JPH0659285B2 - Ultrasonic diagnostic equipment - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an ultrasonic diagnostic apparatus for making a medical diagnosis using ultrasonic waves.

[Prior art]

In the ultrasonic diagnostic apparatus, usually, electronic focusing and deflection control are performed for ultrasonic wave transmission and reception. That is, the ultrasonic probe is composed of a large number of ultrasonic transducer elements, one driving pulse is delayed and given to each of the elements, and the transmitted ultrasonic pulse is focused on one point by controlling the delay amount. The received signal from each element is delayed, and the delay amount is controlled to set a certain point as the receiving focus. Further, by making the delay amount asymmetric, the focus position is tilted and deflected.

[Problems to be Solved by the Invention]

However, when the electronic control of ultrasonic waves is performed in this manner, there is a problem that image shift or distortion occurs. In particular, when so-called dynamic focusing is performed in which the receiving focus is switched when one echo is received, if there is a large change in the aperture surface (the number of elements that are driven simultaneously) at each focus stage, a shift occurs in the distance direction on the image. An accurate image cannot be obtained. An object of the present invention is to provide an ultrasonic diagnostic apparatus which is improved so as not to cause image shift or distortion.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, in an ultrasonic diagnostic apparatus according to the present invention, a probe having a large number of ultrasonic transducer elements, a delay device for delaying a transmitted signal and a received signal for each element, and a simultaneous reception Focusing by adjusting the delay amount of each element so that the received signal from the same point where the echo from the same point appears the latest, among other received signals from each element Alternatively, a control device for controlling the deflection, an image display circuit to which the received signals from the respective delayed elements are combined and sent, and a clock signal of the image display circuit are delayed corresponding to the above-mentioned image forming time. It is characterized in that it is provided with a delay circuit.

[Work]

The delay amount of each of the plurality of elements that simultaneously transmit or receive waves is determined by the focal length, the deflection angle, or the aperture plane. The image formation time is also determined according to this delay amount. Corresponding to this image forming time, the clock signals of the image display circuit, which are combined and sent from the delayed received signals from the respective elements, are delayed. Then, the time axis of the screen is changed in accordance with the image formation time, so that the influence of the different image formation time does not appear on the screen at all.

【Example】

An embodiment of the present invention will be described below in detail with reference to the drawings. In FIG. 1, a clock signal having a cycle of, for example, 25 ns is generated from the basic clock generating circuit 1, and this is divided by the frequency dividing circuit 2 to become a clock signal having a cycle of 100 ns or 200 ns. This clock signal is sent to the delay line 3 and is delayed in units of 25 ns, for example. The clock signal before being delayed and many delayed clock signals delayed by 25 ns are input to the multiplexer 4, and one of them is selected. This selected clock signal is sent out as a clock signal for an image display circuit (not shown). The multiplexer 4 is controlled by the data from the memory 5 which is read by being controlled by the counter 6 which starts counting the basic clock signal in response to the trigger signal. That is, as shown in FIG. 3, from the trigger signal, first the data of Δt1 and then the Δt1
2 data, ... Are sequentially read from the memory 5, and a clock signal having a delay amount corresponding to the data is selected and output from the multiplexer 4. As shown in FIG. 2, the ultrasonic diagnostic apparatus is usually provided with an ultrasonic probe 7 having a large number of ultrasonic transducer elements, and each of the elements has a transmission delay line 8 and a receiving wave line. Delay lines 9 and 10 are connected. The transmission drive pulse is delayed through the transmission delay line 8 and then given to each element, and the reception signal from each element is delayed through the reception delay line 9 or 10, respectively. After that, they are combined and sent to the image display circuit. Two sets of wave receiving delay lines 9 and 10 are provided because they are used alternately during wave receiving dynamic focusing. The delay amount of each of the delay lines 8, 9 and 10 is controlled by control data. This control data is stored in advance in a memory such as a RAM or a ROM as delay data for deflection and focusing. In the image display circuit, the A / D converter 11 and the image memory 1
2, the received signal synthesized through the receiving delay line 9 or 10 is first sampled and A / D converted by the A / D converter 11, and designated by the address control circuit 13 of the image memory 12. Is written to the specified address. When the writing for one screen is completed, the contents of the image memory 12 are read by the reading circuit 14 according to the display system of the display device 15 and displayed by the display device 15. The clock signal output from the multiplexer 4 (FIG. 1) is sent to the A / D converter 11 and the address control circuit 13 of the image display circuit, and the received signal is received according to the clock signal. The timing of signal sampling / A / D conversion and the timing of changing the write address of the image memory 12 are controlled. Here, giving a delay to each element of the probe during transmission and reception will be described in detail. First, let us consider that the ultrasonic wave from the point F1 is received by the seven elements E arranged on the plane in the probe as shown in FIG. Assuming that this point F1 is on the normal line passing through the center of the element array, the ultrasonic wave from F1 reaches the central element at the earliest point and reaches the upper and lower end elements at the latest point. Therefore, a delay amount dt shown by an arrow is given to the received signal of each element. Then, after the delay, the ultrasonic wave signals from the point F1 are at the same time, and the focus at the time of reception is F1 as in the case where each element is arranged on the curved surface as shown by the dotted line. become. This is shown in FIG. 5 when the received signal waveform is shown. FIG. 5 is a sound pressure waveform when a sound wave is generated at time T,
Waveform A is the waveform of the received signal obtained from the central element, waveform B is from both adjacent elements, waveform C is from both adjacent elements, and waveform D is from both end elements. It is from. In this way, the sound pressure waveform is earliest in the center closest to the distance, and is delayed because the distance increases from the center. Therefore, if each of the sound pressure waveforms is delayed so that the time is aligned with that of the slowest one, the sound pressure waveforms are overlapped and imaged at the time of the latest one, and the signal sensitivity near the point F is increased. In this case, the delay time dt1 for the central element is the largest, and delaying by this time dt1 means that the received signal obtained is the actual point F1 by a distance corresponding to the delay time dt1 when viewed from the central element. It means that it is treated as being from a point F1 'farther from. When the delay time is determined with the center element as the origin, the image appears deeper than it actually is on the screen. Looking at a point F2 farther than the point F1, this point F2
It can be seen that the difference between the time when the ultrasonic waves from 2 reach the central element and the time when they reach the upper and lower end elements is smaller than that at the point F1. That is, the delay amount dt2 to be given to the central element may be smaller than dt1. Therefore, the point F2 when this delay amount is given
The shift amount from the point F2 ′ to the point F2 ′ is smaller than the shift amount from the point F1 to the point F1 ′. Therefore, due to the difference in the amount of deviation that occurs when the focal length is changed in this way, when performing dynamic focusing that changes the focal length while receiving one echo signal, the switching distance of the focal length is changed. An image will be displaced in the vicinity. The same applies when the opening surface is changed. As shown in FIG. 6, the delay time dt1 must be given to the central element when receiving by 7 elements, but when receiving by 5 elements excluding the both ends, Element with a shorter delay time dt2
Should be given. That is, as shown in FIG. 7, the sound pressure waveform that arrives latest is waveform C when there are five elements, so the received signal (waveform A) from the earliest central element is at the same time as it. Because you can delay it. Therefore, when the aperture surface is large, the image formation time is later than when the aperture surface is small. In the case of the deflection, as shown in FIG. 8, the imaging time differs when the deflection angle is different even if the focal length is the same. For example, the time required for the sound wave from the point F1 in FIG. 8 to reach the upper element is longer than the time required for the sound wave from the point F2 to reach the upper element. The received signal waveform of each element is the 9th
It becomes like the figure. Waveforms A to G correspond to each element from the upper end to the lower end. The solid line shows the sound pressure waveform from point F1,
The dotted line shows the sound pressure waveform from point F2. Therefore, even if the received signal from each element is delayed by giving a delay time,
The matching times are different. Further, the delay time given to the central element is also different from dt1 and dt2, and as a result, when viewed from the central element, F1 to F1 ′,
There will be a shift from F2 to F2 ', and
The amount of deviation is different, resulting in image distortion in which the arc is represented as an ellipse. Although the wave reception has been described, the same applies to the wave transmission. Therefore, the deviation of the image formation time at the time of wave reception is added to the deviation of the image formation time at the time of wave transmission, resulting in a larger deviation or distortion in the image. Become. When the switching of the focal lengths, the change of the aperture plane, and the deflection are combined, the steps and distortions of those images overlap. Therefore, especially when a B-mode image in dynamic focus is obtained, when a screen is enlarged using a probe having a high resolution of, for example, 7.5 MHz, a step difference is noticeable at the focus switching point. Therefore, the clock signal of the image display circuit is changed by Δ as described above.
By delaying by t (Δt1, Δt2, ...), the deviation of the image formation time of the received signal is compensated. This delay time Δt is dt1 and dt in FIGS. 4 and 5.
2 and time difference, dt1 and dt2 in FIGS. 6 and 7.
Corresponds to the time difference between the imaging times in FIGS. 8 and 9. Even with dynamic focus,
In FIG. 2, when the focus is changed to the focus F1 as the first focus in a region close to the element and the focus F2 is changed to the focus F2 in the adjacent region as the second focus, Δt1 = 0 of the first focus and Δt2 of the second focus = td1
If -td2 is set, the sampling / A / D conversion timing and the image memory 12 are adjusted in accordance with the difference in the amount of shift in the image formation time between the first focus and the second focus.
Since the advance of the write address can be stopped, the images formed in the memory 12 have no difference in the deviation amount of the image formation time. That is, on the image, the shift amount from F2 to F2 'in FIG. 4 is matched with the shift amount from F1 to F1'. This data Δt is calculated in advance for each focus stage and written in the memory 5 composed of RAM or ROM. The calculation is a CP built into the ultrasonic diagnostic equipment.
You may go in U. It is calculated as the difference of each delay amount with respect to the maximum value of the delay amount of the imaging time. For example, in the case of 32 stages of dynamic focus, the imaging time of the received signal for one echo is set to 32 ways, and the imaging time delay is 32 ways. Therefore, each focus is determined from the maximum value of the delay amount. By subtracting the amount of delay in the first stage,
The delay times Δt1, Δt2, ..., Δt32 for the respective second, ..., 32nd focus stages are obtained. This is stored in the memory 5, and by the counting of the basic clock signal of the counter 6 started by the trigger signal corresponding to the transmission drive pulse, as shown in FIG.
It is determined whether it is a step focus or a second step focus, and the data of Δt1, Δt2, ... Are sequentially read from the memory 5 in accordance with the determination, and Δt1, Δt2, , The clock signals to which the delay times are given are sequentially obtained from the multiplexer 4. Although the delay line 3 and the multiplexer 4 are used to delay the clock signal supplied to the image display circuit, a circuit that stops the clock signal by Δt may be used.

【The invention's effect】

According to the ultrasonic diagnostic apparatus of the present invention, the shift or distortion of the B-mode image at the time of dynamic focus is eliminated. Since the received signal itself is not excessively delayed, it is possible to avoid characteristic deterioration due to the received signal passing through an extra delay line.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are block diagrams showing respective portions of an embodiment of the present invention, FIG. 3 is a time chart for explaining the operation, FIGS. 4 and 6. , FIG. 8 is a schematic diagram showing the relationship between transmission of ultrasonic waves, element arrangement and delay time, and FIGS. 5, 7, and 9 are waveform diagrams. 1 ... Basic clock generation circuit, 2 ... divider circuit, 3 ...
Delay line, 4 ... Multiplexer, 5 ... Memory, 6 ... Counter, 7 ... Probe, 8 ... Transmission delay line, 9, 10 ... Reception delay line, 1
1 ... A / D converter, 12 ... Image memory, 13 ... Address control circuit, 14 ... Read circuit, 15 ... Display device.

Claims (1)

[Claims] 1. A probe having a large number of ultrasonic transducer elements, a delay device for delaying a transmitted signal and a received signal for each element, and a received signal from each element received at the same time, the same point. The echo control unit controls the focus or deflection by adjusting the delay amount of each element so that the received signal which appears the latest is matched with each of the other received signals to form an image. And an image display circuit to which the received signals from the respective elements are combined and sent, and a delay circuit for delaying the clock signal of the image display circuit in accordance with the image formation time. Diagnostic device.