JPH09108223A - Ultrasonic diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve image quality by improving deterioration in the ratio of signal to noise due to the attenuation of the receiving signal caused by varieties in the distances between oscillators and reflection points according to respective channels. SOLUTION: A compensating gain generator 18 calculates steering angle compensating amplification factors in relation to respective channels using coordinates of oscillators and a steering angle obtained from scanning control signals 14. An attenuation compensating circuit 15 multiplies this compensating amplification factor by a receiving signal 12 of each channel by a multiplier and a receiving signal formed by compensating attenuation of the receiving signal 12 dependent on the steering angle is output.

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 for displaying a tissue tomographic image inside a living body and a moving reflector speed, and more particularly to an ultrasonic diagnostic apparatus having a plurality of transducers for electronic focusing.

[0002]

2. Description of the Related Art In an ultrasonic diagnostic apparatus, a plurality of transducers for transmitting and receiving ultrasonic waves are arranged in an array, and the delay amount of a delay circuit connected to each transducer is adjusted so that the ultrasonic beam electronic The focus is on. Electronic focus includes transmission focus and reception focus. In transmission focus, the transmission delay amount of each transducer is set so that the time phases of the transmission waves from each transducer match at a predetermined point, and beam forming is performed so that the ultrasonic beam is focused toward this point. Is realized. On the other hand, in reception focus, after delaying the reception signal of each transducer so that the time phase of the reception wave from a predetermined point is matched, this reception signal is added to determine the distance and azimuth of the reception signal. The resolution of can be improved.

A pulse of an ultrasonic beam travels in a transmission-focused direction and is reflected by reflection points existing at various depths in this direction. The reflected waves return to the vibrator in order from those reflected near the vibrator. The depth of the reflection point can be calculated from the speed of sound of the ultrasonic pulse and the response time (time from transmission to reception). The entire points having the same depth form an arc-shaped curve (or spherical curved surface) centering on the transducer array, but the reception focus can increase the reception sensitivity for a part of this curve. .
Directivity can be realized also in the receiving direction by the dynamic focus that temporally changes the receiving focus position in association with the response time. That is, a straight reception beam can be obtained. In the electronic sector scanning, a sector-shaped image is obtained by changing the directivity direction of transmission / reception electronic focus with time.

The received signals from different depths have different amounts of attenuation from the time of transmission. Ie the response time is slow,
The farther the reflected wave is, the more strongly it is attenuated in the living body and the weaker the received wave is. For this reason, the TGC (Time Gain Comp.
ensation) processing or STC (Sensitivity Time Contr)
ol) processing is performed.

Conventionally, for a received signal of a certain depth,
Regardless of the steering angle of the ultrasonic beam, all the transducer channels were multiplied by a uniform amplification factor.

FIG. 5 is a block diagram showing the configuration of a conventional reception processing system. The reflected wave is received by the N oscillators 51 as an N-channel signal. The reception signal 52 from each transducer is delayed by the delay unit 53 for each channel. This delay time is controlled by the scan control signal 54 so as to realize dynamic focus. The reception signal output from the delay unit 53 is subjected to processing to be described later in the STC processing circuit 55 and then added by the adder 56 to be an addition signal 57, which is output to each processing unit that performs display processing.

Now, the processing of the STC processing circuit 55 will be described. The STC gain generator 58 generates a gain signal 59 which is an amplification factor for correcting the attenuation difference due to the generation depth of the received signal in the living body. Hereinafter, this amplification factor will be referred to as a depth compensation amplification factor. This depth compensation amplification factor changes depending on the response time of the received signal, but is common to each channel. The received signal 52 is multiplied by the gain signal 59 in the multiplier 60, amplified, and the amplitude attenuation amount is corrected. Since the processing of the STC processing circuit 55 is common to each channel, it can be performed on the addition signal 57.

[0008]

When steering an ultrasonic beam, an ultrasonic wave is generally transmitted from each transducer, reflected at a certain point in the living body, and returned to each transducer with a path length of generally the transducer. Differ between The greater the steering angle, the greater the difference in travel. Since the influence of frequency-dependent attenuation also differs depending on this path difference, the received signal strength also differs between channels. In the past, amplification was performed uniformly without considering the difference in intensity between channels. Therefore, the larger the steering angle, the smaller the intensity of the signal obtained by adding each channel, and the signal-to-noise ratio deteriorates, which causes a problem that the image quality deteriorates when an image is displayed using this signal.

It is an object of the present invention to provide an ultrasonic diagnostic apparatus with improved signal-to-noise ratio and improved image quality.

[0010]

An ultrasonic diagnostic apparatus according to claim 1 of the present invention compensates a difference in attenuation rate of a received signal amplitude due to a difference in path length between transducers up to a focus point. It is characterized by having an attenuation compensation processing circuit for amplifying a received signal for each transducer.

That is, the received signal of the transducer having a larger distance from the focus point is more strongly attenuated, so that it is amplified with a larger amplification factor.

In the ultrasonic diagnostic apparatus according to the second aspect of the present invention, the attenuation compensation processing circuit uses the steering angle of the ultrasonic beam and the position of the transducer for each transducer according to the difference in the attenuation rate. And a channel signal amplification unit that amplifies the received signal amplitude from each transducer using the amplification factor.

In the ultrasonic diagnostic apparatus according to claim 3 of the present invention, the compensation gain calculation unit calculates the difference in attenuation rate between the two transducers at both ends of the probe, and interpolates and approximates this difference to obtain another transducer. It is characterized in that the amplification factor of each oscillator is determined by obtaining the attenuation factor of.

In the ultrasonic diagnostic apparatus according to claim 4 of the present invention, the attenuation compensation processing circuit is a table in which the steering angle of the ultrasonic beam and the position of the transducer of the amplification factor for compensating for the attenuation difference are parameters. And a channel signal amplification unit that reads out the amplification factor and amplifies the amplitude of a received signal from each transducer.

[0015]

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

[First Embodiment] FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus embodying the present invention. The probe 1 has a transducer array, and transmits and receives ultrasonic waves while the transducer array is pressed against a living body. An ultrasonic pulse is radiated into the living body from the transducer array by the transmission signal generated by the transceiver 2. The ultrasonic pulse generates a reflection having an intensity corresponding to a change in the acoustic impedance of the tissue in the living body. The reflected wave is detected by the transducer array and becomes a reception signal of a plurality of channels, and the reception signal is subjected to addition processing between the transducers in the transceiver 2. The scanning controller 3 outputs a scanning control signal to the transceiver 2, controls the steering of the ultrasonic beam by electronic focus at the time of transmission, and controls the dynamic focus at the time of reception in conjunction with the response time of the reflected wave. Under the control of the scan controller 3, the transceiver 2 outputs a reception signal obtained by performing a sector scan on the inside of the living body. The tissue tomographic echo processing unit 4, the color Doppler processing unit 5, or the spectrum Doppler processing unit 6 processes / processes the received signals, respectively, and converts the video signal into a DSC (Digital Scan Converter).
Output to 7. The DSC 7 is used to read an image written in a sector scan cycle in accordance with the frame rate of the display 8.

FIG. 2 is a block diagram showing the configuration of the reception processing system in the transceiver 2. The N-channel reception signal 12 received by the N transducers 11 is delayed by the delay unit 13 for each channel. This delay time depends on the scan control signal 14
Is controlled to realize dynamic focus. The reception signal output from the delay unit 13 is compensated for each channel by the attenuation compensation processing circuit 15, which is a characteristic component of the present invention, for the difference in the attenuation amount according to the path difference of the reception signal 12 in the living body. And the intensity is adjusted, adder 1
The addition signal 17 added in 6 is output to each processing unit that performs display processing. The compensation gain generator 18 that constitutes the attenuation compensation processing circuit 15 has a built-in compensation gain calculation unit, and the compensation gain calculation unit uses the coordinates of the transducer and the steering angle obtained from the scan control signal 14 for each channel. The steering angle compensation amplification factor for is calculated.
The compensation gain generator 18 calculates the depth compensation amplification factor of the conventional STC processing together with this steering angle compensation amplification factor, and outputs the product of both amplification factors as a gain signal 19. The gain signal 19 is multiplied by the received signal for each channel in the channel signal amplifier 20 to compensate for the frequency dependent attenuation in the living body. Here, the channel signal amplification unit 20 is composed of a multiplier provided for each channel.

Although the compensation gain generator 18 outputs the product of the steering angle compensation amplification factor and the depth compensation amplification factor, the feature of the present invention is that the reception signal is compensated for each channel by the steering angle compensation amplification factor. There is a point to do.
Here, an STC gain generator similar to the conventional one that generates the depth compensation gain common to the channels may be separately provided, and the compensation gain generator may generate only the steering angle compensation amplification factor.

Next, the processing of the compensation gain generator 18 will be described in detail. FIG. 3 is a schematic diagram for explaining the path difference of the received signal due to the steering of the ultrasonic beam. It is assumed that the transducer array is of a linear type and is arranged in a line segment PQ on the x axis. A transducer of channel 0 is arranged at point P, a transducer of channel (N-1) is arranged at point Q, and channel m (m = m
The x coordinate of the oscillator of 0 to N-1) is defined as x _m . Here, since the coordinate origin is taken as the middle point of PQ, if x ₀ = ξ, then x _N−1 = −ξ. D is both ends P and Q of the transducer array
Is the distance between and is defined as the probe aperture. The steering angle θ is an angle formed by the ultrasonic beam and the z axis. The point R is a reflection point of ultrasonic waves, and the distance between this point and the origin is r. Now, assuming that ΔL = | PR−QR |, the path difference at both ends of the probe opening is the difference between the round trip distances from both points to R, 2ΔL. Triangle OPR, OQR
By calculating PR and QR using the cosine theorem,
L is represented by the following formula.

ΔL≈D sin θ (1) Let f _{0 be} the center frequency of the ultrasonic wave, α be the frequency-dependent attenuation coefficient in the living tissue, and A be the amplitude ratio of the ultrasonic waves before and after propagating the distance d. = Exp (-αf ₀ d) and when d is very small, it is represented by A〓1-αf ₀ d (2). For example, when the reflection point is near the point P as shown in FIG. 3, the received signal of Q is attenuated more than the received signal of P, and P
The amplitude ratio A _N-1 (θ) of Q to
= 2ΔL, A _N-1 (θ) = 1-2αf ₀ Dsin θ (3)

Consider an added signal 17 in which all channels of the received signal are added by the adder 16. FIG. 4 shows the addition signal 17
5 is a graph showing the contribution (addition efficiency) of the received signal of each channel to. FIG. 4A is a graph of the addition efficiency when it is assumed that there is no difference in attenuation due to the path difference between the received signals of the respective channels. The addition efficiency is 1 for each channel, and the graph area S ₀ = D in this case is used as the comparison reference of the addition signal 17. Now, in reality, there is a difference in the amount of attenuation between each channel. FIG. 4B is a graph of the addition efficiency in the case illustrated in FIG. The addition efficiency is the amplitude ratio of the received signal of each channel to the point P. Accurately, the addition efficiency is a curve as shown in the figure, but if this is approximated by a straight line passing through the addition efficiency values at points P and Q, the graph area S will be S〓D (1-αf ₀ Dsin θ) ... (4) and S / S ₀ = 1-αf ₀ Dsin θ (5) Therefore, it is understood that the larger the steering angle θ, the more the added signal 57 subjected to the conventional STC processing that does not correct the path difference of the received signal between the respective channels is strongly influenced by the attenuation and becomes smaller.

Therefore, the compensation gain generator 18 multiplies the received signal f _m (θ, r) of the channel m by the gain signal 1
As 9, the amplification factor G _m (θ, r) that compensates for the attenuation depending on the steering angle is output. G _m (θ,
r) is represented by the product of the steering angle compensation amplification factor κ _m (θ) and the depth compensation amplification factor λ (r).

G _m (θ, r) = κ _m (θ) .λ (r) (6) The depth compensation amplification factor λ (r) is the same as the amplification factor used in the conventional STC processing. Therefore, the description is omitted here.

The steering-dependent damping factor has a maximum value of 2αf ₀ Dsin θ at either end of the probe aperture. Here, if it is approximated that the attenuation rate at each transducer position changes linearly according to the distance from the probe opening end,

(Equation 1) It is. However, θ is assumed to be positive when the point R is near the point P. If the addition signal 17 is F (θ, r),

(Equation 2) It is. The addition signal 17 compensates for the deterioration of the addition efficiency depending on the steering angle, and a good signal-to-noise ratio can be obtained regardless of the steering angle. Further, together with this, the signal level in the region where the steering angle is large or the region deep in the living body is compensated and improved, so that the image quality of the image becomes uniform and improved.

The compensation gain calculator has a microprocessor and calculates the compensation gain for each channel.

[Second Embodiment] The block configuration of an ultrasonic diagnostic apparatus according to the present embodiment is the same as that shown in FIGS. However, the compensation gain generator, instead of the compensation gain calculator,
A feature is that a compensation gain storage unit, which is a ROM (Read Only Memory) storing a table of the steering angle compensation amplification factor κ _m (θ), is incorporated. That is, κ _m (θ)
Is not calculated by equation (7) step by step, but κ _m (θ) is calculated and stored in advance in a table using the steering angle θ and the channel number m as parameters, and when processing the received signal, This is read and compensation processing is performed.

The number N of transducer elements constituting the transducer array is 128, and these are arranged symmetrically with respect to the center thereof. In addition, the range of the sector scan angle is -π / 2 to π /
2, and this range is divided into 256. From the symmetry of the arrangement of the transducer elements, κ _m (θ) = κ _Nm-1 (−θ) (9), so it is possible to reduce either the number of parameters of θ or the number of parameters of m by half. it can. When one κ _m (θ) is represented by using a single precision floating point number represented by 4 bytes, the memory capacity required to store the table is about 65 Kbytes.

As described above, by storing κ _m (θ) in the table and storing it in the ROM, the processing speed can be increased as compared with the sequential calculation. In addition, since the calculation is performed in advance, an accurate value of κ _m (θ) can be calculated / stored and used instead of the approximation like the equation (7) of the first embodiment, and the compensation accuracy is improved. In particular, this ultrasonic diagnostic apparatus is effective when using a convex probe. Because the expression of the steering angle compensation amplification factor for the convex probe in which the transducers are arranged in a convex curve is
This is because it is more complicated than the equation (7) corresponding to the linear probe, and it takes time to calculate the steering angle compensation amplification factor one by one using the expression.

[0029]

According to the ultrasonic diagnostic apparatus of the present invention, the attenuation of the received signal due to the difference in the distance between the transducer and the reflection point in each channel is compensated for, and the signal-to-noise ratio is improved. It has the effect of improving the image quality.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a configuration of a reception processing system in a transceiver according to the present invention.

FIG. 3 is a schematic diagram illustrating a path difference of a reception signal due to steering of an ultrasonic beam.

FIG. 4 is a graph showing the contribution of the received signal of each channel to the added signal.

FIG. 5 is a block diagram showing a configuration of a conventional reception processing system.

[Explanation of symbols]

1 probe, 2 transceiver, 3 scanning controller, 4 tissue tomography echo processing unit, 5 color Doppler processing unit, 6 spectral Doppler processing unit, 7 DSC, 8 display device, 1
1,51 Transducer, 12,52 Received signal, 13,53
Delay unit, 14, 54 Scan control signal, 15 Attenuation compensation processing circuit, 16, 56 Adder, 17, 57 Addition signal, 18 Compensation gain generator, 19, 59 Gain signal, 20 channel signal amplification unit, 55 STC processing circuit , 58 STC gain generator.

Claims (4)

[Claims] 1. An ultrasonic diagnostic apparatus comprising a plurality of transducers for transmitting and receiving ultrasonic beams, wherein a delay circuit is connected to each transducer to perform electronic focusing of the ultrasonic beam, in each transducer up to a focus point. An ultrasonic diagnostic apparatus having an attenuation compensation processing circuit for amplifying a received signal for each transducer so as to compensate the difference in the attenuation rate of the received signal amplitude due to the difference in the path length. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein the attenuation compensation processing circuit uses the steering angle of the ultrasonic beam and the position of the oscillator for each transducer according to the difference in the attenuation rate. An ultrasonic diagnostic apparatus, comprising: a compensation gain calculation unit that calculates and outputs the amplification factor of 1. and a channel signal amplification unit that amplifies the received signal amplitude from each transducer using the amplification factor. 3. The ultrasonic diagnostic apparatus according to claim 2, wherein the compensation gain calculation unit calculates the difference in attenuation rate between the two transducers at both ends of the probe and interpolates and approximates the difference between the other transducers. An ultrasonic diagnostic apparatus characterized in that an attenuation factor is obtained to determine an amplification factor for each transducer. 4. The ultrasonic diagnostic apparatus according to claim 1, wherein the attenuation compensation processing circuit stores a table of the amplification factor for compensating for the attenuation difference, using the steering angle of the ultrasonic beam and the position of the transducer as parameters. An ultrasonic diagnostic apparatus comprising: a stored compensation gain storage unit; and a channel signal amplification unit that reads out the amplification factor and amplifies a received signal amplitude from each transducer.