JPH0331458B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electronic scanning ultrasonic diagnostic apparatus that transmits and receives ultrasonic pulses using a transducer array, receives reflected waves, and displays images.

(Prior art) Ultrasonic diagnostic equipment irradiates ultrasonic pulse signals into the subject, and detects reflected waves by utilizing the characteristics of ultrasonic waves for the subject, that is, the degree of attenuation and reflection that differs depending on the tissue and its lesion. This device performs diagnosis by displaying tomographic images formed by the CRT on an image display device such as a cathode ray tube display (hereinafter referred to as CRT). FIG. 4 shows a schematic configuration of a conventional ultrasonic diagnostic apparatus. In the figure, a high frequency signal generated by a high frequency oscillator 1 is pulse-modulated by a transmitting signal generator 2 and input to a transmitting beamformer 3. The transmission beam former 3 applies a phase delay to the input high frequency signal according to a predetermined program, and separates the input high frequency signal into signals of, for example, 64 channels so as to form an ultrasonic beam. The signals of the 64 channels described above are power amplified by a transmitting/receiving circuit 4 including a transmitting amplifier, a transmitting/receiving switch, a receiving image width filter, etc., and then inputted to a transducer array 5. The transducer array 5 converts the input high-frequency pulse signal into an ultrasonic signal and transmits it into the subject. The ultrasonic signal reflected from the reflector within the subject is received again by the transducer array 5 and converted into a high frequency electrical signal, which is input to the receiving beamformer 6 via the transmitting/receiving circuit 4. The input signals of the 64 channels are each subjected to a phase delay in the receiving beamformer 6, and are then outputted after being phased and summed. The logarithmic amplifier 7 is an amplifier that logarithmically compresses the wide dynamic range of the received signal to a range suitable for image display. The signal compressed and amplified by the logarithmic amplifier 7 is detected by the rectifier 8 and then converted to a digital scan converter (hereinafter referred to as DSC).
) 9, the signal is converted into a television format signal and displayed on a CRT 10.

(Problems to be Solved by the Invention) In the above-mentioned ultrasonic diagnostic apparatus, noise called speckle noise appears like a textile or satin material in an image generated by reflected waves from a reflector inside the subject. It is not possible to obtain images of good quality. This noise is caused by phase interference of reflected waves from a scattering object smaller than the wavelength of the ultrasonic wave.

FIG. 5 is a diagram showing a scan method called a compound scan. Figure A is a diagram in which a single probe 21 is applied to a subject 22 for observation. When the single probe 21 is moved to the position 21', the angle relative to the scatterer changes and speckle reduction becomes effective. Figure B is Sector Scan 23,
23 is a diagram illustrating a state in which a compound scan is performed while shifting to the position 23'. This overwriting method called compound scan is very effective for speckle reduction, but it has problems such as being difficult to operate and not being able to keep up with fast movements.
A compound scan cannot be performed solely for speckle reduction.

The present invention was made in view of the above problems.
The purpose is to reduce noise such as speckle noise and white noise caused by interference of minute scatterers without reducing resolution, and to realize an ultrasonic diagnostic apparatus with improved image quality.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, uses an electronic scanning type ultrasound system that transmits and receives ultrasound pulses using a transducer array, receives reflected waves, and displays images. In the diagnostic device, there is an ultrasonic beam generating means that sweeps in an angle or scanning pitch unit smaller than the beam resolution, a receiving beam formatting means that performs phasing and summation of received signals, and a receiving beam formatting means that performs phasing and summation of the received signals, and converts the phasing and summation of the received signals into a substantially logarithmic function. , an amplification means for amplifying the received signal, a storage means for temporarily storing the received signal, and an arithmetic means for calculating the correlation between the signal from the storage means and the received signal received with a delay of one sound line. This method is characterized in that a received signal corresponding to the above is synthesized from a plurality of highly correlated received signals.

(Operation) Received signals based on sound rays transmitted in angular units smaller than the beam resolution are phased and summed, temporarily stored in a storage means after logarithmic amplification, and a correlation calculation is performed with a received signal based on the next sound ray.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the sector scanning of the present invention. In the figure, parts equivalent to those in FIG. 4 are given the same reference numerals. In the figure, 11
is an AD that converts analog signals into digital signals.
The digital signal of the converter is input to a one-line buffer memory 12 that temporarily stores data for one line of sound rays, and is also input to a correlation calculator 13. The correlation calculator 13 adds and averages the previous data stored in the 1-line buffer memory 12 and the current data from the AD converter 11.

Next, the operation of the apparatus of the embodiment configured as described above will be explained. The high-frequency signal generated by the high-frequency oscillator 1 is pulse-modulated by the transmitting signal generator 2, subjected to delay processing in the transmitting beam former 3, and transmitted from the transducer array 5 via the transmitting/receiving circuit 4 as shown in FIG. This is the same as described for the conventional device. The transducer array 5 transmits, for example, a first acoustic ray A, then swings the beam slightly and transmits a second acoustic ray B having an acoustic path difference smaller than the beam resolution that can identify the smallest pin target. waves and scans the tomographic plane by changing the angle one after another.

The reflected wave based on the first acoustic ray A (hereinafter referred to as the first acoustic ray A signal) is received by a transducer array 5, passes through a transmitting/receiving circuit 4, and is phased and summed by a receiving beamformer 6. This output signal is logarithmically compressed and amplified by the logarithmic amplifier 4, converted into a digital signal by the AD converter 11, and temporarily stored in the 1-line buffer memory 12.
3 is also input. Next, the received signal based on the second sound ray B (hereinafter referred to as the second sound ray B signal) is sent to the AD converter 1.
1, it is converted into a digital signal and input to the 1-li buffer memory 12. By this input, the data of the first sound ray A signal previously stored is pushed out to the correlation calculator 13, and the data of the first sound ray A signal stored previously is pushed out to the correlation calculator 13,
, and the second acoustic ray B signal inputted to the correlation calculator 13. This averaged signal is envelope-detected by the rectifier 8 and converted to a television format signal by the DSC 9.
Displayed on CRT10.

The situation of the above signal processing will be explained. FIG. 2 is an explanatory diagram of signal processing of the first sound ray A signal and the second sound ray B signal. A is a diagram showing the first sound ray A signal and a second sound ray B signal transmitted from the transducer 5, and B is a diagram showing the orientation of the transducer 5 when transmitting to the first sound ray A. The characteristics indicate the reception sensitivity of the reception beam. Figure C shows signal waveforms at point p, point q, and point r shown in FIG. In the figure, 15
is a pin target larger than the minimum resolution of the transmitted beam, and the angle Δθ formed by sound ray A and sound ray B is smaller than the angle at which the pin target 15 is viewed. 16 is a waveform of a reflected signal from the pin target 15, 17 is a speckle noise waveform due to reflection from a minute scatterer, and 18 is a signal waveform subjected to envelope detection. The waveform of the first sound ray A signal at point p is shown in Figure C a. Speckle noise 17 appears relatively large.
Figure b is the waveform of the second sound ray B signal at point p,
The pin target reflection signal 16 has approximately the same magnitude as in the case of FIG. Figure c is an output waveform obtained by adding and averaging the first sound ray A signal and the second sound ray B signal at point q by the correlation calculator 13. In this waveform, the pin target reflection signal 16 remains unchanged, but the speckle noise 17 is reduced. Figure d shows a signal waveform envelope-detected by the rectifier 8.

FIG. 3 shows the signal processing sequence. Figure A shows sound rays successively transmitted from the transducer 5. Figure B is a diagram showing the state of time-division multiplexing of the reflected signals from each sound ray in Figure A. The sound ray A signal is stored in the 1-line buffer memory 12, and the sound ray B signal is stored in the 1-line buffer memory 12.
After the signal arrives, it is calculated by the correlation calculator 13, and at the same time, the sound ray B signal is stored in the 1-line buffer memory 12. Next, when the sound ray C signal arrives, the sound ray B signal is output to the correlation calculator 13, and the sound ray C signal and the sound ray C signal are averaged.

The pin target 15 has a size equivalent to the beam width, and even if the amplitude and phase change slightly within the beam width, there is a sufficiently large correlation in the amplitude and phase, so a signal with almost no change can be obtained. The reflection from the body is a reflection from an object that is smaller than the wavelength, and the first sound ray A and the second sound ray B rarely have the same pattern. The correlation calculation process according to this embodiment is an arithmetic average, but since the signal is amplified by the logarithmic amplifier 7, it is essentially a multiplication, and the process also includes high frequency and phase information, so it does not exist in each sound ray at the same time. The product of speckle noise disappears in the calculation by the correlation calculator 13. White noise also has no correlation and is similarly eliminated by averaging processing. Therefore, a high-quality image with extremely low speckle noise and white noise is displayed on the CRT while maintaining a high enough resolution to identify the pin target.

Note that the present invention is not limited to the above embodiments. The one-line buffer memory used for temporarily storing signals can be used more flexibly by using a plurality of line buffer memories, such as for correlation processing of polyphonic lines. Although the correlation calculator is shown as one that performs simple addition and averaging, weighted addition may be used, and furthermore, an operator whose correlation function changes with depth may be used.

Detection has been explained using envelope detection, but other detection methods may be used. Furthermore, it goes without saying that the scan method can be applied to various scans such as linear scan, sector scan, and convex scan.

(Effects of the Invention) As explained in detail above, according to the present invention,
Uncorrelated white noise is suppressed without affecting the received signal from the fixed target, improving the SN ratio, and
Speckle noise is also removed and image quality is improved.
The practical effects are significant.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.
Fig. 2 is an explanatory diagram of signal processing using two sound lines, Fig. 3 is a diagram showing the sequence of signal processing, Fig. 4 is a schematic diagram of a conventional ultrasonic diagnostic device, and Fig. 5 is an explanatory diagram of compound scan. It is. 3... Transmission beam former, 5... Transducer array, 6... Receiving beam former, 7...
... Logarithmic amplifier, 8 ... Rectifier, 9 ... DSC,
10...CRT, 11...AD converter, 12...1
Line buffer memory, 13... Correlation calculator, 1
5... Pin target, 16... Pin target reflected signal, 17... Speckle noise.

Claims (1)

[Claims] 1 In electronic scanning ultrasound diagnostic equipment that transmits and receives ultrasound pulses using a transducer array, receives reflected waves, and displays images, ultrasound beam generation that sweeps at an angle or scanning pitch unit smaller than the beam resolution means, receiving beam forming means for phasing and adding the received signals, amplifying means for amplifying the phasing and adding received signals by a substantially logarithmic function, storage means for temporarily storing the received signals, and the storage means. and a calculation means for calculating the correlation between the signal from the source and the received signal received with a delay of one sound line, and is capable of synthesizing the received signal corresponding to one scanning line from a plurality of highly correlated received signals. Features of ultrasonic diagnostic equipment.