JPH0548130B2 - - Google Patents

Description

Detailed Description of the Invention Field of Industrial Application The present invention is an ultrasonic temperature measurement method that transmits and receives ultrasonic waves into a subject, measures acoustic propagation characteristics within the subject, and determines temperature changes within the subject. It is related to the device.

2. Description of the Related Art An example of a method for obtaining acoustic information inside a subject using ultrasound is an ultrasound diagnostic apparatus. The mainstream of ultrasonic diagnostic devices uses a pulse reflection method in which ultrasonic waves are transmitted into a living body and information about the inside of the living body is obtained by reflected waves from the living body. Normally, the pulse reflection method collects and displays in-vivo information two-dimensionally from the reflected echo intensity from interfaces with different acoustic impedances, that is, the amplitude values and the propagation time of ultrasound waves, to obtain tomographic images. It's something you get. However, in recent years, there has been an increasing demand for ultrasonic diagnostic apparatuses that mainly determine the shape of living tissues to obtain information on not only the shape but also the quality of living tissues. Such information regarding the quality of living tissue can be obtained, for example, by measuring the magnitude of attenuation of ultrasonic waves, the speed of sound, etc., which have specific values in various organs within the living body. As a method for measuring the attenuation coefficient of ultrasonic waves, for example, see Ultrasonic IMAGING, Vol. 5, No. 2.
1983, pp. 117-135 is known. Hereinafter, a conventional ultrasonic attenuation coefficient measuring method will be explained with reference to FIG.

In FIG. 7, 101 is a subject, 102 is an ultrasound probe that transmits and receives ultrasound to and from the subject 101, 103 is a pulse driver that drives the ultrasound probe 102, and 104 is an ultrasound probe. A receiving circuit that amplifies the received signal of the toucher 102, 105 is a receiving circuit 1
A frequency analyzer 106 performs frequency analysis on the output of the frequency analyzer 105;

The operation of the above configuration will be explained below.

First, a driving pulse is sent out by the pulse driver 103 and applied to the ultrasound probe 102, and the ultrasound probe 102 generates an ultrasound pulse. The generated ultrasonic pulses propagate through the object 101 and are successively scattered in accordance with the acoustic properties of the tissue.
A portion of the signal travels backward along the propagation path, that is, the acoustic scanning line, reaches the ultrasound probe 102, and is converted into a received signal. In this process, the ultrasound pulse is affected by the ultrasound attenuation characteristics and ultrasound scattering characteristics of the living tissue. The received signal is amplified by the receiving circuit 104, and the center frequency is determined by the frequency analyzer 105. The center frequency can be determined using a zero-cross counter method, FFT, or the like. This center frequency is a value that depends on the propagation distance and the attenuation coefficient of the ultrasonic wave. The calculation unit 106 calculates the attenuation coefficient of the ultrasonic wave from the center frequency output of the frequency analyzer 105. In the above description, it is assumed that there is no influence of the ultrasonic scattering coefficient of the subject 101.

Problems to be Solved by the Invention However, with the above configuration, the ultrasound scattering state of the subject 101 changes considerably even if the location is slightly different even in the same tissue. There was a problem in that the error in determining the ultrasonic attenuation coefficient from the frequency was very large.

The present invention solves the above-mentioned problems of the prior art, and it is possible to detect a received signal without being affected by the ultrasonic scattering characteristics of a subject that has complex ultrasonic scattering characteristics, such as a living body. Measure the center frequency,
The purpose of this method is to obtain an ultrasonic attenuation coefficient and utilize the temperature dependence of this ultrasonic attenuation coefficient to obtain a relative temperature change at a specific site within a living body with high precision.

Means for Solving the Problems The present invention provides a pump wave ultrasonic transducer that sends out pump wave ultrasonic pulses, and a probe wave ultrasonic wave that sends out probe wave ultrasonic pulses having a higher frequency than the pump wave ultrasonic pulses. a transducer, controlling the drive of the pump wave ultrasonic pulse and the probe wave ultrasonic pulse, and controlling the drive of the pump wave ultrasonic pulse and the probe wave ultrasonic pulse to a region where the particle velocity of the pump wave ultrasonic pulse changes from a minimum to a maximum, and where the rate of change is greatest. 1 position,
and a control drive for superimposing the probe wave ultrasonic pulse on the pump wave ultrasonic pulse at a second position in a region where the particle velocity of the pump wave ultrasonic pulse changes from a maximum to a minimum and the rate of change is largest. a delay time difference calculation unit that calculates a delay time difference of the probe wave ultrasound pulse generated by the pump wave ultrasound pulse; and a delay time difference calculation unit that calculates a delay time difference of the probe wave ultrasound pulse generated by the pump wave ultrasound pulse; a frequency analyzer that calculates the spectral distribution of the received signal and the spectral distribution of the received signal from the subject when superimposed on the second position;
a cross frequency calculation unit that calculates the frequency at which two spectral distributions intersect at a position; a pulse drive unit that changes the intensity of the pump wave ultrasonic pulse; an output of the cross frequency calculation unit and an output of the delay time calculation unit. a center frequency calculation unit that calculates the center frequency of the received signal of the probe wave ultrasonic pulse from the center frequency calculation unit; an attenuation calculation unit that calculates the ultrasonic attenuation characteristic from the output of the center frequency calculation unit; The above object is achieved by providing a temperature change calculating section that calculates a relative temperature change from a change in acoustic wave attenuation characteristics.

Effects With the above configuration, the present invention calculates the crossing frequency of the spectral distribution of the received signal corresponding to each of two specific superimposed states of the pump wave pulse and the probe wave pulse realized in the subject. By changing the intensity and determining the delay time difference, the center frequency of the spectral distribution of the received signal can be determined with high precision, and temperature changes can be measured with high precision.

Examples Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an ultrasonic temperature measuring device in one embodiment of the present invention. In Figure 1,
1 is a pump wave ultrasonic transducer that sends out a pump wave ultrasonic pulse in a low frequency band (hereinafter referred to as a pump wave pulse), and 2 is a probe wave ultrasonic pulse having a higher frequency than the pump wave ultrasonic pulse (hereinafter referred to as a probe). 3 is a control drive unit that drives the pump wave ultrasound transducer 1 and the probe wave ultrasound transducer 2 in a phase controlled manner. The control drive unit 3 includes a variable output pulse driver 31 that drives the pump wave ultrasonic transducer 1, a pulse driver 32 that drives the probe wave ultrasonic converter 2,
It is comprised of a delay control section 33 that controls the difference in pulse generation timing between the pulse drivers 31 and 32. Further, 4 is a receiving circuit that amplifies the output of the probe wave ultrasound converter 2, and 5 is a signal processing section that performs signal processing on the output of the receiving circuit 4. The signal processing unit 5 includes an A/D converter 51 that converts the output signal of the receiving circuit 4 into a digital signal, a memory 52 that stores the output of the A/D converter 51, and performs frequency analysis on the output data of the memory 52. It is comprised of a frequency analyzer 53 and a crossing frequency calculation unit 54 that calculates the frequency at which a plurality of frequency spectra output from the frequency analyzer 53 intersect. Furthermore, 6 is a clock source that supplies clocks to the control drive section 3 and the like, and 7 is a delay time difference producing section connected to the receiving circuit 4. The delay time difference calculating section 7 includes an A/D converter 71 that converts the output signal of the receiving circuit 4 into a digital signal;
A memory 72 that stores the output of the memory 72, a phase calculation section 73 that calculates the phase of the output data of the memory 72, a phase shift amount calculation section 74 that calculates the phase shift amount based on the output of the phase calculation section 73, and a phase shift amount calculation section 74 that calculates the phase shift amount based on the output of the phase calculation section 73. The delay time difference conversion section 75 calculates a delay time difference based on the output of the section 74. 8 is a memory that stores the output of the signal processing section 5 and the output of the delay time difference calculation section 7; 9 is a center frequency calculation section that calculates the center frequency from the data stored in the memory 8; and 10 is the output of the center frequency calculation section 9. 11 is a memory that stores the output of the attenuation calculation section; 12 is a section that calculates the relative temperature change from the data stored in the memory 11 and the output of the attenuation calculation section 10; 13 is a display unit that displays the output of the temperature change calculation unit 12; 14 is a main control unit that controls the entire system; and 15 is a subject.

The operation of the above configuration will be explained below.

First, an example of a probe wave pulse is shown in FIG. 2a, and an example of a pump wave pulse is shown in FIG. 2b. Figure 2c,
d is a diagram showing the position of two specific types of superposition of pump wave pulses and probe wave pulses;
Some of these waveforms correspond to changes in the output state of the control drive unit 3. The center frequency of the pump wave pulse is, for example, 0.3 MHz, and the center frequency of the probe wave pulse is, for example, 3 MHz, and the values of these center frequencies are selected to be significantly different from each other. Figure 2c
In , the center of gravity of the waveform of the probe wave pulse is at the timing when the particle velocity (sound pressure) of the pump wave pulse is near the atmosphere and the particle acceleration shows a positive peak (the particle velocity of the pump wave pulse changes from the minimum to the maximum). area and the position where the rate of change is greatest)
This state is called phase state A ⁺ . On the other hand, in Figure 2 d, the center of gravity of the waveform of the probe wave pulse is located at the timing when the particle velocity of the pump wave pulse is near the atmosphere and the particle acceleration reaches a negative peak (the particle velocity of the pump wave pulse changes from the maximum to the minimum). and the position where the rate of change is the largest), and this state is called the phase state.
Call it ^A- . Further, when the wavelength of these pump wave pulses is Λ and the pulse length of the probe wave pulse is t, it is desirable to set 2t<Λ (1). If the relationship of equation (1) is satisfied,
The modulation characteristics of probe wave pulses can be easily analyzed.

Next, the manner in which each pulse shown in FIG. 2 is distorted while propagating inside the subject 15 will be explained in detail.

The pump wave pulse shown by the broken line in FIG. 3a is distorted in the direction of the arrow shown depending on the particle velocity (sound pressure) as it propagates, and as a result is modulated into a waveform as shown by the solid line. More specifically, this strain depends on the size of the particle velocity; the part where the particle velocity is positive (the upper part of the waveform in the figure) experiences strain in the same direction as the propagation direction; In the portion where the velocity is negative (the lower portion of the waveform in the figure), distortion occurs in the opposite direction to the propagation direction. Although the degree of this phenomenon varies depending on the nonlinearity of the object, it is uniquely determined. Figures 3b and 3c show how the superimposed probe wave pulse is modulated by the distortion of the pump wave pulse. In Figure 3b, the center frequency of the superimposed probe wave pulse in phase state A ⁺ shifts to the higher frequency side as it propagates, and in Figure 3c, the center frequency of the probe wave pulse superimposed in phase state A ^- shifts to the higher frequency side as it propagates. This shows how the frequency shifts to the lower frequency side. More specifically, as shown in Fig. 3b, when the pump wave pulse is overlapped with a region where the pump wave pulse changes from its minimum point to its maximum point, the waveform of the pump wave pulse in the overlapped portion becomes "in a standing state" as it propagates. The superimposed probe wave pulses are compressed in the time domain. That is, in the frequency domain, it is shifted to the high frequency side.

On the other hand, when the pump wave pulses are overlapped between the maximum point and the minimum point, the waveform of the pump wave pulse in the overlapped part is distorted into a "lying state" as it propagates, as shown in Figure 3c, and the probe wave The pulses are stretched in the time domain and shifted to lower frequencies in the frequency domain.

By the way, the frequency characteristic T(f) of the probe wave pulse is
It is assumed to be Gaussian as shown in equation (2).

T(f)=exp{-(f-f _C ) ² /B} ...(2) However, f: frequency, f _C : center frequency, B: constant. Phase state A ⁺ where the center frequency shifts to the higher frequency side due to nonlinear interaction of pump number pulses
and a phase state in which the center frequency shifts to the lower frequency side.
Let T ⁺ (f) and T ^- (f) be the spectra of the probe wave pulse superimposed at A ^- when it propagates through the object 15. As the center frequencies of T ⁺ (f) and T ^- (f) change due to the nonlinear interaction of the pump wave pulses, the value of B shown in equation (2) changes. That is, the value of B for T ⁺ (f), where the center frequency shifts to the high frequency side, becomes large, and conversely, the value of B for T ^- (f), where the middle frequency shifts to the low frequency side, becomes small. Furthermore, the center frequency of the probe wave pulse propagating within the subject 15 shifts to the lower frequency side due to the influence of attenuation accompanying propagation, and the amplitude becomes smaller. Due to the influence of this attenuation and the influence of nonlinear interaction, the shapes of T ⁺ (f) and T ^- (f) become as shown in Figure 4. Note that the frequency-dependent attenuation characteristic α(f) of ultrasonic waves is expressed by the following equation.

α(f)=A ₀ (f/f ₀ ) ⁿ ...(3) However, A ₀ ; Ultrasonic attenuation coefficient n at frequency f ₀ ; Approximately 1 for normal biological soft tissue Next probe wave is pump wave When the pump wave is superimposed on the particle velocity peak part, the propagation velocity changes compared to when there is no pump wave. As a result, a propagation time difference (hereinafter referred to as delay time τ) occurs when propagating in a minute interval Δx, as shown in the following equation.

τ=△x (1/C ₀ -1/C) ...(4) However, C ₀ ; Speed of sound at infinitesimal amplitude C; Propagation velocity of pump wave pulse particle velocity peak part When there is no pump wave pulse, that is, propagation Figure 4 shows the change in the center frequency of the incident probe wave pulse with respect to the propagation distance due only to the effect of attenuation associated with The change in the frequency at which the two T ⁺ (f) T ^- (f) shown above intersect with respect to the propagation distance is as shown in FIG. For example, the intensity of pump wave pulses is used in ordinary ultrasound diagnostic equipment,
Assuming 0.25w/ ^cm3 , τ is approximately for △x=1cm
1n ^sec . Set the center frequency of the pump wave pulse to
0.3MHz, the center frequency of the incident probe wave pulse
3MHz, sound propagation speed 1480m/ ^sec , object 1
5, the propagation distance is 20 cm, and the center frequency f _C of T(f)
On the other hand, the frequency at which T ⁺ (f) and T ^- (f) intersect is approximately several percent larger. Furthermore, when the delay time difference τ changes by changing the output state of the control drive unit 3 and the intensity of the pump wave pulse, the frequency at which T ⁺ (f) and T ^- (f) intersect for the same propagation distance of the object 15 is calculated. demand. FIG. 6 shows the relationship between the delay time difference and the intersecting frequency for an arbitrary propagation distance measured multiple times while changing the intensity of the pump wave pulse in this way.

In Figure 6, τ ₀ on the horizontal axis (i.e., τ=0
) when there is no pump wave pulse, that is, it is due only to the effect of attenuation accompanying propagation, and when τ ₀ , the crossover frequency f _C is determined by multiple delay time differences, for example, as shown in Fig. 6, as shown by the solid line. τ ₁ , τ ₂ , τ ₃ , τ ₄
It is possible to estimate f _C by approximating data of intersecting frequencies corresponding to and respectively with a high-order curve. Crossing frequency f _C when this τ ₀
can be considered as the changing center frequency of the incident probe wave pulse with respect to the propagation distance due only to the effect of attenuation. That is, as shown in FIG. 6, it has become clear in principle that the center frequency f _C of the incident probe wave pulse for a specific propagation distance can be determined with high accuracy using data on multiple delay time differences and crossing frequencies.

Furthermore, by determining the propagation distance dependence in the object 15 of the shift amount in the center frequency of the spectral distribution of the received signal, it is possible to determine the attenuation characteristics of the ultrasonic waves in the object 15 using a conventionally known method. It is. Further, since this attenuation characteristic is a quantity that is temperature dependent, it is also possible to obtain a temperature change by determining a change in the attenuation characteristic.

Next, a method for measuring the delay time difference τ, which is used for correction in order to accurately measure the center frequency, will be described. Various methods are known for measuring the delay time difference τ, and for example, it can be realized by measuring the amount of phase shift of the probe wave pulse.
First, the pulse driver 32 of the control drive unit 3 is operated to drive the ultrasonic transducer 2 and send only probe wave pulses into the subject 15 . Probe wave pulses propagating through the object 15 are successively scattered in response to changes in the acoustic properties of the object 15, and the scattered ultrasound waves are received by the probe wave ultrasound transducer 2. The received signal is amplified by the receiving circuit 4 and sent to the delay time difference calculating section 7. In the delay time difference calculating section 7, an A/D converter 71 converts the output of the receiving circuit 4 into a digital signal. A/D
The sample timing of converter 71 is determined by clock source 6.
controlled by clock pulses. It is assumed that this sample timing is synchronized with the pulse drivers 31 and 32. The output of A/D converter 71 is stored in memory 72. Using the data stored in the memory 72, a phase calculation section 73 calculates the phase of the incident probe wave pulse. Next, the delay controller 33 of the control driver 3 operates the pulse driver 31 and the pulse driver 32 to send out pump wave pulses and probe wave pulses into the subject 15 . At this time, the probe wave pulse is superimposed on the timing at which the particle velocity of the pump wave pulse is at its maximum, that is, at the peak position of the pump waveform. The probe wave pulse and the pump wave pulse that are crossed and superimposed in the test object 15 perform nonlinear interaction while propagating through the test object 15, and at the same time
The ultrasound waves are successively scattered in response to changes in the acoustic properties of the waves 5, and the scattered ultrasound waves are received by the ultrasound transducer 2. The phase calculation unit 73 calculates the phase of the incident probe wave pulse on the received reception signal in the same way as when there is no pump wave pulse. Next, the phase shift amount calculation unit 74 calculates the amount of phase shift due to nonlinear interaction from these two phases, that is, the phase relationship between the case where there is no pump wave pulse and the case where there is a pump wave pulse, that is, the positional relationship of superposition.
The delay time difference converter 75 calculates the delay time difference τ from the relationship shown in equation (5), for example.

τ = −∂φ/∂ω ...(5) where φ: phase, ω: angular frequency As described above, the delay time difference τ due to the nonlinear interaction of pump wave pulses of a certain strength can be found.

Next, a process of obtaining and processing a received signal from the subject 15 using the waveform shown in FIG. 2 corresponding to a change in the state of the output of the control drive unit 3 will be described.

First, the pulse driver 31 and pulse driver 32 of the control drive section 3 are operated to drive the pump wave ultrasonic transducer 1 and the probe wave ultrasonic transducer 2 to achieve phase state A ⁺ in the subject 15. do. At this time, the pulse driver 31 transmits a drive pulse to the pump wave ultrasonic transducer 1 to send out a pump wave pulse of the same intensity into the subject 15 as when calculating the delay time difference τ described above.
shall be sent to. The pump wave pulse and the probe wave pulse that have crossed and overlapped in the subject 13 are scattered in the subject 15, and the scattered ultrasound waves are received by the ultrasound transducer 2. The received signal is amplified by the receiving circuit 4 and sent to the signal processing section 5. In the signal processing section 5, an A/D converter 51
converts the output of the receiving circuit 4 into a digital signal.
The sample timing of A/D converter 51 is controlled by clock pulses from clock source 6. It is assumed that this sample timing is synchronized with the pulse drivers 31 and 32. The output data of A/D converter 51 is stored in memory 52. Next, the memory 52
Among the data stored in , the frequency analyzer 53 performs frequency analysis on the data corresponding to the window section corresponding to the depth Z ₁ of the subject 15 to obtain the frequency characteristics, that is, the spectral distribution P ⁺ (Z ₁ , f). demand. However, f is the frequency. The length of the window section is, for example, about 1 cm. Furthermore, the spectral distribution P ⁺ for the data corresponding to the window section corresponding to depth Z ₂
Find (Z ₂ , f). Next, a phase state A ⁻ is realized in the subject 15 . The implementation method is phase state A ⁺
The phase relationship between the pump wave pulse and the probe wave pulse, that is, the positional relationship of superposition, can be achieved by shifting the phase by 180 degrees with respect to the pump wave pulse, or by reversing the polarity of the output voltage of the pump wave pulse. be. Similarly, for the received signal obtained in the phase state A ^- , _the spectral distribution P ^- (Z ₁ ,
f), spectral distribution P at depth Z ₂ ^- (Z ₂ , f)
seek. The spectral distribution of these received signals can be expressed as follows using the spectral distribution T of the incident probe wave pulse at each test depth described above and the frequency characteristic S of ultrasonic scattering.

P ⁺ (Z ₁ , f) = T ⁺ (Z ₁ , f) × S (Z ₁ , f) ... (6) P ^- (Z ₁ , f) = T ^- (Z ₁ , f) × S ( Z ₁ , f) ……(7) P ⁺ (Z ₂ , f)=T ⁺ (Z ₂ , f)×S(Z ₂ , f) ……(8) P ^- (Z ₂ , f)=T ^- (Z ₂ , f) × S (Z ₂ , f) ... (9) That is, as mentioned above, when the spectral distribution of the incident probe wave pulse when there is no pump wave pulse is T, the phase state A ⁺ In phase state A, the spectral distribution T ⁺ of the incident probe wave pulse shifts to the high frequency side, and in phase state A ^-, the spectral distribution T ^- of the incident probe wave pulse shifts to the low frequency side. or,
Due to the influence of the frequency-dependent attenuation of the ultrasound of the object 15, the spectral distribution T (Z ₂ , f) of the incident probe wave pulse at depth Z ₂ changes to the spectral distribution T (Z ₁ , f) at depth Z ₁ . It shifts to the lower frequency side. By determining the dependence of the amount of shift in the center frequency of the spectral distribution of the received signal on the propagation distance in the subject 15, it is possible to determine the attenuation characteristics of the ultrasound in the subject 15. However, in reality, determining the center frequency of a received signal from a subject 15 having a complex ultrasound scattering characteristic S such as a living body has a problem in that the error is extremely large due to the frequency dependence of this ultrasound scattering characteristic S. It was hot.
In order to eliminate the influence of this ultrasonic scattering characteristic S, (6) and
The frequency at which the value of P coincides with equation (7), and equations (8) and (9) is determined by the cross frequency calculation unit 54. That is, the spectral distribution T ⁺ at the depth Z ₁ of the object 15
Spectral distribution T ⁺ at the frequency and depth Z ₂ corresponding to the intersection of (Z ₁ , f) and T ^- (Z ₁ , f)
Find the frequency corresponding to the intersection of (Z ₂ , f) and T ^- (Z ₂ , f). As described above, the delay time difference calculation unit 7 calculates the delay time difference between pump wave pulses of a certain intensity, and the signal processing unit 5 calculates the ^delay time difference of the propagation distance Z ₁ for pump wave pulses of the same intensity _.
The cross frequencies of ^{T + (} Z _{2 ,} f) and T ^- (Z ₂ , f) at the propagation distance Z ₂ are determined and stored in the memory 8'. The delay time difference at this time is τ ₁ , and the crossing frequency of propagation distance Z ₁ is f ₁
(Z ₁ ), and the crossing frequency of the propagation distance Z ₂ is f ₂ (Z ₂ ).

Next, the pulse driver 31 of the control drive section 3 transmits a drive pulse for changing the intensity of the pump wave pulse to an ultrasonic transducer in order to obtain a delay time difference different from the delay time difference τ ₁ described above according to the control signal of the main control section 14. 1, and a pump wave pulse that produces a delay time difference different from the delay time difference τ ₁ is sent into the subject 15. Similarly to the above explanation, the delay time difference calculation section 7 calculates the delay time difference, and the signal processing section 5 calculates the delay time difference at the propagation distance _Z1 .
Find the crossing frequencies of T ⁺ (Z ₁ , f) and T ^- (Z ₁ , f) and the crossing frequencies of T ⁺ (Z ₁ , f) and T ^- (Z ₁ , f) at the propagation distance Z ₂ and store them in memory. Store in 8. The delay time difference at this time is τ ₂ , and the propagation distance Z ₁ is T ⁺
The intersection frequency of (Z ₁ , f) and T ^- (Z ₁ , f) is f ₂ (Z ₁ ),
Let f ₂ (Z 2 ) be the crossing frequency of T ⁺ (Z ₂ , f) and T ^- (Z ₂ , f) at propagation _{distance Z 2 .} Next, the center frequency calculation unit 9 calculates the cross frequency f ₁ (Z 1 ) of the delay time difference _{τ 1 and} the cross frequency f ₂ (Z ₁ ) of the delay time difference τ ₂ with respect to the propagation distance Z ₁ stored in the memory 8. As shown in Figure 6, the frequency at the delay time difference τ ₀ is determined from the intersection with a straight line passing through the two points, and the propagation distance is
Let it be the center frequency at Z ₁ . Similarly, the propagation distance Z ₂
From the crossing frequency f ₁ (Z ₂ ) of the delay time difference τ ₁ and the crossing frequency f ₂ (Z ₂ ) of the delay time difference τ ₂ , the propagation distance Z ₂
Find the center frequency at . Based on the center frequencies at the propagation distances Z ₁ and Z ₂ of the received signals obtained in this way, the attenuation calculation unit 10 calculates the propagation distances Z ₁ and Z _{2 .}
An ultrasonic attenuation characteristic, for example an ultrasonic attenuation coefficient, is calculated from the change in the center frequency between the two and stored in the memory 11.

Next, the temperature of the subject 15 is heated and changed using, for example, microwaves or powerful ultrasonic waves. As mentioned above, the center frequency calculation unit 9 calculates the center frequency at the inspection depths Z _{1 and Z 2 at the same site in the subject 15 from the two types of delay time differences τ 1 and τ 2 and the} corresponding crossing frequencies, Further, the attenuation calculation unit 10 calculates the ultrasonic attenuation coefficient between the test depths Z ₁ and Z ₂ .
Next, the temperature change calculation unit 12 calculates the ultrasonic attenuation coefficient between the test depths Z ₁ and Z ₂ before heating, which is stored in the memory 11, and the ultrasonic attenuation coefficient after heating, which is the output of the attenuation calculation unit 10. Using the ultrasonic attenuation coefficient between the probe depths Z ₁ and Z ₂ , the amount of temperature change before and after heating is determined and displayed on the display unit 13 .

In the above explanation, when calculating the center frequency, the center frequency for any propagation distance is calculated by the intersection frequency of the spectral distributions T ⁺ (f) and T ^- (f ₎ at two types of delay time differences τ ₁ and τ 2. Although the method for determining the cross frequency for three or more types of delay time differences has been described, it is also possible to determine the cross frequencies for three or more types of delay time differences and approximate them using a higher-order curve in FIG. 6, and in this case, the accuracy of the center frequency will be higher.

As is clear from the above explanation, according to this embodiment, a received signal can be arbitrarily selected from data at frequencies at which a plurality of delay time differences and the spectral distributions T ⁺ (f) and T ^- (f) corresponding to the delay time differences intersect. It is possible to obtain the center frequency at the depth to be tested, and obtain the ultrasonic attenuation coefficient from the change in this center frequency at different depths to be tested, and further calculate the amount of temperature change from the change in the ultrasonic attenuation coefficient. It is possible to obtain Furthermore, by changing the measurement location, it is possible to measure the distribution of the ultrasonic attenuation coefficient over a wide range, and it is also possible to measure the amount of temperature change over a wide range.

Effects of the Invention As described above, the present invention sends pump wave pulses and probe wave pulses into a subject by a control drive unit, and by nonlinear interaction, the delay time difference and the pump wave pulse and probe wave realized in the subject are realized. By finding the crossing frequency of the spectral distribution of the received signal corresponding to each phase state of the pulse A ⁺ and A ^- , and then changing the pump wave pulse intensity multiple times and changing the delay time difference to find the crossing frequency. The center frequency can be accurately determined from the spectral distribution of the received signal, and the ultrasonic attenuation characteristics can be obtained from the changes in this center frequency at different depths of inspection, and the temperature can also be determined from the changes in the ultrasonic attenuation characteristics. The amount of change can be determined, and it can be used, for example, as a temperature monitor for cancer thermotherapy, which is highly effective.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram of an ultrasonic temperature measuring device according to an embodiment of the present invention, FIGS. Figures a to c are waveform diagrams explaining that distortion occurs in the ultrasonic pulse waveform due to nonlinear propagation phenomena; Figure 4 is a spectral characteristic diagram of an incident probe wave pulse in an embodiment of the present invention; Figure 5
The figure is a propagation distance characteristic diagram of the center frequency and cross frequency in one embodiment of the present invention, FIG. The figure is a functional block diagram illustrating conventional ultrasonic attenuation characteristic measurement. 1, 2... Ultrasonic transducer, 3... Control drive unit,
4... Receiving circuit, 5... Signal processing section, 6... Clock source, 7... Delay time difference calculation section, 8... Memory, 9... Center frequency calculation section, 10... Attenuation calculation section, 11... Memory, 12...Temperature change calculation section,
13...display unit, 14...main control unit, 15...subject.

Claims (1)

[Scope of Claims] 1. A pump wave ultrasonic transducer that sends out a pump wave ultrasonic pulse; a probe wave ultrasonic converter that sends out a probe wave ultrasonic pulse having a higher frequency than the pump wave ultrasonic pulse; A first position that controls the drive of the pump wave ultrasonic pulse and the probe wave ultrasonic pulse, and is a region where the particle velocity of the pump wave ultrasonic pulse changes from a minimum to a maximum and the rate of change is greatest;
and a control drive for superimposing the probe wave ultrasonic pulse on the pump wave ultrasonic pulse at a second position in a region where the particle velocity of the pump wave ultrasonic pulse changes from a maximum to a minimum and the rate of change is largest. a delay time difference calculation unit that calculates a delay time difference of the probe wave ultrasound pulse generated by the pump wave ultrasound pulse; and a delay time difference calculation unit that calculates a delay time difference of the probe wave ultrasound pulse generated by the pump wave ultrasound pulse; a frequency analyzer that calculates the spectral distribution of the received signal and the spectral distribution of the received signal from the subject when superimposed on the second position;
a cross frequency calculation unit that calculates the frequency at which two spectral distributions intersect at a position; a pulse drive unit that changes the intensity of the pump wave ultrasonic pulse; an output of the cross frequency calculation unit and an output of the delay time calculation unit. a center frequency calculation unit that calculates the center frequency of the received signal of the probe wave ultrasonic pulse from the center frequency calculation unit; an attenuation calculation unit that calculates the ultrasonic attenuation characteristic from the output of the center frequency calculation unit; An ultrasonic temperature measurement device comprising a temperature change calculating section that calculates a relative temperature change from a change in acoustic wave attenuation characteristics.