JP4431341B2 - Spatial filter and ultrasonic diagnostic apparatus - Google Patents

Description

  The present invention relates to a spatial filtering method, a spatial filter, and an ultrasonic diagnostic apparatus, and more particularly, to a method and a spatial filter for performing spatial filtering on a flow image, and an ultrasonic having such a spatial filter. The present invention relates to an ultrasonic diagnostic apparatus.

In the ultrasonic diagnostic apparatus, a flow image relating to blood flow or the like is taken using a Doppler shift of ultrasonic echo (echo). In order to obtain a flow image, the echo reception signal is subjected to MTI (moving target indication) processing and further subjected to autocorrelation calculation (see, for example, Patent Document 1).
JP 2001-128976 A (page 5-6, FIGS. 1 and 7)

  In the flow image, the outline of the peripheral portion tends to be a stepped line (jag), that is, a so-called jagged line. This is due to the performance limitations of the device. The jagged edge can be reduced by spatial filtering, but is accompanied by problems such as a decrease in spatial resolution and contrast or image expansion.

  Therefore, an object of the present invention is to realize a spatial filtering method and a spatial filter that reduce the jaggedness in the peripheral portion of the flow image without adverse effects, and an ultrasonic diagnostic apparatus having such a spatial filter.

  (1) According to one aspect of the invention for solving the above-described problem, a flow image whose pixel value can be either positive or negative depending on the polarity of the flow, the pixel value is set to a positive and negative threshold value. The first group having a value larger than the positive threshold, the second group having a value between the positive and negative thresholds, and the third group having a value smaller than the negative threshold are divided into pixel values of the first group. Is replaced with a weighted average value of the pixel value and the pixel values belonging to the first group and the second group among the pixel values of the peripheral region around the pixel value, and the pixel values of the second group are For each pixel, the pixel value is replaced with a weighted average value of the pixel value of the peripheral region centered on it, and for the third group of pixel values, for each pixel, the pixel value and the peripheral region centered on it Weighted average of pixel values belonging to the second group and the third group Replaced by a spatial filtering method characterized by.

  (2) In another aspect of the invention for solving the above-described problem, a flow image whose pixel value can be either positive or negative depending on the polarity of the flow is assigned a positive and negative threshold value. Classifying means for dividing into a first group having a value greater than a positive threshold, a second group having a value between positive and negative thresholds, and a third group having a value smaller than a negative threshold, based on For the pixel value, for each pixel, the pixel value is replaced with a weighted average value of the pixel values belonging to the first group and the second group among the pixel values of the peripheral region centering on the pixel value, and the pixel values of the second group For each pixel, the pixel value is replaced with a weighted average value of the pixel value of the peripheral region centered on the pixel value, and for the third group of pixel values, the pixel value and the center of the pixel value are set for each pixel. Pixel values belonging to the second group and the third group among the pixel values of the surrounding area It is a spatial filter which is characterized by comprising a correction means for replacing in weighted average value.

  (3) According to another aspect of the invention for solving the above-described problem, a flow image in which a pixel value can be either positive or negative depending on a flow polarity based on an ultrasonic echo irradiated to a target. An ultrasonic diagnostic apparatus comprising: an imaging unit that captures the image; and a spatial filter that processes the flow image, wherein the spatial filter determines pixel values of the flow image based on positive and negative threshold values. Classification means for dividing the first group having a value greater than the positive threshold, the second group having a value between the positive and negative thresholds, and the third group having a value smaller than the negative threshold, and the pixel values of the first group Is replaced with a weighted average value of the pixel value and the pixel values belonging to the first group and the second group among the pixel values of the peripheral region around the pixel value, and the pixel values of the second group are For each pixel, its pixel value and its center It replaces with the weighted average value with the pixel value of the peripheral region, and for the pixel values of the third group, for each pixel, the pixel value and the pixel values of the peripheral region centering on the pixel value are classified into the second group and the third group. An ultrasonic diagnostic apparatus comprising: a correction unit that replaces a weighted average value with a pixel value to which it belongs.

  It is preferable in terms of speeding up the operation that the weighted average value is not replaced when neither the pixel value nor the pixel value in the peripheral region centering on the pixel value belongs to the second group. When the pixel values and the pixel values in the peripheral region around the pixel values all belong to the same group, it is preferable that the replacement by the weighted average value is not performed in terms of speeding up the operation. It is preferable that the pixels and the pixels in the peripheral area centering on the pixels are pixels of a 3 × 3 matrix from the viewpoint of performing appropriate filtering.

  In the present invention, the pixel values of the flow image are determined based on the positive and negative thresholds, the first group having a value larger than the positive threshold, the second group having a value between the positive and negative thresholds, and the negative threshold. Dividing into a third group having a smaller value, for the pixel values of the first group, for each pixel, the pixels belonging to the first group and the second group among the pixel values and the pixel values of the peripheral region centering on the pixel value The second group of pixel values is replaced with the weighted average value of the pixel value and the pixel value of the peripheral area centered on each pixel, and the third group of pixel values. Is replaced with the weighted average value of the pixel value and the pixel values belonging to the second group and the third group among the pixel values of the peripheral region centering on the pixel value for each pixel. Filtering method and sky Filter, and it is possible to realize the ultrasonic diagnostic apparatus having such a spatial filter.

  The best mode for carrying out the invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the best mode for carrying out the invention. FIG. 1 shows a block diagram of the ultrasonic diagnostic apparatus. This apparatus is an example of the best mode for carrying out the invention. An example of the best mode for carrying out the present invention relating to an ultrasonic diagnostic apparatus is shown by the configuration of the present apparatus.

  As shown in FIG. 1, this apparatus has an ultrasonic probe 2 (probe). The ultrasonic probe 2 has an array of a plurality of ultrasonic transducers (not shown). Each ultrasonic transducer is made of a piezoelectric material such as PZT (titanium (Ti) zirconate (Zr) acid) ceramics. The ultrasonic probe 2 is used in contact with an object 4 to be photographed by an operator.

  The ultrasonic probe 2 is connected to the transmission / reception unit 6. The transmission / reception unit 6 sends a drive signal to the ultrasonic probe 2 to transmit ultrasonic waves. The transmission / reception unit 6 also receives an echo signal received by the ultrasonic probe 2.

  A block diagram of the transceiver 6 is shown in FIG. As shown in the figure, the transmission / reception unit 6 includes a transmission timing generation unit (unit) 602. The transmission timing generation unit 602 periodically generates a transmission timing signal and inputs the transmission timing signal to a transmission beamformer 604. The period of the transmission timing signal is controlled by the control unit 18 described later.

  The transmission beamformer 604 performs beamforming of the transmission, and generates a beamforming signal for forming an ultrasonic beam having a predetermined direction based on the transmission timing signal. The beam forming signal is composed of a plurality of drive signals to which time differences corresponding to directions are given. Beam forming is controlled by the control unit 18 described later. The transmission beam former 604 inputs the transmission beam forming signal to the transmission / reception switching unit 606.

  The transmission / reception switching unit 606 inputs a beamforming signal to the ultrasonic transducer array. In the ultrasonic transducer array, a plurality of ultrasonic transducers constituting a transmission aperture each generate an ultrasonic wave having a phase difference corresponding to a time difference of drive signals. An ultrasonic beam along a sound ray in a predetermined direction is formed by the wavefront synthesis of these ultrasonic waves.

  A reception beam former 610 is connected to the transmission / reception switching unit 606. The transmission / reception switching unit 606 inputs a plurality of echo signals received by the reception aperture in the ultrasonic transducer array to the reception beam former 610. The receiving beam former 610 performs received beam forming corresponding to the sound ray of the transmitted wave, adjusts the phase by giving a time difference to a plurality of received echoes, and then adds them to generate sound in a predetermined direction. An echo reception signal along the line is formed. The beam forming of the received wave is controlled by the control unit 18 described later.

  Transmission of the ultrasonic beam is repeated at predetermined time intervals by a transmission timing signal generated by the transmission timing generation unit 602. In accordance with this, the direction of the sound ray is changed by a predetermined amount by the transmission beam former 604 and the reception beam former 610. Thereby, the inside of the object 4 is sequentially scanned by sound rays. The transceiver unit 6 having such a configuration performs scanning as shown in FIG. 3, for example. That is, the fan-shaped two-dimensional region 206 is scanned in the θ direction by the sound ray 202 extending in the z direction from the radiation point 200, and so-called sector scan is performed.

  When the transmission and reception apertures are formed by using a part of the ultrasonic transducer array, the apertures are sequentially moved along the array to perform scanning as shown in FIG. 4, for example. That is, by moving a sound ray 202 emitted from the radiation point 200 in the z direction along a linear locus 204, a rectangular two-dimensional region 206 is scanned in the x direction, and a so-called linear scan is performed. Do.

  When the ultrasonic transducer array is a so-called convex array formed along an arc extending in the ultrasonic wave transmission direction, for example, as shown in FIG. As described above, the so-called convex scan can be performed by moving the radiation point 200 of the sound ray 202 along the arc-shaped locus 204 and scanning the fan-shaped two-dimensional region 206 in the θ direction.

  The transmission / reception unit 6 is connected to a B-mode processing unit 10 and a Doppler processing unit 12. The echo reception signal for each sound ray output from the transmission / reception unit 6 is input to the B-mode processing unit 10 and the Doppler processing unit 12.

  The B-mode processing unit 10 forms a B-mode image. As shown in FIG. 6, the B mode processing unit 10 includes a logarithmic amplification unit 102 and an envelope detection unit 104. The B mode processing unit 10 logarithmically amplifies the echo reception signal by the logarithmic amplification unit 102, envelope detection by the envelope detection unit 104, and a signal representing the echo intensity at each reflection point on the sound ray, that is, an A scope A (scope) signal is obtained, and a B-mode image is formed using the instantaneous amplitude of the A scope signal as a luminance value.

  The Doppler processing unit 12 forms Doppler measurement data. The Doppler measurement data includes speed data, dispersion data, and power data, which will be described later. As shown in FIG. 7, the Doppler processing unit 12 includes a quadrature detection unit 120, an MTI filter (moving target indication filter) 122, an autocorrelation calculation unit 124, an average flow velocity calculation unit 126, a dispersion calculation unit 128, and a power calculation unit. 130 is provided.

  The Doppler processing unit 12 performs quadrature detection of the echo reception signal by the quadrature detection unit 120 and performs MTI processing by the MTI filter 122 to obtain a Doppler shift of the echo signal. Further, the autocorrelation calculation unit 124 performs autocorrelation calculation on the output signal of the MTI filter 122, the average flow velocity calculation unit 126 obtains the average flow velocity V from the autocorrelation calculation result, and the dispersion calculation unit 128 calculates the flow velocity from the autocorrelation calculation result. The variance T is obtained, and the power calculation unit 130 obtains the power PW of the Doppler signal from the autocorrelation calculation result.

  As a result, an echo source moving within the object 4, for example, an average flow velocity V of blood or the like, its dispersion T, and data representing the power PW of the Doppler signal are obtained for each sound ray. These data show the average flow velocity, dispersion and power at each point on the ray. Hereinafter, the average flow velocity is simply referred to as speed. The speed is obtained as a component in the sound ray direction. Further, a direction approaching the ultrasonic probe 2 is distinguished from a direction moving away. The echo source is not limited to blood, and may be, for example, a micro balloon contrast agent injected into a blood vessel or the like. Hereinafter, an example of blood will be described, but the same applies to the case of a microballoon contrast agent.

  The B mode processing unit 10 and the Doppler processing unit 12 are connected to the image processing unit 14. The image processing unit 14 generates a B-mode image and a Doppler image based on data input from the B-mode processing unit 10 and the Doppler processing unit 12, respectively. Hereinafter, the Doppler image is also referred to as a flow image.

  As shown in FIG. 8, the image processing unit 14 includes an input data memory 142, a digital scan converter 144, an image memory 146, and a processor connected by a bus 140. 148.

  The B-mode image and Doppler measurement data input for each sound ray from the B-mode processing unit 10 and the Doppler processing unit 12 are stored in the input data memory 142, respectively. Data in the input data memory 142 is scan-converted by the digital scan converter 144 and stored in the image memory 146. The processor 148 performs predetermined data processing on the data in the input data memory 142 and the image memory 146, respectively. Data processing includes spatial filtering. Spatial filtering will be described later.

  A display unit 16 is connected to the image processing unit 14. The display unit 16 receives an image signal from the image processing unit 14 and displays an image based on the image signal. Note that the display unit 16 is configured by a graphic display or the like that can display a color image.

  A control unit 18 is connected to the transmission / reception unit 6, B-mode processing unit 10, Doppler processing unit 12, image processing unit 14, and display unit 16. The control unit 18 gives control signals to these units to control their operation. Also, various notification signals are input from each part to be controlled. A portion including the ultrasonic probe 2, the transmission / reception unit 6, the Doppler processing unit 12, the image processing unit 14, and the control unit 18 is an example of an imaging unit in the present invention. The processor 148 in the image processing unit 14 is an example of a spatial filter in the present invention.

  Under the control of the control unit 18, the B mode operation and the Doppler mode operation are executed. An operation unit 20 is connected to the control unit 18. The operation unit 20 is operated by an operator and inputs appropriate commands and information to the control unit 18. The operation unit 20 includes, for example, an operation panel including a keyboard, a pointing device, and other operation tools.

  The operation of this apparatus will be described. The operator abuts the ultrasonic probe 2 on a desired portion of the object 4 and operates the operation unit 20 to perform an imaging operation using both the B mode and the Doppler mode, for example. As a result, under the control of the control unit 18, B-mode shooting and Doppler mode shooting are performed in a time-sharing manner. That is, for example, every time the Doppler mode scan is performed a predetermined number of times, the mixed scan of the B mode and the Doppler mode is performed at a rate of performing the B mode scan once.

  In the B mode, the transmission / reception unit 6 scans the inside of the object 4 in the order of sound rays through the ultrasonic probe 2 and receives the echoes one by one. The B-mode processing unit 10 logarithmically amplifies the echo reception signal input from the transmission / reception unit 6 by the logarithmic amplification unit 102, detects the envelope by the envelope detection unit 104, obtains an A scope signal, and based on the A scope signal, A B-mode image is formed. The image processing unit 14 stores the B-mode image for each sound ray input from the B-mode processing unit 10 in the input data memory 142. As a result, a sound ray data space for the B-mode image is formed in the input data memory 142.

  In the Doppler mode, the transmitter / receiver 6 scans the inside of the object 4 in the order of sound rays through the ultrasonic probe 2 and receives the echoes one by one. At that time, ultrasonic waves are transmitted and echoes are received a plurality of times per sound ray.

  The Doppler processing unit 12 performs quadrature detection on the echo reception signal by the quadrature detection unit 120, performs MTI processing by the MTI filter 122, obtains autocorrelation by the autocorrelation calculation unit 124, and calculates the average by the average flow velocity calculation unit 126 from the autocorrelation result. The flow rate is obtained, the dispersion is obtained by the dispersion operation unit 128, and the power is obtained by the power operation unit 130.

  The image processing unit 14 stores the Doppler measurement data for each sound ray and each pixel input from the Doppler processing unit 12 in the input data memory 142. As a result, a sound ray data space for each Doppler measurement data is formed in the input data memory 142.

  The processor 148 scan-converts the B-mode image and Doppler measurement data in the input data memory 142 by the digital scan converter 144 and writes them in the image memory 146. At this time, the Doppler measurement data is written as a color flow mapping (CFM) image and a power Doppler imaging (PDI) image in which dispersion is added to the speed.

  The processor 148 writes the B-mode image, CFM image, and PDI image in separate areas. The B-mode image shows a tomographic image of the body tissue on the sound ray scanning plane. The CFM image is an image showing a two-dimensional distribution such as a blood flow velocity on the sound ray scanning plane. In this image, the display color is varied depending on the direction of blood flow. Further, the brightness of the display color is varied according to the speed. In addition, the purity of the display color is changed by increasing the color mixture ratio of a predetermined color according to the dispersion. Thereby, the magnitude, direction, and dispersion of the speed are displayed with good visibility. The PDI image is an image indicating the presence of blood flow or the like on the sound ray scanning plane. The display color is different from the color used for the CFM image. The brightness of the display color is changed according to the signal intensity. Both the CFM image and the PDI image are flow images.

  When these images are displayed on the display unit 16, for example, a B-mode image and a CFM image are superimposed and displayed. Thereby, a blood flow velocity distribution image with a clear positional relationship with the body tissue can be observed. In addition, the B-mode image and the PDI image are displayed in a superimposed manner. In this case, it is possible to observe a blood vessel running state in which the positional relationship with the body tissue is clear.

  For the flow image, the processor 148 performs spatial filtering to reduce jugging. A functional block diagram of the processor 148 focusing on spatial filtering is shown in FIG. This figure shows the configuration of the spatial filter. An example of the best mode for carrying out the present invention relating to the spatial filter is shown by the configuration of the present filter. An example of the best mode for carrying out the present invention relating to a spatial filtering method is shown by the operation of the present filter.

  As shown in the figure, this filter has a pixel value classification unit 802 and a pixel value correction unit 804. Each unit is part of the function of the processor 148. The pixel value classification unit 802 classifies the pixel values of the input image according to the values. The pixel value correction unit 804 corrects the pixel value of the input image based on the classification result of the pixel value classification unit 802. The method of correction differs for each classification. The corrected image is output as an output image. The pixel value classification unit 802 is an example of classification means in the present invention. The pixel value correction unit 804 is an example of correction means in the present invention.

  A flow chart of the operation of this filter is shown in FIG. As shown in the figure, this filter performs pixel value classification in a stage 901. Pixel value classification is performed by a pixel value classification unit 802. The pixel value classification is for classifying individual pixels in accordance with the pixel value of the input image. Classification criteria are defined by thresholds.

  FIG. 11 shows the threshold and the procedure for pixel value classification based on the threshold. As shown in the figure, the pixel value of the input image takes a value from + Max to -Max. The value of Max is 128, for example. + Max corresponds to the maximum flow velocity in the approaching direction, and −Max corresponds to the maximum flow velocity in the direction of moving away. For such pixel values, two threshold values + TH and -TH are defined. The value of TH is 10, for example. These threshold values are preferably individually variable from the viewpoint of appropriate filtering.

  Pixel values larger than + TH are classified into the first group, those between + TH and -TH are classified into the second group, and those smaller than -TH are classified into the third group. Those matching + TH are classified into the first group or the second group, and those matching -TH are classified into the second group or the third group.

  Next, in stage 903, 905 or 907, pixel value correction according to the group to which the pixel value belongs is performed. Pixel value correction is performed by a pixel value correction unit 804. Stage 903 is correction for the first group, stage 905 is correction for the second group, and stage 907 is correction for the third group.

  The correction for the first group is performed as follows. That is, for example, as shown in FIG. 12, when the coordinates of a pixel to be corrected are (x, y) and the pixel value belongs to the first group, an n × n matrix (matrix) centered on this pixel is used. The pixel values belonging to the first group and the pixel values belonging to the second group are extracted to obtain a weighted average of these pixel values, and the pixel value of the central pixel (x, y) is replaced with this weighted average value.

  In addition, although the value of n is 3, for example, it is not restricted to this. However, the 3 × 3 matrix is preferable in that the spatial filtering is effectively performed with a minimum matrix size (matrix size). Hereinafter, an example of a 3 × 3 matrix will be described, but the same applies to other matrix sizes.

  The correction for the second group is performed as follows. That is, when the coordinates of the pixel to be corrected are (x, y) and the pixel value belongs to the second group, a weighted average of pixel values of an n × n matrix centered on this pixel is obtained, and this weighted average Replace the pixel value of the center pixel (x, y) with the value.

  The correction for the third group is performed as follows. That is, when the coordinates of the pixel to be corrected are (x, y) and the pixel value belongs to the third group, the pixel value belonging to the third group and the second value are determined from the n × n matrix centered on this pixel. Pixel values belonging to the group are extracted to obtain a weighted average of the pixel values, and the pixel value of the center pixel (x, y) is replaced with the weighted average value.

  In this way, when the pixel value of the target pixel belongs to the first group or the third group, only the pixel values belonging to the group to which the target pixel belongs and the adjacent group among the pixel values in the n × n matrix are weighted averages. A pixel value belonging to a group adjacent to one another is not used for calculating a weighted average. Since the pixel values belonging to one adjacent group have the same absolute value and the opposite signs, if they are used in the calculation of the weighted average, they cancel each other and diminish the attribute of the central pixel. Since the group combination does not perform weighted averaging, the attribute of the center pixel does not fade.

  When the pixel value of the target pixel belongs to the second group, the pixels in the n × n matrix are used for calculation of the weighted average value regardless of the group to which the pixel belongs. For this reason, both the pixel values belonging to the first group and the pixel values belonging to the third group may be used for calculating the weighted average value. However, since the pixel value of the central pixel belonging to the second group is close to 0, Even if the pixel values belonging to the first group and the pixel values belonging to the third group cancel each other, the attribute of the central pixel is not greatly affected.

An example of calculating the weighted average value will be described. In the following calculation, it is assumed that the pixel value of the input image is in _{x, y} and the pixel value of the output image is out _{x, y} .

In the case where there is at least one pixel value belonging to the second group in the 3 × 3 matrix centered on in _{x, y} ,
When in _{x, y} > −TH, an average value ave_p of pixels in the 3 × 3 matrix excluding the central pixel (peripheral pixels) whose pixel value is greater than −TH is obtained,
When in _{x, y} <+ TH, an average value ave_m of peripheral pixels having a pixel value smaller than + TH is obtained,
Using these ave_p and ave_m and in _{x, y} , a weighted average value is calculated by the following equation.

Here, k is a weighting factor, for example, a value that can be adjusted from 0 to 19. Thereby, the effect of filtering can be adjusted appropriately.

When the central pixel belongs to the first group, in _{x, y} > −TH, so that the neighboring pixels have a pixel value larger than −TH (pixel values belonging to the first group and pixel values belonging to the second group) ) Average value ave_p is obtained, and this is weighted averaged with the central pixel value in _{x, y} . Accordingly, a correction value for the first group is obtained.

When the central pixel belongs to the third group, in _{x, y} <+ TH, so that the peripheral pixels having pixel values smaller than + TH (pixel values belonging to the second group and pixel values belonging to the third group) An average value ave_m is obtained, and this is weighted and averaged with the center pixel value in _{x, y} . Therefore, a correction value for the third group is obtained.

When the central pixel belongs to the second group, in _{x, y} > −TH and in _{x, y} <+ TH, so that the peripheral pixels have a pixel value larger than −TH (pixel values belonging to the first group) And the average value ave_p of the pixel values belonging to the second group) and the average value ave_m of the pixel values smaller than + TH (the pixel values belonging to the second group and the pixel values belonging to the third group) are obtained as the central pixel value In weighted average with in _{x, y} . Therefore, a correction value for the second group is obtained.

  Since the pixel value of the target pixel is corrected by such a weighted average, it is possible to reduce the jagged edge of the flow image without causing adverse effects such as a decrease in spatial resolution, contrast, or image expansion.

If there is no pixel value belonging to the second group in the 3 × 3 matrix centered on in _{x, y} , the weighted average is not performed, and the pixel value of the input image is directly used as the pixel value of the output image by the following equation. To do.

  The above expression represents skipping spatial filtering. This can speed up filtering. Further, the spatial resolution and contrast of the input image can be maintained as they are.

  In addition to the above case, spatial filtering may be skipped also when the pixel values in the 3 × 3 matrix all belong to the same group. This can further speed up filtering. Further, the spatial resolution and contrast of the input image can be maintained as they are.

The fact that there is no pixel value belonging to the second group in the 3 × 3 matrix centered on in _{x, y} , or that all the pixel values in the 3 × 3 matrix belong to the same group. This means that there is no peripheral edge of the input image in the range, so skipping spatial filtering will not adversely affect juggling.

It is a block diagram of an ultrasonic diagnostic apparatus. It is a block diagram of a transmission / reception part. It is a figure which shows the concept of sound ray scanning. It is a figure which shows the concept of sound ray scanning. It is a figure which shows the concept of sound ray scanning. It is a block diagram of a B mode processing unit. It is a block diagram of a Doppler processing unit. It is a block diagram of an image processing part. It is a block diagram of a spatial filter. It is a flowchart of operation | movement of a spatial filter. It is a figure which shows the classification | category of a pixel. It is a figure which shows a pixel matrix.

Explanation of symbols

2 Ultrasonic probe 4 Imaging target 6 Transmission / reception unit 10 B mode processing unit 12 Doppler processing unit 14 Image processing unit 16 Display unit 18 Control unit 20 Operation unit 802 Pixel value classification unit 804 Pixel value correction unit

Claims (8)

A first group having a value greater than the positive threshold based on the positive and negative thresholds for the flow image whose pixel values can be either positive or negative depending on the polarity of the flow, positive and negative thresholds a second group and classifying means Ru divided into third group having a negative threshold value smaller than that having a value between,
For the pixel values of the first group, each pixel is replaced with a weighted average value of the pixel value and the pixel values belonging to the first group and the second group among the pixel values of the peripheral region around the pixel value,
For the second group of pixel values, for each pixel, replace it with a weighted average value of the pixel value and the pixel value of the peripheral area centered on it,
Correction means for replacing the pixel values of the third group for each pixel with a weighted average value of the pixel values and the pixel values belonging to the second group and the third group among the pixel values of the peripheral region centering on the pixel value ; ,
Space filter, characterized in that it comprises a. The correction means does not perform the replacement by the weighted average value when the pixel value and the pixel value of the peripheral region around the pixel value do not belong to the second group,
Spatial filter according to claim 1, characterized in that. The correction means does not perform the replacement by the weighted average value when the pixel value and the pixel values of the peripheral region around the pixel value all belong to the same group,
Spatial filter according to claim 1, characterized in that. The pixel and the pixel in the peripheral area centering on the pixel are pixels of a 3 × 3 matrix.
Spatial filter according to any one of claims 1 to 3, characterized in that. An imaging unit that captures a flow image in which the pixel value can be either positive or negative depending on the polarity of the flow , based on an ultrasonic echo irradiated to the object ;
A spatial filter for processing the flow image;
An ultrasonic diagnostic apparatus comprising:
The spatial filter is
For the flow image , the pixel values are based on positive and negative thresholds, a first group having a value greater than the positive threshold, a second group having a value between the positive and negative thresholds, and a value less than the negative threshold. Classification means for dividing into a third group having
For the pixel values of the first group, each pixel is replaced with a weighted average value of the pixel values and the pixel values belonging to the first group and the second group among the pixel values of the peripheral area centered on the pixel value, For the pixel value of the group, for each pixel, the pixel value is replaced with a weighted average value of the pixel value of the peripheral region centered on the pixel value. For the pixel value of the third group, the pixel value and Correction means for replacing with a weighted average value of the pixel values belonging to the second group and the third group among the pixel values of the peripheral area centered on it;
An ultrasonic diagnostic apparatus comprising: The correction means does not perform the replacement by the weighted average value when the pixel value and the pixel value of the peripheral region around the pixel value do not belong to the second group,
The ultrasonic diagnostic apparatus according to claim 5. The correction means does not perform the replacement by the weighted average value when the pixel value and the pixel values of the peripheral region around the pixel value all belong to the same group,
The ultrasonic diagnostic apparatus according to claim 5. The pixel and the pixel in the peripheral area centering on the pixel are pixels of a 3 × 3 matrix.
The ultrasonic diagnostic apparatus according to claim 5, wherein the ultrasonic diagnostic apparatus is any one of claims 5 to 7.

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