Patent Publication Number: US-2021177271-A1

Title: Living Body Internal Temperature Measuring Device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry of PCT Application No. PCT/JP2019/018377, filed on May 8, 2019, which claims priority to Japanese Application No. 2018-094362, filed on May 16, 2018, which applications are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an in-vivo temperature measurement device that detects a temperature change in a living body. 
     BACKGROUND 
     In recent years, asocial jet-lag has become a problem. The social jet-lag may cause various physical and mental disorders due to inconsistency between a social time and a biological clock or a biorhythm of each person who lives a life, and may lead to lifestyle diseases. A human&#39;s biological clock can be known from various endocrine substances or vital information. Measurement of the endocrine substances requires several hours, resulting in imposing a burden on a research subject mentally and physically. 
     On the other hand, it is known that a human&#39;s biorhythm is usefully grasped by measuring a change in deep body temperature as vital information. When a depth exceeds a certain depth from the skin to the core, a temperature region not being affected by a change in outside air temperature exists, and a temperature at such a region is called a deep body temperature (core temperature). Examples of methods of measuring the deep body temperature include a method of inserting a probe of a thermometer into a body and a method of swallowing the thermometer, but all of the methods may have hygiene problems and may also impose a burden on a research subject mentally and physically. Therefore, methods of measuring the temperature with a non-invasive manner from the outside of the body are demanded, and it can be said that a percutaneous temperature measurement method is particularly useful in terms of easy and daily body temperature management. For example, it is useful to measure the temperature at a core site of the living body, for example, rectal temperature. 
     Conventionally, a thermometer using a MEMS heat flux sensor has been proposed as a means for percutaneously measuring a deep body temperature (see Non-Patent Literature 1). However, the percutaneous thermometer may be difficult to grasp the change in deep body temperature without delay. The reason why the percutaneous thermometer is difficult to grasp the change in deep body temperature is that there is a delay time until the deep body temperature is reflected in the skin, the delay time changes due to a change in blood flow, and a skin temperature changes due to outside air. 
     CITATION LIST 
     Non-Patent Literature 
     
         
         Non-Patent Literature 1: Shinya Nakagawa, et al., “Wearable core temperature thermometer implemented by the MEMS heat flux sensor”, The transactions of the Institute of Electrical Engineers of Japan E, Vol. 135, No. 8, p. 343-348, 2015. 
       
    
     SUMMARY 
     Technical Problem 
     Embodiments of the present invention have been made to solve the above problems, and an object thereof is to provide an in-vivo temperature measurement device capable of grasping a temperature change in a living body without delay. 
     Means for Solving the Problem 
     An in-vivo temperature measurement device of embodiments of the present invention includes: an ultrasonic wave irradiation unit that irradiates a living body with an ultrasonic wave; an ultrasonic wave detection unit that receives an ultrasonic wave reflected by the living body; a frequency calculation portion that calculates a frequency of an ultrasonic wave amplified in the living body, based on information on a structure of the living body; a frequency analysis portion that performs frequency analysis on the ultrasonic wave received by the ultrasonic wave detection unit and acquires an amplitude spectrum of the ultrasonic wave; a frequency identification portion that identifies, from the amplitude spectrum, a peak frequency closest to the frequency calculated by the frequency calculation portion; a frequency change calculation portion that calculates an amount of frequency change, from two peak frequencies identified by ultrasonic wave irradiations in twice; and a temperature change calculation portion that calculates an amount of temperature change in the living body from the amount of frequency change. 
     An in-vivo temperature measurement device of embodiments of the present invention includes: an ultrasonic wave irradiation unit that irradiates a living body with an ultrasonic wave; an ultrasonic wave detection unit that receives an ultrasonic wave reflected by the living body; a frequency calculation portion that calculates a frequency of an ultrasonic wave amplified in the living body, based on information on a structure of the living body; an ultrasonic wave irradiation control portion that sweeps a repetition frequency at which an ultrasonic wave is emitted from the ultrasonic wave irradiation unit within a predetermined range centered on the frequency calculated by the frequency calculation portion; a lock-in detector that detects an ultrasonic wave of the repetition frequency from the ultrasonic waves received by the ultrasonic wave detection unit; an amplitude spectrum acquisition portion that collects amplitude values of signals sequentially output from the lock-in detector and acquires an amplitude spectrum of the ultrasonic wave; a frequency identification portion that identifies, from the amplitude spectrum, a peak frequency closest to the frequency calculated by the frequency calculation portion; a frequency change calculation portion that calculates an amount of frequency change from two peak frequencies obtained by sweeping the repetition frequency twice; and a temperature change calculation portion that calculates an amount of temperature change in the living body from the amount of frequency change. 
     An in-vivo temperature measurement device of embodiments of the present invention includes: an ultrasonic wave irradiation unit that irradiates a living body with an ultrasonic wave; an ultrasonic wave detection unit that receives an ultrasonic wave reflected by the living body; a frequency calculation portion that calculates a frequency of an ultrasonic wave amplified in the living body, based on information on a structure of the living body; an ultrasonic wave irradiation control portion that sweeps a repetition frequency at which an ultrasonic wave is emitted from the ultrasonic wave irradiation unit within a predetermined range centered on the frequency calculated by the frequency calculation portion; a lock-in detector that detects a phase of an ultrasonic wave of the repetition frequency from the ultrasonic waves received by the ultrasonic wave detection unit; a phase spectrum acquisition portion that collects phase values sequentially output from the lock-in detector and acquires a phase spectrum of the ultrasonic wave; a phase identification portion that identifies, from the phase spectrum, a phase of a peak frequency of an amplitude spectrum of the ultrasonic wave; a phase change calculation portion that calculates an amount of phase change from phases of two peak frequencies obtained by sweeping the repetition frequency twice; and a temperature change calculation portion that calculates an amount of temperature change in the living body from the amount of phase change. 
     In one configuration example of the in-vivo temperature measurement device of embodiments of the present invention, the frequency calculation portion calculates a frequency of an ultrasonic wave amplified in the living body, based on the information on the structure of the living body and a value of a sound speed in the living body, the value of the sound speed being registered in advance. 
     In one configuration example of the in-vivo temperature measurement device of embodiments of the present invention, the information on the structure of the living body is a distance between structures in the living body. 
     Effects of Embodiments of the Invention 
     According to embodiments of the present invention, it is possible to estimate the amount of temperature change in the living body and to non-invasively obtain the temperature change in the living body that is changing every moment, without being affected by the outside air or the skin temperature, by irradiating the living body with the ultrasonic wave, performing the frequency analysis on the ultrasonic wave received by the ultrasonic wave detection unit and acquiring the amplitude spectrum of the ultrasonic wave, and calculating the amount of frequency change from two peak frequencies identified by ultrasonic wave irradiations in twice. 
     According to embodiments of the present invention, it is possible to estimate the amount of temperature change in the living body and to non-invasively obtain the temperature change in the living body that is changing every moment, without being affected by the outside air or the skin temperature, by irradiating the living body with the ultrasonic wave while sweeping the repetition frequency, detecting the ultrasonic wave of the repetition frequency from the ultrasonic waves received by the ultrasonic wave detection unit to acquire the amplitude spectrum of the ultrasonic wave, and calculating the amount of frequency change from two peak frequencies obtained by sweeping the repetition frequency twice. 
     According to embodiments of the present invention, it is possible to estimate the amount of temperature change in the living body and to non-invasively obtain the temperature change in the living body that is changing every moment, without being affected by the outside air or the skin temperature, by irradiating the living body with the ultrasonic wave while sweeping the repetition frequency, detecting the phase of the ultrasonic wave of the repetition frequency from the ultrasonic waves received by the ultrasonic wave detection unit to acquire the phase spectrum of the ultrasonic wave, and calculating the amount of phase change from phases of two peak frequencies obtained by sweeping the repetition frequency twice. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of an in-vivo temperature measurement device according to a first embodiment of the present invention. 
         FIG. 2  is a flowchart for describing an operation of the in-vivo temperature measurement device according to the first embodiment of the present invention. 
         FIG. 3  is a view for describing an in-vivo temperature measurement method using the in-vivo temperature measurement device according to the first embodiment of the present invention. 
         FIG. 4  is a view showing an example of a waveform of an ultrasonic wave reception signal detected by an ultrasonic wave detection unit of the in-vivo temperature measurement device according to the first embodiment of the present invention. 
         FIG. 5  is a block diagram showing a configuration example of a calculation unit of the in-vivo temperature measurement device according to the first embodiment of the present invention. 
         FIG. 6  is a view showing an example of an amplitude spectrum of the ultrasonic wave reception signal. 
         FIG. 7  is a view showing an example of a relation between a temperature and a speed of sound. 
         FIG. 8  is a view showing an example of a relation between a temperature change and a frequency change of a sound wave. 
         FIG. 9  is a view for describing an effect of the in-vivo temperature measurement device according to the first embodiment of the present embodiment. 
         FIG. 10  is a block diagram showing a configuration of an in-vivo temperature measurement device according to a second embodiment of the present invention. 
         FIG. 11  is a flowchart for describing an operation of the in-vivo temperature measurement device according to the second embodiment of the present invention. 
         FIG. 12  is a block diagram showing a configuration example of a calculation unit of the in-vivo temperature measurement device according to the second embodiment of the present invention. 
         FIG. 13  is a block diagram showing a configuration of an in-vivo temperature measurement device according to a third embodiment of the present invention. 
         FIG. 14  is a flowchart for describing an operation of the in-vivo temperature measurement device according to the third embodiment of the present invention. 
         FIG. 15  is a block diagram showing a configuration example of a calculation unit of the in-vivo temperature measurement device according to the third embodiment of the present invention. 
         FIG. 16  is a view showing an example of a phase spectrum of an ultrasonic wave reception signal. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     First Embodiment 
     Embodiments of the present invention will be described below with reference to the drawings.  FIG. 1  is a block diagram showing a configuration of an in-vivo temperature measurement device according to a first embodiment of the present invention. The in-vivo temperature measurement device  1  includes an ultrasonic wave irradiation unit  2  that irradiates a living body  10  with ultrasonic waves, an ultrasonic wave detection unit  3  that receives the ultrasonic waves returned from the living body  10 , an amplifier  4  that amplifies an electric signal obtained from the ultrasonic wave detection unit  3 , a calculation unit  5  that calculates the amount of temperature change in the living body  10  based on the output of the amplifier  4 , a storage unit  6  that stores various data and calculation results necessary for calculation, and a communication unit  7  that communicates with an external device. 
       FIG. 2  is a flowchart for describing an operation of the in-vivo temperature measurement device  1  of the present embodiment, and  FIGS. 3(A) and 3(B)  are views for describing an in-vivo temperature measurement method using the in-vivo temperature measurement device  1  of the present embodiment.  FIG. 3(A)  is a side view showing a positional relation between the in-vivo temperature measurement device  1  and the living body  10 , and  FIG. 3(B)  is a rear view. In  FIG. 3(B) , reference numeral  100  indicates a spine of the living body  10 , and reference numeral  101  indicates ribs. 
     In the present embodiment, the in-vivo temperature measurement device  1  is disposed such that a transmission/reception surface of the in-vivo temperature measurement device  1  provided with the ultrasonic wave irradiation unit  2  and the ultrasonic wave detection unit  3  comes in contact with a site on a back of the living body  10  (human body) at an approximate rib-height level (see  FIGS. 3(A) and 3(B) ). 
     The ultrasonic wave irradiation unit  2  irradiates the living body  10  with ultrasonic waves (step S 100  in  FIG. 2 ). The ultrasonic wave detection unit  3  receives the ultrasonic wave returned from the living body  10  (step S 101  in  FIG. 2 ). 
       FIG. 4  shows an example of a waveform of an ultrasonic wave reception signal detected by the ultrasonic wave detection unit  3 . The amplifier  4  amplifies the ultrasonic wave reception signal detected by the ultrasonic wave detection unit  3 . 
       FIG. 5  is a block diagram showing a configuration example of the calculation unit  5 . The calculation unit  5  includes an ultrasonic wave irradiation control portion  50 , a frequency analysis portion  51 , a frequency calculation portion  52 , a frequency identification portion  53 , a frequency change calculation portion  54 , and a temperature change calculation portion  55 . 
     The frequency analysis portion  51  of the calculation unit  5  acquires time change data (time series data) of the ultrasonic wave reception signal detected by the ultrasonic wave detection unit  3  and amplified by the amplifier  4  (step S 102  in  FIG. 2 ), and obtains an amplitude spectrum of the ultrasonic wave reception signal by performing frequency analysis on the time series data by a method such as FFT (Fast Fourier Transform) (step S 103 , S 104  in  FIG. 2 ).  FIG. 6  shows an example of the amplitude spectrum of the ultrasonic wave reception signal obtained by the frequency analysis portion  51 . In  FIG. 6 , reference numeral  60  indicates a first measurement result, and reference numeral  61  indicates a second measurement result, for example. 
     As is clear from  FIG. 6 , the ultrasonic waves emitted from the ultrasonic wave irradiation unit  2  have various frequency components. The ultrasonic waves are reflected and scattered in the living body  10 , but become a peak at various frequencies depending on the shape of the living body  10  and in-vivo structures such as internal organs and bones. In particular, sound waves are strongly reflected at a place where acoustic impedance is largely different. Therefore, sound waves amplified by repeating reflection between bones having different biological tissues and acoustic impedances are strongly observed. Frequencies of the sound waves to be observed are different from each other depending on the distance between bones and tissues such as fat and muscle. In other words, the different in the frequency of the sound waves is due to a difference in a speed of sound. The speed of sound also changes with a temperature, and the distance between bones and the tissues such as fat and muscle do not change with time. Therefore, the change in the peak frequency of the ultrasonic waves to be observed reflects the temperature change inside the living body  10 , and the amount of frequency change corresponds to a change amount of deep body temperature. 
     As shown in  FIGS. 3(A) and 3(B) , when the in-vivo temperature measurement device  1  is disposed at the site on the back of the living body  10  (human body) at an approximate rib-height level, the ultrasonic waves emitted from the ultrasonic wave irradiation unit  2  are repeatedly reflected between the ribs of the living body  10 , and the ultrasonic waves of an appropriate frequency are amplified. When a distance between the ribs is defined as L and the speed of sound when a temperature is T is defined as V(T), a frequency f of the sound wave amplified by the reflection between the ribs is generally given by the following formula. 
     
       
         
           
             
               
                 
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                     nL 
                   
                 
               
               
                 
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     In Formula (1), n is a fixed number. When an average speed of sound V in the living body  10  is 1490 m/s and the distance L between the ribs is 1 cm, an ultrasonic wave having a frequency of approximately 298 kHz and an ultrasonic wave having a frequency of an integral multiple thereof are amplified. The living body is composed of various tissues, but a typical ingredient of the living body is water. As shown in  FIG. 7 , the speed of sound V in water changes almost linearly with the temperature T. In this way, a relation between a temperature change ΔT and a frequency change Δf of the sound wave when the speed of sound V changes linearly with the temperature T changes as shown in  FIG. 8  according to the following formula. 
     
       
         
           
             
               
                 
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     The ultrasonic waves emitted from the ultrasonic wave irradiation unit  2  are reflected and scattered in the living body  10 , some of the ultrasonic wave is observed by the ultrasonic wave detection unit  3 , and an amplitude spectrum as shown in  FIG. 6  is obtained by the frequency analysis described above. An amplitude spectrum denoted by  60  in  FIG. 6  indicates an amplitude spectrum before the temperature in the living body  10  changes, and amplitude spectrum denoted by  61  in  FIG. 6  indicates an amplitude spectrum after the temperature inside the living body  10  changes. As described above, when the ultrasonic wave is amplified in the living body  10 , a peak appears in the amplitude spectrum. 
     As is clear from Formula (2) and  FIG. 6 , when the temperature inside the living body  10  changes by ΔT, a peak frequency of the amplitude spectrum changes by Δf. At this time, a relation between the temperature change ΔT in the living body  10  and the peak frequency change Δf of the amplitude spectrum is expressed by the following formula. 
       Formula 3 
         Δf=CΔT   (3)
 
     In Formula (3), C is a fixed number. Thus, when the peak frequency change Δf of the amplitude spectrum can be obtained, it can be understood that the temperature change ΔT in the living body  10  can be estimated. As for the ultrasonic waves, since the higher the frequency, the greater the attenuation, not harmonic waves that are integral multiples of a fundamental sound, but a fundamental sound defined by Formula (1) may be used. The peak frequency change Δf of the amplitude spectrum is affected by the proportion of fat in the living body  10 , but the temperature change ΔT in the living body  10  and the peak frequency change Δf can obtain a substantially linear response. Further, the peak frequency change Δf changes depending on the distance between structures in the living body  10 , but as described above, the temperature change ΔT and the frequency change Δf can obtain a substantially linear response. 
     Specific processing in the present embodiment is as follows. The frequency calculation portion  52  of the calculation unit  5  calculates the frequency f of the ultrasonic wave amplified in the living body  10  using Formula (1) (step S 105  in  FIG. 2 ). At this time, since the temperature inside the living body  10  is undetermined, the frequency calculation portion  52  uses the average speed of sound V in the living body  10  instead of the speed of sound V(T) when the temperature is T. The value of the speed of sound V, the value of the distance L between the structures in the living body  10  (referred to as the distance between the ribs in the present embodiment), and the fixed number n are registered in the storage unit  6  in advance. The value of the fixed number n can be determined, for example, by previous experiment in which the living body is irradiated with ultrasonic waves and the peak frequency of the amplitude spectrum of the ultrasonic waves is obtained. 
     The frequency identification portion  53  of the calculation unit  5  identifies a peak frequency closest to the frequency f calculated by the frequency calculation portion  52 , from the amplitude spectrum obtained by the frequency analysis portion  51  (step S 106  in  FIG. 2 ). Then, the calculation unit  5  returns to step S 100  when the identification of the peak frequency in step S 106  has not been completed twice (NO in step S 107  in  FIG. 2 ). In this way, the processes of steps S 100  to S 104  and S 106  are repeated twice. 
     The frequency change calculation portion  54  of the calculation unit  5  calculates the amount of peak frequency change Δf, that is, a difference Δf (=f 2 −f 1 ) between a second peak frequency f 2  and a first peak frequency f 1  obtained by the frequency identification portion  53  (step S 108  in  FIG. 2 ). 
     Then, the temperature change calculation portion  55  of the calculation unit  5  calculates, from the amount of peak frequency change Δf, the amount of temperature change ΔT in the living body  10  using Formula (3) (step S 109  in  FIG. 2 ). The fixed number C is registered in the storage unit  6  in advance. Note that the value of the fixed number C can be determined by, for example, previous experiment in which a probe of a thermometer is inserted into the living body to obtain a change in deep body temperature. 
     The value of the amount of temperature change ΔT calculated by the temperature change calculation portion  55  is transmitted to the outside via the communication unit  7 . In this way, the in-vivo temperature measurement device  1  repeats the processes of steps S 100  to S 104  and S 106  to S 109  until a user gives an instruction to stop the measurement. 
       FIG. 9  is a view for describing the effect of the present embodiment. In  FIG. 9 , reference numeral  90  indicates the deep body temperature in the living body obtained by insertion of the probe of the thermometer into the living body, and reference numeral  91  indicates the peak frequency change obtained in the present embodiment. It can be seen from  FIG. 9  that the change in the deep body temperature and the peak frequency change fully coincide with each other. 
     Second Embodiment 
     A second embodiment of the present invention will be described below.  FIG. 10  is a block diagram showing a configuration of an in-vivo temperature measurement device according to the second embodiment of the present invention, and the same components as those in  FIG. 1  are denoted by the same reference numerals. An in-vivo temperature measurement device  1   a  of the present embodiment includes an ultrasonic wave irradiation unit  2 , an ultrasonic wave detection unit  3 , a lock-in detector  4   a , a calculation unit  5   a , a storage unit  6 , and a communication unit  7 . 
       FIG. 11  is a flowchart for describing an operation of the in-vivo temperature measurement device  1   a  of the present embodiment, and  FIG. 12  is a block diagram showing a configuration example of the calculation unit  5   a  of the present embodiment. The calculation unit  5   a  includes an ultrasonic wave irradiation control portion  50   a , an amplitude spectrum acquisition portion  51   a , a frequency calculation portion  52   a , a frequency identification portion  53 , a frequency change calculation portion  54 , and a temperature change calculation portion  55 . 
     In the present embodiment, first, the frequency calculation portion  52   a  of the calculation unit  5   a  calculates a frequency f of an ultrasonic wave amplified in the living body  10  as in step S 106  (step S 200  in  FIG. 11 ). 
     In the first embodiment, the ultrasonic wave irradiation control portion  50  of the calculation unit  5  only needs to control the ultrasonic wave irradiation unit  2  to transmit the ultrasonic wave. On the other hand, the ultrasonic wave irradiation control portion  50   a  of the present embodiment sweeps a repetition frequency, at which the ultrasonic wave is emitted from the ultrasonic wave irradiation unit  2 , within a range of frequency f±α (α is a predetermined width) calculated by the frequency calculation portion  52   a  (step S 201  in  FIG. 11 ). 
     The lock-in detector (phase amplifier)  4   a  detects an ultrasonic wave reception signal having the above-described repetition frequency from the ultrasonic wave reception signals obtained by the ultrasonic wave detection unit  3  (step S 202  in  FIG. 11 ). 
     Thus, by emitting the ultrasonic wave while sweeping the repetition frequency to detect the ultrasonic wave reception signal at each repetition frequency and collecting an amplitude value (sound pressure) of the signal to be sequentially output from the lock-in detector  4   a , the amplitude spectrum acquisition portion  51   a  can acquire an amplitude spectrum of the ultrasonic wave reception signal (step S 204  in  FIG. 11 ). The amplitude spectrum obtained at this time is similar to the amplitude spectrum shown in  FIG. 6 , for example. 
     The frequency identification portion  53  of the calculation unit  5   a  identifies a peak frequency closest to the frequency f calculated by the frequency calculation portion  52   a , from the amplitude spectrum acquired by the amplitude spectrum acquisition portion  51   a  (step S 205  in  FIG. 11 ). 
     Operations (steps S 206  to S 208  in  FIG. 11 ) of the frequency change calculation portion  54  and the temperature change calculation portion  55  are as described in steps S 107  to S 109 . 
     The in-vivo temperature measurement device  1   a  repeats the processes of steps S 201  to S 208  until a user gives an instruction to stop the measurement, for example. Thus, it is possible to obtain an effect of the present embodiment similar to that of the first embodiment. 
     Third Embodiment 
     A third embodiment of the present invention will be described below.  FIG. 13  is a block diagram showing a configuration of an in-vivo temperature measurement device according to the third embodiment of the present invention, and the same components as those in  FIGS. 1 and 10  are denoted by the same reference numerals. An in-vivo temperature measurement device  1   b  of the present embodiment includes an ultrasonic wave irradiation unit  2 , an ultrasonic wave detection unit  3 , a lock-in detector  4   b , a calculation unit  5   b , a storage unit  6 , and a communication unit  7 . 
       FIG. 14  is a flowchart for describing an operation of the in-vivo temperature measurement device  1   b  of the present embodiment, and  FIG. 15  is a block diagram showing a configuration example of the calculation unit  5   b  of the present embodiment. The calculation unit  5   b  includes an ultrasonic wave irradiation control portion  50   a , a phase spectrum acquisition portion  51   b , a frequency calculation portion  52   a , a phase identification portion  53   b , a phase change calculation portion  54   b , and a temperature change calculation portion  55   b.    
     Operations (steps S 300  and S 301  in  FIG. 14 ) of the frequency calculation portion  52   a  and the ultrasonic wave irradiation control portion  50   a  of the calculation unit  5   b  are as described in steps S 200  and S 201 . 
     The lock-in detector (phase amplifier) can detect not only an amplitude but also a phase by an angular frequency at the same time. Therefore, the lock-in detector  4   b  of the present embodiment detects a phase of the ultrasonic wave reception signal having the above-described repetition frequency from the ultrasonic wave reception signals obtained by the ultrasonic wave detection unit  3  (step S 302  in  FIG. 14 ). 
     In this way, by emitting the ultrasonic wave while sweeping the repetition frequency to detect phase of the ultrasonic wave reception signal at each repetition frequency and collecting a phase value to be sequentially output from the lock-in detector  4   b , the phase spectrum acquisition portion  51   b  can acquire a phase spectrum of the ultrasonic wave reception signal (step S 304  in  FIG. 14 ). 
       FIG. 16  shows an example of the phase spectrum of the ultrasonic wave reception signal acquired by the phase spectrum acquisition portion  51   b . A phase spectrum denoted by  160  in  FIG. 16  indicates a phase spectrum before the temperature inside the living body  10  changes, and a phase spectrum denoted by  161  in  FIG. 16  indicates a phase spectrum after the temperature inside the living body  10  changes. 
     Next, the phase identification portion  53   b  of the calculation unit  5   b  identifies a phase φ of a peak frequency of the amplitude spectrum, from the phase spectrum acquired by the phase spectrum acquisition portion  51   b  (step S 305  in  FIG. 14 ). Specifically, the phase identification portion  53   b  may identify a phase of an inflection point of the phase spectrum as the phase φ of the peak frequency of the amplitude spectrum. Then, the calculation unit  5   b  returns to step S 301  when the identification of the phase p in step S 305  has not been completed twice (NO in step S 306  in  FIG. 14 ). In this way, the processes of steps S 301  to S 305  are repeated twice. 
     The phase change calculation portion  54   b  of the calculation unit  5   b  calculates the amount of phase change Δφ of the peak frequency, that is, a difference Δφ(=φ 2 −φ 1 ) between a phase φ 2  of a second peak frequency and a phase φ 1  of a first peak frequency obtained by the phase identification portion  53   b  (step S 307  in  FIG. 14 ). 
     Then, the temperature change calculation portion  55   b  of the calculation unit  5   b  calculates, from the amount of phase change Δφ of the peak frequency, the amount of temperature change ΔT in the living body  10  using the following formula (step S 308  in  FIG. 14 ). 
       Formula 4 
       Δϕ= KΔT   (4)
 
     In Formula (4), K is a fixed number. The fixed number K is registered in the storage unit  6  in advance. Note that the value of the fixed number K can be determined by, for example, previous experiment in which a probe of a thermometer is inserted into the living body to obtain a change in deep body temperature. 
     The value of the amount of temperature change ΔT calculated by the temperature change calculation portion  55   b  is transmitted to the outside via the communication unit  7 . The in-vivo temperature measurement device  1   b  repeats the processes of steps S 301  to S 308  until a user gives an instruction to stop the measurement, for example. Thus, it is possible to obtain an effect of the present embodiment similar to that of the first embodiment. 
     In the first to third embodiments, the in-vivo temperature measurement device  1 ,  1   a , or  1   b  is disposed on the back of the living body  10  (human body) as an example, but the in-vivo temperature measurement device  1 ,  1   a , or  1   b  may be disposed to contact with, for example, a front arm of the living body  10  without being limited thereto. In this case, the distance L between the structures in the living body  10  may be a distance between the radius and the ulna. 
     In the in-vivo temperature measurement devices  1 ,  1   a , and  1   b  described in the first to third embodiments, the calculation units  5 ,  5   a , and  5   b  and the storage unit  6  can be realized by a computer including a CPU (Central Processing Unit), a storage device, and an interface and a program for controlling these hardware resources. The CPU executes the processes described in the first to third embodiments according to the program stored in the storage device. 
     INDUSTRIAL APPLICABILITY 
     Embodiments of the present invention are applicable to a technique for detecting a temperature change in a living body. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 ,  1   a  in-vivo temperature measurement device 
               2  ultrasonic wave irradiation unit 
               3  ultrasonic wave detection unit 
               4  amplifier 
               4   a ,  4   b  lock-in detector 
               5 ,  5   a ,  5   b  calculation unit 
               6  storage unit 
               7  communication unit 
               10  living body 
               50 ,  50   a  ultrasonic wave irradiation control portion 
               51  frequency analysis portion 
               51   a  amplitude spectrum acquisition portion 
               51   b  phase spectrum acquisition portion 
               52 ,  52   a  frequency calculation portion 
               53  frequency identification portion 
               53   b  phase identification portion 
               54  frequency change calculation portion 
               54   b  phase change calculation portion 
               55 ,  55   b  temperature change calculation portion.