JPH0331059B2 - - Google Patents

Description

[Detailed Description of the Invention] (A) Technical Field of the Invention The present invention relates to a device for measuring nonlinear parameter distribution of an ultrasonic medium, and particularly to a method for measuring the spatial distribution of physical properties of an ultrasonic medium such as a living tissue. Taking advantage of the fact that the parameter is nonlinear with respect to sound pressure, which is a constant value as a first approximation, but is proportional to the sound pressure as a second approximation, the spatial distribution of this nonlinearity parameter can be expressed as a characteristic value of the medium. The present invention relates to a measuring device that can perform measurements and, if necessary, visualize its spatial distribution quickly and easily. Furthermore, the present invention particularly relates to an apparatus capable of measuring the above-mentioned nonlinear parameters by a reflection method rather than a so-called transmission method.

(B) Technical background and problems The principle of the nonlinear parameter imaging method used in the present invention is disclosed in Japanese Patent Application No. 57-167036 or Japanese Patent Application No. 58-119100.
Details are given in the issue. In the former, a relatively low-frequency pumping plane pulse wave is crossed from a direction orthogonal to a relatively high-frequency continuous measurement ultrasound beam, and the measurement wave phase-modulated by the pumping pulse is phase-demodulated. The nonlinear parameter B/A on the measurement wave beam scanning line was determined at high speed. In addition, in the latter case, instead of applying the pumping pulse perpendicularly to the measurement beam, by applying it coaxially with the measurement beam and with the traveling direction opposite to the measurement beam,
The measurement beam received pumping pulses of approximately the same shape almost everywhere, which had the effect of eliminating large mechanical structures.

However, all of these methods use the so-called transmission method, in which the signal is emitted from the measurement wave transmitting transducer, passes through the measured medium, and is received by the measurement wave receiving transducer. Because
When attempting to obtain tomographic images in actual clinical applications, the applicable site is limited to areas such as the breast where the observed site can be placed between a pair of measurement transducers, or the site to be observed is surrounded by a pillow of water. There were major operational problems, such as the need to scan the measurement transducer pair.

(C) Object and Structure of the Invention The present invention, instead of using a continuous wave as a measurement wave, transmits a burst-shaped pulse wave from a measurement wave transducer that is used for both transmission and reception, and also transmits a burst pulse wave from a measurement wave transducer that is used for both transmission and reception. As shown in Figure 1, relatively low-frequency ultrasound pulses for pumping are sent into the observed medium in almost the same direction from The driving timing of the transducer is adjusted so that the measurement burst wave is superimposed on the measurement pulse (part), and when both the pumping pulse and the measurement pulse are transmitted, the reception signal of the measurement pulse that is reflected back is By finding the difference between the phase and the phase of the received signal of the measurement pulse that is reflected and returned when only the measurement pulse is transmitted, the phase modulation of the measurement pulse due only to the influence of the pumping pulse can be detected using the reflection method. Then, the ultrasonic nonlinear parameter B/ in the observed medium is
This is an attempt to find A.

In the present invention, when focusing on one point on a traveling measurement wave, the nonlinear parameter B/A (however, a function of the location) of the area through which the measurement pulse passes before that point reaches the reflector. By utilizing the phase modulation determined by the integral value of the product of the pumping wave and the sound pressure P (which is a function of location due to the effect of attenuation),
This method attempts to obtain the B/A distribution by differentiating the phase signal obtained by demodulating the received signal.
Therefore, the present invention is characterized by having the structure described in the claims. This will be explained in detail below.

(D) Embodiment of the invention The sound speed when the sound pressure in the ultrasonic medium is zero is C ₀ ,
If the density is ρ ₀ , the sound speed C when a sound pressure of P is applied is C=C ₀ +1/2ρ ₀ C ₀・B/A・P …(1) (However, B/A=2ρ ₀ C ₀ (aC/aP) _s (however, the subscript S indicates isentropy)). Therefore, due to the sound pressure P of the pumping pulse, the sound speed C changes by ΔC=1/2ρ ₀ C ₀ B/AP (2).

Now, as shown in Fig. 2, a burst-shaped ultrasonic pulse W _n is sent into the medium to be measured from the measurement wave ultrasonic transducer X _n placed at Z = 0 in the Z-axis direction of the figure, and is reflected. Consider the case where a reflected wave from a body M is received. At this time, from the pumping pulse transmitting transducer X _p installed at almost the same location as the measurement pulse W _n ,
Pumping pulse W _p is sent in the Z-axis direction as shown. In the following, for the sake of simplicity, it will be assumed that W _p and W _n are superimposed. Also, the sound pressure W _n is the sound pressure W _p
, and P in equations (1) and (2) is W _p
It is only necessary to consider the Until the measurement pulse W _n reaches the reflector M at Z = Z, at each Z, according to equation (2), the sound speed changes depending on the location ΔC (Z) = 1/2ρ ₀ C ₀・B /A(Z)・P(Z)…(
3) Therefore, it will receive a phase change proportional to ΔC (Z) that differs depending on the location (Z). Therefore, when reaching the reflector M, the phase change Φ (Z) = K∫ ^z ₀ ΔC (Z) dZ (K: constant of proportionality) = K∫ is proportional to the integral value of the change in sound speed shown by the third equation. ^z ₀ 1/2ρ ₀ C ₀・B/A(Z)・P(Z)dZ…(4). After being reflected by the reflector M, there is no pumping pulse until it is received by the transducer X _n (more precisely, the reflected wave of the pumping pulse returns together with the reflected wave of the measurement pulse) is sufficiently small compared to the sound pressure on the outward path), so if the reflected wave of the measurement pulse received by the transducer X _n is phase demodulated, Φ (Z) shown by the fourth equation You will get it.

By differentiating Φ(Z) with respect to Z, dΦ(Z)/dZ=K1/2ρ ₀ C ₀・B/A(Z)・P(Z
)...(5) is obtained, and the left side of equation 5 is the value obtained by actual measurement, and the right side K, ρ ₀ and C ₀ are constants, so if P(Z) can be known, B/A(Z ) can be found.

As an example of ultrasonic frequency, pumping pulse W _p
As such, the attenuation within living tissues is not very large.
About 500KHz is used, and the measurement wave pulse W _n
A frequency of about 5MHz, which is about an order of magnitude higher than that, is used. In living tissues, ultrasound waves are almost
It is well known that the attenuation is 1dB/MHz/cm, and in the case of _Wp of 500KHz, the attenuation is approximately 0.5dB/cm. Therefore, P(Z) in the fifth equation
For example, P(Z) may be estimated using the following formula. In this case, from equation 5, However, K′=2ρ ₀ C ₀ /KP(0) α=0.5/20log _e 10 In other words, the differentiated phase demodulation output Φ(Z) is
B/A(Z) can be obtained by multiplying by a coefficient K′e ⁺ 〓 ^Z that increases with distance Z.

If the assumption that the attenuation in biological tissue is constant regardless of location, such as 1 dB/MHz/cm, does not hold, then the distance A so-called TGC that can give a free gain as shown in Figure 3 for each Z.
It goes without saying that it is also good to use (Time Gain Control).

Furthermore, when the average sound speed in the medium is C ₀ , Z≒Cot
(t: time since the ultrasonic wave was transmitted), so dZ=Co dt ∴dΦ(Z)/dZ=1/C ₀ dΦ(Z)/dt...(8), and Z in the fifth equation Needless to say, the differentiation by can be replaced by the time differentiation.

In the above explanation, it was assumed that the phase Φ(Z) of the reflected wave from the reflector at distance Z can be found, but
This is not easy for the following reasons.

First, in order to detect the phase, a phase comparison is made between a reference signal and a received signal as shown in FIG. 4a. However, in the case of the reflection method, as shown in Fig. 4b and c, just a difference in the distance between the transducer and the reflector causes a large change in the phase of the received signal with respect to the reference signal, resulting in B/A(Z). This hides the phase shift due to the influence of P(Z).

Second, as shown in Figure 5, reflected waves from within living tissues are often superimposed on each other, and as shown in Figure 5c, the combined received signal is not the same as any of the original signals. Both signals a and b will have significantly different phases, which will hide the phase shift due to the influence of B/A(Z) and P(Z).

In order to eliminate this phenomenon, in Japanese Patent Application No. 58-227949 previously filed by the present applicant, the phase of the received signal when the measurement pulse is transmitted together with the pumping pulse, and the phase of the reception signal when the measurement pulse is transmitted without sending the pumping pulse. The difference from the phase of the received signal when only the pulse is transmitted is determined. As shown in Fig. 4 or 5 above, the phase change due to propagation or pulse superimposition appears in the same way whether a pumping pulse exists or not, so the phase demodulation output in each case is memorized. By obtaining the difference between
It is possible to extract the phase change Φ(Z) due only to the influence of B/A(Z) and P(Z), excluding the influence of propagation or pulse superimposition.

In contrast, in the present invention, as shown in Fig. 6, the measurement wave is superimposed on the high sound pressure portion (positive sound pressure) of the pumping wave, and the measurement wave is By comparing the amount of phase change of the measured wave with the case where waves are superimposed,
The B/A distribution can be detected with higher sensitivity than in the case of comparing the amount of phase change of the measurement wave depending on the presence or absence of the pumping wave as described in No. 58-227949.

An example of the configuration of the embodiment will be described below with reference to the drawings.
In FIG. 7, 1 is a timing control unit that generates the timing of pumping pulse transmission, 2 is a continuous wave oscillator for measurement wave burst pulses, 3 is a driver for pumping pulses, and 4 is a specific phase ( A gate circuit for cutting out the output of the oscillator 2 so that the measurement burst pulse is superimposed on the phase where the sound pressure is usually maximum or minimum;
5 is a driver for driving the measurement vibrator 7;
6 is a transducer for generating pumping pulses, 7 is a transducer for generating measurement pulses, 8 is an ultrasonic medium to be measured, 9 is a receiving amplifier, 10 is a phase detection circuit, 11
12 is a memory for temporarily storing the output of the phase detector 10, and 12 is a memory for temporarily storing the output of the phase detector 10.
A subtraction circuit for subtracting an output of 0, 13 a differentiation circuit, and 14 a so-called time gain control circuit. FIGS. 7b and 7c show an example of the structure of the vibrators 6 and 7, with a sketch (FIG. 7b) and a sectional view (FIG. 7c). FIG. 8 shows time waveforms in the main parts shown in FIG. 7. When the pulse of FIG. 8a is applied to the pumping pulse driver 3 of FIG. 7, the waveform of FIG. 8c is applied to the pumping pulse generating vibrator 6 of FIG.
On the other hand, the output of the continuous wave oscillator 2 in FIG. 7 is extracted by the gate circuit 4 at a timing such that, for example, a measurement pulse is sent out only at the high sound pressure portion of the pumping pulse (left end in FIG. 8b). , a drive signal as shown in FIG. 8d is applied to the measuring vibrator 7 in FIG. 7 through the driver 5. As a result, the pumping pulse and the measurement pulse can be set at the seventh pulse while maintaining the timing relationship as shown in FIG.
It will proceed through the ultrasonic medium 8 to be measured shown in the figure. The reflected wave from the medium to be measured is received by the vibrator 7, amplified by the reception amplifier 9 as shown in FIG. 8e, and then input to the phase detection circuit 10. The output of the continuous wave oscillator 2 is given as a reference signal to the other input of the phase detection circuit, and the phase difference between these two inputs is outputted from the phase detection circuit 10 and sent to the storage circuit as shown in FIG. Sent to 11.

The storage circuit 11 is given the pumping wave drive timing shown in FIG. 8a and the gate timing shown in FIG. 8b as trigger signals,
The signal is stored for a period of one scanning line (period A in FIG. 8 f) from the gate timing immediately after the pumping wave drive timing, and the stored contents are outputted and sent to the subtraction circuit 12 at the next gate timing pulse. . The subtraction circuit 12 subtracts the output of the phase detection circuit 10 (B in Fig. 8 f) from the output of the memory circuit 11 (A in Fig. 8 f), and the measurement wave is superimposed on the high sound pressure part of the pumping wave. The difference in the output of the phase detection circuit between the case where the sound pressure is superimposed on the low sound pressure part and the case where the sound pressure is superimposed on the low sound pressure part is obtained as shown in FIG.
The signal is sent to the gain control circuit 14. Time gain
The control circuit 14 is given the gate timing signal shown in FIG. 8b as a trigger signal, and synchronized with the transmission of the measurement pulse, the output of the differential circuit 13 shown in FIG. For example, the third
Time-varying amplification as shown in the figure is performed to obtain the final output B/A(Z). It goes without saying that the memory circuit 11 may be an analog type using a delay line such as a BBD or CCD, or a digital type using a combination of an A/D converter and a memory or a shift register.

As described above, according to the present invention, the spatial distribution of the nonlinear parameter B/A(Z) of the ultrasonic medium can be obtained by the reflection method instead of the conventional transmission method, which is necessary for the transmission method. In addition to completely eliminating the need for large mechanical structures such as a water tank, the object can be observed from various parts, and operability can be greatly improved. In comparison, the detection sensitivity of B/A can be improved approximately twice.

The above description of the embodiments was related to claims 1, 3, and 4. Claim 1 provides a phase difference between the case where the measurement wave is superimposed on the high sound pressure part of the pumping pulse and the case where it is superimposed on the low sound pressure part by subtraction between the phase detection results. On the other hand, the second claim claims that the measurement wave is superimposed on the high sound pressure part of the pumping wave.
By directly comparing the phases of the RF signal and the received RF signal when the measurement wave is superimposed on the low sound pressure part of the pumping wave, we can compare the received RF signal when the measurement wave is superimposed on the high sound pressure part of the pumping wave and the low sound pressure part. The objective is to find the phase difference between the received signal and the case where it is superimposed on the received signal. A configuration example is shown in FIG. 9. In FIG. 9, the same components as in FIG. 7 are given the same numbers, and their explanations will be omitted. What is different from Figure 7 is that
The order of the phase detection circuit 10 and the memory circuit 11 is reversed, and the subtraction circuit 12 is eliminated. When using the configuration shown in FIG. 9, the memory circuit 11 may be an analog (by CCD, etc.) or digital (by an A/D converter and memory or shift register) that is fast enough to directly store the RF received signal. A storage circuit is required. The operation of the system shown in FIG. 9 can be easily inferred from the operation of the system shown in FIG. 7, so a description thereof will be omitted.

Claim 5 relates to means for improving the S/N ratio of the measured B/A(Z) distribution. When the amount of phase change of the measurement pulse due to the product of the nonlinear parameter and the sound pressure is small, noise generated in the circuit and elsewhere cannot be ignored with respect to the original amount of phase change Φ(Z). Furthermore, in order to obtain B/A(Z), Φ(Z) is differentiated, but this differentiation operation also causes increased noise. Therefore, the obtained B/A(Z) is likely to contain noise. This situation is shown in FIG. By adding the noise N shown in FIG. 10B to the noise-free B/A(Z) output shown in FIG. 10A, a signal as shown in FIG. 10C is actually output. As a countermeasure for this, measure the same part K times and measure S ₁ to S _K shown in Figure 10C.
If we take a signal with added noise like , and add these points at the same Z coordinate, the signal component at each point will be multiplied by K in amplitude, but the noise component will be multiplied by K in power.
If the noise is random noise, the noise amplitude at each point is only multiplied by √. Therefore, the S/N ratio is improved by a factor of √, and an output as shown in FIG. 10D is obtained.

An example of the configuration of a system using this method is shown in FIG. In FIG. 11, the same components as in FIG. 7 are given the same numbers, and their explanations will be omitted. In FIG. 11, 16 is a delay circuit that delays the signal by the transmission repetition period T of the pumping pulse, and may be realized by analog means such as BBD or CCD, or by an A/D converter and a shift circuit. Needless to say, it may be realized by digital means using registers or memory. 15
is an adder, and may be of either analog or digital type depending on the type of delay circuit. In the case of the configuration shown in Figure 11, Time Gain Control
It is clear that the output of the circuit 14 is added for each point on the same Z-axis coordinate, and the S/N ratio can be improved by so-called synchronous addition.

In the present invention, it is further possible to obtain a two-dimensional or three-dimensional distribution of B/A(Z), as shown in claim 6. As is clear from the above explanation, since the distribution of B/A(Z) on a specific scanning line can be obtained, the relative positions of the pumping pulse transducer 6 and the measuring pulse transducer 7 can be kept constant. If you move it in the x or/and y direction while maintaining the same position and store the value of B/A (Z) in the memory address corresponding to each x or/and y coordinate, you can create a two-dimensional representation of B/A (Z). Or/and a three-dimensional distribution can be obtained.

For example, as shown in FIG. 12, if a so-called electronic scan is performed using a pumping pulse transducer X _p and a measuring pulse transducer X _n as array transducers, B/A(Z) can be easily obtained. It is clear that we can obtain a two-dimensional distribution of . Also the 12th
By expanding the illustrated transducer array in the y-axis direction of the figure and using a transducer array configured as shown in FIG. 13, for example, a three-dimensional distribution of B/A(Z) can be easily obtained. It is clear that

In the above explanation, we have explained the case where a transducer array as shown in Fig. 12 or Fig. 13 is used to obtain a two-dimensional or three-dimensional B/A(Z) distribution. It goes without saying that a two-dimensional or three-dimensional distribution of B/A(Z) may be obtained by mechanically scanning in one or two dimensions using a vibrator.

Furthermore, in the above explanation, the pumping pulse vibrator and the measurement pulse vibrator are provided side by side at laterally shifted positions, but as shown in claim 7, for example, As shown in FIG. 14, the pumping pulse vibrator X _p and the measurement pulse vibrator X _n may be superimposed. In this case, the measuring pulse transducer X _n shown in Fig. 14 is, for example, a so-called PVDF, which is flexible and has an acoustic impedance close to that of living tissue, and the pumping pulse transducer X _p is, for example, a so-called PZT, which is hard and has a large acoustic impedance. When used, the pumping pulse can pass through the PVDF layer with little attenuation,
Moreover, the PZT layer is a packing layer compared to the PVDF layer.
It is possible to realize an extremely suitable vibrator structure, such as acting as a BK.

(E) Effects of the invention As described above, according to the present invention, compared to the previously proposed method for measuring the nonlinear parameter B/A(Z) of an ultrasonic medium, a more compact device configuration is possible.
Furthermore, the distribution of B/A (Z) can be measured using the reflection method, which is easier to operate.
It is possible to perform measurements that are about twice as sensitive as those shown in No. 58-227949.

[Brief explanation of drawings]

Figures 1 and 2 are explanatory diagrams explaining the premise concept of the present invention, and Figure 3 is a so-called Time Gain
An explanatory diagram explaining the concept of control, Figures 4 and 5 are explanatory diagrams explaining the concept of the phase of reflected waves, and Figure 6 shows the measurement ultrasonic pulse and pumping ultrasonic pulse used in the present invention. FIG. 7 is an explanatory diagram illustrating the transmission timing of the configuration shown in FIG. 7, FIG. 8 is an explanatory diagram illustrating the operation of the configuration shown in FIG. 7, and FIG. Example configuration, FIG. 10 is an explanatory diagram for explaining the concept of synchronous addition, FIG. 11 is an example configuration for performing synchronous addition, and FIGS. 12 to 14 are various embodiments of the vibrator. Give an example. In the figure, 1 is a timing control section, 2 is a continuous wave oscillator, 3 is a pumping pulse driver, 4 is a gate circuit, 5 is a measurement pulse driver, 6 is a pumping pulse vibrator,
7 is a measurement pulse transducer, 8 is an ultrasonic medium to be measured, 9 is a receiving amplifier, 10 is a phase detection circuit, 11
is a memory circuit, 12 is a subtraction circuit, 13 is a differentiation circuit,
14 represents a time gain control circuit, 15 represents an adder circuit, and 16 represents a delay circuit.

Claims (1)

[Scope of Claims] 1. (a) An ultrasonic transducer for both transmitting and receiving purposes that sends out an ultrasonic pulse of relatively high frequency and low sound pressure for measurement into an ultrasonic medium; (b) The ultrasonic pulse for measurement an ultrasonic transducer that sends a relatively low frequency and high sound pressure ultrasonic pulse for pumping into the ultrasonic medium from almost the same place in almost the same direction; (c) the measuring ultrasonic pulse is for pumping; (d) means for controlling the drive timing of the transducer so that the ultrasonic pulse is transmitted so as to be superimposed on any one of a plurality of predetermined specific phases of the ultrasonic pulse; (d) the measuring ultrasonic wave; means for detecting the phase of a received signal consisting of a reflected wave of a pulse from within the ultrasonic medium; (e) measuring so as to be superimposed on any one of the specific phases of the pumping ultrasonic pulse The phase (function of time) of the received signal detected when transmitting the ultrasonic pulse for measurement and the received signal detected when transmitting the ultrasonic pulse for measurement so as to be superimposed on another specific phase part of the ultrasonic pulse for pumping. The equivalent nonlinearity of the ultrasonic medium is obtained by differentiating the phase difference as a function of time obtained in (f) and (e). 1. A nonlinear parameter distribution measuring device for an ultrasonic medium, comprising means for determining the spatial distribution of parameters on the measurement beam. 2. The ultrasonic wave according to claim 1, wherein the plurality of predetermined specific phases are a high sound pressure part (positive sound pressure) and a low sound pressure part (negative sound pressure) of the pumping wave. Device for measuring nonlinear parameter distribution of media. 3. As a means of compensating for the effect that the sound pressure of the pumping ultrasonic wave decreases as it goes inside the ultrasonic medium, an amplifier whose gain increases with time is installed after the differential output in the first term (f). An apparatus for measuring nonlinear parameter distribution of an ultrasonic medium according to claim 1 or 2, characterized in that: 4. Any one of items 1 to 3, characterized by having a so-called synchronous addition circuit that adds nonlinear parameter values corresponding to the same position on the same measurement beam line each time multiple ultrasound pulses are transmitted and received. Nonlinear parameter distribution measuring device for ultrasonic media. 5. Having a scanning unit/display unit for obtaining a two-dimensional or three-dimensional equivalent nonlinear parameter distribution image by scanning a set of measurement and pumping transducers one-dimensionally or two-dimensionally. 5. A nonlinear parameter distribution measuring device for an ultrasonic medium according to any one of items 1 to 4, characterized in that: 6 Pumping oscillators are made of so-called materials.
It is a single plate or array vibrator using piezoelectric ceramic such as PZT, and the measuring vibrator is a single plate or array vibrator using an organic piezoelectric film such as so-called PVDF as a material, and the latter is different from the former. 6. A nonlinear parameter distribution measuring device for an ultrasonic medium according to any one of claims 1 to 5, characterized in that the device uses a vibrator arranged so as to cover the front surface of the ultrasonic medium. 7 (a) An ultrasonic transducer for both transmitting and receiving purposes that sends out ultrasonic pulses of relatively high frequency and low sound pressure for measurement into an ultrasonic medium; (c) an ultrasonic transducer that sends an ultrasonic pulse of relatively low frequency and high sound pressure for pumping in a direction into the ultrasonic medium; (d) means for controlling the driving timing of the vibrator so as to be transmitted so as to be superimposed on any one of the plurality of specific phases of the pumping ultrasonic pulse; and (d) any of the specific phases of the pumping ultrasonic pulse Received signal (so-called RF signal) when ultrasonic pulses for measurement are transmitted so as to be superimposed on one
RF is the phase difference between the received signal (RF signal) when the measuring ultrasonic pulse is sent out so as to be superimposed on another specific phase part of the pumping ultrasonic pulse.
The equivalent nonlinear parameters of the ultrasonic medium are determined on the measurement beam by means of calculating the phase difference between the signals, and by differentiating the phase difference as a function of time obtained in (e) and (d). 1. A nonlinear parameter distribution measuring device for an ultrasonic medium, characterized in that it has means for determining a spatial distribution of. 8. The ultrasonic wave according to claim 7, wherein the plurality of predetermined specific phases are a high sound pressure part (positive sound pressure) and a low sound pressure part (negative sound pressure) of the pumping wave. Device for measuring nonlinear parameter distribution of media. 9. As a means of compensating for the effect that the sound pressure of the pumping ultrasonic wave decreases as it goes inside the ultrasonic medium, an amplifier whose gain increases with time is installed after the differential output in item 7 (e). An apparatus for measuring nonlinear parameter distribution of an ultrasonic medium according to claim 7 or 8. 10. Any one of items 7 to 9, characterized by having a so-called synchronous addition circuit that adds nonlinear parameter values corresponding to the same position on the same measurement beam line every time an ultrasound pulse is transmitted and received a plurality of times. Nonlinear parameter distribution measurement device for ultrasonic media. 11 Having a scanning unit/display unit for obtaining a two-dimensional or three-dimensional equivalent nonlinear parameter distribution image by scanning a set of measurement and pumping transducers one-dimensionally or two-dimensionally. 11. The nonlinear parameter distribution measuring device for an ultrasonic medium according to any one of items 7 to 10, characterized in that: 12 The pumping resonator is a single plate or array vibrator using a piezoelectric ceramic such as PZT as a material, and the measuring vibrator is a single plate or array vibrator using an organic piezoelectric film such as PVDF as a material. The nonlinear parameter of an ultrasonic medium according to any one of claims 7 to 11, characterized in that the latter uses a vibrator arranged so as to cover the front surface of the former. Distribution measuring device.