JPS6238358A - Weighting method for ultrasonic probe - Google Patents

Abstract

PURPOSE:To reduce the side lobe of an ultrasonic wave by composing an array type ultrasonic probe of an array of plural piezoelectric elements and weighting transmission/reception sensitivity given to the respective elements curvedly so that the extent of the weighting is larger at the center part and smaller at both end parts. CONSTITUTION:More than tow piezoelectric elements are weighted equally at the center part (x1--X1) of the opening of the probe to obtain a flat characteristic, elements are weighted differently between the center part and both end parts (x1-X2 and -x1--x2) to obtain a steep characteristic, and elements are weighted at different pitches of >=2 elements at both end parts (x2-x3 and -x2--x3) to obtain slot characteristic. Thus, the weighting is carried out as shown by a polygonal line (dotted line) and approximated to a weighting function X(x) to simplify the circuit. Then, a constant voltage source 20 generates weighting levels W1, W2 ... and weight is selected according to the signal of memory 22 and inputted to switches 31=3N. Outputs of the switches 31-3N are supplied to buffers 41-4N to obtain their outputs EW1-EWN. Consequently, the weighting is performed stepwise to obtain an excellent sound pressure distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of weighting transmitted and received pulses applied to each element of an array type ultrasonic probe.

[Conventional technology]

Ultrasonic diagnostic equipment transmits ultrasonic waves to the subject and receives the reflected waves or transmitted waves to perform diagnosis. There are devices in which side lobes are reduced, beam convergence is achieved, or electronic scanning is performed by arranging individual elements and changing the driving mode of each element.

FIG. 6 is a diagram explaining side lobes, 10 is a linear array type probe, 1). 12. . . . IN is each element (piezoelectric element such as PZT). When a common pulse voltage is applied to these piezoelectric elements to generate ultrasonic waves, and the sound pressure distribution in the X-axis direction (element arrangement direction) is determined, the solid line curve C1 shows that in addition to the main lobe ML, there are many ultrasonic waves. A side lobe SL occurs. When the pulse voltage applied to each piezoelectric element during transmission is made large at the center as shown by curve C3 and small at both ends, the side lobe is reduced as shown by dotted curve C2. During reception, similar results can be obtained by setting the amplification factor of the receiving circuit for each element as shown by curve C3.

Simplification of the circuit section is an important issue in array type probes. In other words, each piezoelectric element has a transmitting and receiving circuit, so the number of elements is 4.
If it is 0 to 50, the same number of transmitting circuits and receiving circuits are required,
The circuit scale becomes considerably large.

In linear array type probes, grating lobes (gr)
The number of elements increases if the output (ating 1 obe) is prevented. Figure 7 shows C+ when the pitch of the piezoelectric element is 1.231 m, and C2, 0, 4 when the pitch is 0.817 mm.
The sound pressure distributions are C3 when the crane is used, and 04 when the distance is 0.2 m, and large grating lobes (the peak at the middle of the curve) are generated at C1 and C2, which adversely affects the image. Grating lobes hardly occur after C3, so 03 and above are suitable for practical use.
Since the pitch is small, the number of elements is large. In terms of number of elements,
C+ is 16, C2 is 24, C3 is 49, and C4 is 98, and after C3, which is suitable for practical use, the number of transmitting and receiving circuits is 49 or more even just for the aperture.

[Problem that the invention seeks to solve]

Side lobes can be reduced by weighting each element in a linear array probe (driving voltage weighting and/or receiver circuit gain weighting), but the effective weighting curve for the low side lobe range is shown in Figure 6. It is like the curve C3, which is a curve that changes continuously. Therefore, the number of elements is 4
5, the values of the curve C3 at 45 points on the X-axis are determined and used as the weighting coefficients for each element, but the amount of circuitry for this part is also considerably large. The present invention aims to improve these points and provide a weighting method that can simplify the circuit configuration.

[Means for solving problems]

The present invention provides an approximation of the weighting function for each piezoelectric element in an aperture selected during transmission or reception in a method of weighting transmission and reception sensitivity to each element of an array-type ultrasonic probe in which a plurality of piezoelectric elements are arranged. The number of weighting stages is determined by applying the same weight to two or more elements in the center of the aperture, changing the weight by pinching two or more elements at both ends of the aperture, and giving a different m to each element between these. This feature is characterized in that the circuit configuration of the weighting part is simplified by reducing the weighting part.

[Effect]

The weighting curve is called a weighting function and is represented by W (X). In the present invention, the weighting curve is approximated by a polygonal line such as the dotted line in FIG. ±X+, ±x2 are the X coordinates of the bending points, and ±x3 are the X coordinates of the end points. Weighting function W (X
As shown in the figure, l is generally flat at the center of the aperture (X=0), gentle at both ends of the aperture, and has a relatively steep slope between these. Therefore, the dotted curve is -X l < X≦X+ Flat (parallel to the X axis), ■X l < X≦X2.-XI
≧X≧−x2, the slope is steep; ■x2≦X≦X3. −X2≧
For X≧−x3, each straight line has a gentle slope, for ■, the weighting coefficient is changed in a pinch of two or more elements, for ■, the weighting coefficient is changed for each element, and for ■, the weighting coefficient is changed for each plurality of elements.

In this way, the weighting circuit can be simplified.

When linear electronic scanning of an ultrasonic beam is performed, the beam is generated by driving some piezoelectric elements of an array type probe.
Remove one element at one end of the driven piezoelectric element group, take in one non-driven element at the other end, drive this as a new element group, and repeat the same operation to direct the ultrasound beam from one part to another. A method of scanning toward the end is used, but in this case, the weighting function W (X) is given to the simultaneously driven element group (the aperture element group).

The weighting function can be generated by a D/A converter, but in this method, even if an error of ±3% is allowed, the input to the D/A converter requires 5 bits or more. This DAC method uses a plurality of weighting levels Wl, W2 .・・・・・・
...It is easier to prepare Wm in advance and select it using an analog switch. In this way, 8 levels of weighting levels at unequal intervals can be selected by inputting 3 bits.

Figure 2 shows the hardware.

In FIG. 2, 20 is a constant voltage source, and the weighting level Wl,
W2. ...is generated. 31.32...
・ is a selection switch, and the output W + of the constant voltage source 20
.

One of W 2 , . . . is selected by a signal from the memory 22. 41, 42. . . . are buffers, and switches 31, 32 . . . . outputs the selected weighting level. EWI, EV2.・
...is the output. 8 weighting levels (
In the case of N=8), the switch control signal output from the memory 22 only needs to be 3 bits, and the hardware can be simplified. When electronic scanning is performed, the weighting applied to the capacitive elements changes for each scanning line, and the memory 22 is for this purpose, storing the patterning of each element in each scanning line, which is read out using the scanning line address. to produce a weighting level selection output for that scan line.

An example of the configuration of the switch 31 is shown in FIG. In this example, there are eight weighting levels, and the 3-bit switch control signals Bo, B1 . Select with B2.

The same applies to the switches 32...3N.

The outputs Ew l , EV 2 , . . . are power amplified during transmission and then serve as power sources for transmission pulses, and during reception enter the AGC circuit to control the gain of the receiving circuit.

The buffer 41 is connected as shown in FIG.
w + may be generated.

If you want to make the aperture variable by performing GuinamiSoku focus, you can approximate it by changing the correspondence between W (X) and X (correspondence between the switch control signal and the scanning line address). Depending on the number of dynamic focus stages, the constant voltage is changed from W1 to W8 to W1 to W e', and further to W
It is sufficient to change it to I" to W8". Even if such a change is made, the load on the circuit is not large because the constant voltage source is common to each element.

FIG. 5 shows an example of a circuit in which nine weighting levels are generated using a switch 31 having eight contacts.

〔Example〕

In the present invention, the weighting curve W (Xl is approximated by a dotted line curve as shown in Fig. 1. In the flat part (■), the weight of each element is the same for two or more elements, and in the steep part (■), the weight is set for each element separately. 8 and 1), and the weights are changed for each of the plurality of elements in the gently sloped part (3). The simulation results of the sound pressure distribution with and without such a method are shown in FIGS. 8 to 1).

FIG. 8 shows an outline of the probe used in the simulation, in which the number of piezoelectric elements is 45 and the aperture 2a has 2×9 fins. P is the observation point, and θ is the angle between the straight line Z passing through the aperture center 0 and the straight line OP; ... is this angle θ. The weighting function is W(xi = e (1,3X"/
)2, and this is shown in Figure 9 (a), (b), (C
) as (approximated), i.e. (for al, element 1
Elements 1-23 (only one side is shown, but actually both sides, the same applies hereafter) from the aperture end to the vicinity of the center of the aperture, with the same weight.
For No. 16, the weight was changed for each element, giving a total of 17 levels of weighting. In (b), element 9 at the center of the opening
The same weight was given to elements 1 to 23, and the other elements 1 to 8 were given different weights for each l element. (C) is an example of weighting according to the present invention, in which the same weight is applied to elements 17 to 23 in the center of the aperture, and weights that are changed for each element to elements 13 to 16 in the steeply sloped part, and For the elements in the gently sloped part, weights were given that were changed for each of the plurality of elements 1 to 4.5 to 7.8 to 10.1) to 12. Note that the weight that is changed for each element or multiple elements approximates the required weighting function, and does not necessarily change in uniform steps.

A sound pressure distribution of curve 1 in FIG. 9 (al weighted in FIGS. 6 and 1) is obtained. This sound pressure distribution curve has no noticeable grating lobes and is practical, but 17
The weighting of stages is too much. Figure 9 (The weighting of BL is in 9 stages, and it has been halved, but the sound pressure distribution curve becomes the curve ■ in Figure 10, and grating lobes are generated, which are marked with *, and the sound field is deteriorated. Figure 9 (C) shows the same 9
Although it is a stage, the sound pressure distribution curve becomes the curve ■ in Figure 1),
It is almost the same as the 17-step curve ■ = Thus, according to the present invention, the aperture with a fairly large diameter (in this example, 1
8), good characteristics can be obtained by weighting in a small number of stages, 9 stages.

〔Effect of the invention〕

As described above, according to the present invention, a high-quality sound pressure distribution can be obtained by performing weighting in a small number of steps, and the weighting circuit can be simplified.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the main parts of the present invention, FIG. 2 is a block diagram showing the hardware section of the present invention, FIGS. 3 to 5 are diagrams showing examples of switch circuits, and FIG. 6 is a side lobe An explanatory diagram, Fig. 7 is an explanatory diagram of grating lobes, Fig. 8 is an explanatory diagram of the elements used in the simulation, Fig. 9 is an explanatory diagram showing an example of element weighting, and Figs. 10 and 1) are simulation results. This is a graph showing. In the drawing, lO is a probe, 1), 12. ... is the piezoelectric element, W (Xl is a weighting function, 31 to 3N are analog switches, and 20 is a circuit that generates a plurality of weighting levels.

Claims (2)

[Claims] (1) In the weighting method of transmitting and receiving sensitivity given to each element of an array-type ultrasonic probe in which a plurality of piezoelectric elements are arranged, the aperture is 2 for the central element
A weighting method for an ultrasonic probe characterized in that the same weight is given to each element or more, different weights are given to the pitch of two or more elements at both ends of the aperture, and different weights are given to each element between these parts. (2) The weight given to each element is obtained by selecting the outputs of a circuit that generates weighting levels corresponding to the number of weighting stages using an analog switch.
A weighting method for an ultrasound probe according to claim 1.