JPH03277357A - Ultrasonic diagnostic device - Google Patents

Abstract

PURPOSE:To almost completely eliminate an external noise without exerting an undesirable influence on other picture elements by eliminating a larger picture element gradation value as a noise, in the case a difference of the picture element gradation values of the same position of two pieces of tomography images obtained at an interval of a prescribed time exceeds a threshold. CONSTITUTION:When a signal from a detecting circuit 14 for detecting a tomography image of a body to be examined is sent to a noise eliminating circuit 16 through an ADC circuit 15, an external noise is eliminated. In such a state, to an output of a selector 23, data ND inputted later timewise is outputted, and to an output of a selector 24, on the contrary, older data OD1 is outputted. An adder 25 adds a threshold outputted from a threshold setting circuit 26 to the data OD1, and outputs it as data OD2. The data ND and OD2 are sent to a comparator 27, compared, and when ND is larger than OD2, an output (SEL) of the comparator 27 becomes a high level H, and at the time of the contrary, it becomes a low level. A data selector 28 selects OD1 and ND, when the SEL is a high level, and when it is an L level, respectively, and outputs them to a frame memory 17, therefore, image data from which an external noise is eliminated is stored in a memory 17.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an ultrasonic measuring device, and particularly to an ultrasonic diagnostic device capable of removing external noise.

[Conventional technology] Ultrasonic waves are transmitted from an ultrasound transducer into the subject, and the echo signals reflected by a reflector inside the subject are received again by the ultrasound transducer and amplified, S-wave, etc. Ultrasonic diagnostic apparatuses are known that display images on a display after processing. In such an ultrasonic measurement device, the better the delivery sensitivity of the ultrasonic transducer, the better the image resolution can be obtained.

However, if the transmission sensitivity of the ultrasonic transducer improves, it will be easier to pick up not only echo signals from inside the subject but also noise from the outside, and even if the performance of the shield is improved, it will not be possible to sufficiently remove noise. is difficult. In particular, when an ultrasonic measuring device is used during surgery, noise from the ultrasonic scalpel or the like may be picked up, making diagnosis difficult.

At present, when using an ultrasonic scalpel or the like, it is extremely difficult to output an ultrasonic image without superimposing extraneous noise.

Furthermore, when using the noise reduction image filters that are currently used, it is extremely difficult to remove extraneous noise without adversely affecting pixels on which extraneous noise is not superimposed. be.

[Problem to be solved by the invention] Among the currently known noise reduction filters,
For example, in averaging processing, not only is it not possible to sufficiently remove extraneous noise that is considered to be a singular point compared to surrounding pixels, but also the edge portions of the image become dull. Also,
With the median filter, most of the extraneous noise can be removed, but the image becomes mosaiced and takes a long processing time, so it requires an expensive SP (digital signal processor) to display it in real time on an ultrasonic diagnostic device. ) must be used. Therefore, the device also becomes complicated.

The present invention eliminates the above-mentioned drawbacks and uses a simple algorithm to produce ultrasound tomographic images that do not adversely affect other pixels and almost completely remove external noise, without changing the size of the device. The purpose of the present invention is to provide an ultrasonic diagnostic device that outputs.

[Means for Solving the Problems] The present invention provides an ultrasonic measuring device that repeatedly scans an ultrasound beam into a subject and displays a tomographic image of the subject using echo signals reflected from the subject. a threshold setting means for setting a threshold for pixel gradation values constituting a tomographic image;
A comparing means detects that the difference in pixel gradation values at the same position of two tomographic images obtained at a predetermined time interval exceeds a threshold, and as a result of the comparison by the comparing means, The present invention is characterized in that it includes a noise removing means that removes the larger pixel gradation value as noise when the difference between pixel gradation values at the same position exceeds a threshold value.

Further, when the threshold value dth is set and one of the two pixel gradation values is dl and the other is dc-1 between pixels at the same position in the two images, dt-, dt, >dth
Or using the inequality d, /, dt-, > dth,
This method is characterized by constructing an image from which extraneous noise components have been removed from two pieces of image data.

Further, the threshold value dth is characterized in that the setting value is changed according to the expected magnitude of external noise, and the method for removing the external noise component is based on dl and dt−
It is characterized by performing averaging with weighting including 0 with +.

[Function] In the ultrasonic diagnostic apparatus of the present invention, if the difference between the pixel gradation value of one pixel and the other pixel in the same position of two images is larger than the threshold value, noise is generated in one of the images. If the difference does not exceed the threshold, output the gradation value data that is considered to be superimposed and that the noise does not weigh heavily, and output the gradation value data as it is. External noise can be easily removed without affecting pixels that are not weighed. The gradation value data that is considered not to have any superimposed noise is obtained by performing weighted averaging between the pixel gradation values at the same position of each pixel.

[Example] Hereinafter, an example of the ultrasonic diagnostic apparatus according to the present invention will be described in detail with reference to the drawings.

First, the principle of removing external noise in the present invention will be explained.

Consider two images that are to be output by an ultrasound diagnostic device. It is assumed that the two images are output at similar times.

For example, let T be the period at which one frame of ultrasound images is updated in real time, one image is output at time t2, and the other image is output at time t + = t z
Assume that the image is output to T. Also, both images are vertical
The width is composed of m x n pixels, the i-th vertical pixel and the J-th horizontal pixel of the image are P and J, the image gradation value output at time t1 is d '' l 1, and the image gradation value output at time t2 is Let the value be d'', .

- When extraneous noise is superimposed on an ultrasonic echo signal, the pixel on which the noise is superimposed has significantly higher luminance than surrounding pixels. This is because while ultrasonic echo signals have specific frequency components, external noise has frequency components unrelated to it, and therefore is very rarely canceled out by interference. In addition, in real-time display ultrasound diagnostic equipment, the time interval between output images is
It takes about a few tenths of a second in terms of projection, and the change in gradation value at the same position pixels is gradual between images where no extraneous noise is superimposed.

Furthermore, there is almost no correlation between the two images in the position where the external noise appears.

Therefore, when considering the value of d ``i d ''+J, when the value is around 0, d ``i J+ d ''
Both i and j are considered normal echo signals, but d", -
If d'' is a large positive value, it is considered that external noise is superimposed on d''. Moreover, if it is a large negative value, it is considered that external noise is heavy on dt l, .

Therefore, in order to remove extraneous noise from the two tomographic images output at time t and +2, consider the inequality d '', -d ''i, > d th, and if this inequality holds, then , external noise is superimposed on the gradation value data d +2 , J of pixels P and J at the time of +2, and if the above inequality does not hold, then external noise is superimposed on d t'', 4. It is thought that there is no.

The output data when the above inequality is satisfied is a dt
2, , +βd tl , J. Note that here a + β: 1.0≦(2<1, 0<β≦1, and α,
β is a weighting coefficient.

The output data when the above inequality is not satisfied is d”□
, is said to be. In this way, external noise can be removed. By applying processing based on such a principle to the entire image area, extraneous noise can be removed without affecting surrounding pixels.

Further, although d''+4 has been described as the tone value of one pixel P, J of one image at time 1+, the above processing is not limited to the pixel tone value of one pixel unit.

In other words, d t+, J is the gradation value of P and J at time t1, and by using the formula (k, 1 are values that indicate the size of the surrounding pixels), it is calculated as the average value with the surrounding pixels. Similar processing is also possible. In addition to the average value, similar processing is also possible by using a median value with respect to surrounding pixels, a mode value, or a value that is a combination of these values. In this case, by increasing the value of 1 in the above equation, the number of operations during processing can be reduced, and high-speed processing becomes possible.

The average value, median value, and mode of pixel gradation values at the same position of multiple pieces of image data that differ in time, or a value that combines these values, or the average value, median value, and mode with surrounding pixels There is also a method of using a value that is a combination of these pixels. by this.

If d″' l J l d t” + J were each calculated from one image, d ”iJ+ d ”++
However, by determining dt l , , from a plurality of images, it becomes possible to remove the extraneous noise more effectively. In the following explanation, for the sake of simplicity, processing will be performed in units of I pixels, and dt l and J will use one image data.

The weighting coefficient is α=0. The principle of the present invention when β=1 is shown in FIGS. 4A to 4F.

Tomographic image at time t in Figure 4A, time t in Figure 4B
Each tomographic image in No. 2 is composed of m×n pixels in length and width. The graph in FIG. 4C showing the image gradation value of the vertical p-th line of the tomographic image in FIG. 4A has Pp+ to Pp+ on the horizontal axis.
Similarly, the graph of FIG. 4D shows the p-th vertical pixel tone value of the tomographic image of FIG. 4B. The graph in FIG. 4E is a graph showing pixel gradation values when extraneous noise is removed by the above processing from the pixel pigs in the graphs in FIGS. 4C and 40.
The output tomographic image in figure F shows the tomographic image that is output when the above processing is performed on all images.

The threshold value dth is used when the graph of FIG. 4E is synthesized from the data of the graphs of FIGS. 4C and 4D. In this case, noise is superimposed on the fourth and fifth pixels from the left in the graph in Figure 4D, and the difference between these two pixels and the pixel gradation value in the graph in Figure 4C exceeds dth. Therefore, for these two pixels, the pixel gradation values in the graph of FIG. 4C are used in the graph of FIG. 4E, and for the other pixels, the data in the graph of FIG. 4B is used.

By performing such processing on all pixels, an image from which noise has been removed can be obtained.

In this case, the rate of noise removal changes depending on what value the threshold value is set to.

If the ISl value is set to a small value, relatively small noise can be removed, but the resolution of the original image will be slightly degraded. Further, if the H value is set to a large value, the resolution of the image is improved compared to the case where the threshold value is set small, but only noise having a relatively high level can be removed. In this way, since the properties of the image obtained change depending on the setting of the threshold value, the ultrasonic diagnostic apparatus of the present invention can set the threshold value of an image that is easy to observe as desired by the operator.

In the above description, the weighting coefficient is set to α=0.8=1, and pixels determined to have superimposed noise are completely removed. However, in this case, since past data (for example, 1 frame I\it) is displayed in the removed pixel, the real-time performance of that pixel is slightly degraded. When the repetition period of the external noise pulse is sufficiently long compared to the frame rate of the ultrasonic diagnostic device, this decrease in real-time performance is hardly perceptible visually.
As the repetition period increases, the J time characteristics of many pixels decreases, resulting in an unnatural image.
In the ultrasonic diagnostic apparatus of the present invention, it is possible to vary the values of α and β according to the operator's wishes or the frequency of extraneous noise. By displaying the weighted sum of the data and the current (t2) data, it is possible to remove noise within a range that does not impair real-time performance.

FIG. 1 shows the configuration of an ultrasonic diagnostic apparatus according to the present invention. This device is a noise removal circuit 1 that removes foreign noise.
5. As shown in the figure, this device
The ultrasonic transducer 11 has an electronic array type ultrasonic transducer 11 connected to the transmitter/receiver circuit I2. A drive signal is sent from the transmitting/receiving circuit 12 to the ultrasound transducer 11, and the ultrasound signal is transmitted from the ultrasound transducer 11 to the subject 10. The transmitted ultrasound signal is reflected by a reflector inside the subject and is received by the ultrasound transducer 11 again. The received ultrasonic signal is converted into an electrical signal and sent to the transmitter/receiver circuit 1.
Sent to 2. A logarithmic amplifier circuit 13 is connected to the transmitter/receiver circuit 12, and the logarithmic amplifier circuit 13 logarithmically amplifies the signal sent from the transmitter/receiver circuit 12. A detection circuit 14 is connected to the logarithmic amplifier circuit 13, and the detection circuit 14 detects a tomographic image of the subject from the signal sent from the logarithmic amplifier circuit 13. The signal from the detection circuit 14 is converted into digital signal data by the ADC circuit 15.

Thereafter, the data from the ADC circuit 15 is sent to the noise removal circuit 16, and external noise is removed according to the above-mentioned algorithm. The data from which external noise has been removed is sent to the frame memory 17 and stored therein, read out in synchronization with the raster sweep of the CRT 19, sent to the DAC circuit 18, converted into an analog signal, and displayed on the CRT 19. Ru.

In the embodiment shown in Fig. 1, the ultrasonic transducer is of an electronic array type, but it is not limited to the electronic array type, and vibrations of ultrasonic diagnostic equipment that perform real-time display such as a mechanical sector type or an electronic convex type are used. External noise can also be removed in the child with a similar configuration.

Next, a detailed description of the first embodiment of the noise removal circuit 16 will be explained in a second embodiment.
As shown in the figure.

In addition, in order to facilitate understanding of the explanation, the weighting coefficients described above are set to α=0. Let β=1.

In the same figure, the data output from the ADC circuit 15 of FIG.
are stored alternately. For example, when the nth frame image is written in the memory 21, the image written in the n-1st frame is stored in the memory 22, and then the n+1th frame image data is written in the memory 22. At this time, the image written in the n-th frame is stored in the memory 21.

These notes' J21 and 22 are dual port RA
Like M, writing and reading are performed in independent cycles, and stored image data is sequentially output pixel by pixel to each output port.

This pixel data is output at the same timing and at the same position (
Since the same address) is accessed, bare pixel data at the same position obtained with a time difference of one frame is output to both output ports. However, the read address is specified in such a way that the pixel data read in each frame cycle is updated (that is, newly written) in that frame cycle. Memo 1/2 of this image data bear
1 side is PE I, and memory 22 flVII is PE 2.

PE l and PE 2 are each data selector 23
and 24. Data selector 23 and 2
4 is a data selector of the same type, but a write enable signal is outputted from a system not shown; the selector 23 receives the write enable signal WEl, and the other 24 receives a signal -E2 which is an inversion of IIE1. be done. When data is written to the memory 1, the selector 23 selects PE 1 and the selector 24 selects PE 2. Conversely, when data is written to the memory 2, the selector 23 selects PE 2 and the selector 24 selects PE 1. Therefore, the output of the selector 23 is the newer one of PE 1 and PE 2, that is, the data that was input later in terms of poetry. Let this data be ND. Conversely, the older data is output as the output of the selector 24. Let this data be 001.

001 is sent to the adder 25, and the adder 25 adds the threshold output from the threshold setting circuit 26 to 00I and outputs the result as data 002. Data ND and 002 are sent to comparator 27 and compared.

As a result of the comparison, if ND is greater than 002, the output fsEL1 of the comparator 27 will be at H (high) level, and if the opposite is true, it will be at L (low) level. The output SEL of the comparator 27 is input to the control terminal of the data selector 28. The outputs ND and 001 of the data selectors 23 and 24 are input to the data input terminal of the data selector 28, and if SEL is at H level, 001 is selected, and conversely, when SEL is at L level, NO is selected and It operates to output to the frame memory 17 shown in FIG. 1 (this output is designated as PEO).

In other words, if the image data being written is greater than the threshold value compared to the data one frame before, the frame memory 17
outputs the data from the previous frame, otherwise outputs the data that has been written. Since the number of pixels on which extraneous noise is superimposed is very small, most of the contents of the frame memory 17 are updated to the latest data every frame, and even the data that is not updated is almost always within one frame. It will be updated later. This is because the probability that external noise will be superimposed on the same pixel between frames is very low. As a result, image data from which extraneous noise has been removed is stored in the frame memory 17 without impairing real-time performance.

Above, a:0. The embodiment has been described in the case of β: 1, but if the weighting coefficient is set to a=0.5.820.5, a circuit as shown in FIG.
This can be achieved by inserting it into the input side of 8. That is, O.D.
1. Assuming that the ND is data consisting of 4 bits, the top 3 bits of each are added by the adder 30, passed through the data selector 31, and then changed to 003 instead of 001, which is manually input to one of the data selectors 28 in FIG. It is connected to the. The data selector 31 selects 003=OD l or 003=0.5ND + by the SEL 2 signal.
Select one of 0.5001. This selection can be made manually by the operator, or automatically when the signal status of the device, for example, the frequency of the SEL signal in Figure 2 being at H (high) level exceeds a certain value.
A possible method is to switch from 0D3 to 0.5ND + 0.5001.

In this embodiment, the frame memory 17 is used for the second section of the image after noise removal, but this frame memory 17 is not necessarily necessary. If this is the case, it is possible to directly display the PEO on the display via a DAC circuit (not shown) without storing it in the frame memory.

In this way, extraneous noise is removed. In the above embodiment, two image memories and two adders were required.
Furthermore, the circuit configuration has been simplified, and both the image memory and adder are integrated into one.
It is also possible to get away with it.

This example is shown in FIG. 3 as a second embodiment.

An input from the ADC circuit 15 shown in FIG. 1 is input to the image memory 101. For example, assume that the image data of the nth line of the tth frame passes through an ADC circuit (not shown) and is stored in the image memo [01. Before starting data writing for the t-th frame, the already stored 1-
] It is assumed that among the image data of the frame, the image data of the l-th line is stored in the line buffer 102.

Now, data for the first line of frame t is sequentially written to the image memory 101 pixel by pixel, and at the same time data for the second line of frame t-1, which has already been stored in the image memory 101, is written to the line buffer 102. Each pixel is written sequentially.

Since the line buffer 102 is of the PIFO (first-in-first-out) format, the oldest written data is output at the same time as writing. This output data is assumed to be 001.

The output of OD1 is performed sequentially from the first pixel of the first line of frame 1-1, and is synchronized with writing to the image memory 101. In other words, the pixel data written to the image memory 101 and the pixel data output from the line buffer 102 are pixels at the same position, and are obtained exactly one frame apart. The pixel data output from the line buffer 102 is added to the threshold value output from the threshold value setting circuit 104 by the adder 103, and the obtained data 002 is sent to one input of the comparator 105. Data ND input to the image memory 101 is sent to the other input of the comparator 105.

Comparator 105 compares ND and 002. NO
When 002 is larger than ND2, the output SEL of the comparator 105 becomes L (low) level, and conversely, when 002 is larger than ND, it becomes H (high) level. The output SEL of the comparator 105 is input to the write enable input (not shown) of the frame memory 17 in FIG. , SEL is H
Frame memory 1 in Figure 1 only when the (high) level is set.
7. That is, in the case of ND where the external noise is not heavy, SEL becomes high level and the contents of the frame memory 17 are updated, and if the external noise is heavy, SEL is at low level and the frame memory 17 is not updated.

If this operation is performed to analyze the number of ultrasonic scanning lines in order from the first line, most of the image for one frame in the frame memory 17 will be updated.

For the reason described in the first embodiment, even pixels that are not updated are updated after one frame in most cases, so that it is possible to display a real-time image with extraneous noise removed.

In this embodiment, a method is used in which writing to the frame memory 17 is controlled by a write enable input, but this part can be replaced by adding a data selector in front of the frame memory 17 as in the embodiment shown in FIG. But it's okay. In that case, one of the data input to the data selector is N
D, the other data input may be set to 001. By doing so, it is also possible to create a configuration in which the frame memory is not included, as described in the embodiment shown in FIG.

In the embodiment described above, data 002 is ODl
+Dth because the output of the ADC circuit 15 is the result of logarithmic transformation of the ultrasonic echo signal.

It is very common to display images by performing logarithmic transformation on ultrasound echo signals, but there are also cases in which logarithmic transformation is performed after being stored in frame memory, and there are also cases in which images are displayed without logarithmic transformation. .

In this case, it is more appropriate to set the data 002 in the form 0DlxDth. In this case, the adders in FIGS. 2 and 3 may be replaced with multipliers.

Furthermore, in the above embodiments, the circuit for removing external noise from digital signals has been described.

Similar external noise removal is possible for analog signals as well.

That is, in the embodiment of FIG.
A DAC circuit is placed immediately after each, and the pig selectors 23, 24, and 28 are connected to analog switches 23, 2, respectively.
4.28 and replacing the adder 25 with an operational amplifier, it becomes possible to easily remove foreign noise from the analog signal. In this case, the output signal from the analog switch 28 is sent to a display device such as a CRT. Processing using analog signals in this manner has the effect of simplifying the circuit configuration compared to processing using digital signals.

As described above, according to the above embodiment, an ultrasound image from which extraneous noise has been removed can be obtained.

[Effects of the Invention] According to the present invention, the ultrasonic diagnostic apparatus can combine one tomographic image from at least two tomographic images obtained at a predetermined time interval and remove the superimposed extraneous noise. . According to the present invention, compared to currently known image filters, images can be easily diagnosed at high speed and with almost no negative effects such as blurring of image edges or pixelation. It is effective in providing the following.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram showing one embodiment of the ultrasonic diagnostic apparatus according to the present invention, and FIGS. 2 and 3 are functional blocks showing first and second embodiments of the noise removal circuit in FIG. Figures 4A to 4F are explanatory diagrams showing the principle of the present invention. FIG. 5 is a diagram showing a circuit example of an additional part when weighting processing is included in the embodiment of FIG. 1. - Explanation of main parts, , noise removal circuit, memory. Data selector, adder, WA value setting circuit, comparator 16. 21.22 23.24.28.31 25.30.103. 26.104. . 27, tOS, .

Claims (1)

[Scope of Claims] 1. In an ultrasonic diagnostic apparatus that repeatedly scans an ultrasound beam into a subject and displays a tomographic image of the subject using echo signals reflected from the subject, the tomographic image is constructed. a threshold value setting means for setting a threshold value for a pixel gradation value to be determined; and detecting that a difference between pixel gradation values at the same position in the two tomographic images obtained at a predetermined time interval exceeds the threshold value. a comparison means; and as a result of the comparison by the comparison means, if the difference between the pixel tone values at the same position in the two tomographic images exceeds the threshold value, removing the larger pixel tone value as noise; An ultrasonic diagnostic apparatus comprising a noise removing means. 2. The device according to claim 1, wherein the comparison means:
The threshold value dth is set using the pixel gradation values at the same position of the two tomographic images, the gradation value obtained later is set as d_t, the gradation value obtained first is set as d_t_-_1, and d_t- d_t_
-_1>dth or d_t/d_t_-_1>dth
If the above condition is satisfied, αd
An ultrasonic diagnostic apparatus characterized in that _t+βd_t_-_1 is the gradation value of the pixel, and if the condition is not satisfied, d_t is displayed as the gradation value of the pixel. 3. The ultrasonic diagnostic apparatus according to claim 2, wherein the threshold value dth is variable. 4. The ultrasonic diagnostic apparatus according to claim 2, wherein the weighting coefficients α and β are variable within the above range. 5. The device according to claim 1, comprising first and second memories that alternately input and store the data for one frame forming an image and output the stored data. , one memory that does not input data outputs data at the same position one frame before the data output by the other memory that inputs data, and new data N output from the first and second memories
first and second selection means for selecting D and old data OD, respectively; threshold addition means for adding a predetermined threshold TH to data OD and outputting the result; comparing the output of the threshold addition means with ND; N
If D-OD>TH, output OD, otherwise N
An ultrasonic diagnostic apparatus comprising: third selection means for outputting D. 6. The apparatus according to claim 1, comprising: a storage means for continuously inputting the data constituting an image and outputting the data with a delay of one frame; and a data OD output from the storage means. A threshold value adding means for adding a predetermined threshold value TH to and outputting the result, and comparing the data OD from the threshold value adding means and the data N input to the storage means, ND
-If OD>TH, output OD, otherwise,
An ultrasonic diagnostic apparatus comprising: a selection means for outputting ND.