JPS631052B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an ultrasonic tomographic diagnostic apparatus in which ghosts are dispersed in a real image by randomizing the scanning timing, scanning order, or both of a plurality of ultrasonic beams scanning the same specimen. In conventional ultrasonic diagnostic apparatuses, when multiple beams scan the same specimen, the beams from the other beams mix in, causing ghosts. To reduce this, different frequencies have been used or beams have been time-divisionally scanned one by one, but the former has problems in that complete frequency separation is not possible and each beam pattern is different. However, the latter has the disadvantage that the number of frames decreases by the value divided by the number of beams. SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic tomographic diagnostic apparatus which eliminates the above-mentioned drawbacks and which disperses ghosts generated between a plurality of ultrasonic beams to obtain apparently high-quality images. In order to achieve the above object, an ultrasonic tomography apparatus of the present invention has a plurality of ultrasonic beam transmission sources and scans the same specimen with the plurality of beams, in which the difference in transmission timing between the plurality of beams is reduced. The present invention is characterized by comprising means for randomly providing the beams, means for randomizing the scanning order of the plurality of beams, or a combination of both. The present invention will be described in detail below with reference to examples. FIG. 1 is a general explanatory diagram of ghosts in ultrasound beam scanning. In the figure, two beams 2 and 2' are simultaneously transmitted radially from ultrasonic beam transmission sources 1 and 1' to
When scanning is performed in the order of #128, the self-reflected wave mainly becomes a real image for the specimen at the intersection point 3 of the beams, and the wrap-around reflected wave from the other beam becomes a ghost. If each frame is scanned with the beam at the same timing and in the same scanning order, a ghost will occur at the same location in each frame. To the human eye, ghosts that appear continuously in the same place cannot be distinguished from a real image, but if the ghosts are discontinuous or appear in different places in each frame, the ghosts are dispersed and become thinner, resulting in a real image. can be clearly distinguished. FIGS. 2a, b, and c and FIGS. 3a and 3b are explanatory diagrams of the principle of the present invention. If the two beams, the main beam 2 and the sub-beam 2', scan at the same timing, a continuous ghost 4 as shown in FIG. 2a, for example, will occur. In contrast, in the present invention, in order to cause ghosts to appear in different locations, a first method randomly changes the scanning timing of the ultrasonic beam, a second method randomly changes the scanning order, and a combination of the two. It is designed to use one of the following methods. First, the first step is to randomly change the scanning timing.
The method is similar to the timing difference △t _n between the main beam B _n and the sub beam B _n scanned in the same frame, that is, in the order of #1 to #128, as shown in Figure 3 a, a, and b. By randomly setting the timing difference △t _n+1 between the main beam B _n+1 and the sub beam B _n+1 , the ghost is made into a discontinuous point ghost 5 as shown in Figure 2b. Can be done. Next, as shown in Fig. 3b, a, and b, the main beam and sub beam B ₁ in the same frame are
The timing difference △t _o between ~B ₁₂₈ is constant, but by randomly changing the timing difference to △t _o and △t _o+1 according to frames #n and #n+1 for each frame, ghosts can be eliminated. As shown in FIG. 2c, a plurality of thin continuous ghosts 6 are generated, but they are distributed in a plurality of areas, so they are not noticeable. Furthermore, by using the two methods shown in Figure 3 a and b in combination, changing the timing difference △t _n in one frame, and randomly changing the corresponding timing difference in the next frame, the ghost can be removed from the second frame.
By making the image discontinuous as shown in Figure b and distributing the locations where ghosts appear differently depending on the frame as shown in Figure c, it is possible to thin the image in a more dispersed manner. The second method of changing the scanning order is to change the scanning order between the main beam frame and sub beam frame.
By selecting (1) in order, (2) random within one frame, and (3) long-period random (random over multiple frames), five types of combinations shown in Table 1 can be obtained. First, the main beam is scanned in order from #1, and the sub-beams are randomly distributed within one frame in one-to-one correspondence with the main beam. An example is shown in Table 2. The appearance of ghosts at this time is almost the same as that shown in FIG. 2b.

【table】

【table】

[Table] Second, the main beam and the sub-beam do not have a one-to-one correspondence, but as shown in Table 3, the sub-beam is randomly selected with a long period that is different from the previous frame. The period at this time may be a plurality of sufficiently long periods. Thirdly, the main beam and sub beams are repeated at random within one frame. Fourth, the main beam is random within one frame.
The sub-beams are long-period random, and the fifth beam is both long-period random. By doing this, the degree of dispersion of the ghost becomes uniform over a wide range, and at the same time it becomes thinner and becomes less noticeable in the real image. Due to the above processing, ghosts from other beams become impulse-like and have a large difference in image quality from the real image, so the image processing circuit can reduce ghosts from other beams. FIG. 4 is an explanatory diagram showing the configuration of an embodiment of the present invention according to the above-described principle. In the same figure, a timing pulse is sent to a main beam scan controller 10 and a sub beam scan controller 11, and in the main beam scan controller 10, a fixed delay circuit 12 is used to send a timing pulse to the address counter 13 from the address #1 to #128.
The addresses are read out and sent to the main beam transmission source with a predetermined delay, respectively, to generate beams in order. On the other hand, the sub-beam scan controller 11 uses the random delay circuit 14 shown in FIG. 5 to output the aforementioned random address within one frame from the random address counter 15 shown in FIG. 6, and further randomly delays the address. It is sent to a sub-beam transmission source and generates a beam with random addresses and delay amounts. In the embodiment, both the address and the delay amount are combined, but only one may be used. FIG. 5 shows a specific circuit example of the random delay circuit 14 shown in FIG. In the figure, a timing pulse is input into a triangular wave generation circuit 21, a rising triangular wave is formed by the timing pulse, and is input to a comparator 24, while a seventh
M (maximum period) sequence noise generator 22 illustrated in the figure
A digital noise output is generated, which is converted to an analog pulse signal by the D/A converter 23 and used as another input of the comparator 24. If a coincidence signal is output, a random delay amount starting from the rising edge of the timing pulse can be created. can be sent to the sub-beam transmission source. As an example is shown in FIG. 7, the M-sequence noise generator 22 inputs the first and final stage outputs of the n-stage shift register 31 via the EOR circuit 32 and outputs a predetermined digit Q _{1 .}
〜Q _o is extracted. The NOR circuit 34 is initially set to all "1's" and is configured so that it does not become all "0" during operation. Figure 6 shows the random address counter 1 in Figure 4.
A specific circuit example of No. 5 is shown below. That is, the clock for each bit is inputted to the main beam address counter 25 as an input, and after being cleared by the clock for each frame, the address is counted.
Set the address corresponding to #128 to 1 of each EOR circuit 26.
The parallel output of the M-sequence noise generator 22 mentioned above is taken out and used as the other input, and each EOR circuit 26
The random output from the subbeam address is sent to the subbeam transmission source as the subbeam address. Since the ghost is dispersed by the method described above and becomes impulsive, it can be made even less noticeable by the averaging image processing circuit shown in FIG. In the figure, 35 is an image memory;
6 to 38 are weighting circuits, and 39 is an adder. As explained above, according to the present invention, ghosts can be dispersed and made almost inconspicuous by randomizing the scanning timing, scanning order, or both of multiple ultrasound beams scanning the same specimen. The real image can be clearly seen.

[Brief explanation of the drawing]

Fig. 1 is a general explanatory diagram of ghosts in ultrasound beam scanning, Figs. 2 a to c, and Figs. 3 a and b are explanatory diagrams of the principle of the present invention, and Fig. 4 is an explanatory diagram showing the configuration of an embodiment of the present invention. 5 to 7 are detailed explanatory views of the embodiment shown in FIG. 4, and FIG. 8 is an explanatory view of main parts of another embodiment. In the figures, 1 and 1' are beam transmission sources, 2 is the main beam, 2' is the sub beam, 3 is the ghost source,
4, 5, 6 are ghosts, 10 is a main beam scan controller, 11 is a sub beam scan controller, 12 is a fixed delay circuit, 13 is an address counter, 14 is a random delay circuit, 15 is a random address counter, 35 is an image memory , 36~
38 is a weighting circuit, and 39 is an adder.

Claims (1)

[Claims] 1. In an ultrasonic tomographic diagnostic apparatus that has a plurality of ultrasound beam transmission sources and scans the same specimen with the plurality of beams, means for randomly setting transmission timing differences between the plurality of beams, or randomizing the scanning order of the plurality of beams. An ultrasonic tomographic diagnostic apparatus characterized by comprising a means or a combination of both.