WO2019026434A1

WO2019026434A1 - Ultrasonic imaging device and image processing device

Info

Publication number: WO2019026434A1
Application number: PCT/JP2018/022632
Authority: WO
Inventors: 崇豊村; 貞一郎池田; 美咲広島; 栗原　浩
Original assignee: 株式会社日立製作所
Priority date: 2017-08-03
Filing date: 2018-06-13
Publication date: 2019-02-07
Also published as: JP2019025247A

Abstract

Devices for obtaining, in a short imaging time, an ultrasonic image with reduced artifacts associated with side lobes. Ultrasonic waves are transmitted to a region to be imaged, a signal is then obtained by receiving the ultrasonic waves returning from the region to be imaged, and an image of the region to be imaged is generated. Side lobe artifacts are cancelled by determining the pixel value distribution of the image in a predetermined direction based on the angle of incidence of the ultrasonic waves on the region to be imaged, and cancelling a noise component included in a high frequency component of the pixel value distribution.

Description

ULTRASONIC IMAGING DEVICE, AND IMAGE PROCESSING DEVICE

The present invention relates to an ultrasonic imaging technique for imaging an image in a subject using ultrasonic waves.

In general, ultrasonic imaging technology is a technology for non-invasively imaging the inside of a subject including a human body using a high frequency sound wave of 20 kHz or higher. A medical ultrasound diagnostic apparatus will be briefly described as one example. The ultrasound probe transmits ultrasound into the patient's body and receives echo signals reflected from the patient's body. The reception signal is subjected to signal processing in one or both of the ultrasonic probe and the ultrasonic diagnostic apparatus main body, and is then delivered to the image display unit to display an ultrasonic image. Specifically, for example, in a transmission beam former disposed in the ultrasonic diagnostic apparatus main body, a transmission signal delayed so as to focus on a predetermined transmission focus is generated, and after passing through a transmission / reception separation circuit (T / R) , And are sent to a plurality of elements of the ultrasound probe. The plurality of elements of the ultrasound probe transmit the focused transmission beam focused on a predetermined transmission focus to the subject by converting the received transmission signal into an ultrasonic wave. The ultrasound probe receives an echo signal from the subject and transmits the received signal to the main body. In the main body, the reception signal is passed to the reception beam former through the transmission / reception separation circuit, subjected to phasing processing in the reception beam former, and transmitted to the image processing unit. In the image processing unit, various image processing such as various filters and scan conversion are executed to generate an ultrasonic image. Finally, an ultrasound image is displayed on the image display unit.

The reception beam former is a delay time in which the amount of delay is distributed in a concave shape according to the relationship between the reception focal point position and the position of the element with respect to each reception signal (reception data) of a plurality of elements constituting the ultrasonic probe By focusing on virtually one point in space (reception focus), the reception signal data is added. The phasing and addition data generates the value of the pixel at the position of the reception focus in the imaging area. This method is called phasing by the delay addition method. In this delay-and-add method, received data received by a plurality of elements of the ultrasonic diagnostic apparatus may be multiplied by a fixed weight vector stored in the diagnostic apparatus, weighted and then added. Note that the delay addition processing is performed for each of a plurality of reception focal points on the reception scanning line set in the imaging region.

In an imaging method for transmitting a focused transmission beam, one or several reception scanning lines are set within the imaging region irradiated with the transmission beam, and after delay addition to a plurality of reception focal points on the reception scanning lines Data is acquired. Therefore, in order to obtain delayed post-addition data for the entire imaging region, it is necessary to transmit the transmission beam a plurality of times while shifting the position, and there is a problem that it takes time for imaging.

In response to this problem, plane wave ultrasonic waves are transmitted from a plurality of elements of the ultrasonic probe, the ultrasonic waves are irradiated in one transmission over the entire imaging area, and a plurality of reception scanning lines are set over the entire imaging area. There is an imaging method for shortening the imaging time by obtaining delayed post-addition data for the reception focus on each reception scan line and generating an image. However, in the imaging method for transmitting plane-wave ultrasonic waves, side-lobes are easily generated because the ultrasonic waves to be transmitted are not focused, and echo signals generated by the side-lobes are reflectors (actual images) in an actual object. Create artifacts around the As a technique to compensate for this defect, the transmission angle of the plane wave is changed, transmission is performed a plurality of times, an image is generated for each transmission, and the generated images are added to increase the signal strength of the real image, Patent Document 1 describes a method for enhancing the contrast to an artifact.

U.S. Patent No. 6,551,246

Since the method of Patent Document 1 relatively enhances the contrast on the image of the real image against the artifact due to side lobes, it is necessary to add many ultrasound images in order to obtain sufficient contrast. Therefore, it is necessary to image a plurality of ultrasonic images while changing the transmission angle of the plane wave, and there is a problem that the reduction effect of the imaging time can not be sufficiently obtained.

An object of the present invention is to obtain an ultrasound image with a short imaging time and reduced artifacts due to side lobes.

In order to solve the above problems, the ultrasonic imaging apparatus of the present invention transmits an ultrasonic wave to an imaging area, and then receives a signal that has received an ultrasonic wave returned from the imaging area, and generates an image of the imaging area. The pixel value distribution of the image is determined in a predetermined direction according to the incident angle of the ultrasonic wave to the image generation area and the imaging region, and the side lobe artifact is obtained by removing the noise component included in the high frequency component of the pixel value distribution. And an image processing unit to be removed.

According to the present invention, it is possible to obtain an ultrasound image with a short imaging time and reduced artifacts due to side lobes.

(A)-(c) is an explanatory view showing the incidence angle of the ultrasonic wave to an imaging field, and the direction of the side lobe artifact of the acquired ultrasonic image. FIG. 1 is a block diagram showing the configuration of an ultrasound imaging apparatus according to a first embodiment. FIG. 7 is a block diagram showing the configuration of an ultrasound imaging apparatus according to a second embodiment. FIG. 7 is a block diagram showing the configuration of a signal conversion unit according to a second embodiment. (A) A block diagram showing the function of the multiple resolution analysis unit according to the second embodiment, (b) A diagram showing a resolution (frequency component) analysis image in which low frequency component images and high frequency component images extracted by the multiple resolution analysis unit are arranged. . FIG. 7 is a view showing a resolution (frequency component) analysis image in which low-frequency component images and high-frequency component images which are multiply extracted by the multi-resolution analysis unit of the second embodiment are arranged. (A) A diagram showing a resolution analysis image, a resolution analysis image from which noise of an LH component image is removed, and a side lobe artifact removal image when the ultrasound incident angle is 0 degree according to the second embodiment, (b) The figure which shows the resolution analysis image in case an ultrasonic incident angle is 0 degree-90 degree, the resolution analysis image which removed the noise of the HH component image, and the side lobe artifact removal image. FIG. 7 is a block diagram showing the configuration of an ultrasound imaging apparatus according to a third embodiment. FIG. 16 is a view showing incident angles of ultrasonic waves in a small area in the imaging area according to the third embodiment. FIG. 7 is a block diagram showing the configuration of a signal conversion unit according to a fourth embodiment. Explanatory drawing which shows the noise removal process and addition process of the resolution analysis image concerning Embodiment 4. FIG. FIG. 7 is a block diagram showing the configuration of a signal conversion unit according to a fifth embodiment. FIG. 16 is a block diagram showing the configuration of a signal conversion unit according to a sixth embodiment. FIG. 14 is a block diagram showing the configuration of a signal conversion unit according to a seventh embodiment. FIG. 18 is an explanatory view showing a flow of processing of a side lobe estimation unit according to a seventh embodiment;

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<< First Embodiment >>
In the present embodiment, the side lobes of the ultrasonic waves 10 are artifact-induced by making use of the fact that the direction in which the artifacts 11 are generated in the ultrasonic image by the side lobes of the transmitted ultrasonic waves 10 depends on the direction of incidence of the ultrasonic waves 10 onto the imaging region. Remove. That is, as shown in FIGS. 1A to 1C, the side lobe artifact of the reflector 12 in the imaging region in the ultrasound image appears in the direction along the wavefront of the ultrasound 10 incident on the reflector 12. Particularly in the present embodiment, the pixel value distribution of the image is determined in a predetermined direction according to the incident angle of the ultrasonic wave of the ultrasonic image, and the side lobe artifact is removed by removing the noise component from the pixel value distribution. Do. More specifically, the pixel value distribution of the ultrasonic image is determined in at least two directions, and is separated into high frequency components and low frequency components, respectively, and side lobes included in high frequency components in a predetermined direction corresponding to the incident direction of ultrasonic waves. By removing the noise, a side lobe artifact removed image is generated.

An ultrasound imaging apparatus according to the present embodiment will be described with reference to FIG.

The ultrasound imaging apparatus according to the present embodiment includes an image generation unit 3 and an image processing unit 21. The image processing unit 21 includes a component extraction unit 4, a side lobe noise removal unit 5, and a side lobe removed image. And at least a generation unit 7. At this time, the ultrasonic imaging apparatus may not necessarily include the ultrasonic probe 101 or the like, and another apparatus transmits an ultrasonic wave to the subject and the received signal such as an echo thereof is It may be configured to be received from the device. Here, as shown in FIG. 2, the case where the ultrasonic imaging apparatus is configured to include the ultrasonic probe 101, the transmitting unit 2, and the transmission / reception separation circuit 102 will be described.

When ultrasonic waves 10 are transmitted from the plurality of acoustic conversion elements of the ultrasonic probe 101 to the imaging area 20, ultrasonic waves such as echoes are returned to the ultrasonic probe 101 from the imaging area 20, and the plurality of acoustic conversions are performed. It is received by the element. The image generation unit 3 receives the reception signal of the acoustic conversion element, and generates an image of the imaging region 20. Any method may be used as a method of generating an image. For example, a plurality of reception scanning lines are set in the imaging area 20, and each reception signal is delayed so as to focus the reception signal on the reception focus on the reception scanning line and then added. It is possible to use a method of generating an ultrasound image by arranging in the image space pixels for which the delayed and added signal is a pixel value.

The component extraction unit 4 obtains pixel value distributions in at least two directions of the image generated by the image generation unit 3 and extracts high frequency components and low frequency components constituting pixel value distributions (signals) in the two directions. The two directions may be any directions, but one example is two directions orthogonal to the horizontal direction and the vertical direction of the image. Since sidelobe artifacts occur in the direction along the wavefront of the ultrasonic wave around the reflector 13 in the imaging area 20, the pixel value distributions in the two directions according to the incident angle of the ultrasonic wave 10 on the imaging area 20 The noise generated by the side lobes of the ultrasonic wave 10 is included in one or both of the two. For example, as shown in FIG. 1 (b), when ultrasonic waves 10 of plane waves parallel to the horizontal direction of the imaging region 20 are transmitted, side lobe artifacts 11 occur along the horizontal direction of the real image 13 of the reflector 12 of the image. . Therefore, it is necessary to remove noise (a part of high frequency components) of the pixel value distribution in the vertical direction of the image. Therefore, the side lobe noise removing unit 5 selects at least one of the two directions according to the incident angle of the ultrasonic wave 10 to the imaging region 20, and a noise component included in the high frequency component in the selected direction (hereinafter referred to as a side lobe) Remove noise). For example, a component whose absolute value included in the high frequency component is equal to or less than a predetermined value is removed as a noise component.

The side lobe removal image generation unit 7 generates a side lobe artifact removal image of the imaging region 20 using at least high frequency components from which noise components have been removed in the direction selected by the side lobe noise removal unit 5. Specifically, the side lobe removal image generation unit 7 does not select the high frequency component and the low frequency component from which noise components have been removed and the side lobe noise removal unit 5 in the direction selected by the side lobe noise removal unit 5. The side lobe artifact removed image of the imaging region is generated using the high frequency component and the low frequency component of the different directions. For example, the image is generated again by performing the reverse process of the method when extracting the high frequency component and the low frequency component. As a result, only the noise component is removed from the pixel value distribution, and the other components are maintained, so that the side lobe artifact 11 can be removed while suppressing the pixel value reduction of the real image.

As described above, according to the imaging method of the present embodiment, the side lobe artifact can be removed from the imaged ultrasonic image, so that an image with a short imaging time and reduced artifacts due to the side lobe can be obtained. Can.

Hereinafter, more specific embodiments will be described according to the second embodiment and later.

<< Embodiment 2 >>
FIG. 3 is a block diagram showing the configuration of the ultrasonic imaging apparatus of the second embodiment. In FIG. 3, the same components as those of the apparatus of the first embodiment are denoted by the same reference numerals.

As shown in FIG. 3, the ultrasonic diagnostic apparatus comprises an ultrasonic probe (hereinafter referred to as an ultrasonic element array) 101 in which a plurality of ultrasonic elements (ultrasound transducers) are arranged along a predetermined direction; It has a transmission / reception separation circuit 102 for separating a signal to be transmitted / received through the ultrasonic element array 101, and a transmission unit 2 for delivering a transmission signal to each ultrasonic element of the ultrasonic element array 101 via the transmission / reception separation circuit 102. Here, the transmission unit 2 generates a transmission signal delayed for each ultrasonic element so that the imaging region 20 is irradiated with a plane wave from a predetermined direction.

In the ultrasonic imaging apparatus according to the second embodiment, as the image generation unit 3, the phases of the signals received by the respective ultrasonic elements of the ultrasonic element array 101 are phased (delayed) according to the position of the reception focus, A phasing processing unit 103 is disposed which obtains a signal after phasing / addition by combining (addition). The phasing processing unit 103 sets a plurality of reception scanning lines in the entire imaging region 20, obtains signals after phasing addition for each of a plurality of reception foci on each reception scanning line, and obtains the signals after phasing addition. An ultrasound image is generated by using the pixel value of the pixel corresponding to the position of the reception focus. Thereby, one ultrasound image can be obtained by transmitting a plane wave once. Since this ultrasound image is an image obtained by transmitting a plane wave once, it includes artifacts due to side lobes, etc., and has low resolution.

The ultrasound imaging apparatus according to the second embodiment includes, as the component extraction unit 4, a multiresolution analysis unit 104 that extracts high frequency components and low frequency components by wavelet transformation, and further includes a side lobe noise removal unit 5 and side components. And a lobe removal image generation unit 7. In the second embodiment, the side lobe noise remover 5 and the side lobe removed image generator 7 constitute a signal converter 105 as shown in FIG. Further, the side lobe removed image generation unit 7 is called an inverse transform unit 404 in order to generate an image from which the side lobes have been removed by inverse wavelet transform.

The control unit 108 and the image display unit 106 are connected to the signal conversion unit 105. Further, a console 109 is connected to the control unit 108 and the image display unit 106. The console 109 is configured of a touch panel, a keyboard, a trackball, and the like, and receives user input. The control unit 108 instructs the transmission unit 2, the phasing processing unit 103, and the signal processing unit 105 on the incident direction of the ultrasonic wave, which is a plane wave, to the imaging region 20 based on the user's input received by the console 109. The image display unit 106 is configured by a display or the like, and displays an image or the like generated by the signal conversion unit 105 to the user.

The processes of the multiresolution analysis unit 104 and the signal conversion unit 105 will be described below.

The multiresolution analysis unit 104 obtains pixel value distributions (signals) in two directions of the ultrasonic image generated by the phasing processing unit 103, and extracts high frequency components and low frequency components, respectively. Here, a plurality of different frequency bands are extracted by wavelet transformation. Here, the two directions to be extracted are the horizontal direction and the vertical direction of the ultrasonic image.

The process of the multiresolution analysis unit 104 will be specifically described using FIG. 5 (a). The multiresolution analysis unit 104 includes a horizontal direction analysis unit 41 and a vertical direction analysis unit 42. The horizontal direction analysis unit 41 includes a low pass filter 201a, a high pass filter 201b, a downsampling unit 202a, and a downsampling unit 202b. On the other hand, the vertical direction analysis unit 42 includes

low pass filters

203a and 203c, high pass filters 203b and 203d, and downsampling units 204a to 204d.

The horizontal direction analysis unit 41 of the multiresolution analysis unit 104 first sequentially samples pixel values of the ultrasonic image 43 generated by the phasing processing unit 103 for pixels aligned in the horizontal direction to indicate a horizontal pixel value distribution. The direction signal 43a is generated. The horizontal direction signal 43a is generated for each position (pixel) in the vertical direction. Then, low frequency components below a predetermined band are extracted by passing the horizontal direction signal 43a through the low pass filter 201a, and then the 2: 1 down sampling unit 202 extracts two pixels adjacent in the horizontal direction. An average or the like of signal values is obtained to generate signal values for one pixel. Thus, the horizontal direction is constituted by the low frequency components of the pixel value distribution in the horizontal direction of the ultrasonic image 43, and the vertical direction includes all components of the pixel value distribution of the ultrasonic image 43 and the size in the horizontal direction Is a half of the ultrasound image 43, and a horizontal low frequency image 44 whose size in the vertical direction is the same as that of the ultrasound image 43 is generated.

Similarly, after passing the horizontal direction signal 43a through the high pass filter 201b to extract high frequency components from a predetermined band, the 2: 1 down sampling unit 202b outputs signals for two pixels adjacent in the horizontal direction. An average value or the like of values is obtained to generate a signal value for one pixel. Thus, the horizontal direction is constituted by the high frequency component of the pixel value distribution in the horizontal direction of the ultrasonic image 43, the vertical direction includes all components of the pixel value distribution in the ultrasonic image 43, and the size in the horizontal direction is A horizontal high frequency image 45 is generated which is half the size of the ultrasound image 43 and does not differ in size in the vertical direction from the ultrasound image 43.

Next, the vertical direction analysis unit 42 sequentially samples the pixel values of the horizontal low frequency image 44 with respect to the pixels aligned in the vertical direction to generate a vertical direction signal 44a indicating a pixel value distribution in the vertical direction. The vertical direction signal 44a is generated for each position (pixel) in the horizontal direction. Then, the vertical direction analysis unit 42 extracts low frequency components below a predetermined band by passing the vertical direction signal 44 a through the low pass filter 203 a and then using the 2: 1 down sampling unit 204 a in the vertical direction. A signal value for one pixel is generated by obtaining an average or the like of signal values for two pixels adjacent to one another. Thereby, the horizontal direction is constituted by the low frequency component of the pixel value distribution in the horizontal direction of the ultrasonic image 43, the vertical direction is constituted by the low frequency component of the pixel value distribution in the vertical direction of the ultrasonic image 43, and A “horizontal low-frequency component / vertical low-frequency component (hereinafter referred to as LL component) image 46” in which the size in the horizontal direction and the vertical direction is one half of that of the ultrasonic image 43 is generated.

Similarly, the vertical direction analysis unit 42 extracts a high frequency component larger than a predetermined band by passing the vertical direction signal 44a through the high pass filter 203b, and then the 2: 1 down sampling unit 204b performs the vertical direction. A signal value for one pixel is generated by obtaining an average or the like of signal values for two pixels adjacent to one another. Thus, the horizontal direction is constituted by the low frequency component of the pixel value distribution in the horizontal direction of the ultrasonic image 43, and the vertical direction is constituted by the high frequency component of the pixel value distribution in the vertical direction of the ultrasonic image 43, and A “horizontal low frequency component / vertical high frequency component (hereinafter referred to as LH component) image 47 in which the size in the horizontal direction and the vertical direction is one half of that of the ultrasonic image 43 is generated.

Furthermore, the vertical direction analysis unit 42 sequentially samples the pixel values of the horizontal high-frequency image 45 for pixels aligned in the vertical direction to generate a vertical direction signal 45 a. Then, the vertical direction analysis unit 42 extracts low frequency components below a predetermined band by passing the vertical direction signal 45 a through the low pass filter 203 c, and then the 2: 1 down sampling unit 204 c performs the vertical direction. A signal value for one pixel is generated by obtaining an average or the like of signal values for two pixels adjacent to one another. Thus, the horizontal direction is constituted by the high frequency component of the pixel value distribution in the horizontal direction of the ultrasonic image 43, the vertical direction is constituted by the low frequency component of the pixel value distribution in the vertical direction of the ultrasonic image 43, and A “horizontal high-frequency component / vertical low-frequency component (hereinafter referred to as HL component) image 48” in which the size in the horizontal direction and the vertical direction is one half of that of the ultrasonic image 43 is generated.

Similarly, the vertical direction analysis unit 42 extracts a high frequency component larger than a predetermined band by passing the vertical direction signal 45a through the high pass filter 203d, and then the 2: 1 down sampling unit 204d performs the vertical direction. A signal value for one pixel is generated by obtaining an average or the like of signal values for two pixels adjacent to one another. Thus, the horizontal direction is constituted by the high frequency component of the pixel value distribution in the horizontal direction of the ultrasonic image 43, and the vertical direction is constituted by the high frequency component of the pixel value distribution in the vertical direction of the ultrasonic image 43 A “horizontal high-frequency component / vertical high-frequency component (hereinafter referred to as HH component) image 47” in which both the size in the direction and the vertical direction is 1⁄2 of the ultrasound image 43 is generated.

When the obtained LL component image 46, LH component image 47, HL component image 48, and HH component image 49 are arranged in the order of high frequency components to low frequency components, a resolution (frequency component) analysis image 205 as shown in FIG. Is obtained.

Further, the LL component image 46 is further processed in the same manner as described above by the horizontal direction analysis unit and the vertical direction analysis unit 42 to obtain the LL component image 50, the LH component image 51, the HL component image 52, and the HH component image 53. It is also good. Again, the LL component image 50 may be processed to obtain the LL component image 54, the LH component image 55, the HL component image 56, and the HH component image 57. When the obtained images are arranged in the order of the high frequency component and the low frequency component, an arrangement as shown in FIG. 6 is obtained. As a result, a multi-resolution analysis image 205 is obtained in which the pixel value distribution of ultrasonic waves is separated into low frequency components and high frequency components in multiple stages.

The side lobe noise removing unit 5 determines one or more images determined in advance according to the incident direction of the ultrasonic wave from the images 47 to 49 including high frequency components among the resolution analysis images 46 to 49 generated by the multiresolution analysis unit 104. Select and remove side lobe noise components. That is, since the side lobe artifact occurs along the direction (parallel to the wavefront of the ultrasonic wave) orthogonal to the direction of propagation of the ultrasonic wave, the side lobe noise removing unit 5 removes this. The side lobe noise removing unit 5 receives the incident direction of the ultrasonic wave from the control unit 108.

For example, when the ultrasound incident angle is 0 degree (see FIG. 1B), it is estimated that the side lobe artifact is generated along the horizontal direction of the ultrasound image, so the side lobe noise removing unit 5 The LH component image 47 of the low frequency component and the high frequency component in the vertical direction is selected. Then, the side lobe noise removing unit 5 replaces the intensity of the pixel whose intensity is equal to or less than a threshold value with 0. As a result, the high frequency component having a small absolute value can be replaced with 0, so that the side lobe noise component can be removed.

Similarly, for example, in the case where the absolute value of the ultrasonic incident angle is a value larger than 0 degree and smaller than 90 degrees (see FIGS. 1A and 1C), the side lobe artifact is determined as the incident angle from the horizontal direction. The side lobe noise removing unit 5 selects the HH component image 49, which is a high frequency component in both the horizontal direction and the vertical direction, since it is estimated to occur in the direction having the same inclination. Then, the side lobe noise removing unit 5 replaces the intensity of the pixel whose intensity is equal to or less than a threshold value with 0. As a result, the high frequency component having a small absolute value can be replaced with 0, so that the side lobe noise component can be removed.

As shown in FIG. 6, when the LH component image 51, the HL component image 52, the HH component image 53, etc. are obtained at multiple resolutions, the side lobe noise removing unit 5 generates noise of corresponding component images of different resolutions. Remove the ingredients too. For example, when the ultrasonic incident angle is 0 degree (see FIG. 1B), the side lobe noise removing unit 5 not only determines the LH component image 47 but also the LH component image 51 of other resolutions and the like. Remove the lobe noise component. The same is true for the other ultrasonic incident angles.

The inverse transform unit 404 performs inverse wavelet transform on the high frequency component image selected by the side lobe noise removal unit 5 and from which the side lobe noise component is removed and the remaining component image not selected, and has the same resolution as the original image Generate an image of For example, as shown in FIG. 7A, when the incident angle of the ultrasonic wave is 0 degree, a resolution analysis image including the low frequency component image 46 and the high frequency component images 47 to 49 extracted by the multiresolution analysis unit 104 In 401, the side lobe noise removing unit 5 selects the LH component image 47 and removes the noise component to obtain the LH 'component image 47a, which is replaced with the LH component image 47 and resolution analysis after noise removal An image 501 is obtained (FIG. 7 (a-2)). The inverse transformation unit 404 performs a wavelet inverse transformation on the resolution analysis image 501 (the LH ′ component image 47 a and the other low frequency and high

frequency component images

46, 48, 49) after the noise removal to obtain a side lobe artifact removed image 502 is generated (FIG. 7 (a-3)).

Further, as shown in FIG. 7 (b-1), when the absolute value of the incident angle of the ultrasonic wave is a value larger than 0 degree and smaller than 90 degrees, the low frequency component image 46 and the high frequency component extracted by the multiresolution analysis unit 104 The side lobe noise removing unit 5 selects the HH component image 49 out of the resolution analysis image 402 composed of the images 47 to 49, and removes the noise component to obtain the HH 'component image 49a. And the resolution analysis image 503 after noise removal is obtained (FIG. 7 (b-2)). The inverse transform unit 404 performs inverse wavelet transform on the resolution analysis image 503 (the HH ′ component image 49 a and the other low frequency and high frequency component images 46 to 48) after noise removal to obtain the side lobe artifact removed image 504. It generates (FIG. 7 (b-3)).

The generated image is displayed on the image display unit 106.

As described above, according to the present embodiment, it is possible to selectively remove the side lobe artifact component of the ultrasonic image according to the incident angle of the ultrasonic wave to the imaging region 20.

The multiresolution analysis unit 104, the signal conversion unit 105, and the control unit 108 are configured by a computer including a central processing unit (CPU) which is an arithmetic processing unit and a memory, and the CPU executes a program in the memory. These functions can be realized by software. Further, part or all of the multi-resolution analysis unit 104, the signal conversion unit 105, and the control unit 108 can be realized by hardware. For example, a part of the multiple resolution analysis unit 104, the signal conversion unit 105, and the control unit 108 using a custom IC such as an application specific integrated circuit (ASIC) or a programmable IC such as a field-programmable gate array (FPGA) Configure the whole and design the circuit to realize these functions.

In the present embodiment, the processing for removing the side lobe artifact from the image obtained by phasing and adding the received ultrasonic signal has been described. However, the RF (high frequency) signal before phasing addition is performed by phasing processing unit 103 It is also possible to apply the processing of the multiresolution analysis unit 104 and the signal conversion unit 105 to (reception signal).

Further, in the present embodiment, the side lobe noise removing process is performed for each specific one of the high-frequency component images 47 to 49 when the incident angle is 0 degree and any value larger than 0 degree and smaller than 90 degrees. Although the application example has been described, two or more of the high-frequency component images 47 to 49 may be subjected to noise removal processing in order to perform appropriate side lobe noise removal for an arbitrary incident angle.

Furthermore, in the present embodiment, the side lobe noise removing unit 5 determines the pixel value smaller than the predetermined threshold among the pixel values of the high frequency component images 47 to 49 as the side lobe noise component and replaces it with 0. However, the threshold may be received from the user through the console 109. Further, as the threshold value, a value set in advance may be used according to an imaging object such as a human heart or liver. Furthermore, the method of removing the side lobe noise component is not limited to the method of replacing the pixel value of the signal intensity smaller than the threshold of the high frequency component images 47 to 49 with 0, but a method capable of reducing the noise component Any processing method may be used.

The threshold value of the filter in which the horizontal direction analysis unit 41 and the vertical direction analysis unit 42 in FIG. 5A extract high frequency components and low frequency components from the pixel value distribution is not a fixed threshold value, but a value received from the user, It is also possible to use preset values according to the imaging target.

<< Third Embodiment >>
An ultrasonic imaging apparatus according to the third embodiment will be described with reference to FIGS. 8 and 9.

In the first and second embodiments, the case where the ultrasonic wave transmitted to the imaging area 20 is a plane wave has been described. However, the ultrasonic wave may not necessarily be a plane wave, and a spherical wave focusing at a transmission focus located inside or outside the imaging area 20 It may be When the ultrasonic waves to be transmitted are spherical waves, the incident angles of the ultrasonic waves are different for each of a plurality of areas in the imaging area 20. Therefore, the third embodiment further includes the incident angle calculation unit 107 that obtains the incident angle of the ultrasonic wave for each of a plurality of regions in the imaging region 20. The side lobe noise removing unit 5 selects, for each of the plurality of regions, a high frequency component from which noise is removed, in accordance with the incident angle of the ultrasonic wave calculated by the incident angle calculating unit 107.

The configuration different from that of the second embodiment will be described in detail below. The incident angle calculation unit 107 calculates an ultrasonic incident angle for each predetermined small area in the imaging area 20 according to the transmission condition of the ultrasonic wave. The small area is an area obtained by dividing the entire imaging area 20 into a predetermined sufficiently small size. FIG. 9 is a view showing the incident angle 305 of ultrasonic waves in a certain small area 303. As shown in FIG. In FIG. 9, the horizontal direction is parallel to the direction 301 in which the ultrasonic elements of the ultrasonic element array 101 are arranged, and the vertical direction is the depth direction 302 of the imaging region 20. In a small area 303 sufficiently small, an angle formed by the direction of travel 304 of the ultrasonic wave with respect to the depth direction 302 is defined as an incident angle 305. The incident angle calculation unit 107 receives the transmission conditions (the position of the transmission focus, etc.) of the ultrasonic waves from the control unit 108, and calculates the value of the incident angle 305 for each small area according to the received transmission conditions. The incident angle 305 calculated by the incident angle calculation unit 107 is stored in the form of a table or the like in the memory incorporated in the incident angle calculation unit 107 in association with the position of the small area.

When the side lobe noise removing unit 5 selects any one of the high frequency component images 47 to 49 in order to remove noise of the resolution analysis image 401 generated by the multi-resolution analysis unit 104, The ultrasonic incident angle 305 of the small area 303 is read from the table, one or more of the high frequency component images 47 to 49 corresponding to the incident angle 305 are selected, and an area corresponding to the small area of the selected high frequency component image To remove the noise component.

For example, since it is estimated that sidelobe artifacts occur along the horizontal direction for a small area with an incident angle of 0 degrees, an LH component image 47 is selected, and pixels of the area corresponding to the small area are selected. Performs sidelobe noise removal processing. Similar to the second embodiment, the noise removal process is a side lobe by replacing the pixel value of a pixel in a region corresponding to the small region 303 of the LH component image 47 with a pixel value of 0 with a pixel value of 0. Remove the ingredients. Similarly, for a small area where the incident angle is greater than 0 degrees and smaller than 90 degrees, it is estimated that the side lobe component will occur in the direction from the horizontal with an inclination equal to the incident angle, so select the HH component image 49 Then, sidelobe noise removal processing is performed on the pixels in the area corresponding to the small area.

The inverse transformation unit 404 inversely transforms the resolution analysis image 501 from which the side lobe component has been removed, thereby generating an image of the same resolution as the original ultrasound image from which the side lobe artifact has been removed.

According to the above configuration, it is possible to generate a side lobe artifact removed image from which a side lobe artifact component that occurs according to a small area in the imaging region is removed.

<< Embodiment 4 >>
The ultrasonic imaging apparatus according to the fourth embodiment will be described with reference to FIG.

In the fourth embodiment, a plurality of transmissions with different incident angles of ultrasonic waves to the imaging region 20 are performed, high frequency components and low frequency components are generated for each transmission with different incident angles, and side lobe noise is removed. And an image addition unit (hereinafter, referred to as a combination unit) 607 for adding each component. The high frequency component and the low frequency component after the addition are inversely transformed to synthesize a side lobe artifact removed image. Thereby, an image with high contrast can be obtained.

With reference to FIG. 10, only the blocks having a change from the second embodiment will be described below, and the description of the same configuration as the second embodiment will be omitted. FIG. 10 is a block diagram of the signal conversion unit 105 in the present embodiment. The signal conversion unit 105 of the present embodiment includes two side lobe

noise removal units

605 and 606. The two side lobe

noise removing units

605 and 606 transmit ultrasonic waves of plane waves to the imaging area 20 so as to have different incident angles, and an image generated from a received signal such as an echo obtained from the imaging area 20 Remove the side lobe noise from the pixel value distribution. Here, the incident angle of the plane wave to the imaging region 20 is defined by the angle formed by the ultrasonic element array direction of the ultrasonic element array 101 and the wavefront (that is, the angle formed by the traveling direction of the ultrasonic wave with respect to the depth direction). Be done.

For example, in the first transmission, an ultrasonic wave of a plane wave is transmitted from the ultrasonic element array 101 to the imaging region 20 at an incident angle of 0 degrees (see FIG. 1B). A received signal output from the ultrasonic element array 101 that has received an echo or the like is processed by the phasing processing unit 103 to generate an ultrasonic image, and the multiresolution analysis unit 104 generates an ultrasonic image as shown in FIG. 7 (a-1). The high frequency component images 47 to 49 and the low frequency component image 46 are extracted. The side lobe noise removing unit 605 selects the LH component image 47 by the same method as in the second embodiment and removes the side lobe noise component to obtain the LH ′ component image 47 a (FIG. 7 (a-2)). .

Next, in the second transmission, the side lobe noise removing unit 606 transmits, from the ultrasonic element array 101, a plane wave ultrasonic wave whose incident angle is greater than 0 degree and smaller than 90 degrees (see FIG. 1 (c)). . A received signal output from the ultrasonic element array 101 that has received an echo or the like is processed by the phasing processing unit 103 to generate an ultrasonic image, and the multiresolution analysis unit 104 generates an ultrasonic image as shown in FIG. 7 (b-1). The high frequency component images 47 to 49 and the low frequency component image 46 are extracted. The side lobe noise removing unit 606 selects the HH component image 49 by the same method as in the second embodiment and removes the side lobe noise component to obtain the HH 'component image 49 a. Thereby, the resolution analysis image 503 is obtained (FIG. 7 (b-2)).

FIG. 11 is a diagram showing the flow of addition / combination processing. As illustrated in FIG. 11, the combining unit 607 adds and combines the resolution analysis image 501 and the resolution analysis image 503 from which the side lobe noise components have been removed by the side lobe noise removing unit 605 and the side lobe noise removing unit 606. , And a resolution analysis image 703 after synthesis. The inverse transform unit 404 inversely transforms the combined resolution analysis image 703 to generate an image from which the side lobe artifact has been removed at the same resolution as the original ultrasound image.

As described above, after adding and synthesizing a plurality of resolution analysis images from which the side lobe noise component has been removed, an inverse conversion is performed to improve the contrast of the real image 13 of the reflector 12 in the image while removing side lobe artifacts. can get.

In the present embodiment, an example is described in which two resolution-analyzed

resolution analysis images

501 and 503 generated from received signals obtained by transmitting ultrasonic waves at two different incident angles are combined. After the resolution analysis image after noise removal corresponding to the incident angle of the ultrasonic wave is synthesized, inverse conversion may be performed.

<< Embodiment 5 >>
An ultrasonic imaging apparatus according to the fifth embodiment will be described with reference to FIG.

In the fifth embodiment, a plurality of transmissions with different incident angles of ultrasonic waves with respect to the imaging region 20 are performed, a side lobe artifact removed image is generated for each transmission with different incident angles, and image addition is performed to add the plurality of obtained images. A part (hereinafter referred to as a combining part) 803 is included. An image with higher contrast can be obtained by combining a plurality of side lobe artifact removed images with different incident angles of ultrasonic waves.

Referring to FIG. 12, only the configuration different from that of the fourth embodiment will be described below. FIG. 12 is a block diagram of the signal conversion unit 105 in the present embodiment. The signal conversion unit 105 of the present embodiment includes two side lobe

noise removal units

605 and 606 as in the fourth embodiment, but unlike the fourth embodiment, the side lobe

noise removal units

605 and 606 and the combining unit 803

Inverse transformation units

801 and 802 are respectively disposed between them. The inverse transformation unit 801 inversely transforms the resolution analysis image 501 from which the noise component has been removed by the side lobe noise removal unit 605 to generate a side lobe artifact removed image 511. The inverse transformation unit 802 inversely transforms the resolution analysis image 503 from which the noise component has been removed by the side lobe noise removal unit 606 to generate a side lobe artifact removed image 513. The combining unit 803 combines the image 511 and the image 513 generated by the

inverse conversion units

801 and 802.

Thereby, it is possible to obtain an image in which the contrast of the real image 13 of the reflector 12 in the image is improved while removing the side lobe artifact.

<< Embodiment 6 >>
The ultrasonic imaging apparatus according to the sixth embodiment will be described with reference to FIG.

As shown in FIG. 13, the signal processing unit 105 of this embodiment has the same configuration as the signal processing unit 105 of FIG. 10 of the fourth embodiment, but in this embodiment, a spherical wave is used as an ultrasonic wave to be transmitted. The position of the transmission focus is made to differ between one transmission and the second transmission.

In the case of using a spherical wave, since the incident angle for each small area of the imaging area differs depending on the position of the transmission focus, the side lobe

noise removing units

605 and 606 receive the incident angle from the incident angle calculation unit 107 for each small area and receive them. One or more of the high frequency component images 47 to 49 corresponding to the incident angle are selected, and the noise removal processing of the area corresponding to the small area is performed as in the third embodiment.

The synthesizing unit 607 adds the

resolution analysis images

501 and 503 after noise removal to each corresponding component, and the inverse transformation unit 404 inverse-transforms the resolution analysis image after addition to remove side lobe artifacts. Generate an image.

By the above processing, the position of the transmission focal point is made different by using the spherical wave, side lobes are removed from the reception signal obtained by performing transmission multiple times, and the contrast of the real image of the reflector is enhanced. You can get an image.

In the present embodiment, after the plurality of

resolution analysis images

501 and 503 from which the side lobes have been removed are added, the inverse conversion is performed, but the inverse conversion may be performed first and then the combination may be performed.

<< Embodiment 7 >>
In the seventh embodiment, from the high frequency component images 47 to 49 of the

resolution analysis images

401 and 402 generated by plane waves transmitted at a plurality of different incident angles in the fourth embodiment, the pixels of the side lobe noise component in the high frequency component images 47 to 49 are Estimate the range. Then, the noise component included in the range of the estimated side lobe noise component is removed. Thereby, the side lobe removal is performed more appropriately.

The signal conversion unit 105 of this embodiment will be described with reference to FIG. However, in FIG. 14, only the configuration different from that of the signal conversion unit 105 in FIG. 10 of the fourth embodiment will be described below. FIG. 14 is a block diagram of the signal conversion unit 105 in the present embodiment. The signal conversion unit 105 of the present embodiment has a side lobe estimation unit 901 that estimates the range of the pixel of the side lobe noise component using the

resolution analysis images

401 and 402.

A flow of processing of the side lobe estimation unit 901 is shown in FIG. As described in the fourth embodiment, the resolution analysis image 401 used for estimation is the high frequency component image 47 to 49 and the low frequency component image 46 generated by the multi-resolution analysis unit 104 from the received signal obtained by transmission at an incident angle of 0 degrees. It consists of Since the side lobe artifact occurs along the horizontal direction when the incident angle is 0 degree, the side lobe estimation unit 901 selects the LH component image 47 as the side lobe noise removal unit 605 does. On the other hand, the resolution analysis image 402 includes high-frequency component images 47 to 49 and a low-frequency component image 46 obtained by transmission with an incident angle of more than 0 degree and less than 90 degrees. In this case, the side lobe estimation unit 901 selects the HH component image 49 as the side lobe noise removal unit 606 does.

The side lobe estimation unit 901 obtains the difference between the two selected

component images

47 and 49. Side lobe noise is generated in different regions (pixels) in the two

component images

47 and 49, so the difference between the

component images

47 and 49 cancels the real image 13 contained in the

component images

47 and 49. On the other hand, the pixel value of the side lobe noise does not cancel out, and is extracted as the difference image 1003. That is, a pixel having a value in the difference image 1003 indicates an area in which side lobe noise occurs.

The side lobe estimation unit 901 notifies the side lobe noise removal unit 605 and the side lobe noise removal unit 606 of the difference image 1003. The side lobe

noise removing units

605 and 606 respectively select predetermined high

frequency component images

47 and 49 from the high frequency component images 47 to 49 as in the fourth embodiment, and the range of pixels having the pixel value of the difference image 1003, ie, The noise is removed by replacing the pixel values of the high

frequency component images

47 and 49 corresponding to the area where the side lobe noise occurs with a pixel value equal to or less than the threshold value to zero.

The processes of the synthesizing unit 607 and the inverse transforming unit 404 perform the same processes as in the fourth embodiment to generate a side lobe artifact removed image.

As described above, the side lobe estimation unit 901 estimates the region (pixel) in which side lobe noise occurs in advance, and removes the noise in the region (pixel), thereby setting the pixel value equal to or less than the threshold value to 0. Only the side lobe noise can be removed more accurately than the configuration of the fourth embodiment to be replaced.

The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the embodiments described above have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to the embodiments provided with all the described configurations. In addition, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and addition, deletion, or replacement of the configuration of one embodiment can be performed using another configuration. .

Further, each of the above configurations, functions, processing units, processing means, etc. may be realized by hardware by designing part or all of them with, for example, an integrated circuit. Further, each configuration, function, etc. described above may be realized by software by the processor interpreting and executing a program that realizes each function. Information such as a program, a table, and a file for realizing each function can be placed in a memory, a hard disk, a recording device such as a solid state drive (SSD), or a recording medium such as an IC card, an SD card, or a DVD.

101 Ultrasonic Element Array 102 Transmission / reception separation circuit 103 Phasing processing unit 104 Multiresolution analysis unit 105 Signal conversion unit 106 Image display unit 107 Incident angle calculation unit 108 Control unit 109 Console

Claims

An image generation unit configured to transmit an ultrasonic wave to an imaging area, receive a signal from the ultrasonic wave returned from the imaging area, and generate an image of the imaging area;
A pixel value distribution of the image is obtained in a predetermined direction according to an incident angle of the ultrasonic wave to the imaging region, and a side lobe artifact is removed by removing a noise component included in a high frequency component of the pixel value distribution. An ultrasonic imaging apparatus having an image processing unit.
The ultrasonic imaging apparatus according to claim 1, wherein
The image processing unit
A component extraction unit which obtains a pixel value distribution in at least two directions of the image and extracts a high frequency component and a low frequency component of the pixel value distribution for each direction;
A side lobe noise removing unit that selects at least one of the two directions according to the incident angle of the ultrasonic wave with respect to the imaging region and removes noise components included in the high frequency components in the selected direction;
A side lobe removed image generation unit that generates a side lobe artifact removed image of the imaging region using at least the high frequency component from which the noise component has been removed in the direction selected by the side lobe noise removing unit;
An ultrasonic imaging apparatus characterized by having:
The ultrasonic imaging apparatus according to claim 2, wherein the side lobe removal image generation unit removes the noise component in the direction selected by the side lobe noise removal unit, the high frequency component and the low frequency component, And an ultrasonic imaging apparatus that generates a side lobe artifact removed image of the imaging region using the high frequency component and the low frequency component in a direction not selected by the side lobe noise removing unit.
The ultrasonic imaging apparatus according to claim 1, wherein the image processing unit removes a component having an absolute value included in the high frequency component equal to or less than a predetermined value as a noise component.
The ultrasonic imaging apparatus according to claim 2, wherein the image generation unit, the component extraction unit, the side lobe noise removal unit, and the plurality of transmissions with different incident angles of the ultrasonic wave with respect to the imaging region. An ultrasonic imaging apparatus, further comprising: an image addition unit that adds the side lobe artifact removed image obtained by the processing of the side lobe removed image generation unit.
The ultrasonic imaging apparatus according to claim 2, wherein a plurality of transmissions with different incident angles of the ultrasonic wave with respect to the imaging region are respectively generated by the image generation unit, the component extraction unit, and the side lobe noise removal unit. The signal processing apparatus further includes an addition unit that adds the high frequency component and the low frequency component after noise component removal obtained by the processing for each corresponding component,
The ultrasonic imaging apparatus characterized in that the side lobe removed image generation unit generates the side lobe artifact removed image using the high frequency component and the low frequency component added by the addition unit.
The ultrasonic imaging apparatus according to claim 2, further comprising: an incident angle calculation unit for obtaining an incident angle of the ultrasonic wave for each of a plurality of small areas in the imaging area, wherein the side lobe noise removing unit An ultrasonic imaging apparatus, wherein at least one of the two directions is selected for each of the plurality of small regions in accordance with the incident angle of the ultrasonic wave calculated by the incident angle calculation unit.
The ultrasonic imaging apparatus according to claim 1, further comprising: a transmitting / receiving unit for receiving an ultrasonic wave from the imaging area after transmitting an ultrasonic wave of a plane wave to the imaging area at a predetermined incident angle. An ultrasonic imaging apparatus characterized by
8. The ultrasonic imaging apparatus according to claim 7, further comprising: a transmitting / receiving unit for receiving an ultrasonic wave from the imaging area after transmitting an ultrasonic wave of a non-plane wave to the imaging area. Ultrasonic imaging device.
10. The ultrasonic imaging apparatus according to claim 9, wherein the transmitting and receiving unit performs transmission a plurality of times with different positions of the transmission focus with respect to the imaging region,
An image addition unit that obtains the side lobe artifact removed image by the processing of the image generation unit, the component extraction unit, the side lobe noise removal unit, and the side lobe removal image generation unit for each of the plurality of transmissions, and then adds them. An ultrasonic imaging apparatus further comprising:
An ultrasonic image of an imaging area is received, and a pixel value distribution of the image is determined for a predetermined direction according to an incident angle when the ultrasonic wave is irradiated to the imaging area, and is included in the high frequency component of the pixel value distribution. An image processing apparatus characterized by removing side lobe artifacts by removing noise components.