JPH11113896A - Ultrasonograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display new information representing the character of tissue. SOLUTION: In this device, a receipt signal is converted into a complex signal in an orthogonal detection circuit 16. In a divider 26, a real part in the complex signal is divided by an imaginary part, while in a divider 28, the imaginary part is divided by the real part. On the basis of the output from the divider 26 or 28, a B mode image or an M mode image is formed. A ratio of the real part to the imaginary part. is related to phase information contained in a reflection signal, and by means of the ratio, new disease diagnostic information can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an ultrasonic diagnostic apparatus that forms an ultrasonic image using a complex signal after quadrature detection.

[0002]

2. Description of the Related Art Ultrasonic waves have the property of being reflected at boundaries having different acoustic characteristics (between tissues), and the intensity of a reflected wave, that is, the amplitude of a received signal, corresponds to the difference in intrinsic acoustic impedance between tissues. I do. Utilizing such properties of ultrasonic waves, in a conventional ultrasonic diagnostic apparatus, a received signal obtained by transmitting and receiving an ultrasonic pulse is converted into a baseband signal by envelope detection, and the amplitude of the signal is converted to a luminance. , A B-mode image and an M-mode image are formed. Conventionally, the evaluation of the texture is performed based on the contrast and the texture in the luminance image as described above.

[0003]

By the way, it is known that the phase changes when the ultrasonic wave is reflected. In particular, the ultrasonic wave changes from a tissue having a low specific acoustic impedance to a tissue having a high specific acoustic impedance. When the sound is reflected, the phase is maintained and becomes positive.On the other hand, when the ultrasonic wave is reflected from a tissue having a high specific acoustic impedance to a tissue having a low specific acoustic impedance, the phase is inverted and the phase is reversed. It is known that Here, assuming the fact that the amount of phase shift (phase difference) at the time of ultrasonic reflection differs due to the difference in acoustic characteristics between tissues, it is possible to express some property of the tissue by the information related to the phase or the phase difference. I come to the conclusion.

[0004] The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide an ultrasonic diagnostic apparatus capable of displaying new information indicating the properties of a tissue.

[0005]

To achieve the above object, the present invention provides a complex signal converting means for converting a received signal obtained by transmitting and receiving an ultrasonic wave into a complex signal, and a real part of the complex signal. And a ratio calculating means for calculating a ratio between the real part and the imaginary part, and a display means for displaying a ratio between the real part and the imaginary part. Here, the ratio calculating means calculates the ratio by dividing the real part by the imaginary part or by dividing the imaginary part by the real part.

According to the above configuration, the received signal is converted into a complex signal by, for example, quadrature detection, and the ratio between the real part and the imaginary part of the complex signal is calculated. It is recognized that the ratio indicates the property of the living tissue, and according to the present invention, it is possible to provide new information that cannot be displayed by the conventional ultrasonic diagnostic apparatus.

[Modeling related to reflection of ultrasonic waves] The modeling related to reflection of ultrasonic waves will be described below.
Clarify how the phase and amplitude of the received signal are related to the medium.

(1) Conventional Concept Two acoustic media [0] and [1] having different acoustic characteristics are joined, and reflection of ultrasonic waves from the boundary surface is considered. If the density and the sound velocity in each medium are defined as ρ ₀ , ρ ₁ , c ₀ , c ₁ , respectively, the specific acoustic impedances Z ₀ , Z _{1 of} each medium
Is

(Equation 1) It is expressed as Reflection coefficient R of sound pressure at the boundary surface
_p is

(Equation 2) It is expressed as Then, the incident sound pressure P _in Tosureba received sound pressure P _r is,

(Equation 3) It is expressed as

According to this conventional modeling, reflecting a slight change in the specific acoustic impedance between the media,
The strength of the received signal will be stronger where the difference in intrinsic acoustic impedance is large. The sign of the reflection coefficient indicates the direction of rotation of the phase when the ultrasonic wave is reflected.When the ultrasonic wave enters from a medium having a large specific acoustic impedance to a medium having a small specific acoustic impedance, the ultrasonic wave is It is considered that the light is inverted and reflected.

However, in this conventional modeling, it is assumed that a plane traveling wave enters a boundary surface where two different media are in contact with each other, and a condition that the medium 1 into which the wave enters continues at infinity. Become.

In ultrasonic diagnosis, in an actual living body,
The boundary surface is complicated and complicated, and it is generally impossible to perform the ideal modeling as described above.
Ultrasound reflections also need to be discussed in a more general way. Therefore, modeling using a complex signal is introduced as follows.

(2) Concept of acoustic reflection by complex signal Since a wave in a certain medium is a combination of a plane traveling wave and a wave in the opposite direction, the sound pressure P in the medium [0] and the medium [1] which are joined to each other is considered. _0, P ₁ and the particle velocities v ₀ , v ₁ are expressed as follows.

[0013]

(Equation 4) However, the angular frequency ω is constant,

(Equation 5) Represents a phase constant, and x represents a position.

The vector A ₀ ,
B ₀ , A ₁ , and B ₁ are complex constants determined by conditions. Since sound pressure and particle velocity are continuous at the interface,

(Equation 6) Condition can be given. Therefore, it becomes as follows.

[0015]

(Equation 7) Since the acoustic impedance density is considered to be continuous at the boundary,

(Equation 8) Is obtained. Therefore, the reflection coefficient R _p of the sound pressure at the boundary
Is

(Equation 9) It is expressed as Here, Z ₀ is the intrinsic acoustic impedance of the medium [0], and Z _1L is the acoustic impedance density of the medium [1] at the interface with the medium [0]. The complex constants A ₁ and B ₁ cannot be determined unless other boundary conditions of the medium [1] are given.

The above equation (A9) will be further studied. Since the fractional function between complex numbers is still a complex number,

(Equation 10) Toki, and

[Equation 11] Then, the following equation is derived. Here, Z _1a is the acoustic impedance density in the medium [1] on the incident side, and θ ₁
Represents the phase component of the acoustic impedance density.

[0017]

(Equation 12) Therefore, reflected sound pressure P _r with respect to the input sound pressure P _in is as follows.

[0018]

(Equation 13) Thereby, the amplitude Amp ₁ and the phase Arg ₁ of the reflected signal are obtained.
Are represented as follows.

[0019]

[Equation 14] Here, when only a plane traveling wave exists on the medium [1] side, since B ₁ = 0 in the above formula (A8), Z
_1a = ρ ₁ c ₁ = Z ₁ , and it can be seen that the expression (A13) is the same as the expression (A3).

The expressions (A14) and (A15) show that the reflected signal does not simply reflect the change in the specific acoustic impedance, but reflects the difference in the acoustic impedance density Z _{1L that} changes according to the boundary conditions. That is to do.

In short, the amplitude of the reflected signal and the phase rotation (phase difference) of the reflected signal depend on the difference in acoustic impedance density at the boundary where acoustic reflection occurs. In other words, the information related to the acoustic impedance density is included in the received signal.

(3) Examination of the above modeling By the way, when the equation (A9) is interpreted graphically, a graphic as shown in FIG. 1 is obtained. Here, it is assumed that Z _1L is fixed.
(A9) molecule [Z _1L -Z _0] of the equation, the radius about a point that is displaced by -Z ₀ on the real axis | moves circumferential upper | Z _1L.
The denominator [Z _1L + Z ₀ ] in the equation (A9) moves on the circumference of the radius | Z _1L | about the point shifted by + Z ₀ on the real axis. (A
Considering the absolute value of the expression 9), the denominator and the numerator are expressed as a distance from the origin to a point (intersection) at which each circle and an imaginary value intersect a certain straight line. Then, it can be seen that the phase is given as a difference between the respective phases.

When the numerical values are actually substituted into the expressions (A13) and (A15) and calculated, the magnitude and phase of the reflection coefficient are expressed as shown in the following figures.

FIG. 2 shows the change in the reflection coefficient of each Z _1a on a complex plane. However, in equation (A13), the reflected signal is standardized, and P _in = 1. Figure 3 is a tried with the absolute value of the reflection coefficient for Z _1a each θ value. 4 and 5 show θ ₁
Respectively represent the amplitude characteristic and the phase characteristic. As described above, the reflection amplitude or the reflection phase changes with the change in the acoustic impedance density.

The acoustic impedance density will be considered again.

[0026]

(Equation 15) After all,

(Equation 16) Becomes In FIG. 4, the phase θ _{1 of the} acoustic impedance density is shown.
Is less than -π / 2 or more than π / 2, the reflection coefficient exceeds 1, and the reflected sound pressure becomes larger than the incident sound pressure. As can be seen from equation (A17), the condition for providing such a state is when the real part of the acoustic impedance density is negative, that is, when a <b. This means that the backward wave is larger than the traveling wave in the medium [1], which is impossible unless another sound source exists.

(4) Calculation of ratio between real part and imaginary part The phase angle obtained by the above equation (A15) reflects Z _1a and θ ₁ . Where Z _1a and θ ₁
The calculation of the phase difference is not necessarily required for the purpose of detecting. That is, new information representing the properties of the living tissue can be obtained from the ratio between the real part and the imaginary part. The following (B
Equation (1) represents the imaginary part I / real part R, and the following (B)
Expression 2) expresses the opposite real part R / imaginary part I.

[0028]

[Equation 17] When the equations (B1) and (B2) are calculated under the condition that Z _1a is _close to 1, the graphs of FIGS. 6 and 7 are obtained. The horizontal axis of FIG. 6 represents θ ₁ , and the vertical axis thereof is (B
1) represents the calculated value of the equation. The horizontal axis in FIG. 7 represents Z _1a , and the vertical axis represents the calculated value of equation (B2).
As shown in FIG. 6, for the theta ₁ shows the correlation good R _IR, as shown in FIG. 7, R _RI indicates a good correlation to Z _1a. Therefore, the properties of the living tissue can be represented by the ratio between the real part and the imaginary part.

[0029] It has now, should be further noted that, unlike the above-described (A14), is that the (B1) to the equation and (B2) formula, contains no component of the input sound pressure P _in.

In general, a currently used ultrasonic diagnostic apparatus requires a dynamic range of 60 to 90 dB. In an ordinary system, to achieve this, the received signal is subjected to non-linear processing such as LogAmp to compress the signal amplitude. However, as shown in FIGS. 4 and 5, when a sufficiently weak reflected signal is obtained, the magnitude Z of the acoustic impedance density of the target medium is obtained.
_1a becomes a value close to specific acoustic impedance Z ₀ of the peripheral medium, the phase is near zero. The intrinsic acoustic impedance of each part of the living tissue varies from several percent to at most ten and several percent when viewed from the measured values. Therefore, the dynamic range of the received signal should be only a few dB.
This inconsistency arises from the fact that the measurement result obtained by the conventional ultrasonic diagnostic apparatus does not directly reflect a change in the specific acoustic impedance in the living body. The intensity of the reflected signals are integrated incident sound pressure P _in the inputted thereto, conventional ultrasonic diagnostic apparatus, it is better thought of as captured this change is reasonable. Since the sound pressure incident on a specific tissue is determined as a result until the sound reaches the specific tissue, it is natural that the sound pressure generally decreases as the sound depth increases. Even if the same depth, varies greatly situations sites medium to reach there, yet in order to influence situation is integrated up to the site, resulting in very each site of P _in It seems to make a big difference. Tens dB ones the dynamic range is rather considered to be corresponding to the fluctuation range of P _in.

[0031] In contrast, in the formula (B1) and (B2) type, and P _in is erased, therefore, Z _1a and θ
The change of ₁ directly reflects. This reduces the dynamic range required in the final display stage,
Rather, considering that the amount of change in impedance is sufficiently small, when displaying the calculated values of the equations (B1) and (B2), it is necessary to expand, rather than compress, the values.

The dynamic range of several tens of dB is
Since this is a request due to the presence of sound attenuation before the display system, a dynamic range of several tens of dB is basically required for each of the real part and the imaginary part.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 8 shows a preferred embodiment of the ultrasonic diagnostic apparatus according to the present invention, and FIG. 8 is a block diagram showing the entire configuration.

The probe 10 is an ultrasonic probe used in contact with the surface of a living body or inserted into a body cavity, and the probe 10 transmits and receives ultrasonic waves. Will be By electronic scanning of the ultrasonic beam,
A two-dimensional echo data capturing area is formed. In this case, examples of the electronic scanning method include an electronic linear scanning and an electronic sector scanning. Of course, the present invention is also applicable to a case where a so-called mechanical scan is performed.

A transmitter 12 is connected to the probe 10. A transmission signal is supplied from the transmitter 12 to the probe 10. Further, a receiver 14 is connected to the probe 10. The receiver 14 performs processing such as amplification on the received signal.

The quadrature detection circuit 16 is a circuit for converting a received signal output from the receiver 14 into a complex signal. Specifically, the quadrature detection circuit 16 includes two mixers 18 and 20 for mixing two reference signals having phases different from each other by 90 degrees with respect to the received signal, and a baseband region of the signals output from the mixers. And low-pass filters (LPFs) 22 and 24 for extracting signal components in the inside. The quadrature detection circuit 16 itself is a known circuit.

The complex signal output from the quadrature detection circuit 16 is input to two dividers 26 and 28. Specifically, a real part and an imaginary part constituting the complex signal are input to dividers 26 and 28, respectively. Here, the divider 26
Is a circuit for dividing the real part R by the imaginary part I, while the divider 28 is a circuit for dividing the imaginary part I by the real part R. That is, these dividers 26 and 28 are circuits for calculating the ratio between the real part and the imaginary part. Divider 26,
The signal output from the signal 28 is expressed by the above-described equation (B1) and
It is represented by the expression 2).

The display processing circuit 30 includes dividers 26 and 2
The display processing circuit 30 selects one of the signals and outputs the selected signal to the display device 32. Display device 3
In 2, the tomographic image representing the result obtained by dividing the real part by the imaginary part or the tomographic image representing the result obtained by dividing the imaginary part by the real part is displayed.

FIG. 9 shows a main part configuration according to another embodiment. The real part R and the imaginary part I output from the quadrature detection circuit 16 are respectively input to a switch 34, which outputs signals corresponding to a numerator and a denominator to a divider 36. For example, when calculating R / I, R is output from the switch 34 as the numerator and I is output as the denominator. On the other hand, when the I / R operation is performed, I is output from the switch 34 as the numerator and R is output as the denominator. Divider 36
Is output to the display device 32 via the display processing circuit 30, and the selected division result is displayed as a B-mode image or an M-mode image.

According to the ultrasonic diagnostic apparatus described above, the ratio of the real part to the imaginary part, which cannot be obtained by the conventional ultrasonic diagnostic apparatus, can be displayed as an ultrasonic image, so that there is an advantage that new disease diagnostic information can be provided. . In particular, it has been confirmed that the ratio between the real part and the imaginary part represents the properties of the tissue, and the effect of improving the accuracy of disease diagnosis can be obtained. Note that an input unit or the like may be provided for the user to select an R / I image or an I / R image. Further, the two images may be displayed in parallel. Alternatively, two images are distinguished by a predetermined hue,
In addition, a composite display thereof may be performed. Alternatively, an overlay display may be performed on (√ (I ² + Q ² )) of the conventional B or M image.

[0042]

As described above, according to the present invention,
There is an advantage that the ratio between the real part and the imaginary part can be displayed as an ultrasonic image, and thereby new information representing the tissue properties can be provided as disease diagnosis information.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a relationship between a numerator and a denominator in a calculation expression representing a reflection coefficient.

FIG. 2 is an explanatory diagram showing a calculated value of a reflection coefficient.

FIG. 3 is an explanatory diagram showing a calculated value of a reflection coefficient.

FIG. 4 is an explanatory diagram showing calculated values of amplitude characteristics.

FIG. 5 is an explanatory diagram showing calculated values of phase characteristics.

FIG. 6 is a diagram illustrating a calculation result when an imaginary part is divided by a real part.

FIG. 7 is a diagram illustrating a calculation result when a real part is divided by an imaginary part.

FIG. 8 is a block diagram showing an embodiment of an ultrasonic diagnostic apparatus according to the present invention.

FIG. 9 is a block diagram showing a main configuration of another embodiment of the ultrasonic diagnostic apparatus according to the present invention.

[Description of Signs] 10 probe, 12 transmitter, 14 receiver, 16 quadrature detection circuit, 26, 28 divider, 30 display processing circuit, 32 display device.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masao Kobayashi Aloka Co., Ltd. 6-22-1, Mury, Mitaka-shi, Tokyo

Claims (3)

[Claims] 1. A complex signal conversion means for converting a reception signal obtained by transmission and reception of an ultrasonic wave into a complex signal, a ratio calculation means for calculating a ratio between a real part and an imaginary part of the complex signal, and the real part And a display means for displaying a ratio of an imaginary part and an ultrasonic diagnostic apparatus. 2. An ultrasonic diagnostic apparatus according to claim 1, wherein said ratio calculating means divides a real part by an imaginary part. 3. The ultrasonic diagnostic apparatus according to claim 1, wherein said ratio calculating means divides an imaginary part by a real part.