JPS6232005Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to a focal length control device that electronically controls the focal length of an ultrasound beam in an electronic scanning ultrasound diagnostic apparatus.

Conventional technology In conventional electronic scanning ultrasound diagnostic equipment, a so-called electronic focusing device is used to focus an ultrasound beam at a certain depth Rf (referred to as focal length) from the patient's body surface to which a transducer is applied. is added. This makes it possible to improve azimuth resolution.

This electronic focusing device is based on the following principle. First, an ultrasonic transducer used in an electronic scanning ultrasonic diagnostic device consists of rectangular piezoelectric vibrators having a thickness t, a width a, and a length b, spaced apart by #1 and #1 at intervals of d, as shown in Fig. 2. 2, #3, . . . #N, which are called array transducers, are arranged on the same plane. Each vibrator is provided with electrodes on its upper and lower surfaces, and a driving voltage is applied between these electrodes to drive the vibrator. Note that the acoustic radiation area of each vibrator is a×b.

The deflection of the ultrasonic beam can be explained as shown in FIG. When the center of the array transducer is Q and the observation point is O, and the ultrasound beam is deflected by an angle θ ₀ from the central axis, the wavefront is A.
Since it is sufficient to align them on the −A′ plane (′⊥), it is sufficient to change the drive time of each vibrator and delay the vibrator with a larger number. This delay time is calculated from each transducer by straight line B-B' (straight line A passing through the center of transducer #1).
-A' (a straight line parallel to A') divided by the speed of sound v in the sound field medium. In other words, the delay time Td(θ ₀ )i for the i-th oscillator is Td(θ ₀ )i={(i-1)d sinθ ₀ }/v
...(1) becomes.

Next, the focusing of the ultrasonic beam can be explained as shown in FIG. Here, the focal length is Rf (=), and in order to form a focused ultrasound beam at observation point O, the fourth
As shown in the figure, each transducer may be driven with a delay so that the ultrasonic waves emitted from each transducer arrive at point O at the same time. In this case, the delay time Tf(θ ₀ )i of the i-th vibrator is determined as follows. First, draw an arc C-C' with radius r ₁ that passes through the first oscillator with point O as the center, extend the straight line ri connecting the i-th oscillator and point O, and find the point of intersection with arc C-C'. Let it be Si. And Tf(θ ₀ )i is O from the oscillator
From the distance (r ₁ - ri), which is the difference between the longest distance ri to the point and the distance ri from the i-th oscillator to point O, it is determined as Tf (θ ₀ )i = (r ₁ - ri)/v . When the i-th transducer is driven by giving this delay time Tf(θ ₀ )i, the ultrasonic waves emitted from the i-th transducer and the ultrasonic waves emitted from the first transducer are at the same point. Reach the time. this
Tf(θ ₀ )i is expressed as follows.

Tc (θ ₀ )i = (N-i) (i-1) d ₂ (1-θ ₀ ² )/2R
_f v...(3) Here, the unit of θ ₀ is radian. In equation (2), the first term on the right side is the delay time necessary to deflect the ultrasound beam, and the second term is the delay time necessary to focus it. In other words, the delay time Tf (θ ₀ ) required to focus the ultrasound at a certain distance from the array transducer is expressed as the sum of the deflection delay time Td (θ ₀ ) and the focusing delay time Tc (θ ₀ ). expressed.

The above has explained the case of transmitting waves, but in the case of receiving waves, if the same delay time as that of transmitting waves is given to the received signal obtained from each transducer and the signals are combined, the same directivity as that of transmitting waves can be obtained. It will be done. In this case, the transmitting and receiving waves are confocal.

Problems that the invention aims to solve However, with conventional devices, the focal length Rf can only be set in stages (for example, Rf = 50 mm, 75 mm, 100 mm, etc.). Therefore, it is not possible to observe with high resolution an object that exists at a focal length Rf that cannot be set. Of course, the focal length Rf
It would be possible to increase the number of set values of and change the focusing delay time Tc (θ ₀ ) accordingly, but this would complicate the configuration, make the device expensive, and increase the failure rate due to the increased number of parts. The problem arises.

The object of this invention is to provide a continuously variable focal length control device that has a simple configuration, can be realized at low cost, and can set any focal length.

Means for Solving the Problems The focal length control device of the ultrasonic diagnostic apparatus according to this invention includes a delay circuit that can change the delay time for each quantization delay time _QT , and a distance between each transducer that is d and the sound velocity. A memory circuit that stores in advance each value of d ² (1-θ ₀ ² )/vQ _T regarding each deflection angle θ ₀ when v is a counter, a counter that generates the number i of the oscillator, and a desired Focal length
When ^the device for _setting Rf and the ^total number of _oscillators are N, calculate The delay time of the delay circuit is selected by the integer part [X] of the X, and the focusing delay time of [X]Q _T is obtained.

Effect By rearranging the above equation (3), Tc(θ ₀ )i={d ² (1−θ ₀ ² )/vQ _T } ×(N−i)・(i−1) ……(4) get. When this equation (4) is quantized by time Q _T , Tc (θ ₀ )i=[d ² (1-θ ₀ ² )/2vQ _T・(N-i)(i-1)/Rf+0.5]Q _T ……
(5) becomes. Here, [ ] is a Gaussian symbol, and only the integer part is used. Manipulate the inside of this Gauss symbol and transform it as follows.

X=1/2{d ² (1-θ ₀ ² )/vQ _T (N-i) (i-1)/Rf+1} ...(6) In this formula (6), the inside of { } is an integer operation. It becomes possible.

Here, d ² (1-θ ₀ ² )/vQ _T is considered to be a constant with respect to i. Therefore, for each deflection angle θ ₀ , the value of d ² (1−θ ₀ ² )/vQ _T is calculated in advance. Each of these values is stored in the storage circuit described above. Each of these values is read out by the selection signal of the deflection angle θ ₀ , the above calculation of X is performed, and the quantization delay time [X] Q _T is obtained from the integer part [X].

Embodiment In FIG. 1, the total number N of oscillators is given to the subtracter 1 in advance, and (N-i) is obtained in this subtracter 1. This i is the output of the counter 2 that counts the count signal, and corresponds to the vibrator number. This i is also held in register 4, and i-1 is taken out by register 4 and multiplied by multiplier 3 (N-i)/(i-
1) is obtained. The storage circuit 6 stores d ² (1-θ ₀ ² )/vQ _T calculated for each deflection angle θ ₀ , which is read out by the selection signal of the deflection angle θ ₀ and sent to the multiplier 5 . Multiplication of {d ² (1−θ ₀ ² )/vQ _T }×(N−i)·(i−1) is performed. Then, division is performed by the focal length Rf set in the divider 7 to obtain {d ² (1−θ ₀ ² )/vQ _T }×{(N−i)·(i−1)/Rf}. Specifically, the focal length Rf is set using an input device (not shown) that can specify an arbitrary focal length by, for example, key operation. The result of this division is transferred to the counter 8, and the counter 8 is further incremented by +1. Then, the calculation inside {} of the above equation (6) has been performed. If this counter 8 is of a binary type, by shifting one bit in the direction of the lower digits, the calculation of x1/2 is performed and equation (6) can be obtained. This calculation process is all performed using integers, so the above
This means that the numerical value inside the Gauss symbol in equation (5) has been obtained.

The delay circuit 9 is a delay circuit whose delay time can be changed for each quantized delay time Q _T , such as a delay line with taps where the delay time between taps is Q _T , and the delay is controlled by an analog switch or the like based on a control signal from the counter 8. Time is selected. As a result, the quantized focusing delay time Tc (θ ₀ ) given by the above equation (5)
i is given to the trigger pulse or received signal.

In the embodiment shown in FIG. 1, individual arithmetic elements are combined, but similar arithmetic operations can be easily performed using a programmable arithmetic element such as a microprocessor.

Effects of the invention According to this invention, the ultrasonic beam can be focused at an arbitrary depth from the patient's body surface, so the azimuth resolution at a specified distance (focal length) is improved. As a result, clear tomographic images can be obtained. Furthermore, since the configuration is simple, it can be realized at low cost.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of this invention, Fig. 2 is a perspective view showing an array transducer, Fig. 3 is a schematic diagram for explaining the deflection of an ultrasonic beam, and Fig. 4 is a FIG. 3 is a schematic diagram for explaining focusing of an ultrasonic beam. 1...Subtractor, 2,8...Counter, 3,5...
... Multiplier, 4 ... Register, 6 ... Memory circuit, 7
...Divider, 9...Delay circuit.

Claims (1)

[Claims for Utility Model Registration] A delay circuit that can change the delay time for each quantized delay time Q _T , and d ² related to each deflection angle θ ₀ when the interval between each vibrator is d and the speed of sound is v. A memory circuit that stores each value of (1-θ ₀ ² )/vQ _T in advance, a counter that generates the transducer number i, and a desired focal length
When ^the device for _setting Rf and the ^total number of _oscillators are N, calculate a focal length control device for an ultrasonic diagnostic apparatus, the focal length control device having an arithmetic circuit for performing an ultrasonic diagnosis, and selecting a delay time of the delay circuit according to the integer part [X] of the X to obtain a focusing delay time of [X] _QT . .