JPH02213330A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

PURPOSE:To suppress a lowering of resolving power without reducing the number of receiving vibrators even in their end part scanning and to obtain an image of a wide visual field width by deflecting the receiving directionality of an ultrasonic wave when the signal of the arrangement end part of the vibrators to be obtained. CONSTITUTION:When an end part image is obtained, control performing dynamic focusing while receiving directionality is turned to the outside is performed by a transmission system 2, a vibrator selection switch 11 and a digital receiving system 10. When receiving directionality is turned to the outside, control reducing the angle of deflection thereof with the depth of a covering point is also performed in the same way. The scanning direction of the (n-1)-th transducer is divided into fine sections in the same way as the scanning direction of the n-th transducer and 1-N is used from the vibrators 1-(N-M+1) of an array type probe to converge the beam to the fine sections. The same operation is repeated up to the n/2-th scanning and, in the (n/2+1)-th scanning, vibrators from 1-2 to 1-(M+1) are used to allow the centers of (M) vibrators to coincide with a scanning position.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an ultrasonic diagnostic apparatus that obtains tomographic images of a living body using ultrasonic waves, and in particular realizes highly accurate receiving dynamic focus. The present invention relates to an ultrasonic diagnostic apparatus that reduces deterioration in resolution at the edges of images and significantly improves image quality.

(Prior technology) Ultrasonic diagnostic methods emit ultrasound pulses into the living body and obtain biological information from reflected waves from each tissue.There is no irradiation damage like with X-rays, and it is possible to detect soft tissues without a contrast agent. It has the advantage of being diagnostic.

The probes of ultrasonic diagnostic equipment, which are widely used today, use array-type ultrasonic transducers (probes). A drive signal for generating a sound wave or a reflected wave from within the living body is received by the vibrator. At this time, by giving a predetermined delay time to the received signal, the ultrasonic beam is focused at a predetermined distance (position) to improve azimuth resolution and obtain a tomographic image with excellent resolution.

FIG. 3 shows a conventional example of this type of ultrasonic diagnostic apparatus. Third
The figure shows a block diagram of a linear electronic scanning ultrasound diagnostic device.Repetitive pulses output from two pulse generators that determine the interval between ultrasound pulses emitted into a living body are sent to a transmission delay circuit. In 2B-1 to 2B-N, after a predetermined delay time determined from the radiation direction and convergence point of the transmitted ultrasound is given, the transducer drive circuit (balsa) 3A-1
~3A-N to form a drive pulse. This driving pulse selectively drives a predetermined M number (for example, 1-1 to 1-M (M < N)) of the N array type ultrasonic transducers 1-1 to 1-N by the transducer selection switch 11. The ultrasonic waves are then emitted into the living body.

On the other hand, the ultrasound beam reflected from inside the living body is received by the array type ultrasound transducers 1-1 to 1-N,
Only the received signals of the transducers 1-1 to 1-H are sent by the transducer selection switch 11 to preamplifiers 3A-1 to 3A-N, and further sent to reception delay circuits 2B-1 to 2B-N. Here, almost the same delay time as that given in the transmission delay circuits 2B-1 to 2B-N is given, and then the adder 3c adds the signal received from the other vibrators.

The output signal of this adder 3C is sent on one side to the B-mode processing system 4 for displaying the tomographic image, and on the other hand to the D-mode processing system 5 for calculating blood flow information. Signal processing is performed. First, in the B-mode processing system 4, the signal amplitude is logarithmically converted in the logarithmic amplifier 4A, and then the envelope line of the received signal is detected in the envelope line detection circuit 4B, and the A/
Image memory 6A after passing through D converter (A/D-C) 4C
Stored in

Next, the D mode processing system 5 will be described. Adder 3C
The outputs of the ultrasonic signal are quadrature-phase detected by the phase detection circuits 5Aa and 5Ab, and a reference signal having approximately the same frequency as the ultrasonic signal frequency by the reference signal generator 5B and π/2 phase shifter 5c. The phase detection outputs with different phases of 90 degrees (π/2) are processed by low-pass filters (L, P, F) 5Da, 5
A/D converter (A/D-C) 5Ea through Db.

5Eb, and is then temporarily stored in a buffer memory (not shown).

To obtain a Doppler signal, the same location is scanned at predetermined intervals, and the blood flow velocity is determined from the phase shift amount (Doppler shift amount) within a unit time of the reflected signal from the blood cells obtained thereby. For example, the same location is scanned 10 times with exactly the same transducer selection and transmit/receive beam convergence delay amount, and the received signals obtained thereby are sequentially stored in the Doppler buffer memory as described above. .

Next, the velocity of blood cells at a predetermined depth is detected from the in-vivo reflection signals obtained by scanning the same location 10 times in this manner. At this time, each reflected signal contains a mixture of reflections from moving objects such as blood cells and reflected waves from stationary objects that hardly move, such as blood vessel walls, and the latter is dominant. It has become. Therefore, first, in order to remove the reflected waves (clutter signal) from the fixed reflector,
Ten signals obtained at a predetermined depth are input to MTI filters 5Fa and 5Fb.

Since the MTI filter technique is generally known in the radar field, its details will be omitted.

Then, the clutter signal is removed by the MTI filters 5Fa and 5Fb, and only the reflected waves from the blood cells are sent to the arithmetic circuit 5.
Sent to G. Here, frequency analysis is performed using the 10 pieces of data at a predetermined depth, the center or spread (dispersion) of the spectrum is calculated, and the value is stored in the blood flow signal memory in the image memory 5G. Stored. In this way, a tomographic image signal and a Doppler signal are obtained by transmitting and receiving ultrasound beams in a predetermined direction.

Next, the transducer selection switch 11 selects 1-2 to 1- (M
al) is selected, and ultrasonic waves are transmitted and received. A tomographic signal and a Doppler signal in the transmission/reception direction are obtained in the same manner as described above, and these are stored in the tomographic image memory and blood flow signal memory in the image memory 6A, respectively.

(Problems to be Solved by the Invention) In this way, in the linear electronic scanning system, the array type ultrasonic transducers 1-1 to 1-N are selected by the transducer selection switch 11.
By shifting and selectively driving one book at a time, the inside of a living body can be scanned. In this case, in conventional scanning, there is a method of always keeping the number of simultaneously driven transducers constant, and in edge scanning, there is a method of reducing the number of transducers.

For example, in the former method, if the total number of oscillators is N1 and the number of simultaneously driven oscillators is M, then scanning starts with 1-1 to 1-H oscillators, and 1-(N-M+1) to 1 The process ends at the (N-M+1)th scan using -N transducers, and blood flow imaging is obtained using one tomographic image and blood flow signals. In this case, the field of view becomes narrow because an area corresponding to M transducers is not imaged.

On the other hand, in edge scanning, the field of view is not so narrow if the number of transducers is reduced, but since scanning is performed with fewer transducers at the edges, the ultrasound beam is not converged sufficiently, resulting in poor image quality. I can't get it.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an ultrasonic diagnostic apparatus that can obtain images with a wide field of view while suppressing a decrease in resolution.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems and achieve the objects, the present invention has the following structure. That is, in the present invention, when obtaining a signal at the array end of the vibrator, the ultrasonic reception direction is deflected outward.

(Function) As a result, there is no need to significantly reduce the number of receiving transducers even in edge scanning, so an ultrasonic tomographic image with a wide field of view can be obtained without deterioration in resolution.

(Example) Hereinafter, an example of an ultrasonic diagnostic apparatus according to the present invention will be described with reference to the drawings. First, prior to explaining embodiments, the present invention will be explained in detail.

A schematic diagram of the scanning of the present invention is shown in FIG. In order to realize the present invention, a reception dynamic convergence method that has been widely used in the past is required. The reception dynamic focus method is a technique in which the convergence point is set successively farther away from the probe (oscillator) according to the reception time, and the reflected waves in the scanning direction are always converged and received.

In the present invention, the central part of the tomographic image is as shown in Fig. 2 (
As shown in a), ultrasonic waves are transmitted and received in a direction perpendicular to the direction in which the transducers are arranged. The shaded area in FIG. 2(a) indicates the area where the resolution deteriorates. on the other hand,
In scanning at the end, ultrasonic waves are transmitted and received outward, as shown in FIG. 2(b). The number of transducers of the linear array probe is N, and the number of elements used for one transmission and reception of ultrasound is M. In this case, one tomographic image is created by n scans, and the n-th scan at the end is from 1-(N-M+1) to 1
This is done using M vibrators up to -N.

That is, the n-th scanning direction is divided into minute sections, the ultrasonic beams from the M transducers are converged within each section, and only the received signal from this converged section is extracted. Configure pixels. The same holds true for the (n-1)th scan. That is, the scanning direction of the (n-1)th transducer is divided into minute sections in the same way as the n-th scanning direction, and using the transducers 1-(N-M+1) to 1-N of the array type probe, Beam convergence is performed in the section. −
Similar operations are repeated until the n/2nd scan, and (n/
In the 2+1)th scan, 1-2 to 1-(M+
When the vibrator of 1) is used, the center of the M vibrators used in the same way as in the conventional case coincides with the scanning position. Although the right end portion has been described above, the same applies to the left end portion, so the explanation will be omitted.

The ultrasonic image of the end obtained by the present invention is determined by the directivity of reception, and when transmitting, it is sufficient to scan with an ultrasonic beam with weak directionality. Transmission may be performed with fewer children. However, in this case, the transmission power decreases due to the decrease in the number of oscillators, resulting in S/N deterioration. In order to solve this problem, a method may be adopted in which the driving voltage of the vibrator is increased in transmission at the end. When obtaining an image of the edge, the ultrasound transmission direction may be perpendicular to the transducer arrangement direction or may be deflected slightly outward; however, when deflecting the ultrasound, one transmission can cover all depths. Since it is difficult to suppress the transmission sensitivity within an allowable range in such a case, multiple transmissions may be performed with different deflection angles.

By the way, in order to realize the present invention, it is necessary to make the precision (that is, the interval) of dynamic focus during reception finer than before. Ideally, it is desirable to have a vixel size similar to that of an ultrasound image. Also, a long delay is required to converge the beam at the end. For this reason, it is difficult to obtain sufficient delay characteristics with conventional analog delay circuits, and it is desirable to use digital delay circuits.

FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus in which a receiving circuit is digitalized (digital phasing and addition method) as an embodiment of the present invention. First, a circuit configuration for displaying an ultrasonic tomographic image will be explained.

The basic configuration of the apparatus includes a linear array probe 1, a transmission system 2, a digital reception system 10, a B-mode processing system 8, and an image system 6.

Below, only the parts related to digitization will be explained.

The digital receiving system 10 includes a preamplifier 10A (IOA-
1 to 10A-N) and A/D converter 10C (IOC-1
~10 C-N) and the RAM (Random Access - Memory or Shift Register) IOD that forms the receive delay circuit
(IOD-1 to 10D-N) and an adder 7E. The preamplifier IOA receives echo signals from each of the transducers 1-1 to 1-N of the array probe 1, and amplifies them to an appropriate level for the subsequent stage. A/D converter 10C converts the preamplifier output into a digital signal. The RAM 10D, which serves as a reception delay circuit, temporarily holds the output for each channel from the A/D converter 10C, and then outputs the output after a predetermined time delay. The adder 7E digitally adds the echo signals of each channel after delay control, and the output of this addition is sent to the digitizing B-mode processing system 8. The digitization B-mode processing system 8 includes an envelope detection circuit 8A consisting of an absolute value circuit and a low-pass filter, and a logarithmic conversion table 8B consisting of a ROM or the like. The envelope detection circuit 8A detects the envelope of the echo addition output. Logarithmic conversion table 8B
is the logarithmic transformation of the output signal amplitude of the envelope detection circuit 8A,
It is stored in the image memory 6A of the video system 6.

Next, the digitalization D mode processing system 9 will be explained.

The digitalization D-mode processing system 9 includes sampling circuits 9Aa and 9Ab for realizing orthogonal phase detection in a digital manner, and MTI filters 98a and 9 for removing clutter components.
Bb, an FFT calculation unit for calculating blood flow data, and C
It consists of an arithmetic circuit 9C having a correlation arithmetic section and the like for calculating an FM image. The resampling circuits 9Aa and 9Ab obtain two orthogonal phase detection outputs from the echo addition output using two sampling pulses having different phases by π/2.

The MTI filters 98a and 9Bb remove clutter components associated with the movement of the heart and blood vessel walls contained in the Doppler shift signals in the two orthogonal phase detection outputs. The arithmetic circuit 9C performs frequency analysis on blood flow data such as the average velocity and variance of blood flow using an FFT arithmetic unit, and stores the calculated data in an image memory'.
Furthermore, the velocity, direction, and position of the blood flow are calculated by a correlation calculating section using an autocorrelation method, etc., and color processing is performed to obtain CFM image data, which is stored in the image memory 6A.

Under the above configuration, the control of the present invention, that is, the control of dynamic focusing while directing the reception direction outward when obtaining an edge image, is performed by the transmission system 2° transducer selection switch 11. This is done by the digital receiving system 10. In addition, when the reception directivity is directed outward, the same applies to the control to decrease the deflection angle with the depth of the convergence point,
Furthermore, when the receiving directivity is directed outward, control for setting the transmitting directivity in a direction substantially perpendicular to the transducer surface is also the same.

Although the case of linear scanning has been described above, convex scanning is a scanning method that has become widely used along with sector scanning and linear scanning in recent years. Probes used for sector scanning and linear scanning use transducers arranged in a row on a flat support.
A probe for convex scanning uses a probe in which vibrators are arranged on a convex support. The tomographic image obtained by this convex scanning is fan-shaped, but the transducer driving method during scanning is the same as the linear electronic scanning method.
- The transmission and reception direction is substantially perpendicular to the plane of the central vibrator of a group of vibrators (for example, M vibrators) driven simultaneously. Therefore, as with linear scanning, the image quality at the edges deteriorates in the conventional method, but the present invention can be applied to this case as well, and the image quality at the edges of the fan-shaped field of view obtained by convex scanning can be greatly improved. can be improved.

Although the case of obtaining tomographic signals has been described above, water washing can also be applied to the ultrasonic Doppler method for measuring blood flow velocity. However, since the measured value in this case is angularly dependent, if the deflection angle of the receiving beam is large, a more accurate value can be obtained by correcting it.

[Effects of the Invention] As described above, in the present invention, when obtaining a signal at the end of the array of transducers, the receiving directivity of the ultrasonic waves is deflected outward, thereby reducing the number of receiving transducers even in end scanning. It is possible to provide an ultrasonic diagnostic apparatus that can obtain images with a wide field of view without deteriorating resolution without significantly reducing the number of images.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an ultrasound diagnostic device according to the present invention, FIG. 2 is a diagram showing the principle of the invention, and FIG. 3 is a block diagram of a general electronic linear scanning ultrasound diagnostic device. It is. 1...Array probe, 2...Transmission system, 2A...
Pulse generator, 2B... Transmission delay circuit, 2c... Pulser, 6... Video system, 6A... Image memory, 6B...
...TV monitor, 7E...Adder, 8...Digitalization B-mode processing system, 8A...Envelope detection circuit, 8B
. . . Logarithmic conversion table, 9 . . . Digital D mode processing system, 9Aa. 9Ab...Resample circuit, 9Ba, 9Bb...M
TI filter, 10...Digital reception system, 10A.
...Preamplifier, IOB...A/D converter (A/D-
C), IOC...shift register. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] An ultrasonic diagnostic apparatus that scans the inside of a living body by selectively driving a group of transducers while shifting some of the array-type ultrasonic transducers, and obtains at least one of ultrasonic tomographic image information and blood flow velocity information, An ultrasonic diagnostic apparatus characterized in that when obtaining an image of an array end of the transducers, reception directivity is directed outward.