JPH0155432B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic receiving device, and particularly to a device that uses a split transducer to receive data while changing the focus control to an optimal state depending on the focal length (dynamic focus receiving). It is.

First, in an ultrasonic receiving apparatus using a split transducer, the delay time that should be given to each received signal for the purpose of forming a receiving beam is roughly estimated. As an example, a rough calculation will be made for a linearly arranged split vibrator as shown in FIG. In Fig. 1, the foot of the perpendicular line drawn from the focal point F to the transducer row W is O, the center point of the transducer element of interest is E, and the focal length OF=y, E=x
shall be. The time difference T between the times when the same wavefront diffusing from F reaches O and F is calculated as follows.

T (x, y) = (√ ² + ² - y) / C ... (1) ≒x ² /2yC ... (2) Here, the sound speed of medium 2 is set to C.

On the other hand, the receiving aperture of the split transducer is D(y)
When the ultrasonic wavelength is input, the theoretical resolution Δx and the depth of focus Δy in the azimuth direction of the receiving device are respectively estimated as follows.

Δx＝2λy／D ……(3) Δy＝2yΔx／D ＝4λy ² ／D ² =(Δx) ² ／λ ……(4) In order to form the receiving beam, the time difference τ in equation (1) must be After compensating between elements, in-phase addition (phasing addition) is performed. Assuming that the azimuth resolution to be achieved is Δx and the field of view range is 0≦y≦ _ynax , the maximum value of delay time _Tnax required for phasing and addition can be estimated as follows from equations (2) and (3). .

T _nax ≒ T (D (y _nax ) / 2, y _nax ) = (λ ² / 2C) y _nax / (Δx) ² ... (5) In addition, in order to achieve the desired resolution over the entire field of view, the sound source Change the focal length of the receiving system depending on the distance (so-called dynamic focusing)
There is a need. When the number of focal stages N _f required to realize the azimuth resolution ΔX is roughly estimated from equation (4), it becomes N _f =y _nax /Δy=λy _nax /(Δx) ² ...(6). Based on equations (5) and (6) above, it is possible to roughly estimate the delay time storage capacity required to realize the azimuth resolution Δx over the entire viewing range. In other words, when the delay time quantization unit is _ΔT , two pieces of delay time data of the size of one data (λ ² /2CΔT)y _nax /(Δx) ² are stored ^per receiving element. It is necessary to do so. Both the size and number of data are inversely proportional to (Δx) ² , so in the conventional method of storing the delay time data itself, when trying to achieve high azimuth resolution Δx, the required delay time storage capacity becomes extremely large. The situation has grown and the difficulties in realizing it have been great.

The present invention solves the above-mentioned conventional problems and makes it possible to realize a high-resolution receiving system with a small storage capacity.

The present invention is characterized in that it stores not the quantized delay time value itself required for phasing processing, but the difference value regarding the focal length of the delay time quantized value, and high resolution due to dynamic focus. can be received with a small delay time storage capacity. Delay time T (x, y) required for phasing processing
The size of the difference value with respect to the focal length y is given by formula (2)
Therefore, a small change in y Δy can be estimated as follows.

τ (x, y) = −∂T (x, y) / ∂y・Δy ≒x ² Δy / 2Cy ² ...(7) The delay time data is changed every time the sound source distance changes by the depth of focus. In the case of receiving focus-focused reception, the equation (4) can be substituted for Δy in the equation (7), and the result is as follows.

τ (x, y)≈2λx ² /CD ² (8) Therefore, the necessary maximum value τ _nax of the delay time difference value is approximately calculated as follows.

τ _nax ≒τ(D(y)/2, y) = λ/2C=1/2f (9) where f is the ultrasonic frequency. From formula (9),
The size of one piece of data required to store the delay time quantization difference value is constant and does not directly depend on the azimuth resolution Δx or the maximum sound source distance y _nax , and is 1/
2fΔT. From equations (5) and (9), the size of the required delay time data is (Δx) ² /λy _nax times that of the conventional method, and when the resolution Δx to be achieved is Δx<√ _nax ...(10), this Invention is an advantage. Since the ratio compared to the conventional one is (Δx) ² , especially when Δx is small,
That is, the present invention is extremely advantageous when high resolution is to be achieved. In the present invention, it is also necessary to store at least one delay time quantized value per receiving element, but in the case of a high-resolution device, the number of focal stages N _f becomes large. Since the ratio of the above value to the total storage amount required for receiving beam formation is small, it is omitted in the rough calculation. As an example, when calculating the ratio for a standard ultrasound diagnostic device,
When λ≒0.5 mm, y _nax ≒200 mm, and Δx≒1 mm, it is sufficient that the size of the delay time data is about 1/100.

Although the above description has mainly been given using an example of using a linear array type resolving oscillator, the present invention is effective not only for the linear array type.

By the way, in the case of ultrasonic reception using the pulse echo method, pulse signals are received by each element in the order of signals with a small reflector distance and signals with a large reflector distance, so the focal length in dynamic focus must be monotonically increased. Bye. Therefore, when the method of the present invention is particularly applied to the pulse echo method, the necessary delay time quantization values can be obtained at each step of the integration simply by sequentially integrating the stored delay time quantization difference values. Therefore, the mechanism for reproducing the original value from the difference value is simplified. Therefore, especially in the case of an ultrasonic receiving apparatus using the pulse echo method, the effect of the method of the present invention is significant.

Hereinafter, the present invention will be explained with reference to Examples. Figure 2 is a configuration diagram of an ultrasonic receiving system using a split transducer, where E ₁ to E _N are transducer elements in the receiving aperture, and D ₁ to D _N are elements that are used to form a receiving beam, so that the received signal is The means for providing different delay times, S, is means for adding delayed received signals to obtain a received beam. FIGS. 3 to 5 show examples of configurations in which the present invention is implemented with respect to D ₁ to D _N in FIG. 2. In both cases, the case where the present invention is applied to a pulse echo method apparatus is taken as an example.

Figure 3 shows a tapped LC delay line as a delay means.
This is a configuration example when using DL. The received signal 5 from the transducer element E _o is input to the DL, the input 6 of the DL with different delay times in stages is input to the multiplexer MP, and the output 7 of the multiplexer MP
is input to the adder S. Dynamic focusing is performed by changing the control signal 4 of the multiplexer MP according to the focal length and controlling the delay time from signal 5 to signal 7. 1 is a clock signal that is input to the address counter C every time the focus state is changed, and the delay time quantized difference value 3 read out from the memory M according to the address signal 2 is accumulated by the accumulator AC and delayed. This becomes the time quantization value, that is, the control signal 4 of the multiplexer MP.

FIG. 4 shows a configuration example in which a combination of an A/D converter AD and a shift register SR is used as the delay means. The received signal 8 from the transducer element E _o is converted into a digital signal 11 by the AD according to the conversion clock 9 and then input to the digital interpolator IP. The signal 11 is converted by the IP into a signal 5 every tenth shift clock of the shift register SR, and is then inputted to the SR. The outputs 6 of the SRs having different delay times in stages are input to the multiplexer MP, and the output 7 of the MP is input to the adder S.
Dynamic focus is performed by controlling the MP in the same manner as in Figure 3.

Figure 5 shows a sample hold SH and a line memory LM with variable sampling intervals as delay means.
This is an example of a configuration in which a combination of the following is used. The principle of this reception beam formation is that the signal 5 from E _o is transmitted to the SH at the time when the wavefront diffusing from the reflectors virtually placed at points linearly arranged at equal intervals in the field of view should reach the element E _o of interest. By sampling and holding the data and writing the value 6 into the line memory LM, the signal values corresponding to the above array points are obtained as the output 7 of the LM in the order of the array. When the present invention is applied to such an apparatus, the difference value of the sample interval from the reference value is equivalent to the difference value of the focal length of the delay time described in the present invention. here,
The standard value of the sample interval is the time required for the ultrasonic waves to travel back and forth between the array points. While receiving data without changing the focal length, the sample interval for all elements can remain at the standard value; however, when increasing the focal length, the sample interval must be changed from the standard value to the element position. It will only reduce the amount. The sample clock of the sample hold SH is obtained as the carry output 4 of a counter C1 which counts the basic clock 1 whose period is the delay time quantization unit. The carry output 4 is simultaneously used as a load signal for C1 itself, a write clock for LM, and a clock for address counter C2. The delay time quantized difference value 3 read out by the address signal 2 is loaded into C1 as data, and the next carry output pulse is processed by the product of the delay time quantized difference value 3 and the basic clock interval. The interval, that is, the sample interval becomes smaller than the standard value. The initial sample and hold time can be controlled by the clear input signal 8 of C1. Note that the reading of data written in the LM is controlled by the clock 9.

Although the present invention has been described above with respect to an ultrasonic receiving system, the present invention can also be applied to the case where dynamic focus is performed during transmission, and the present invention is also effective for a transmitting system.

As explained above, according to the present invention, the delay time storage capacity required to realize a high-resolution ultrasonic receiving device that utilizes dynamic focus can be made much smaller than that of conventional methods. This invention is of great significance. Since the storage capacity saving effect of the present invention is proportional to the square of the azimuth resolution to be achieved, the higher the resolution of the device, the more significant the effect of the present invention will be.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the positional relationship between a linearly arranged segmented transducer and a focal point, Fig. 2 is a diagram showing a schematic configuration of an ultrasonic receiving device using segmented transducers, and Figs. 3, 4, and 5. Each figure is a block diagram showing the structure of the delay means in FIG. 2.

Claims (1)

[Claims] 1. In an ultrasonic receiver equipped with an ultrasonic transducer made up of a plurality of elements, and means for forming a moving focus by giving an appropriate delay time to the ultrasonic signal received by each element over time, storage means for storing a delay time given to the received signal of each element as a delay time quantized difference value between moving focal points; and a storage means for storing the delay time given to the received signal of each element as a delay time quantized difference value between the moving focal points, and a received signal of each element by integrating the difference values read from the storage means each time the focal point moves. What is claimed is: 1. An ultrasonic receiving device characterized by comprising: means for delaying.