JP2000023977A - Ultrasonograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively eliminate fog generated on an ultrasonic wave image by providing a tissue speed arithmetic means of tissue speed within a subject, a level adjusting means of echo data based on tissue speed and an image forming means for an ultrasonic wave image utilizing echo data after the level is adjusted. SOLUTION: A correction amount arithmetic device 22 detects a phase difference based on a complex signal after an orthogonal detection and calculates tissue speed as the phase difference. Based on tissue speed and depth at a data fetching point, correction amount 106 is calculated and the correction amount 106 is delivered to a luminance adjusting device 20. In the luminance adjusting device 20, a level adjustment based on the correction amount 106 is executed for an amplitude signal 105. As a result, luminance in an ultrasonic wave signal is varied according to tissue speed and depth. After a signal outputted from the luminance adjusting device 20 is inputted into a display converting device 24 and a prescribed conversion for the formation of an ultrasonic wave image is performed, an image signal is transmitted to a display device 26, and a B mode image and an M mode image to be ultrasonic wave images are displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to noise reduction by adjusting the level of echo data.

[0002]

2. Description of the Related Art A scanning surface is formed when an ultrasonic beam is scanned, and a two-dimensional tomographic image (B-mode image) can be formed by making the size of each echo data in the scanning surface correspond to luminance. Can be formed. Other examples of the luminance image include an M-mode image.

[0003] On such an ultrasonic image, noise called "fog" may be generated in the vicinity of the ultrasonic probe. It is said that the noise is caused by multiple reflection / scattering of ultrasonic waves generated between various boundary surfaces such as an acoustic lens of an ultrasonic probe and a living body surface. In any case, it is desirable to remove the fog in order to improve the image quality.

[0004] The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to effectively remove a fog generated on an ultrasonic image.

It is another object of the present invention to effectively reduce noise and the like caused by other stationary objects in observing a moving organ.

[0006]

In order to achieve the above object, the present invention provides a transmitting / receiving means for transmitting / receiving ultrasonic waves, and a method for transmitting / receiving ultrasonic waves in / from a subject based on echo data obtained by the transmitting / receiving waves. A tissue speed calculating means for calculating a tissue speed;
The image processing apparatus further includes an adjusting unit that adjusts the level of the echo data based on the tissue velocity, and an image forming unit that forms an ultrasonic image using the echo data after the level adjustment.

According to the above configuration, the tissue velocity is detected,
The level of the echo data (received signal) can be adjusted based on the tissue velocity. Therefore, for example, the luminance value of a portion other than the moving organ can be reduced to clearly express the organ.

Preferably, the adjusting means adjusts the level based on the depth position of the echo data in addition to the tissue velocity. That is, since the fogging noise is generated in the vicinity of the ultrasonic probe, the noise can be reduced mainly by considering the depth of the tissue and the depth. That is,
Echo data that is near the ultrasound probe and has a low tissue velocity is likely to be fog noise, so the level of the echo data can be adjusted to eliminate fog noise. That is, preferably, the adjusting means removes fog noise generated near the wave transmitting / receiving means.

Preferably, the tissue velocity calculating means calculates the tissue velocity by calculating the autocorrelation of the echo data between two adjacent ultrasonic beams. In calculating the tissue speed, the speed (speed) does not necessarily have to be strictly measured. Therefore, the speed calculation is performed between adjacent beams with priority given to the processing speed. In this case, for example, the speed is calculated by calculating the autocorrelation of the echo data noise having basically the same depth. In the ultrasonic Doppler method, generally, a plurality of transmissions and receptions of ultrasonic pulses are performed in the same direction in order to improve the accuracy of the speed calculation, and the speed calculation is performed between the ultrasonic beams having the same direction. Done.

In order to achieve the above object, the present invention provides an ultrasonic probe for transmitting and receiving ultrasonic waves, a quadrature detection circuit for quadrature detecting a signal received from the ultrasonic probe,
An amplitude calculation circuit that performs an absolute value calculation on the complex reception signal output from the quadrature detection circuit to generate an amplitude signal, and calculates phase information corresponding to a tissue velocity based on the complex reception signal output from the quadrature detection circuit. A phase information calculation circuit for calculating, a correction amount calculation circuit for calculating a correction amount based on the phase information, and an adjustment circuit for performing level adjustment on the amplitude signal output from the amplitude calculation circuit according to the correction amount And an image forming means for forming an ultrasonic image in which the amplitude value corresponds to the luminance value by using the adjusted amplitude signal.

Preferably, a smoothing circuit is provided between the phase difference calculation circuit and the correction amount calculation circuit for smoothing the phase difference along a beam path direction.

[0012]

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

FIG. 1 shows a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention, and FIG. 1 is a block diagram showing the overall configuration.

In FIG. 1, a probe 10 is an ultrasonic probe which is used, for example, in contact with the surface of a living body and transmits and receives ultrasonic waves. The probe 10 includes an array vibrator composed of a plurality of vibrating elements, and an ultrasonic beam is scanned by electronically scanning the array vibrator.

The probe 10 includes a transmitter 12 and a receiver 14
Is connected. These circuits are controlled by a control unit (not shown).
0 is supplied with a transmission signal. Further, a reception signal output from the probe 10 is input to the receiver 14. Receiver 14
Has a phasing addition circuit, an amplifier, and the like for forming a reception beam. The received signal (echo data) output from the receiver 14 is input to the quadrature detector 16. The quadrature detector 16 is a circuit that performs quadrature detection on the received signal using the reference signal 102, and the quadrature detected complex received signal is sent to the amplitude calculator 18 and the correction amount calculator 22.

The amplitude calculator 18 is a circuit for calculating the level of the echo data, that is, the amplitude, based on the complex signal after quadrature detection. The amplitude signal 105 output therefrom is sent to the brightness controller 20.

On the other hand, the correction amount calculator 22 detects a phase difference based on the complex signal after the quadrature detection, that is, calculates the tissue velocity as the phase difference. The correction amount is calculated based on the tissue velocity and the depth of the data capturing point. The correction amount 106 is sent to the brightness adjuster 20. The brightness adjuster 20 performs level adjustment on the amplitude signal 105 based on the correction amount 106. As a result, the brightness in the ultrasonic image is changed according to the tissue velocity and the depth. Brightness adjuster 2
The signal output from 0 is input to the display converter 24, where a predetermined conversion for ultrasonic imaging is performed,
An image signal is sent from the display converter 24 to the display 26, and a B-mode image, an M-mode image, or the like, which is an ultrasonic image, is displayed on the display 26.

Therefore, according to the apparatus of the present embodiment, the level of the echo data can be adjusted according to the two parameters of the tissue velocity and the depth. It has the advantage of being expressible.

The operation will be described below in detail. FIG. 2 shows a specific circuit configuration of a portion denoted by reference numeral 100 in FIG. The quadrature detector 16 has a known circuit configuration, that is, a π / 2 phase shifter 30 that shifts the phase of the reference signal 102, mixers 28A and 28B, and a low-pass filter (LPF) that extracts a baseband component from the output of each mixer. ) 30A and 30B. With this configuration, a complex signal is output from the quadrature detector 16.

In this embodiment, the amplitude calculator 18 includes an absolute value calculator 32 for executing an absolute value operation based on a complex signal, and a signal compressor 34 for compressing an absolute value as a result of the operation. It consists of. Absolute value calculator 32
Calculates the absolute value by calculating the square root of the square of each of the real part signal and the imaginary part signal constituting the complex signal. The signal compressor is a circuit for compressing the amplitude of the echo signal by nonlinear processing in order to display the echo signal on a display such as a CRT having a narrow dynamic range. The configuration of the amplitude calculator 18 is also known.

The brightness adjuster 20 includes a first adjuster 36 and a second adjuster 38. The second adjuster 38 is a circuit that adjusts the level of the signal based on the depth signal 104.
Such level adjustment depending on the depth is also performed in the conventional apparatus.

In this embodiment, the first adjuster 36 adjusts the level of the amplitude signal (echo data) output from the amplitude calculator 18 based on the correction amount 106 output from the correction amount calculator 22. Have been done. Specifically, signal suppression is performed by subtracting a value corresponding to the correction amount 106 from the amplitude signal 105. This makes it possible to reduce the fogging noise described above.

The correction amount calculator 22 includes a phase difference detector 40
, An absolute value calculator 42, an averager 44, and a converter 46
It is composed of The phase difference detector 40 is a circuit that calculates the speed of each point, that is, the tissue speed by performing an autocorrelation calculation or the like. The absolute value calculator 42 calculates the absolute value of the tissue velocity obtained as described above, and the averager 44 smoothes the phase difference after the calculation of the absolute value. Then, the converter 46 determines a correction amount based on the averaged phase difference and the depth signal 104.

FIG. 3 shows a specific configuration example of the phase difference detector 40. In this example, the phase difference detector 4
0 is composed of two low-pass filters 50A and 50B and an autocorrelation calculator 52. Low-pass filter 5
0A and 50B are provided for each of the real part and the imaginary part, and have a function of extracting echo data of a stationary moving body in a living body. Generally, since the echo data from such a stationary moving object is large, the low-pass filters 50A, 50
OB need not necessarily be provided. Each of the low-pass filters 50A and 50B includes a multiplier 54 and a 1-β arithmetic unit 56.
, An adder 58, a delay line 62, and a multiplier 60
And filtering is performed by performing weighting between the two beams according to a weighting value β input from the outside.

The autocorrelation calculator 52 has a configuration similar to a circuit used for calculating a blood flow velocity in, for example, an ultrasonic Doppler diagnostic apparatus, and has two delay lines 64A and 64B and four multiplications. Vessels 66A, 66B, 66
C, 66D, two adders 68A, 68B, and a circuit 70 for calculating the arc tangent. With such a circuit configuration, the autocorrelation calculation is performed between the beams using the real part and the imaginary part of the complex signal, and finally the speed of the moving body is calculated as the phase difference.

In the conventional ultrasonic Doppler method, ultrasonic pulses are repeatedly transmitted and received in the same direction, that is, the autocorrelation operation is performed in the time axis direction. In the present embodiment, such an autocorrelation operation is performed. Are performed between adjacent beams. That is, an autocorrelation operation is performed using echo data of the same depth between adjacent ultrasonic beams, thereby obtaining velocity information. For this reason, there is an advantage that the frame rate can be doubled as compared with the case of transmitting and receiving the ultrasonic pulse twice in the same direction, for example. Of course, the calculation method of the tissue velocity is not limited to the autocorrelation method as shown in FIG. 3, and a method such as FFT may be used.

FIG. 4 shows a specific example of the configuration of the averaging unit 44 shown in FIG. In this example, the averaging unit 44 includes a plurality of delay lines 72A to 72D, an adder 74, and a divider 76, and each delay line is delayed by one data. Therefore, by using such an averaging unit 44, averaging can be performed over a plurality of echo data along the ultrasonic beam direction. In the adder 74, outputs from the respective delay lines are added, and in the divider 76, an average result is obtained by dividing the output from the adder 74 by the number of additions.

FIG. 5 shows a specific configuration example of the converter 46 shown in FIG. In this example, the converter 46 is configured by a conversion table 78. The conversion table 78 is constituted by, for example, a ROM or a RAM,
When a signal is input to the address specified by the phase difference and depth signal 104, the correction amount stored at that address is output to the outside.

FIG. 6 shows an example of conversion characteristics set in the conversion table 78. In FIG. 6, the horizontal axis corresponds to the absolute value of the phase difference (the absolute value of the tissue velocity), and the vertical axis corresponds to the correction amount. Also, conversion characteristic curves 200 to 203 are prepared for each depth, and when the depth and the absolute value of the phase difference are specified, the correction amount is uniquely determined.

FIG. 7 shows a B-mode image S. For example, when a B-mode image of the heart is formed, a heart wall H appears in the image. At the same time, fogging noise N is generated in the vicinity of the ultrasonic probe due to the influence of the multiple reflection described above. Such noise occurs near the ultrasonic probe, that is, at a shallow position, and the noise itself has no speed information. Therefore, the fogging noise can be effectively removed by suppressing the signal level as the depth becomes shallower and the speed becomes lower. Note that the characteristics shown in FIG. 6 are merely examples, and various characteristics can be set according to the operating conditions of the apparatus.

[0031]

As described above, according to the present invention,
It is possible to effectively remove so-called fogging occurring in a short distance area on the ultrasonic image. Further, in observing a moving organ, it is possible to effectively reduce noise and the like of a stationary object.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a specific example of a configuration denoted by reference numeral 100 in FIG.

FIG. 3 is a diagram illustrating a specific configuration example of a phase difference detector.

FIG. 4 is a diagram illustrating a specific configuration example of an averaging device.

FIG. 5 is a diagram showing a specific configuration example of a converter.

FIG. 6 is a diagram illustrating a characteristic curve set in a conversion table.

FIG. 7 is a diagram for explaining fog noise.

[Explanation of symbols]

Reference Signs List 10 probe, 12 transmitter, 14 receiver, 16 quadrature detector, 18 amplitude calculator, 20 brightness adjuster, 22
Correction amount calculator, 24 display converter, 26 display.

Claims (6)

[Claims] A transmitting / receiving means for transmitting / receiving ultrasonic waves; a tissue speed calculating means for calculating a tissue speed in a subject based on echo data obtained by the transmitting / receiving waves; An ultrasonic diagnostic apparatus comprising: an adjusting unit that adjusts the level of the echo data by using the echo data after the level adjustment; and an image forming unit that forms an ultrasonic image using the echo data after the level adjustment. 2. An ultrasonic diagnostic apparatus according to claim 1, wherein said adjusting means adjusts a level based on a depth position of echo data in addition to said tissue velocity. 3. An ultrasonic diagnostic apparatus according to claim 1, wherein said adjusting means removes fogging noise generated near said wave transmitting / receiving means. 4. The apparatus according to claim 1, wherein said tissue velocity calculating means calculates a tissue velocity by calculating an autocorrelation of echo data between two adjacent ultrasonic beams. Ultrasound diagnostic device. 5. An ultrasonic probe for transmitting and receiving ultrasonic waves, a quadrature detection circuit for quadrature detecting a reception signal from the ultrasonic probe, and a complex reception signal output from the quadrature detection circuit. An amplitude calculation circuit that performs an absolute value calculation to generate an amplitude signal; a phase information calculation circuit that calculates phase information corresponding to a tissue velocity based on a complex reception signal output from the quadrature detection circuit; A correction amount calculation circuit that calculates a correction amount based on the amplitude signal, an adjustment circuit that performs level adjustment on the amplitude signal output from the amplitude calculation circuit in accordance with the correction amount, and using the adjusted amplitude signal. An ultrasonic diagnostic apparatus, comprising: an image forming unit that forms an ultrasonic image in which an amplitude value corresponds to a luminance value. 6. The apparatus according to claim 5, wherein: between the phase difference calculation circuit and the correction amount calculation circuit
An ultrasonic diagnostic apparatus comprising a smoothing circuit for smoothing the phase difference along a beam direction.