is associated with different modes of operation of the thermometer. For instance, if the patient is a child, using the thermometer orally, the heat conduction from his mouth to the thermometer may vary according to the orientation of the tip in the child's mouth and the fact that he opens it from time to time. Another disadvantage of the mercury thermometer is its fragility. In addition, it should be sterilized after each use.
Oral and rectal measurements are also inconvenient for the patient, and in some cases may even be painful. Surface or external measurements, such as by thermometers attached to the skin, are less inconvenient but even less accurate. Optimally, these thermometers measure the skin temperature, which may substantially differ from the relevant inner body temperature by as much as 10° C. and even more, if the contact with the skin is poor. Thermal conduction and heat flow affect surface temperature measurements. For example, the human body is not well insulated from the ambient and there is a constant heat flow from the skin to the ambient and from the body core to the skin. Thus, under normal conditions, the skin temperature is always colder than the core temperature to be measured. In addition, thermal conduction between the skin and the thermometer is affected by several factors, such as adhesion and skin humidity. Additionally, heat is lost by the thermometer to the ambient in an amount depending on the insulation of the thermometer.
Another disadvantage associated with conventional thermometers is the time required to take a temperature. At least a minimum time, which may be more than three minutes, is needed for a reasonable measurement accuracy. Some patients, for instance children, do not stand such relatively lengthy measurements. Further, in hospitals, reading the temperature of each patient several times a day requires an unacceptable part of the nurse's duty time.
Other thermometers use an Infra-Red technology, thereby reducing the measurement time. Temperature is read by inserting the sensor into the ear channel measuring the amount of the IR radiation emitted from the channel, and converting it to temperature values. Still, this measurement is relatively expensive, and often does not correlate well with the body temperature.
U.S. Pat. No. 3,702,076 discloses an electronic thermometer, which provides a temperature measurement output as a direct digital, display. U.S. Pat. No. 3,942,123 describes an electronic thermometer based on an electrical bridge with a thermistor in one arm of the bridge. A shunting impedance is switched into and out of the balancing arm of the bridge in a manner providing indication about the measured temperature, according to the thermistor resistance value. U.S. Pat. No. 3,926,053 describes an apparatus of non-contact surface temperature determination on a rotating part, which comprises a sensing probe unit for temperature and distance detection and a capacitive excursion measurement system. However, each apparatus described in said patents provides only indications about the surface temperature, and still lacks the core temperature measurement capability.
It is an object of the present invention to provide a method and an apparatus for accurate measurements of body core temperatures, which overcome the drawbacks of prior art methods and devices.
It is another object of the invention to provide a non-invasive method and apparatus, which permit the accurate estimation of body core temperature from temperature measurements external to the body.
It is a further object of the invention to provide a method and apparatus for the estimation of body core temperatures, which permit to reduce the time required for the measurement without significant loss of accuracy.
It is a still further object of the invention to provide a method and apparatus which achieve the aforesaid objects in the measurement of the human body temperature without causing discomfort to the patient.
Other purposes and advantages of the invention will appear as the description proceeds.
SUMMARY OF THE INVENTION
In describing the invention, it will be assumed that the body, the temperature of which is to be measured, has an inner portion the temperature of which is substantially constant (hereinafter called “the body core” or “the core”), a surface, from which heat is dissipated into the surrounding ambient, and a layer between the core and the surface (which may be called “subsurface layer”) wherein the temperature gradually decreases from that of the core to that of the surface. In the case of a steady heat flow and a constant conductivity throughout the subsurface layer, said temperature decrease is linear. It is assumed that since there are no heat sources in the body except the core, the temperature falls as a monotonous decreasing function from the core to the surface. Under these conditions, in steady state, if it is found that two intermediate points along a path between two extreme points have the same temperature, the two extreme points must be at the same temperature. This invention is based on the concept that, if a path for heat flow can be created between the core of the body, the temperature of which is to be measured (hereinafter, briefly “the body”), and points outside said body, and the flow of heat along this path can be controlled so that two points of said path are at the same temperature, under thermal equilibrium, this indicates that heat flow has ceased and their temperature will be the same as that of the core.
This invention therefore provides a method of measuring the temperature of the core of a body, which comprises:
a) providing a heat conductive space outside the body and in contact with its surface;
b) monitoring the difference of the temperatures of two points located within said space and at different distances from said body surface;
c) if said temperature difference indicates that heat is flowing from the body surface outwards, generating heat in said space, whereby to reduce said temperature difference; and
d) monitoring said temperature difference, and assuming the temperature of one of said two points, when said temperature difference is zero, as the temperature of body core.
Preferably, said body core temperature is displayed.
In one variant of the invention, the generation of heat in the heat conductive space is continued until the temperature of said two points located within said space has been equalized and the temperature of one of said two points, preferably the one nearer the body surface, is measured. In another variant of the

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