JPH11113895A - Ultrasonograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an image representing the character of tissue from a standpoint of an ultrasonic phase. SOLUTION: A phase is computed by means of a phase computing unit 30 on the basis of a complex signal outputted from an orthogonal detector 20. This phase is displayed in the form of an image as a B mode image or an M mode image. When only the phase with a specific dimension is extracted, a tissue boundary alone, for example, can be displayed in the form of an image. Alternatively, an amplitude image can be synthesized with a phase image so as to be displaced.

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 a property of being reflected at boundaries (between tissues) having different acoustic characteristics, and the intensity of a reflected wave, that is, the amplitude of a received signal, depends on the difference in the specific acoustic impedance between tissues. Equivalent to. 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]

It is known that the phase changes when the ultrasonic wave is reflected. In particular, the ultrasonic wave is transmitted between a tissue having a low specific acoustic impedance and a tissue having a high specific acoustic impedance. When reflected, the phase is maintained and becomes positive.On the other hand, when ultrasonic waves are reflected from a tissue having a high specific acoustic impedance to a tissue having a low specific acoustic impedance, the phase is reversed and the phase is reversed. It is known that Here, given 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, the conclusion is that some property of the tissue can be expressed by the phase itself or its transition. Come back.

In a conventional ultrasonic diagnostic apparatus, phase information is not extracted because a received signal is simply detected by envelope detection. Therefore, it is desired to form an image reflecting the phase information.

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 grasping the properties of a tissue from the viewpoint of the phase of an ultrasonic wave. Another object of the present invention is to form a B-mode image or an M-mode image on which phase information is reflected.

[0006]

In order 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 each sample from the complex signal. It is characterized by including phase calculation means for obtaining the phase of a point, and phase display means for displaying the phase.

According to the above configuration, a phase is calculated for each sample point from the complex signal, and an ultrasonic image is created based on the calculated phase. The phase reflects the acoustic characteristics between the tissue itself and the tissue, and the phase can express the property of the tissue that could not be imaged conventionally or was difficult to image.

[0008] In a desirable mode of the present invention, an extracting means for extracting a sample point having a phase within a predetermined range is included. Thereby, for example, a tissue having a specific property can be extracted.

In a preferred aspect of the present invention, the apparatus includes an amplitude calculating means for calculating an amplitude from the complex signal, and a synthesized image forming means for forming a synthesized image representing the phase and the amplitude of each sample point. According to the above configuration, the phase information for each sample point can be grasped while referring to the amplitude information. Preferably, the composite image forming means expresses one of the phase and the amplitude by luminance information and expresses the other by color information.

A preferred embodiment of the present invention includes means for interconnecting sample points having the same phase to form an isophase diagram. As a result, an image similar to a contour map seen on a map or the like can be constructed, and the form and characteristics of the tissue can be grasped based on the density of the lines and the direction of the line flow.

[Modeling Related to Ultrasonic Reflection] Modeling related to ultrasonic reflection will be described below.
Clarify how the phase and amplitude of the reflected wave 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 come into contact with each other.
The condition is that [1] continues at infinity.

In an 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] joined to each other is _0, P ₁ and the particle velocities v ₀ , v ₁ are expressed as follows.

[0017]

(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.

[0019]

(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.

[0021]

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

[0022]

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

[0023]

[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 merely reflect the change in the specific acoustic impedance but reflects the difference in the acoustic impedance density Z _{1L that} changes depending on 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) Consideration of the above modeling By the way, when the equation (A9) is interpreted graphically, a figure 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 equations (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.

[0030]

(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.

As described above, it is considered that the phase information included in the reflected signal indicates the property of the tissue, and if the phase information is represented as a B-mode image or an M-mode image, useful information useful for disease diagnosis can be provided. .

[0032]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 6 shows a preferred embodiment of the ultrasonic diagnostic apparatus according to the present invention, and FIG. 6 is a block diagram showing the overall configuration.

The probe 10 is an ultrasonic probe used in contact with the surface of a living body or inserted into a body cavity. A transmitter 12 is connected to the probe 10, and a transmission signal is supplied from the transmitter 12 to the probe 10. Further, a receiver 14 is connected to the probe 10, and the receiver 14 performs processing such as amplification on a received signal output from the probe 10. Transmitter 1
A transceiver 16 is constituted by the receiver 2 and the receiver 14, and the transceiver 16 is controlled by a transmission / reception control unit 18. Note that two reference signals for quadrature detection are output from the transmission / reception control unit 18 to a quadrature detector 20 described later. These two reference signals are detection signals having phases different from each other by 90 degrees.

The quadrature detector 20 is a circuit that performs quadrature detection on a received signal and converts the received signal into a complex signal. The quadrature detector 20 includes two mixers 22 and 24 for mixing a reference signal with a received signal, and two band limiting filters 26 and 26 for extracting a signal component in a baseband region from a signal output from the mixer. 28. The configuration itself of the quadrature detector 20 is known.

The phase calculator 30 includes a band limiting filter 2
This is a circuit that calculates the phase for each sample point based on the complex signal that is input through 6 and 28. Specifically, it is configured by a circuit that calculates the arc tangent (tan ^-1 ) of the real part I and the imaginary part Q constituting the complex signal. Thus, the phase calculator 30 outputs the phase φ for each sample point. This phase indicates the properties of the tissue as described above. The information of the phase φ is processed by the display conversion circuit 32 and then sent to the display device 34. The display device 34 displays a B-mode image or an M-mode image whose phase is represented by, for example, luminance. Therefore, the properties of each part and each tissue can be grasped as phase information on the image, and useful information that cannot be obtained with a conventional simple B-mode image or the like can be provided.

FIG. 7 shows the display conversion circuit 32 shown in FIG.
Is shown. This display conversion circuit 3
Reference numeral 2 in this example includes a luminance conversion table 36, a color conversion table 38, and a switch 40 for switching between these tables. The brightness conversion table 36 is for associating the brightness with the size of the phase φ, while the color conversion table 38 is for assigning the hue with the size of the phase φ. The switch 40 is operated by, for example, a user input, and is a means for selecting whether the phase is represented by luminance or color.

FIG. 8 illustrates a luminance function stored in the luminance conversion table 36 for reference. A constant luminance is assigned to the phase φ.
The highest luminance is assigned near 80 degrees. That is, a portion where the phase is considered to be inverted is displayed with high brightness, whereby, for example, a boundary of a tissue can be clearly expressed.

FIG. 9 shows a main configuration of another embodiment of the ultrasonic diagnostic apparatus according to the present invention. The phase information output from the phase calculator 30 shown in FIG.
Is input to The extraction circuit 42 is a circuit for extracting a phase when a predetermined window W includes a phase φ. The interpolation processing circuit 44 is provided to obtain smoothness of the image, and performs an interpolation process on the signal output from the extraction circuit 42. The information after the interpolation processing, that is, the phase information is output to the display conversion circuit 32 described above.

FIG. 10 shows the pass characteristics of the extraction circuit 42 shown in FIG. In this example, a window W is set at a position where the phase φ is around 180 degrees. When the phase φ input into the window W is entered, the sample point is extracted. For this reason, for example, it is possible to extract only the boundary region of the tissue and display only that region with high brightness.

FIG. 11 shows still another embodiment. The same components as those of the embodiment shown in FIGS. 6 and 9 are denoted by the same reference numerals, and the description thereof will be omitted.

The real part I and the imaginary part Q output from the quadrature detector are converted into a phase calculator 30 and an amplitude calculator 50, respectively.
Has been entered. The phase calculated by the phase calculator 30 is input to the color conversion table 52 via the above-described extraction circuit 42 and interpolation processing circuit 44. This color conversion table 52
Assigns a predetermined color to the extracted sample points, thereby forming a phase image in which only the extracted parts are colored.

On the other hand, the amplitude calculator 50 calculates the amplitude of the signal by adding the square of the real part and the square of the imaginary part and calculating the square root thereof. This amplitude is sent to the luminance conversion table 54, and a predetermined luminance is assigned to the magnitude of the amplitude. As a result, a luminance image similar to the conventional B-mode image is formed. Incidentally, the color conversion table 52 and the luminance conversion table 54 correspond to the display conversion circuit 32 described above.

The image synthesizer 56 is a circuit for synthesizing the phase image and the amplitude image output via the color conversion table 52 and the luminance conversion table 54 to create a synthesized image. On this composite image, for example, a portion having a phase near 180 degrees is colored on a tomographic image expressed in black and white. Then, the composite image is displayed on the display device 34.

Next, still another embodiment will be described. For example, the phase φ output from the phase calculator 30 shown in FIG. 6 is temporarily stored in a memory, and the sample points having the same phase size are connected to each other by a line on the memory, so that the phase can be seen on a map or the like. A contour diagram such as a contour diagram can be constructed.

FIG. 12 schematically shows an example of the isophase diagram. For example, if the sample points P1 to P3 have the same phase, they are connected by a line. Such processing is performed for each phase size, and an isophase diagram shown in FIG. 12 is formed. According to the isophase diagram, there is an advantage that the property of the tissue can be observed by, for example, the direction in which the lines flow or the density of the lines. For example, when there is a tumor in the liver, the outline of the tumor can be clearly represented by a line.

[0047]

As described above, according to the present invention,
Since a B-mode image or an M-mode image can be formed based on the phase included in the reflected wave, new information representing the properties of the tissue can be provided. This has the advantage that the disease diagnosis accuracy can be improved.

[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 block diagram showing an embodiment of an ultrasonic diagnostic apparatus according to the present invention.

FIG. 7 is a diagram illustrating a specific configuration example of a display conversion circuit.

FIG. 8 is a diagram illustrating an example of a luminance function included in a luminance conversion table.

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

FIG. 10 is a diagram showing a pass characteristic of the extraction circuit.

FIG. 11 is a block diagram showing still another embodiment of the ultrasonic diagnostic apparatus according to the present invention.

FIG. 12 is a conceptual diagram showing an example of an isophase diagram.

[Explanation of symbols]

10 probe, 16 transceiver, 18 transmission / reception control unit,
20 quadrature detector, 26, 28 band control filter, 3
0 phase calculator, 32 display conversion circuit, 34 display device.

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

Claims (5)

[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 phase calculation means for obtaining a phase of each sample point from the complex signal, and a phase for displaying the phase An ultrasonic diagnostic apparatus comprising: a display unit. 2. The ultrasonic diagnostic apparatus according to claim 1, further comprising an extracting unit that extracts a sample point having a phase within a predetermined range. 3. The apparatus according to claim 1, further comprising: amplitude calculating means for calculating an amplitude from the complex signal; and synthetic image forming means for forming a synthetic image representing the phase and the amplitude of each sample point. An ultrasonic diagnostic apparatus comprising: 4. An ultrasonic diagnostic apparatus according to claim 3, wherein said composite image forming means expresses one of said phase and said amplitude by luminance information and expresses the other by color information. . 5. An ultrasonic diagnostic apparatus according to claim 1, further comprising means for connecting sample points having the same phase to each other to form an isophase diagram.