Ultrasonic image processing apparatus

Abstract

To suppress artifacts generated when a pixel value waves in a depth direction of an ultrasonic image.SOLUTION: An ultrasonic diagnostic apparatus 100 includes an information processing unit 10 constituting an ultrasonic image processing device. The information processing unit 10 executes processing for acquiring spatial frequency distribution data in a depth direction on Doppler image data generated by the transmission and reception of an ultrasonic wave, and processing for executing filter processing based on filter characteristics determined according to the spatial frequency distribution data and characteristics of the transmission ultrasonic wave to the Doppler image data. The information processing unit 10 searches for a spatial frequency corresponding to the maximum value in the distribution shown by the spatial frequency distribution data in a search range determined according to the pulse width of the transmission ultrasonic wave, and obtains the characteristics for suppressing the level of the spatial frequency distribution in the spatial frequency band including the spatial frequency that has been searched for as filter characteristics.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an ultrasonic image processing device, and more particularly to processing of Doppler image data. [Background technology]

[0002] Ultrasound diagnostic devices that measure the blood flow velocity of a subject by Doppler measurement are widely used. Some of these ultrasound diagnostic devices generate image data showing a Doppler image in which an image showing the blood flow velocity by color is superimposed on a B-mode image.

[0003] As shown in the following Patent Document 1, some Doppler measurements involve transmitting ultrasonic waves to the same location multiple times and processing the reflected waves received multiple times. In an ultrasonic diagnostic device, after the previously transmitted ultrasonic waves have traveled back and forth, the next ultrasonic wave is transmitted. Therefore, there is an upper limit to the number of transmissions and receptions per unit time, and there is also an upper limit to the frame rate. Therefore, in order to increase the frame rate, the interval when scanning the transmission beam is made larger than in a process that generates only B-mode image data, and the number of transmission beams per frame is made smaller than in the case of generating only B-mode image data. Furthermore, the resolution of the Doppler image is improved by forming multiple reception beams for one transmission beam and generating image data indicating the blood flow velocity based on multiple reception signals obtained from the multiple reception beams, i.e., signals obtained by parallel reception phasing.

[0004] In addition, the following Patent Document 2 describes, as a technique related to the present invention, a filtering process for spatial frequency distribution about two axes, that is, the depth direction and the azimuth direction, of an ultrasound image. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-87302 A [Patent Document 2] JP 2020-69304 A Summary of the Invention [Problem to be solved by the invention]

[0006] In ultrasound images such as B-mode images and Doppler images generated by parallel receive phasing, pixel values ​​ripple not only in the scanning direction of the transmission beam (the azimuth direction in sector scanning) but also in the depth direction in which the ultrasound is transmitted and received, resulting in spot-like speckles extending in the scanning direction. This can result in stripe patterns extending in the scanning direction appearing as artifacts. These stripe patterns tend to become more noticeable as the scanning interval of the transmission beam becomes larger.

[0007] An object of the present invention is to suppress artifacts caused by rippling of pixel values ​​in the depth direction of an ultrasound image. [Means for solving the problem]

[0008] The ultrasonic image processing device according to the present invention is characterized in that it includes an information processing unit that executes a process of acquiring spatial frequency distribution data in the depth direction for Doppler image data generated by transmitting and receiving ultrasonic waves, and a process of applying a filter process to the Doppler image data based on a filter characteristic determined according to the spatial frequency distribution data and the characteristics of the transmitted ultrasonic waves.

[0009] Preferably, the information processing unit searches for a spatial frequency corresponding to a maximum value in the distribution indicated by the spatial frequency distribution data within a search range determined according to the pulse width of the transmitted ultrasound, and determines, as the filter characteristic, a characteristic that suppresses the level of the distribution indicated by the spatial frequency data in a spatial frequency band including the searched spatial frequency.

[0010] Desirably, the information processing unit changes the filter characteristics when a maximum value of a distribution indicated by the spatial frequency distribution data obtained from the Doppler image data subjected to the filter processing does not satisfy a predetermined condition.

[0011] Desirably, the information processing unit sequentially generates the Doppler image data over time, and applies the same filtering process to a frame of Doppler image data generated later as the filtering process applied to a frame of Doppler image data generated earlier.

[0012] Preferably, when the artifact condition is not satisfied for a frame of Doppler image data generated later, the information processing unit applies the filtering process with the changed filter characteristics to a frame of Doppler image data generated later.

[0013] Desirably, the Doppler image data is obtained by transmitting and receiving ultrasound while scanning an ultrasound transmission beam at a predetermined scanning interval, and the information processing unit applies the filter processing to the Doppler image data when the scanning interval exceeds a predetermined scanning interval threshold.

[0014] Preferably, the scanning interval threshold is determined based on characteristics of the transmitted ultrasonic waves.

[0015] Preferably, the filter characteristic is a characteristic that sets the amount of attenuation in a spatial frequency band corresponding to the width of the blood flow to an attenuation limit value or less.

[0016] Preferably, the information processing section presents at least one of the distribution indicated by the spatial frequency distribution data and the filter characteristics to a user.

[0017] Preferably, a man-machine interface is configured to change the filter characteristics in response to a user's operation. Effect of the Invention

[0018] According to the present invention, it is possible to suppress artifacts caused by pixel values ​​rippling in the depth direction of an ultrasound image. [Brief description of the drawings]

[0019] [Figure 1] 1 is a diagram showing the configuration of an ultrasound diagnostic apparatus according to an embodiment of the present invention. [Diagram 2] 1A and 1B are diagrams illustrating an example of the positional relationship between a transmission beam and multiple reception beams when linear scanning is performed. [Diagram 3] 1A and 1B are diagrams showing an example of the positional relationship between a transmission beam and multiple reception beams when sector scanning is performed; [Figure 4] 1A and 1B are diagrams illustrating a Doppler image and speckles appearing in the Doppler image. [Diagram 5] FIG. 1 is a diagram showing an outline of a spatial frequency distribution. [Figure 6] FIG. 2 is a diagram showing the outline of a transmission pulse transmitted from an ultrasonic probe. [Figure 7] FIG. 2 is a diagram showing a spatial frequency distribution in which a lower limit spatial frequency and an upper limit spatial frequency are indicated. [Figure 8] FIG. 13 is a diagram illustrating a low-pass filter characteristic. [Figure 9] FIG. 13 is a diagram showing band-stop filter characteristics. [Figure 10] FIG. 4 is a diagram showing notch filter characteristics. [Figure 11] 13 is a flowchart of a process for determining unnecessary component suppression filter characteristics and performing a filter process on Doppler image data. [Figure 12] FIG. 13 is a diagram showing a plurality of spatial frequency distributions. [Figure 13] 11A and 11B are diagrams showing the outline of the spatial frequency distribution when a blood vessel image appears in a Doppler image and the characteristics of an unnecessary component suppression filter. [Figure 14] 13 is a flowchart of a process for determining unnecessary component suppression filter characteristics and performing a filter process on Doppler image data. [Figure 15] FIG. 13 is a diagram showing the outline of a spatial frequency distribution obtained for one sample line data in one frame of Doppler image data. [Figure 16] FIG. 13 is a diagram showing an example of an image showing a spatial frequency distribution and an unnecessary component suppression filter characteristic together with a Doppler image. [Figure 17] 13 is a flowchart of a process for determining unnecessary component suppression filter characteristics and performing a filter process on Doppler image data. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An embodiment of the present invention will be described with reference to the drawings. The same components shown in multiple drawings are given the same reference numerals and their description will be omitted. In this specification, when the term "P image data" is used to specify certain image data, the image indicated by the P image data is called a P image.

[0021] 1 shows the configuration of an ultrasonic diagnostic device 100 according to an embodiment of the present invention. The ultrasonic diagnostic device 100 includes an information processing unit 10, a transmitting unit 12, an ultrasonic probe 14, a receiving unit 16, a display unit 18, and an operation unit 20. The information processing unit 10 includes a control unit 40, a memory 44, a B-mode image generating unit 46, a blood flow image generating unit 48, an image processing unit 50, and a filter processing unit 52, and constitutes an ultrasonic image processing device that executes processing related to ultrasonic images.

[0022] The information processing unit 10 may be configured with one or more processors that execute a program to realize the functions of the control unit 40, the B-mode image generating unit 46, the blood flow image generating unit 48, the image processing unit 50, and the filter processing unit 52. The program may be stored in the memory 44.

[0023] The control unit 40 performs overall control over the ultrasound diagnostic apparatus 100. The operation unit 20 includes a keyboard, a mouse, a lever, buttons, etc., and outputs information related to user operations to the control unit 40. When a touch panel is configured on the display screen of the display unit 18, the operation unit 20 may include the touch panel. The control unit 40 may control the ultrasound diagnostic apparatus 100 in response to operations on the operation unit 20.

[0024] An outline of the operation of the ultrasound diagnostic device 100 will be described. The ultrasound diagnostic device 100 transmits ultrasound from the ultrasound probe 14 to the subject 54, and receives the ultrasound reflected by the subject 54 at the ultrasound probe 14. The ultrasound diagnostic device 100 performs each measurement in B mode and Doppler mode. In the B mode operation, the ultrasound diagnostic device 100 generates B mode image data based on the ultrasound reflected by the subject 54, and displays the B mode image on the display unit 18. In the Doppler mode operation, the ultrasound diagnostic device 100 generates Doppler image data of the inside of the subject 54 based on the Doppler shift frequency of the ultrasound received from the subject 54, and displays the Doppler image on the display unit 18. Only one of the B mode operation and the Doppler mode operation may be performed, or measurements in these two modes may be performed in a time-division manner.

[0025] A specific configuration of the ultrasonic diagnostic device 100 and specific processing executed by the ultrasonic diagnostic device 100 will be described. The ultrasonic probe 14 is in contact with the surface of the subject 54. The ultrasonic probe 14 includes a plurality of transducer elements 22. The transmitting unit 12 outputs a transmission signal to each transducer element 22 of the ultrasonic probe 14 under the control of a beam control unit 42 included in the control unit 40. This causes ultrasonic waves to be transmitted from the ultrasonic probe 14. The beam control unit 42 controls the transmitting unit 12 to form a transmission beam in the ultrasonic probe 14 and scan the subject 54 with the transmission beam. That is, the transmitting unit 12 adjusts the delay time or level of each transmission signal under the control of the beam control unit 42, forms a transmission beam in the ultrasonic probe 14, and scans the subject 54 with the transmission beam.

[0026] When the ultrasonic waves reflected in the subject 54 are received by each transducer element 22 of the ultrasonic probe 14, each transducer element 22 outputs an electric signal corresponding to the received ultrasonic waves to the receiving unit 16. The receiving unit 16 performs processing such as amplification, detection, and frequency band limitation on the received signals output from each transducer element 22 according to the control of the beam control unit 42. The receiving unit 16 further performs phasing and addition of the received signals output from each transducer element 22 to generate a phased received signal. As a result, a phased received signal is generated in which the phases of the received signals based on the ultrasonic waves received from a specific direction are adjusted and added so that they are reinforced with each other, and a receiving beam is formed in that specific direction. The receiving unit 16 outputs the phased received signal to the B-mode image generating unit 46 when operating in the B mode, and outputs the phased received signal to the B-mode image generating unit 46 and the blood flow image generating unit 48 when operating in the Doppler mode.

[0027] The operation in B mode will now be described. The B-mode image generator 46 generates B-mode image data based on the phased receive signals obtained for each receive beam direction, and outputs the data to the image processor 50. The B-mode image data based on one scan of the transmit beam and receive beam is one frame of image data, and corresponds to one B-mode image.

[0028] The beam control unit 42, the transmission unit 12, the ultrasonic probe 14, the reception unit 16, and the B-mode image generation unit 46 generate B-mode image data one after another while repeatedly scanning the transmission beam and the reception beam, and output each B-mode image data to the image processing unit 50. The image processing unit 50 generates a video signal for displaying a B-mode image based on the B-mode image data, and outputs it to the display unit 18. The display unit 18 displays the B-mode image based on the video signal.

[0029] Next, the operation in the Doppler mode will be described. In the Doppler mode, the transmitter 12 outputs a transmission signal to each transducer element 22 of the ultrasonic probe 14 N times so that ultrasonic pulses are transmitted N times in one transmission beam direction at a repetition time interval T. The receiver 16 generates N types of phased reception signals corresponding to the N ultrasonic pulses reflected in the subject 54 and received by the ultrasonic probe 14.

[0030] The receiving unit 16 forms multiple M receiving beams in response to one transmission of an ultrasonic pulse. That is, the receiving unit 16 performs parallel receiving phasing on multiple receiving signals output from multiple transducer elements 22 to form M receiving beams. When the transmitting beam is linearly scanned, the receiving unit 16 forms M receiving beams that have the same direction as the transmitting beam and are arranged in parallel. When the transmitting beam is sector scanned, the receiving unit 16 forms M receiving beams that are arranged at equal azimuth intervals. Here, the azimuth angle refers to the angle that defines the direction as seen from the center of the sector scan.

[0031] Figure 2 shows an example of the positional relationship between the transmission beam T0 and the reception beams R0 to R7 when linear scanning is performed. As shown in Figure 2, the transmission beam T0 is formed in the depth direction (positive direction of the r-axis). In this example, eight reception beams R0 to R7 (M=8) are formed at equal intervals, oriented in the negative direction of the r-axis, with the transmission beam T0 at the center at a depth of r=r0.

[0032] Figure 3 shows an example of the positional relationship between the transmit beam T0 and the receive beams R0 to R7 when sector scanning is performed. In Figure 3, the positive r-axis direction is defined as the depth direction, and the θ-axis is defined as the angular direction in which the transmit beam oscillates. Figure 3 shows eight receive beams (M=8) R0 to R7 that are aligned at equal angular intervals and point in the negative r-axis direction, with the transmit beam T0 at the center at a depth of r=r0.

[0033] The receiving unit 16 generates N types of phased receive signals for each of the M receive beams, corresponding to the ultrasonic pulses transmitted N times for one transmit beam, and outputs the N types of phased receive signals for each of the M receive beams to the blood flow image generating unit 48.

[0034] The blood flow image generating unit 48 calculates the blood flow velocity v(r) in the depth direction at each depth r of each of the M receiving beams based on the N types of phased receiving signals generated for each of the M receiving beams, for example, according to the autocorrelation processing shown in Reference 1.

[0035] The blood flow image generating unit 48 generates blood flow image data based on the blood flow velocity v(r) in the depth direction at each depth r of each of the M receiving beams. The blood flow image represented by the blood flow image data is an image that shows a color according to the blood flow velocity v(r) at the position of each depth r on each receiving beam. That is, the blood flow image shows the distribution of the blood flow velocity v(r) in the area where the M receiving beams are arranged by color. In the blood flow image, for example, blue is added to the area where blood flows in the direction away from the ultrasonic probe 14, and red is added to the area where blood flows in the direction toward the ultrasonic probe 14, and the brightness is increased as the blood flow velocity increases. The blood flow image generating unit 48 outputs the blood flow image data to the image processing unit 50.

[0036] The image processing unit 50 generates Doppler image data based on the B-mode image data and the blood flow image data. The Doppler image data indicates a Doppler image in which a B-mode image and a blood flow image are superimposed. The image processing unit 50 generates a video signal for displaying the Doppler image based on the Doppler image data, and outputs the video signal to the display unit 18. The display unit 18 displays the Doppler image based on the video signal.

[0037] In a Doppler image represented by Doppler image data generated by parallel receive phasing, pixel values ​​may ripple not only in the scanning direction of the transmission beam but also in the depth direction, resulting in spot-like speckles extending in the scanning direction. Here, the scanning direction is the direction perpendicular to the transmission beam in linear scanning, and the azimuth direction in sector scanning. The occurrence of such speckles may result in stripe patterns extending in the scanning direction appearing as artifacts. These stripe-like artifacts tend to become more noticeable as the scanning interval increases.

[0038] 4 shows a Doppler image 30 obtained by sector scanning and a speckle 56 appearing in the Doppler image 30. As shown in FIG. 4, a stripe pattern extending in the scanning direction appears as an artifact due to gaps 58 between multiple speckles 56 extending in the scanning direction (azimuth angle direction). The larger the scanning interval, the more obvious the shape of one speckle 56 extending in the scanning direction becomes, and the more prominent the stripe pattern becomes.

[0039] Therefore, in the ultrasound diagnostic device 100 according to this embodiment, the filter processing unit 52 determines filter characteristics for suppressing stripe artifacts based on the Doppler image data. The filter processing unit 52 performs filter processing based on the filter characteristics on the Doppler image data to generate filtered Doppler image data. The image processing unit 50 causes the display unit 18 to display the filtered Doppler image. The specific processing will be described below.

[0040] The image processing unit 50 outputs the Doppler image data to a filter processing unit 52. The filter processing unit 52 extracts depth direction line data representing each pixel value of a plurality of pixels arranged in the depth direction for each of a plurality of azimuth angle directions from the Doppler image data. In Fig. 4, one set of depth direction line data 32 and pixels 34 arranged in the depth direction are conceptually shown on the Doppler image 30.

[0041] The filter processing unit 52 selects one set of the depth direction line data 32 generated for each of the azimuth directions as sample line data. One set of sample line data corresponds to one set of depth direction line data 32 corresponding to one azimuth direction. The filter processing unit 52 performs a spatial Fourier transform on the sample line data to obtain spatial frequency distribution data.

[0042] Fig. 5 shows the outline of the distribution (spatial frequency distribution) indicated by the spatial frequency distribution data obtained for the sample line data. The horizontal axis indicates the spatial frequency, and the vertical axis indicates the level of the spatial frequency component (spatial frequency component level). The speckle spatial frequency fs shown in Fig. 5 corresponds to the maximum value that appears based on the speckle. Also, the speckle spatial frequency band Bs is the spatial frequency band occupied by the speckle.

[0043] The filter processing unit 52 searches for a speckle spatial frequency fs corresponding to a maximum value in the spatial frequency distribution of the sample line data, and defines a speckle spatial frequency band Bs including the speckle spatial frequency fs. The filter processing unit 52 further applies filter processing to the Doppler image data to suppress the spatial frequency components of the speckle spatial frequency band Bs. In detail, the filter processing unit 52 applies filter processing to a plurality of sets of depth direction line data 32 corresponding to a plurality of azimuth directions over the entire area of ​​the Doppler image to suppress the spatial frequency components of the speckle spatial frequency band Bs. In this way, the filter processing unit 52 generates filtered Doppler image data and outputs it to the image processing unit 50. The filtered Doppler image data is composed of a plurality of sets of filtered depth direction line data obtained by applying filter processing to a plurality of sets of depth direction line data 32 corresponding to a plurality of azimuth directions over the entire area of ​​the Doppler image.

[0044] The process of searching for the speckle spatial frequency fs, defining the speckle spatial frequency band Bs, and obtaining the filter characteristics will be described. FIG. 6 shows a schematic diagram of a transmission pulse 60 transmitted from the transducer 22 to generate Doppler image data. The horizontal axis shows time, and the vertical axis shows sound pressure. FIG. 6 shows a pulse width σ as one feature value indicating the characteristics of the transmitted ultrasonic wave. The pulse width σ is defined as, for example, the time length during which the sound pressure becomes half the maximum value for the envelope 62 of the transmission pulse 60. The average value Sr [mm] of the width in the depth direction of the speckle 56 shown in FIG. 4 is approximately expressed as (Equation 1) using the pulse width σ [sec] of the transmission pulse and the sound speed c [mm / sec] in the subject 54.

[0045] (Equation 1) Sr=2.51×σ×c

[0046] It is known that the speckle spatial frequency fs is close to a reference spatial frequency fs0 obtained by multiplying the inverse of Sr by the sound speed c, as shown in (Equation 2).

[0047] (Equation 2) fs0=c×1 / Sr=1 / (2.51σ)

[0048] The filter processing unit 52 acquires a spatial frequency component level corresponding to a spatial frequency while sequentially increasing the spatial frequency from the reference spatial frequency fs0 by an increment width δ within a search range including the reference spatial frequency fs0 (within a spatial frequency band determined according to the pulse width of the transmitted ultrasonic wave). The filter processing unit 52 also acquires a spatial frequency component level corresponding to a spatial frequency while sequentially decreasing the spatial frequency from the reference spatial frequency fs0 by an increment width δ. The filter processing unit 52 determines the spatial frequency at which the spatial frequency component level is maximum as the speckle spatial frequency fs.

[0049] 7, the filter processing unit 52 determines a spatial frequency that is higher than the speckle spatial frequency fs by a predetermined upper frequency width Δb as an upper limit spatial frequency fb of the speckle spatial frequency band Bs. Also, the filter processing unit 52 determines a spatial frequency that is lower than the speckle spatial frequency fs by a predetermined lower limit frequency width Δa as a lower limit spatial frequency fa of the speckle spatial frequency band Bs.

[0050] The filter processing unit 52 configures a band suppression filter having a suppression bandwidth of a speckle spatial frequency band Bs that is equal to or greater than a lower limit spatial frequency fa and equal to or less than an upper limit spatial frequency fb. The band suppression filter has, for example, an unnecessary component suppression filter characteristic that suppresses the level by 6 dB or more in a frequency band that is equal to or greater than a lower limit spatial frequency fa and equal to or less than an upper limit spatial frequency fb. The unnecessary component suppression filter characteristic may be a characteristic that attenuates the level at the speckle spatial frequency fs by 6 dB or more, preferably by 20 dB or more.

[0051] Fig. 8 shows low-pass filter characteristics as an example of unnecessary component suppression filter characteristics. With the attenuation amount at a spatial frequency of 0 being 0 dB, an attenuation amount of 6 dB or more is realized in the frequency band equal to or higher than the cutoff spatial frequency fc. The cutoff spatial frequency fc is set to a spatial frequency lower than the lower limit spatial frequency fa. Note that the attenuation amount is a decibel scale value that increases in the positive direction as the attenuation increases.

[0052] 9 shows band-stop filter characteristics as an example of unnecessary component suppression filter characteristics. When the spatial frequency is 0 and when it is infinity, the attenuation is 0 dB, and an attenuation of 6 dB or more is realized in the spatial frequency band from the low cutoff spatial frequency fc1 to the high cutoff spatial frequency fc2. For example, the low cutoff spatial frequency fc1 is set to the lower limit spatial frequency fa, and the high cutoff spatial frequency fc2 is set to the upper limit spatial frequency fb.

[0053] FIG. 10 shows a notch filter characteristic as an example of an unnecessary component suppression filter characteristic. The notch filter characteristic is a special type of band-stop filter characteristic. In the notch filter characteristic, a notch in which the amount of attenuation is theoretically infinite appears in the attenuation band. For example, the low cutoff spatial frequency fc1 is set to the lower limit spatial frequency fa, and the high cutoff spatial frequency fc2 is set to the upper limit spatial frequency fb.

[0054] The filter processing unit 52 performs filtering based on the unnecessary component suppression filter characteristics on each of the multiple sets of depth direction line data 32 corresponding to multiple azimuth directions over the entire area of ​​the Doppler image, and generates multiple sets of filtered depth direction line data corresponding to multiple azimuth directions over the entire area of ​​the Doppler image. The filter processing unit 52 configures filtered Doppler image data based on the multiple sets of filtered depth direction line data, and outputs the data to the image processing unit 50. The image processing unit 50 generates a video signal for displaying the filtered Doppler image, and outputs the video signal to the display unit 18. The display unit 18 displays the filtered Doppler image based on the video signal.

[0055] FIG. 11 shows a flowchart of a process of determining the unnecessary component suppression filter characteristic and performing a filter process on the Doppler image data. In FIG. 11, the term "unnecessary component suppression filter characteristic" is simplified to "filter characteristic". The B-mode image generating unit 46 and the blood flow image generating unit 48 generate B-mode image data and blood flow image data, respectively (S101). The image processing unit 50 generates Doppler image data based on the B-mode image data and blood flow image data (S102). The filter processing unit 52 extracts sample line data from the Doppler image data (S103), and performs a spatial Fourier transform on the sample line data to obtain a spatial frequency distribution (S104). The filter processing unit 52 calculates a reference spatial frequency fs0 based on the pulse width σ of the transmission pulse according to (Equation 2) (S105). The filter processing unit 52 uses the reference spatial frequency fs0 to search for the speckle spatial frequency fs to determine the unnecessary component suppression filter characteristic (S106). The filter processing unit 52 performs filtering on the Doppler image data based on the determined unnecessary component suppression filter characteristics, and generates filtered Doppler image data (S107).

[0056] According to this process, a reference spatial frequency fs0 is obtained as a characteristic of the transmitted ultrasonic wave based on the pulse width σ of the transmitted pulse according to (Equation 2). Then, a speckle spatial frequency fs at which the level in the spatial frequency distribution is maximized is searched for on the high-frequency side and the low-frequency side of the reference spatial frequency fs0. Furthermore, a spatial frequency higher than the speckle spatial frequency fs by a predetermined upper frequency width Δb is determined as an upper spatial frequency fb, and a spatial frequency lower than the speckle spatial frequency fs by a predetermined lower frequency width Δa is determined as a lower spatial frequency fa, and the unnecessary component suppression filter characteristics in the filter processing unit 52 are determined. This allows the process of determining the unnecessary component suppression filter characteristics for suppressing stripe artifacts to be performed quickly.

[0057] In the above process, the filter processing unit 52 determines a spatial frequency higher than the speckle spatial frequency fs by a predetermined upper frequency width Δb as the upper limit spatial frequency fb, and determines a spatial frequency lower than the speckle spatial frequency fs by a predetermined lower limit frequency width Δa as the lower limit spatial frequency fa. Instead of the process of determining spatial frequencies that are a certain value away from the speckle spatial frequency fs as the upper limit spatial frequency fb and the lower limit spatial frequency fa in this manner, the following process may be executed.

[0058] That is, the filter processing unit 52 may determine, as the lower limit spatial frequency fa, a spatial frequency on the low side at which the level of the spatial frequency distribution drops by a predetermined ratio, based on the maximum value in the speckle spatial frequency fs of the spatial frequency distribution. The filter processing unit 52 may also determine, as the upper limit spatial frequency fb, a spatial frequency on the high side at which the level of the spatial frequency distribution drops by a predetermined ratio. The filter processing unit 52 may execute a process of adaptively determining the lower limit spatial frequency fa and the upper limit spatial frequency fb, as described next.

[0059] The filter processing unit 52 selects multiple K sets of the depth direction line data 32 generated for multiple azimuth angle directions as K sets of sample line data. The filter processing unit 52 performs spatial Fourier transform on each of the K sets of sample line data to obtain K spatial frequency distributions. The filter processing unit 52 searches for a speckle spatial frequency fs for each of the K spatial frequency distributions by a process similar to the process based on one set of sample line data. The filter processing unit 52 obtains the minimum of the K speckle spatial frequencies fs obtained from the K spatial frequency distributions as a lower limit spatial frequency fa and the maximum of the K speckle spatial frequencies fs as an upper limit spatial frequency fb.

[0060] 12 shows a spatial frequency distribution 70 in which the minimum speckle spatial frequency fs1 is obtained, a spatial frequency distribution 72 in which the maximum speckle spatial frequency fs2 is obtained, and a spatial frequency distribution 74 in which a speckle spatial frequency fs3 between the speckle spatial frequencies fs1 and fs2 is obtained. Filter processing unit 52 sets the unnecessary component suppression filter characteristics in filter processing unit 52 by setting the minimum speckle spatial frequency fs1 as the lower limit spatial frequency fa and the maximum speckle spatial frequency fs2 as the upper limit spatial frequency fb.

[0061] The filter processing unit 52 may obtain one spatial frequency distribution by obtaining statistics such as the average, median, maximum, and minimum values ​​of K spatial frequency component levels at each spatial frequency from K spatial frequency distributions obtained from K sets of sample line data. The filter processing unit 52 may execute the same processing as the processing based on the one set of sample line data for one spatial frequency distribution obtained from the K spatial frequency distributions. That is, the filter processing unit 52 may search for a speckle spatial frequency fs for one spatial frequency distribution obtained from the K spatial frequency distributions, and obtain a lower limit spatial frequency fa and an upper limit spatial frequency fb.

[0062] Images of blood vessels may appear in the Doppler image. In this case, the blood vessels may be difficult to see in the filtered Doppler image in which stripe artifacts are suppressed. Therefore, the filter processing unit 52 may execute a process of limiting the amount of attenuation in a spatial frequency band corresponding to the width of the blood flow.

[0063] The upper part of Fig. 13 shows an outline of the spatial frequency distribution when a blood vessel image appears in the Doppler image. In this spatial frequency distribution, a maximum value appears not only at the speckle spatial frequency fs but also at the blood flow width spatial frequency fsB corresponding to the blood flow width. The control unit 40 reads the blood flow width spatial frequency fsB and the spatial frequency band BLD including the blood flow width spatial frequency fsB by the user's operation of the operation unit 20. The blood flow width spatial frequency fsB and the spatial frequency band BLD may be stored in the memory 44 in advance and read by the control unit 40. The filter processing unit 52 determines the unnecessary component suppression filter characteristics under the control of the control unit 40 so that the attenuation amount is equal to or less than a predetermined attenuation amount limit value Lim in the spatial frequency band BLD including the blood flow width spatial frequency fsB.

[0064] 13 shows an example of an unnecessary component suppression filter characteristic 66 in which the amount of attenuation is not limited in the spatial frequency band BLD, and an unnecessary component suppression filter characteristic 68 in which the amount of attenuation is limited in the spatial frequency band BLD. When the filter processing unit 52 applies filtering to the Doppler image data using the unnecessary component suppression filter characteristic 68, stripe artifacts that appear in the Doppler image after filtering are suppressed, and blood vessels and blood flow are clearly shown.

[0065] FIG. 14 shows a flowchart of a process of determining the unnecessary component suppression filter characteristic and performing a filter process on the Doppler image data. This flowchart is different from the flowchart shown in FIG. 11 in that step S201 is added between steps S106 and S107. In this figure, the term "unnecessary component suppression filter characteristic" is simplified to "filter characteristic". The filter processing unit 52 searches for the speckle spatial frequency fs using the reference spatial frequency fs0 to determine the unnecessary component suppression filter characteristic (S106), and then changes the unnecessary component suppression filter characteristic so that the attenuation in the spatial frequency band BLD is equal to or less than the attenuation limit value Lim (S201). The filter processing unit 52 performs a filter process on the Doppler image data based on the unnecessary component suppression filter characteristic changed in step S201, and generates filtered Doppler image data (S107).

[0066] In the ultrasound diagnostic device 100, the B-mode image generating unit 46 sequentially outputs B-mode image data to the image processing unit 50 over time, and the blood flow image generating unit 48 sequentially outputs blood flow image data to the image processing unit 50 over time. The image processing unit 50 sequentially generates Doppler image data over time and outputs it to the filter processing unit 52. The filter processing unit 52 performs filter processing on each of the Doppler image data sequentially output from the image processing unit 50 over time, and sequentially outputs the filtered Doppler image data to the image processing unit 50 over time.

[0067] The filter processing unit 52 may perform a filter process (hereinafter referred to as an adaptive filter process) in which the filter characteristics change adaptively according to the filtered Doppler image data generated in the past, on the Doppler image data sequentially output from the image processing unit 50. The filter processing unit 52 may further sequentially output the filtered Doppler image data to the image processing unit 50 over time.

[0068] Here, the adaptive filter processing will be described. The adaptive filter processing repeats a process of changing filter characteristics when the maximum value of the distribution indicated by the spatial frequency distribution data obtained from the Doppler image data after the filter processing does not satisfy a predetermined condition. Here, the predetermined condition is a condition for suppressing stripe artifacts.

[0069] FIG. 15 shows a schematic of the spatial frequency distribution obtained for one sample line data in the Doppler image data after the filter processing of a certain frame. The level of the component with a spatial frequency of 0 is normalized to 1, and the maximum value at the speckle spatial frequency fs is A. When the target value of the level at the speckle spatial frequency fs is R and R < A holds, the filter processing unit 52 adjusts and changes the unnecessary component suppression filter characteristics so that the attenuation amount at the speckle spatial frequency fs becomes 20 log(A / R) [dB] or more. However, log is a logarithmic function with base 10, and the attenuation amount is a value that increases in the positive direction as the attenuation becomes larger.

[0070] The filter processing unit 52 performs filter processing based on the unnecessary component suppression filter characteristics changed based on the previous Doppler image data on the Doppler image data of one frame output next from the image processing unit 50, and outputs the Doppler image data after the filter processing to the image processing unit 50. When R < A holds again in the spatial frequency distribution obtained for one sample line data in the Doppler image data after the filter processing of one frame output to the image processing unit 50, the filter processing unit 52 changes the unnecessary component suppression filter characteristics so that the attenuation amount at the speckle spatial frequency fs becomes 20 log(A / R) or more.

[0071] In this way, the filter processing unit 52 sets the unnecessary component suppression filter characteristics based on the previous data among the filtered Doppler image data that are sequentially generated over time, and performs filter processing on the Doppler image data of the next frame based on the determined filter characteristics. By the filter processing unit 52 sequentially performing such processing on the Doppler image data that are sequentially generated over time, the unnecessary component suppression filter characteristics converge to ideal characteristics.

[0072] From another perspective, the filter processing unit 52 executes the following process. That is, the filter processing unit 52 performs the same filter processing as that performed on the previously generated one frame of Doppler image data on the Doppler image data of one frame to be generated later. When the condition regarding artifacts is not satisfied for the Doppler image data of the later generated one frame, the filter processing unit 52 performs filter processing with changed filter characteristics on the Doppler image data of the further later generated frame. The condition regarding artifacts is, for example, a condition that A≦R is satisfied for the maximum value A and the target value R at the speckle spatial frequency fs for the spatial frequency distribution obtained for one sample line data.

[0073] Whether or not to perform filtering on the Doppler image data may be determined according to the scanning interval. For example, filtering may be performed when the scanning interval in the azimuth angle direction exceeds a predetermined threshold. When the scanning interval exceeds a predetermined scanning interval threshold, the control unit 40 causes the image processing unit 50 and the filtering unit 52 to perform filtering. On the other hand, when the scanning interval is equal to or less than the scanning interval threshold, the control unit 40 does not cause the image processing unit 50 and the filtering unit 52 to perform filtering on the Doppler image data, and causes the display unit 18 to display a Doppler image based on the Doppler image data that has not been subjected to filtering.

[0074] The scanning interval threshold may be determined based on the theoretical value of the size of the speckle 56 in the scanning direction. The average width Sθ [mm] of the speckle 56 in the scanning direction is approximately expressed as (Equation 3). Here, λ is the wavelength [mm] of the ultrasonic wave, z is the measurement depth [mm], and D is the aperture width [mm]. The aperture width D is the length over which the multiple transducer elements 22 of the ultrasonic probe 14 are arranged on the surface scanned by the ultrasonic beam.

[0075] (Equation 3) Sθ=0.9λz / D

[0076] When the width of the speckle 56 in the scanning direction is expressed by an azimuth angle, the scanning interval threshold θt [rad] may be obtained according to Equation 4.

[0077] (Math. 4) θt≒arctan(Sθ / z)=arctan(0.9λ / D)

[0078] In the ultrasound diagnostic device 100, a man-machine interface may be configured that changes the unnecessary component suppression filter characteristics in response to a user's operation. The man-machine interface may be configured by the image processing unit 50, the display unit 18, and the operation unit 20. That is, the unnecessary component suppression filter characteristics may be set based on the operation of the operation unit 20 by the user referring to the display unit 18. For example, the control unit 40 may read the speckle spatial frequency fs, the lower limit spatial frequency fa, the upper limit spatial frequency fb, the attenuation in the speckle spatial frequency band, the blood flow width spatial frequency fsB, the attenuation in the spatial frequency band BLD including the blood flow width spatial frequency fsB, and the like in response to the operation of the operation unit 20. In this case, the image processing unit 50 may display at least one of the spatial frequency distribution and the unnecessary component suppression filter characteristics obtained for the sample line data on the display unit 18 and present it to the user. The unnecessary component suppression filter characteristics may be represented by a graph with the horizontal axis representing the spatial frequency and the vertical axis representing the attenuation, the phase rotation, and the like.

[0079] 16 shows an example of an image indicating a spatial frequency distribution 80 and an unnecessary component suppression filter characteristic 82 together with a Doppler image 30. Note that the image processing unit 50 may display the actually applied unnecessary band suppression filter characteristic, the type of filter (low-pass filter, band-stop filter, notch filter, etc.) and the like on the display unit 18 using text information or the like.

[0080] The graphical user interface displayed on the display unit 18 when the unnecessary component suppression filter characteristics are set may include, for example, buttons or icons displaying "none," "weak," "medium," "strong," etc. Also, the image processing unit 50 may display on the display unit 18 a graphical user interface for setting the unnecessary component suppression filter characteristics via the operation unit 20.

[0081] FIG. 17 shows a flowchart of a process of determining the unnecessary component suppression filter characteristics and performing a filter process on the Doppler image data. This flowchart is different from the flowchart shown in FIG. 11 in that steps S301 and S302 are added between steps S106 and S107. In addition, the term "unnecessary component suppression filter characteristics" is changed to "filter characteristics" for simplified expression. The filter processing unit 52 searches for the speckle spatial frequency fs using the reference spatial frequency fs0 to determine the unnecessary component suppression filter characteristics (S106), and then reads information for setting the unnecessary component suppression filter characteristics from the operation unit 20 (S301). The filter processing unit 52 changes the unnecessary component suppression filter characteristics based on the information read from the operation unit 20 (S302). The filter processing unit 52 performs a filter process on the Doppler image data based on the unnecessary component suppression filter characteristics changed in step S302, and generates filtered Doppler image data (S107).

[0082] [Configuration of the present invention] Configuration 1: A process of acquiring spatial frequency distribution data in a depth direction for Doppler image data generated by transmitting and receiving ultrasonic waves; and performing a process of filtering the Doppler image data based on a filter characteristic determined according to the spatial frequency distribution data and characteristics of the transmitted ultrasound. Configuration 2: The ultrasonic image processing device according to configuration 1, The information processing unit includes: The ultrasonic image processing device searches for a spatial frequency corresponding to a maximum value in the distribution indicated by the spatial frequency distribution data within a search range determined according to a pulse width of the transmitted ultrasonic wave, and obtains, as the filter characteristic, a characteristic that suppresses the level of the distribution indicated by the spatial frequency distribution data in a spatial frequency band including the searched spatial frequency. Configuration 3: The ultrasonic image processing device according to configuration 2, The information processing unit includes: an ultrasonic image processing device which changes the filter characteristics when a maximum value of a distribution indicated by the spatial frequency distribution data obtained from the Doppler image data subjected to the filtering does not satisfy a predetermined condition. Configuration 4: The ultrasonic image processing device according to any one of configurations 1 to 3, The information processing unit includes: generating the Doppler image data sequentially over time; 13. An ultrasonic image processing device comprising: a filter processing section for performing, on a frame of Doppler image data that is generated later, the same filter processing as that performed on a frame of Doppler image data that is generated earlier. Configuration 5: The ultrasonic image processing device according to configuration 4, The information processing unit includes: and performing the filtering process with the filter characteristics changed on the Doppler image data of one frame generated later when the artifact condition is not satisfied for the Doppler image data of one frame generated later. Configuration 6: The ultrasound image processing according to any one of configurations 1 to 5, The Doppler image data is The ultrasonic wave is transmitted and received while scanning a transmission beam of the ultrasonic wave at a predetermined scanning interval, The information processing unit includes: 2. An ultrasonic image processing apparatus comprising: a processor for processing the Doppler image data by the filtering process when the scanning interval exceeds a predetermined scanning interval threshold value. Configuration 7: 7. The ultrasonic image processing device according to claim 6, The ultrasonic image processing apparatus according to claim 1, wherein the scanning interval threshold is determined based on characteristics of the transmitted ultrasonic waves. Configuration 8: The ultrasonic image processing device according to any one of configurations 1 to 7, The filter characteristics are An ultrasonic image processing apparatus characterized in that it has a characteristic of making an attenuation amount in a spatial frequency band corresponding to a blood flow width equal to or less than an attenuation amount limit value. Configuration 9: The ultrasonic image processing device according to any one of configurations 1 to 8, The information processing unit includes: 2. An ultrasonic image processing apparatus comprising: a display unit that displays at least one of the distribution indicated by the spatial frequency distribution data and the filter characteristics to a user; Configuration 10: 10. The ultrasonic image processing device according to claim 9, An ultrasonic image processing device comprising a man-machine interface configured to change the filter characteristics in response to a user's operation. [Explanation of symbols]

[0083] 10 information processing unit (ultrasound image processing device), 12 transmission unit, 14 ultrasound probe, 16 reception unit, 18 display unit, 20 operation unit, 22 vibration element, 30 Doppler image, 32 sample line data, 34 pixel, 40 control unit, 42 beam control unit, 44 memory, 46 B-mode image generation unit, 48 blood flow image generation unit, 50 image processing unit, 52 filter processing unit, 54 subject, 56 speckle, 58 gap, 60 transmission pulse, 62 envelope, 70, 72, 74, 80 spatial frequency distribution, 82 unnecessary component suppression filter characteristics, 100 ultrasound diagnostic device.

Claims

1. A process of acquiring spatial frequency distribution data in a depth direction for Doppler image data generated by transmitting and receiving ultrasonic waves; and performing a process of filtering the Doppler image data based on a filter characteristic determined according to the spatial frequency distribution data and characteristics of the transmitted ultrasound.

2. 2. The ultrasonic imaging device according to claim 1, The information processing unit includes: The ultrasonic image processing device searches for a spatial frequency corresponding to a maximum value in the distribution indicated by the spatial frequency distribution data within a search range determined according to a pulse width of the transmitted ultrasonic wave, and obtains, as the filter characteristic, a characteristic that suppresses the level of the distribution indicated by the spatial frequency distribution data in a spatial frequency band including the searched spatial frequency.

3. 3. The ultrasonic image processing device according to claim 2, The information processing unit includes: an ultrasonic image processing device which changes the filter characteristics when a maximum value of a distribution indicated by the spatial frequency distribution data obtained from the Doppler image data subjected to the filtering does not satisfy a predetermined condition.

4. 2. The ultrasonic imaging device according to claim 1, The information processing unit includes: generating the Doppler image data sequentially over time; 1. An ultrasonic image processing apparatus comprising: a filter processing section for performing, on a frame of Doppler image data that is subsequently generated, the same filter processing as that performed on a frame of Doppler image data that is previously generated.

5. 5. The ultrasonic image processing device according to claim 4, The information processing unit includes: An ultrasound image processing device characterized in that, when a condition regarding artifacts is not satisfied for the Doppler image data of a frame generated later, the filtering process with the filter characteristics changed is applied to the Doppler image data of a frame generated later.

6. 2. The ultrasound imaging method according to claim 1, The Doppler image data is The ultrasonic wave is transmitted and received while scanning a transmission beam of the ultrasonic wave at a predetermined scanning interval, The information processing unit includes:

2. An ultrasonic image processing apparatus comprising: a processor for processing the Doppler image data by filtering the Doppler image data when the scanning interval exceeds a predetermined scanning interval threshold value.

7. 7. The ultrasonic imaging device according to claim 6, The ultrasonic image processing apparatus according to claim 1, wherein the scanning interval threshold is determined based on characteristics of the transmitted ultrasonic waves.

8. 2. The ultrasonic imaging device according to claim 1, The filter characteristics are An ultrasonic image processing apparatus characterized in that it has a characteristic of making an attenuation amount in a spatial frequency band corresponding to a blood flow width equal to or less than an attenuation amount limit value.

9. 2. The ultrasonic imaging device according to claim 1, The information processing unit includes:

2. An ultrasonic image processing apparatus comprising: a display unit that displays at least one of the distribution indicated by the spatial frequency distribution data and the filter characteristics to a user;

10. 10. The ultrasonic imaging device according to claim 9, 13. An ultrasonic image processing apparatus comprising: a man-machine interface for changing the filter characteristics in response to a user's operation.

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