Thermal measuring and testing – Temperature measurement – Nonelectrical – nonmagnetic – or nonmechanical temperature...
Reexamination Certificate
1999-12-06
2001-09-04
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Temperature measurement
Nonelectrical, nonmagnetic, or nonmechanical temperature...
C374S001000
Reexamination Certificate
active
06283632
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a temperature sensor for medical applications, a method of making the same, and a method of measuring temperature.
BACKGROUND OF THE INVENTION
For use in a microwave hyperthermia therapy against cancers, various thermometers have been used employing an optical fiber for measuring the temperature at local portions of a body. Optical thermometers have been used for the reasons that correct measurement is obtained without interference from electromagnetic waves and no electric shock is given to the living body. It is desired to use the optical thermometer not only for the hyperthermia apparatus but also for extracorporeal blood circulation instruments such as an artificial heart-lung device or an artificial dialysis device, as well as for probing the blood during cardiac catheterization, since it is capable of reducing the danger of electric shock.
At present, there have been proposed optical thermometers employing optical fibers in four principal systems.
A first system is a sensor using a semiconductor as a transducer. That is, the semiconductor usually exhibits an energy gap that varies depending upon a change in the temperature and, hence, exhibits an optical absorption and an accompanying light transmission spectrum that changes thereto. Therefore, there has been proposed an optical fiber sensor by utilizing such properties (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 62-85832). For example, InGaAs and GaAs may be used as semiconductors. FIG.
9
(A) shows an example of the constitution of a temperature sensor using such a semiconductor. A sensor
11
composed of the above semiconductor is fixedly provided to an end of optical fiber
10
on the side closer to a body that is to be measured, and a suitable reflector plate
12
is brought into contact with the sensor. Light having a suitable wavelength is permitted to be incident (L
IN
)on the other end of the optical fiber: the incident light is reflected by the reflector plate
12
via the semiconductor sensor
11
and returns back to the incident end passing through the semiconductor sensor
11
again. The intensity of light at this moment is measured to determined the temperature of the body that is being measured. FIG.
9
(B) shows a relationship between the wavelength of light in the semiconductor and the transmittance factor for a semiconductor sensor having a thickness of 250 &mgr;m, from which it will be understood that the transmittance changes depending upon the temperature. (Curve “A” illustrating the relationship at 53° C., and curve “B” illustrating the relationship at 40° C.) By utilizing these characteristics, therefore, it is possible to fabricate a temperature sensor which works depending upon light. However, this method lacks precision for a change in the temperature and has not been put into practical use in medical applications.
A second method is a sensor utilizing a change in the refractive index of a cladding material. According to this system, there is provided a temperature sensor in which, as shown in FIG.
10
(A), a cladding
13
is removed from the end of the optical fiber
10
, and a cavity
15
containing glycerine
14
therein, is formed at this portion (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 59-160729). The refractive index of the glycerine
14
changes depending upon the temperature and, hence, the angle of reflection of light changes on the interface between the core
16
and the cladding
13
. As a result, the intensity of light returning (i.e., reflected by the reflector plate
12
) from the end of the fiber changes. Measuring the quantity of light that has returned makes it possible to measure the temperature.
That is, as shown in FIG.
10
(B), the DC voltage that is converted through the sensor from the quantity of returned light undergoes a change depending upon a change in the temperature. Therefore, measurement of the DC voltage makes it possible to measure the temperature of the material being measured. In the sensor of this type, however, the end of the probe has insufficient strength. Moreover, it is difficult to fabricate the probe in a small size.
A third system is a sensor which utilizes a change in the color of liquid crystals. According to this system which utilizes a change in the color of liquid crystals depending upon the temperature, there is proposed a sensor obtained by fastening a cavity
15
made of a very narrow glass tube containing liquid crystals
17
at the end of the optical fiber
10
(see, for example, Japanese Unexamined Patent Publication (Kokai) No. 57-63430).
FIG. 11
is a diagram illustrating its principle.
FIG. 11
shows a temperature sensor according to the above-mentioned third system, wherein a cavity
15
containing liquid crystals
17
is placed near the material that is to be measured, and an optical fiber
10
is connected to the cavity
15
. An example consists of permitting the light to be input at a free end of the optical fiber
10
, and measuring the light reflected by the liquid crystals, in order to calculate the temperature of the material that is being measured. That is, the principle is utilized that the color of the liquid crystals change depending upon the temperature, thus the reflection factor of the incident light changes.
According to this system, furthermore, the optical fiber
10
for incident light may be provided separately from the optical fiber
10
′ for measuring the reflected light. In this case, the optical fibers are used in a bundled form in which both optical fibers are bundled together.
However, this system is costly and has poor resolution. Moreover, if the glass tube is broken, the liquid crystals, which are toxic, adversely affect the living body.
Next, a fourth system is a sensor which utilizes a change in the intensity of a fluorescent material. That is, the wavelength of fluorescence of some fluorescent materials is shifted depending upon the temperature. The temperature sensor of this system utilizes this property.
FIGS. 12A
,
12
B, and
12
C illustrate the principle of this system.
FIG.
12
(A) shows that the fluorescence spectrum undergoes a change in intensity and wavelength depending upon the temperature of the sensor (here, it is presumed that the temperatures T
1
, T
2
, and T
3
have a relationship T
1
<T
2
<T
3
). Curve “C” represents the spectrum of the excitation light. Curves D, E, and F represent the fluorescence spectrum of the material at temperatures T
1
, T
2
and T
3
respectively. The fluorescent material having such properties may be GaAs/AlGaAs produced by Asea Co. or an inorganic fluorescent material produced by Luxtron Co. or Omron Co., and can be used as a temperature sensor.
FIG. 12B
further illustrates such a sensor, wherein an optical fiber
10
is connected to a sensor
84
(shown in
FIG. 12C
) and a measuring device
80
. The measuring device
80
comprises a light source
81
(e.g., a light emitting diode), a temperature analyzing portion
82
, and a photodiode
83
. The sensor
84
comprises layers of GaAs
85
and AlGaAs
86
.
However, although these sensors are capable of taking and maintaining high resolution measurements, a problem resides in that the fluorescent materials are expensive.
SUMMARY OF THE INVENTION
The present invention provides a small sized temperature sensor for medical application for measuring local temperatures in the body and for measuring temperatures in an extracorporeal blood circulation circuit, which reduces the possibility of electric shock to the living body and features reduced cost, and increased resolution and reliability.
The present invention further provides a method of measuring temperature including the steps of calibrating a sensor having a source of light which irradiates light, an optical fiber positioned at one end to receive light from the source of light, a transducer positioned near the other end of the optical fiber, the transducer being made up of at least two polymers that have dissimilar temperature dependenci
Burns Doane , Swecker, Mathis LLP
Guadalupe Yaritza
Gutierrez Diego
Terumo Cardiovascular Systems Corporation
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