JPH0595946A - Ultrasonic sound speed measuring method and ultrasonic diagnostic apparatus with sound speed measuring means - Google Patents

Abstract

PURPOSE:To realize an ultrasonic diagnostic apparatus which measures an ultrasonic propagation speed of a tissue in a noninvasive manner from outside. CONSTITUTION:A transmitting vibrator 1 transmits an ultrasonic wave varying an angle thetai of emission at an angle adjustor 13 and a receiving vibrator 2 receives the ultrasonic wave with an angle thetaj being varied by an angle adjustor 14. Time tij elapsed during the period is measured with a time measuring circuit 17 to be stored into a tij memory 18. An assumed sound speed distribution chart is stored into the sound speed memory 19 and a sound line tracking computation circuit 20 sets a sound line path varying an angle of wave reception of the transmitting/receiving vibrators on the sound speed memory 19 based on the sound speed distribution chart while a required time tij of the operation is stored into a tij' memory 21. A comparator 22 inputs an error data by comparison between the tij and tij' into a controller 23, with which an assumed sound speed distribution stored in the sound speed memory 19 is corrected to minimize the error data inputted thereby determining a sound speed from a sound speed distribution obtained finally.

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,
Especially, the sound velocity of ultrasonic waves propagating in the body is measured non-invasively,
The present invention relates to an ultrasonic diagnostic apparatus equipped with a sound velocity measuring method and a sound velocity measuring means for obtaining an image with few errors due to nonuniform sound velocity distribution.

[0002]

2. Description of the Related Art An ultrasonic diagnostic apparatus irradiates an ultrasonic signal from an ultrasonic probe into a subject and receives the signal reflected from a tissue or a lesion in the subject with the ultrasonic probe. It is a device for displaying a tomographic image formed by the reflected signal on the CRT and using it for diagnosis.

The information obtained by this ultrasonic diagnostic apparatus is generally information on the intensity of reflected waves and reflects discontinuity in acoustic impedance and structural discontinuity.
Recently, in the ultrasonic diagnostic apparatus that displays the B-mode image as described above, the resolution is improved and the diagnosis based on the displayed image is almost established, but it is desired to add different information to the diagnostic information. Due to increasing demands, attempts have been made to clinically perform characteristic extraction based on differences in sound velocity and the like.

It is considered that clinically measuring the velocity of the ultrasonic wave propagating in the living body, in particular, the local sound velocity value of the living tissue is extremely useful for diagnosis by the ultrasonic diagnostic apparatus.

[0005]

By the way, the speed of sound in a living body is not uniform at all, and the speed of sound changes every time it passes through different media, and it passes through many media in the process from transmission to reception. In order to achieve this, the speed of sound in each medium is determined by the time difference obtained from the distance from the wave-transmitting oscillator of the wave-transmitting part of the ultrasonic probe to the wave-receiving oscillator of the wave-receiving part through the reflector and the pulse interval. It is not possible.

Conventionally, there are the following methods for measuring the sound velocity of living tissue. (A) A method in which two transducers are arranged facing each other, and a breast or the like is sandwiched between them to obtain the speed of sound from the distance between the transducers and the propagation time of ultrasonic waves.

(B) A method in which the sound velocity set value set when synthesizing tomographic images is used as the sound velocity. (C) Two sets of transducers, which are separated by a predetermined distance, are used for transmission and reception, respectively, and the ultrasonic wave propagation time between them, the ultrasonic wave reception angle, and the distance between the two transducers make the measured point. A method of knowing the speed of sound by obtaining the propagation velocity of ultrasonic waves reaching to.

On the other hand, the above method has the following problems. The following items are described corresponding to the above items. (A) The measurement is limited to the tissue protruding from the body surface such as the breast, and the sound velocity of organs such as the liver cannot be measured.

(B) Focusing an image by setting the speed of sound requires time for the operator to recognize the pattern, which is time consuming and impractical for the operator. (C) It is assumed that the transmission and reception paths of ultrasonic waves are straight lines, and there is a large error due to the influence of refraction that occurs inside the living body, especially at the boundaries of tissues with different sound speeds such as muscles and fat layers under the skin. , Cannot be used as a clinical device.

The present invention has been made in view of the above points, and an object thereof is to realize a sonic velocity measuring method for externally and non-invasively measuring an ultrasonic wave propagation velocity of a tissue and to provide an ultrasonic wave having a sonic velocity measuring means. To provide a diagnostic device.

[0011]

[Means for Solving the Problem] The portion to be measured can be placed in any area.
Virtual sound that has been divided and virtual sound velocity values have been set for each area
The step of creating and storing the velocity distribution, and at least two different
Between the transmitting means and the receiving means arranged at the
Transmitting and receiving ultrasonic waves while changing the transmitting and receiving angle,
Measuring the time at the angle of
From transmission to reception using sound ray approximation method based on cloth
The ultrasonic wave path and its required propagation time are received as the ultrasonic wave incident angle.
Calculation while changing the wave angle, and the actual propagation time
And the virtual propagation time based on the virtual sound velocity distribution are transmitted at the same time.
Accumulate the difference by comparing the case of the same reception angle
The step of obtaining the error function, which is a value, and the virtual sound velocity distribution are repeated.
The convergence operation that returns and changes to minimize the value of the error function
It is characterized by performing. The second invention is
Irradiation angle θ_iTransmit ultrasonic waves to the measurement target while changing the
Incident angle θ of transmitting ultrasonic wave and reflected ultrasonic wave_jChange
While forming a sound ray with the receiving transducer that receives the
A first angle adjuster for controlling the transmission directivity of the oscillator;
Controls the directivity of the receiving oscillator and adjusts the received signal.
The second angle adjuster for phase addition and the reflected wave from the ultrasonic wave transmission
The time until the wave is received_i, Θ_jAbout
Time measuring circuit and time data t obtained by the time measuring circuit
_ijStoring t _ijMemory and arbitrary given virtual speed of sound
Sound velocity memory for storing the distribution of
The sound ray approximation method is used to send the virtual sound velocity distribution.
Propagation time while tracing the propagation paths of the wave packet and received wave packet
t_ijRay tracing calculation circuit for calculating ′, and the ray tracing calculation circuit
Propagation time t by virtual sound ray of output of circuit_ijStore ′
t _ij′ Memory and t_ijMemory and t_ij′ With memory
Comparator that calculates the error by comparing the data stored in
And the error data of the output of the comparator is input, and the error data
Stored in the sonic memory based on changes in data
Repeatedly changing the sound velocity distribution, the error of the output of the comparator
Controller that controls to minimize the value of data
And the sound velocity value and sound velocity component stored in the sound velocity memory.
Characterized by comprising an indicator for displaying cloth
Is.

[0012]

The wave-transmitting oscillator irradiates while changing the irradiation angle θ _i by the first angle adjuster, and the wave-receiving oscillator receives wave while changing the incident angle θ _j by the second angle adjuster.
The time measuring circuit measures the elapsed time during this period and stores it in the t _ij memory. A virtual sound velocity distribution is stored in the sound velocity memory, and based on this sound velocity distribution map, the sound ray tracking calculation circuit changes the wave transmission / reception angle of the wave transmission / reception oscillator on the sound ray memory,
The sound ray path corresponding to each is set, and the required time t
_ij ′ is stored in the t _ij ′ memory.

The comparator compares the corresponding data in the t _ij memory and the corresponding data in the t _ij ′ memory to obtain error data, and the controller outputs the sound stored in the sound ray memory so as to minimize the input error data. The line distribution is corrected, and the sound velocity is calculated from the corrected sound line distribution.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. Now, the method to be carried out by the present invention will be described. FIG. 2 is a plan view showing the propagation of ultrasonic waves in the living body. In the figure, 1 is a wave-transmitting oscillator that transmits ultrasonic waves, and 2 is a wave-receiving oscillator that receives ultrasonic waves reflected from the inside of a living body. The wave transmission oscillator 1 emits ultrasonic waves at an angle θ _i with respect to the perpendicular of the body surface 3. This ultrasonic wave is refracted at the boundary surface between the body surface tissue 4 and the body tissue 5, and then refracted at the boundary surface between the body tissue 5 and the liver 6, and is incident on the liver 6. Similarly, the ultrasonic wave reflected at the reflection point Q is refracted at each boundary surface and is incident on the wave receiving oscillator 2 at an angle θ _j .

The time obtained by measuring the propagation time during which the ultrasonic wave transmitted by the wave-transmitting oscillator 1 reaches the wave-receiving oscillator 2 is t.
_ij . The measured values of the propagation time measured while changing the outgoing angle θ _{i of the} transmitted wave and the incident angle θ _j of the received wave are recorded as follows.

T _ij (θ _i , θ _j ) i = 1, 2, ..., N, j = 1, 2, ..., M (i and j are numbers in the above range throughout this specification) Next FIG. 3 shows an explanatory diagram of a method of creating a virtual sound velocity distribution map, assuming an ultrasonic wave propagation path based on the sound velocity, and obtaining each sound velocity. As shown in the figure, the plane including the wave-transmitting oscillator 1 and the wave-receiving oscillator 2 is divided into a lattice shape, and the sound velocity at each lattice point is appropriately set assuming an average value of 1540 m / s.

The propagation path and the propagation time t of the wave packet of the ultrasonic wave emitted from the transmitting oscillator 1 at an angle θ _i in this plane.
'seek, at the same time the propagation path and propagation time in this plane of the ultrasound wave packet emitted from reception transducer 2 at an angle θ _j t _{j' i} seek. Continue this calculation until both wave packets intersect. The calculated propagation times obtained by changing θ _i and θ _j are recorded as follows.

T _ij ′ (θ _i , θ _j ) = t _i ′ + t _j ′ The propagation path and the propagation time are calculated by using the ray tracing method. The path in the lattice is defined and drawn as follows. That is, generally, in a field where the velocity linearly changes spatially, the sound ray draws an arc. In this method, a triangle is expanded in the direction of sound ray propagation, and the sound velocity distribution within the triangle is approximated to a linear sound velocity field. FIG. 4 shows a triangle that approximates a linear sound velocity field. The coordinates of the vertex P are x ₁ and y ₁ , the speed of sound is c _1, and similarly the Q point,
Let it be that of the R point by x ₂ , y ₂ , c ₂ and x ₃ , respectively.
Let y ₃ and c ₃ . The sound velocity c (x, y) at an arbitrary point x, y in the triangle is calculated by the following equation.

[0019] c (x, y) = c x · x + c y · y + c o ......... (1) (1) equation constants c _x, c _y, c _o vertices P, Q, in the R It can be determined by the sound velocity values c ₁ , c ₂ and c ₃ .

X ₁ · c _x + y ₁ · c _y + c _o = c ₁ x ₂ · c _x + y ₂ · c _y + c _o = c ₂ x ₃ · c _x + y ₃ · c _y + c _o = c _{3 In} FIG. 4, if the direction vectors of the sound ray passing through point P are A _x and A _y , the trajectory of the ultrasonic wave will be a circle represented by the following equation.

(Xx _o ) ² + (yy _o ) ² = {c ₁ / (c _x A _y -c _y A _x )} ² (2) where x _o and y _o are the following equations. It is a point on a straight line that satisfies. c _x x _o + c _y y _o + c _o = 0 In this way, the triangle is expanded and the sound velocity value at each vertex of the triangle is obtained as an interpolated value of the sound velocity value at each lattice point. The inside of the triangle is approximated by the linear sound velocity field shown in equation (1), the sound ray path in the triangle is represented by a part of the circular arc of the circle shown in equation (2), and the arcs are connected to form a sound ray. To do. The propagation time between the start point and the end point of the sound ray path thus obtained is obtained by cumulatively calculating the propagation time in each triangle.

The difference between the measured value t _ij of the propagation time obtained in FIG. 2 and the calculated value t _ij ′ of the propagation time is defined as e, and is calculated by the following equation.

[0023]

[Equation 1]

It is considered that this difference e is caused by the fact that the virtual sound distribution does not accurately reflect the sound velocity distribution in the body.
Therefore, the virtual sound velocity distribution in FIG. 3 is changed, the path of the ultrasonic wave is recalculated, and t _ij ′ is calculated again. This process is repeated until e in the equation (3) becomes the minimum, and the path when it becomes the minimum is set as the path by the sound velocity distribution in the body, and the sound velocity at each lattice point at that time is equal to the sound velocity distribution in the body.

The calculation of equation (3) is performed using a convergence calculation method such as the Newton method. The Newton method will be described below. Let x ₁ , x ₂ , ..., X _p , ..., X _N estimated values be y ₁ , y ₂ , ..., Y _p , ..., y _N. x _p corresponds to t _ij and y _{p in} equation (3) correspond to t _ij ′. The estimated control parameters are c ₁ , c ₂ ,
..., c _q , ..., c _M. In the above, p = 1,
2, ..., N, q = 1, 2, ..., M. Error function e _r
Is calculated by the following formula.

[0026]

[Equation 2]

Equation (4) is a function of c _q . the minimum value of e _r formula of the relationship between e _r and c _q may actually to be determined by differentiating e _r in c _q can not calculation for unknown. Therefore, there is no choice but to find the minimum value of e _r by trial and error using c _q one after another. Newton's method is one of the methods to strive for this and obtain quickly.

FIG. 5 is a diagram for explaining the Newton method. In the figure, 8 is the error curve shown in equation (4).

[0029]

[Equation 3]

When the process is repeated, the minimum error min
It is thought that ( _er ) will be reached. (C _q ^o is tried in the same process for M qs from 1 to M. If this is written as a vector, it becomes as shown in equation (5).

[0031]

[Equation 4]

The equation (5) is a general equation of the Newton method.
It In the equation (5), k and k + 1 are numbers indicating the number of times.
It The meaning of this expression is c at k = 0₁Other than constant
C ₁Change only. The change step at this time is Δ
c. c₁If is over c₂Change only c_MUntil
After that, the same calculation is performed with k = 1. k is in advance
It will be implemented up to the decided value.

Next, an embodiment of an apparatus for carrying out the sound velocity measuring method based on the above principle will be described. FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. In the figure,
The same parts as those in FIG. 2 are designated by the same reference numerals. In the figure,
Reference numeral 11 denotes a clock oscillator that generates a pulse for transmission and also generates a clock that determines the timing of operation of the device, and 12 generates a high-frequency signal for transmission, and modulates this high-frequency signal with the clock pulse. It is a transmission circuit that performs processing such as amplification to various power levels.

An angle adjuster 13 forms a sound ray for focusing the transmitted ultrasonic wave on a target and changes the direction of the sound ray. The angle of the sound ray is electrically adjusted. However, the angle may be adjusted by mechanically moving the wave transmission oscillator 1. Let the ultrasonic wave incident angle of the wave-transmitting oscillator 1 determined by the angle adjuster 13 be θ _i with respect to the vertical line of the body surface 3.

Reference numeral 14 is an angle adjuster for performing beamforming of the received signal of the wave receiving oscillator 2 and controlling the receiving directivity of the wave receiving oscillator 2 in the arrival direction of the wave receiving signal. Set the angle of incidence of the ultrasonic waves on θ _j to θ _j . Reference numeral 15 is a receiving circuit that amplifies the received signal and performs processing such as detection.

Reference numeral 16 is an AD converter for converting an analog signal output from the receiving circuit 15 into a digital signal. Reference numeral 17 is input with the output from the AD converter 16 and compared with a clock from the clock oscillator 11 which is input separately. A time measuring circuit for measuring the time t _ij required from transmission to reception. The measured time data is stored in the t _ij memory 18. The time t _ij is the time required when the ultrasonic wave incident at the angle θ _i is received by the wave receiving oscillator 2 having the angle θ _j , and is a set of times performed for all i and j.

Reference numeral 19 is a sonic velocity memory for virtualizing the lattice shown in FIG. 3 in the living body as described above, setting a virtual sonic velocity at each lattice point, and storing it. Reference numeral 20 is a virtual sound velocity at each lattice point stored in the sound velocity memory 19, and a triangle is expanded in the field to calculate the path of the sound ray. From the transmitting oscillator 1 side and the receiving oscillator 2 side. The time t _ij ′ required to pass through the path when the sound rays of
This is a sound ray tracing calculation circuit that calculates angles for all _i and _j by changing the angles θ _i and θ _j .

Reference numeral 21 is a t _ij ′ memory that stores the required time t _ij ′ at each angle calculated by the sound ray tracing calculation circuit 20. _{Reference numeral} 22 is a comparator which reads out the data stored in the t _ij memory 18 and the t _ij ′ memory 21, compares them, and performs the operation of the equation (3). The error data e calculated by the comparator 22 is input to the controller 23. The controller 23 recognizes the address and data of each lattice point of the sonic velocity memory 19, and the error data e obtained by comparing the time in the velocity distribution shown in FIG. 3 with the actual measurement time and, for example, the coordinates (a ₁ , b). Compare the data of ₁ ) with the error data e when Δc is changed, and if the error is large, change the sound speed of the grid point of the same coordinate by Δc, and if the error is small, change the sound speed of the other grid point. Is controlled by the sonic velocity memory 19 so as to perform a similar calculation. Δc is a sound velocity step for changing the sound velocity of each predetermined grid point.

Reference numeral 24 is a display for displaying the sound velocity value of each lattice point stored in the sound velocity memory 19, and the operator can know the sound velocity and the sound velocity distribution. Next, the operation of the embodiment configured as described above will be described. The clock oscillator 11 generates a clock and sends it to the transmission circuit 12. The high frequency signal generated in the transmission circuit 12 is modulated by a trigger, and the modulated high frequency signal is power-amplified and input to the angle adjuster 13. The angle adjuster 13 forms a beam with the input signal, and sets the emission angle of the acoustic ray of the ultrasonic wave emitted from the wave transmission probe 1 to θ _i .

The sound ray received by the wave receiving oscillator 2 is only the sound ray from the θ _j direction in the angle adjuster 14. This signal is subjected to phasing addition in the angle adjuster 14, subjected to processing such as amplification and detection in the receiving circuit 15, converted into a digital signal in the AD converter 16 and input to the time measuring circuit 17.

A clock signal is input to the time measuring circuit 17, and the propagation time t _ij is measured from this clock signal (same as the transmission time) and the received signal and stored in the t _ij memory 18.

On the other hand, the sonic velocity memory 17 stores the imaginary lattice shown in FIG. 3 and the arbitrarily assumed velocity at each lattice point. The sound velocity tracking calculation circuit 20 reads the virtual velocity of each lattice point, calculates the locus of the sound ray by performing the calculation of the equations (1) and (2), obtains the required propagation time t _ij ′ of this path, and calculates t.
_ij ′ is stored in the memory 21.

The comparator 22 reads out the data stored in the t _ij memory 18 and the t _ij ′ memory 21 and performs the operation of the equation (3) to calculate the error data e. This error data e is input to the controller 23.

The controller 23 changes the data stored in the sonic velocity memory 19 according to the change in the error data e by the data change step Δc, and selects the sonic velocity so that the error data e becomes smaller. When the sound speed data stored in the sound speed memory 19 is set for all grid points so as to minimize the error data e, the measurement is ended. The data of the sonic velocity memory 19 is sequentially displayed on the display 24, and the operator can know the sonic velocity and the sonic velocity distribution.

[0045]

As described in detail above, according to the present invention, the velocity of the ultrasonic wave propagating through the tissue can be externally and non-invasively measured, and the practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view showing the propagation of ultrasonic waves in a living body.

FIG. 3 is a diagram showing a virtual sound velocity distribution for obtaining an ultrasonic wave propagation path.

FIG. 4 is a diagram of a triangle provided to approximate a linear sound velocity field for obtaining a sound ray path.

FIG. 5 is an explanatory diagram of a Newton method.

[Explanation of symbols]

1 wave transmitter 2 wave receiver 13, 14 angle adjuster 17 time measuring circuit 18 t _ij memory 19 sound velocity memory 20 sound ray tracing arithmetic circuit 21 t _ij ′ memory 22 comparator 23 controller 24 indicator

Claims (2)

[Claims] 1. A step of dividing a part to be measured into arbitrary regions and creating and storing a virtual sound velocity distribution in which virtual sound velocity values are defined in each region, and transmitting means arranged at at least two different positions. Ultrasonic waves are transmitted and received while changing the transmission and reception angles with the receiving means, and a step of measuring the time at each angle, based on the virtual sound velocity distribution, from the transmission to the reception using the sound ray approximation method. A step of calculating the path of the sound wave and its required propagation time while changing the ultrasonic incident angle and the receiving angle, and the case where the actual propagation time and the virtual propagation time based on the virtual sound velocity distribution are the same transmission angle and the same reception angle A step of comparing and calculating an error function which is a cumulative value of the difference, and a convergence operation for repeatedly changing the virtual sound velocity distribution to minimize the value of the error function. Fast measurement method. 2. A wave-transmitting oscillator (1) for transmitting ultrasonic waves to a measuring object while changing an irradiation angle θ _i, and a wave-receiving oscillator for receiving reflected ultrasonic waves while changing an incident angle θ _j. (2) a first angle adjuster (13) that forms a sound ray and controls the transmission directivity of the wave transmission oscillator (1), and the directivity of the wave reception oscillator (2). A second angle adjuster (14) for controlling and phasing and adding the received signals, and a time measuring circuit for measuring the time from the ultrasonic wave transmission to the reflected wave reception for each pointing direction θ _i , θ _j (17), a t _ij memory (18) for storing time data t _ij obtained by the time measuring circuit (17), a sonic velocity memory (19) for storing a distribution of an arbitrary given virtual sonic velocity, Propagation of transmission wave packet and reception wave packet using sound ray approximation method based on virtual sound velocity distribution stored in sound velocity memory (19) Propagation time t _ij while tracking path 'acoustic ray tracing calculation circuit for calculating (20) and, the sound ray tracing calculation circuit (20) the propagation time t _ij by the virtual sound ray of the output of' t _ij for storing ' The memory (21), a comparator (22) for comparing the data stored in the t _ij memory (18) and the data stored in the t _ij ′ memory (21) to obtain an error, and a comparator (22) The error data of the output is input, and the sound velocity distribution stored in the sound velocity memory (19) is repeatedly changed based on the change of the error data to minimize the value of the error data of the output of the comparator (22). A sound velocity measuring means comprising: a controller (23) for controlling the sound velocity and a display (24) for displaying a sound velocity value and a sound velocity distribution stored in the sound velocity memory (19). The equipped ultrasonic diagnostic equipment.