Ultrasound imaging method and ultrasound diagnostic apparatus

Abstract

To provide an ultrasonic image formation method which can reduce the image quality deterioration of an ultrasonic image.SOLUTION: An ultrasonic image formation method comprises: a first step (S1) of calculating three-dimensional coordinates of a vibrator from a three-dimensional image in which an array probe is displayed; a second step (S2) of calculating each coordinate of the vibrator in an image space of the ultrasonic image; a third step (S3) of calculating a propagation path to each coordinate of the vibrator from a position of a pixel of the image space; a fourth step (S4) of calculating a propagation distance and a propagation time difference of an ultrasonic echo that propagates along the propagation path; a fifth step (S6) of calculating a pixel value of the pixel by performing addition processing of adding a time signal assumed as a reflection wave from the pixel according to the propagation time difference; and a sixth step (S6) of forming the ultrasonic image. Before the third step, a sound speed in a subject is determined on the basis of sound speed data and a three-dimensional image, and the sound speed distribution in the image space is generated. In the third step, the propagation path is calculated on the basis of the sound speed distribution.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an ultrasonic imaging method and an ultrasonic diagnostic apparatus.

Background Art

[0002] In a conventional ultrasonic diagnostic apparatus, an ultrasonic beam is formed by an ultrasonic pulse output from an array probe in which a plurality of ultrasonic transducers are arranged, and an ultrasonic echo from a subject is acquired while scanning the ultrasonic beam, and a tomographic image (for example, a B-mode image) inside a living body as the subject is obtained.

[0003] In this method, since it is premised that the position coordinates of each arranged ultrasonic transducer are known and the coordinates are represented by a relatively simple function such as a straight line or an arc, the focus and its direction of the ultrasonic beam can be controlled by relatively delaying the pulse voltage signals that excite adjacent arranged ultrasonic transducers. Also, for the received ultrasonic echo (echo signal), the virtual distance difference from the virtual focus to each ultrasonic transducer is calculated, and the echo signal is delayed by the ultrasonic propagation time difference calculated on the assumption that the speed of sound is known and constant from the calculated distance difference. Then, the instantaneous values of the delayed echo signals are added, a signal of a necessary frequency is extracted by quadrature detection or the like, and luminance modulation is performed by taking a logarithm or the like.

[0004] On the other hand, the inventors of the present application have developed an ultrasonic diagnostic apparatus provided with a flexible array probe whose array shape is deformable (see, for example, Patent Document 1). In the ultrasonic diagnostic apparatus described in Patent Document 1, when applying a conventional method effective in the case where the array shape is linear or arc-shaped, there is a problem that the image quality of the obtained ultrasonic image (tomographic image) deteriorates when the coordinates of each transducer in the deformed array shape are not on a straight line or an arc.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] The present invention has been made in view of the above circumstances, and its object is to provide an ultrasound image forming method and an ultrasound diagnostic apparatus that can reduce the degradation of ultrasound image quality. [Means for solving the problem]

[0007] To solve the above problems, the ultrasonic image forming method according to the present invention is An ultrasound imaging method using an ultrasound diagnostic device, A first step is to calculate the three-dimensional coordinates of a plurality of transducers arranged on the array probe from a three-dimensional image showing the subject and the array probe of the ultrasound diagnostic device, A second step involves setting up an image space composed of multiple pixels for forming an ultrasonic image, and calculating the coordinates of each of the multiple transducers in the image space from the three-dimensional coordinates, A third step of calculating the propagation path of each ultrasonic echo that propagates from the pixel position to each coordinate of the plurality of transducers when the plurality of transducers are driven simultaneously to transmit and receive ultrasonic pulses and ultrasonic echoes, A fourth step involves calculating the propagation time or propagation distance of the ultrasonic echo propagating along the propagation path, and calculating the propagation time difference of each ultrasonic echo based on the propagation time or propagation distance. A fifth step involves performing an addition process for each pixel, where the time signals extracted from each ultrasonic echo and having a predetermined time width, which are assumed to be reflected waves from the pixel, are added together according to the propagation time difference, thereby calculating the pixel value of the pixel. A sixth step of forming the ultrasonic image based on the pixel values ​​of the plurality of pixels, Includes, Prior to the third step, the sound velocity inside the subject is determined based on the sound velocity data and the three-dimensional image, and a sound velocity distribution in the image space is generated based on the sound velocity. The third step is characterized by calculating the propagation path based on the sound velocity distribution.

[0008] The aforementioned ultrasonic image formation method is The process further includes an extraction step of extracting a group of oscillators for each of the aforementioned pixels, wherein the angle between the normal vector at each coordinate of the plurality of oscillators and the propagation path falls within a predetermined angular range. In the fifth step, the system can be configured to perform the addition process only for the ultrasonic echoes received by the transducer group for each pixel.

[0009] The aforementioned ultrasonic image formation method is The process further includes an extraction step of extracting a group of oscillators for each pixel, the group consisting of oscillators whose propagation time or propagation distance falls within a predetermined time range or distance range. In the fifth step, the system can be configured to perform the addition process only for the ultrasonic echoes received by the transducer group for each pixel.

[0010] The aforementioned ultrasonic image formation method is Extraction step for each pixel: Extracting a group of oscillators consisting of oscillators whose propagation time or propagation distance falls within a predetermined time range or distance range; The process further includes a selection step of selecting a first central oscillator from the group of oscillators, selecting a first group of oscillators consisting of N oscillators (where N is an integer of 2 or more) centered on the first central oscillator from the plurality of oscillators, selecting a second central oscillator from the group of oscillators, and selecting a second group of oscillators consisting of M oscillators (where M is an integer of 2 or more) centered on the second central oscillator from the plurality of oscillators, In the fifth step, the system can be configured to perform the addition process for each pixel by adding the time signal for the ultrasonic echo received by the first group of transducers and adding the time signal for the ultrasonic echo received by the second group of transducers.

[0011] In the aforementioned ultrasonic image formation method, The extraction step can be configured to allow changing the time range or distance range for each pixel.

[0012] In the aforementioned ultrasonic image formation method, The array probe is a flexible array probe whose array shape can be changed. If the array shape changes after the formation of the ultrasound image, steps 1 through 6 are performed again, If the array shape has not changed after the formation of the ultrasound image, the system can be configured to repeat only steps 5 and 6.

[0013] To solve the above problems, the ultrasonic diagnostic apparatus according to the present invention An array probe that transmits and receives ultrasonic pulses and ultrasonic echoes, A control device for forming an ultrasound image, An ultrasound diagnostic device comprising, The aforementioned array probe is A main body that can change shape to conform to the subject, The main body comprises a plurality of vibrators arranged in the main body, The control device is A drive unit for driving the plurality of vibrators, A first process that calculates the three-dimensional coordinates of the plurality of oscillators from a three-dimensional image showing the subject and the array probe. A second process involves setting an image space composed of multiple pixels for forming the aforementioned ultrasonic image, and calculating the coordinates of each of the multiple transducers in the image space from the three-dimensional coordinates. A third process for calculating the propagation path of each ultrasonic echo that propagates from the pixel position to each coordinate of the plurality of transducers when the plurality of transducers are driven simultaneously to transmit and receive ultrasonic pulses and ultrasonic echoes, A fourth process of calculating the propagation time or propagation distance of the ultrasonic echo propagating along the propagation path, and calculating the propagation time difference of each ultrasonic echo based on the propagation time or the propagation distance. An arithmetic unit that executes, for each pixel, an addition process of adding time signals having a preset time width, which are time signals extracted from each ultrasonic echo and are assumed to be reflected waves from the pixel, according to the propagation time difference, and calculating the pixel value of the pixel, a fifth process. An image forming unit that forms the ultrasonic image based on the pixel values of the plurality of pixels. Comprising: Before the third process, the arithmetic unit determines the speed of sound inside the subject based on the speed of sound data and the three-dimensional image, generates a speed of sound distribution in the image space, and in the third process, calculates the propagation path based on the speed of sound distribution.

[0014] The ultrasonic diagnostic apparatus Further includes an extraction unit that extracts, for each pixel, a group of vibrators composed of vibrators in which the angle formed by the normal line at each coordinate of the plurality of vibrators and the propagation path is included in a predetermined angle range. In the fifth process, the arithmetic unit can be configured to perform the addition process only for the ultrasonic echoes received by the group of vibrators for each pixel.

[0015] The ultrasonic diagnostic apparatus Further includes an extraction unit that extracts, for each pixel, a group of vibrators composed of vibrators in which the propagation time or the propagation distance is included in a predetermined time range or distance range. In the fifth process, the arithmetic unit can be configured to perform the addition process only for the ultrasonic echoes received by the group of vibrators for each pixel.

[0016] The ultrasonic diagnostic apparatus For each pixel, an extraction unit that extracts a group of vibrators composed of vibrators in which the propagation time or the propagation distance is included in a predetermined time range or distance range. The system further comprises a selection unit that selects a first central oscillator from the group of oscillators, selects a first group of oscillators consisting of N oscillators (where N is an integer of 2 or more) centered on the first central oscillator from the plurality of oscillators, selects a second central oscillator from the group of oscillators, and selects a second group of oscillators consisting of M oscillators (where M is an integer of 2 or more) centered on the second central oscillator from the plurality of oscillators, The calculation unit can be configured in the fifth process to perform the addition process for each pixel, adding the time signal for the ultrasonic echo received by the first group of transducers and adding the time signal for the ultrasonic echo received by the second group of transducers.

[0017] In the aforementioned ultrasound diagnostic apparatus, The extraction unit can be configured to change the time range or the distance range for each pixel. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide an ultrasound image forming method and an ultrasound diagnostic apparatus that can reduce the degradation of ultrasound image quality. [Brief explanation of the drawing]

[0019] [Figure 1] This figure shows the configuration of the ultrasound diagnostic apparatus according to the present invention. [Figure 2] The present invention relates to an ultrasound diagnostic apparatus, wherein (A) is a diagram showing the configuration of an array probe, and (B) is a diagram showing the configuration of a marker. [Figure 3] This is a flowchart of the ultrasonic image formation method according to the present invention. [Figure 4] This figure illustrates the method for calculating the propagation path of ultrasonic echoes in image space according to the present invention. [Figure 5] This figure illustrates the method for calculating the propagation time difference of ultrasonic echoes in the image space according to the present invention. [Figure 6](A) A diagram illustrating the addition process after the extraction step of the present invention. (B) A diagram illustrating the addition process after the extraction step and selection step of Modification 1. [Figure 7] This is a diagram illustrating the extraction step in modified example 2. [Figure 8] Here are some examples of ultrasound images: (A) is an image obtained using a conventional method, (B) is an image obtained using the ultrasound diagnostic device of Modification 1, (C) is an image obtained using the ultrasound diagnostic device of Modification 2 with an angular range of 0°≦θ≦5°, and (D) is an image obtained using the ultrasound diagnostic device of Modification 2 with an angular range of 0°≦θ≦2°. [Figure 9] This flowchart shows the post-processing of ultrasound images formed by the ultrasound diagnostic apparatus according to the present invention. [Modes for carrying out the invention]

[0020] Hereinafter, embodiments of the ultrasonic image forming method and ultrasonic diagnostic apparatus according to the present invention will be described with reference to the attached drawings.

[0021] Figure 1 shows an ultrasound diagnostic apparatus 100 according to one embodiment of the present invention. The ultrasound image forming method according to one embodiment of the present invention is performed using the ultrasound diagnostic apparatus 100.

[0022] The ultrasound diagnostic device 100 forms an ultrasound image corresponding to a cross-section (slice image) of an MR image (corresponding to the "three-dimensional image" of the present invention) acquired by an MRI (Magnetic Resonance Imaging) device 200. The ultrasound diagnostic device 100 comprises an array probe 110 attached to a subject 300 (in this embodiment, the abdomen of the human body) and a control device 120 for forming an ultrasound image.

[0023] As shown in Figure 2(A), the array probe 110 is a flexible array probe whose array shape can be deformed, and comprises a main body 111 whose shape can be deformed along the subject 300, a plurality of transducers 112 arranged linearly on the main body, a plurality of markers 113 positioned on both sides of the plurality of transducers 112, and a concave lens positioned on the back side of the main body 111 at the position of the transducers 112.

[0024] The transducer 112 is an ultrasonic transducer configured to irradiate the inside of the subject 300 with ultrasonic pulses and receive ultrasonic echoes (echo signals) reflected back from inside the subject 300. In this embodiment, the transducer 112 consists of 192 transducers, and the number of simultaneously driven channels is 128. The number of transducers 112 and / or the number of simultaneously driven channels can be changed as appropriate.

[0025] As shown in Figure 2(B), the marker 113 consists of a polyacetal (POM) sphere 113b placed inside a cylindrical acrylic case 113a, with liquid 113c (olive oil in this embodiment) filled around the sphere 113b. The configuration of the marker 113 can be modified as appropriate, as long as at least the sphere 113b is visible in the MR image.

[0026] Referring again to Figure 1, the control device 120 is connected to the array probe 110 and is configured to communicate with the MRI device 200 via a communication unit (input / output unit) not shown. The control device 120 comprises a drive unit 121, a calculation unit 122, an extraction unit 123, and an image forming unit 124.

[0027] The drive unit 121 is connected to the array probe 110 via a cable or the like. The drive unit 121 is configured to drive a plurality of transducers 112 and cause the plurality of transducers 112 to transmit and receive ultrasonic pulses and their ultrasonic echoes.

[0028] The calculation unit 122 is composed of a digital circuit such as a microcontroller, or a circuit combining analog and digital circuits, and executes the following first to fifth processes. The calculation unit 122 shares various information (including calculation results, etc.) with the drive unit 121, the extraction unit 123, and the image forming unit 124.

[0029] As will be described in detail later, the calculation unit 122 performs the following: a first process to calculate the three-dimensional coordinates of the transducer 112 from the MR image; a second process to calculate the coordinates of the transducer 112 in the image space for forming an ultrasonic image; a third process to calculate the propagation path of the ultrasonic echo propagating from the pixel position in the image space to the coordinates of the transducer 112; a fourth process to calculate the propagation time or propagation distance of the ultrasonic echo propagating along the propagation path; and a fifth process to calculate the pixel value of the pixels in the image space.

[0030] Furthermore, the calculation unit 122 stores sound velocity data, which includes biological tissue information of the subject 300 and sound velocity information associated with said biological tissue information. Before the third processing, the calculation unit 122 determines the sound velocity inside the subject 300 from the sound velocity data and MR images, generates a sound velocity distribution in image space, and calculates the propagation path based on the sound velocity distribution in the third processing.

[0031] The extraction unit 123, like the calculation unit 122, is composed of digital and / or analog circuits. The extraction unit 123 extracts transducers (corresponding to the "transducer group" of the present invention) that receive ultrasonic pulses whose propagation time or propagation distance, calculated by the calculation unit 122 in the fourth processing, falls within a preset time range or distance range. The time range or distance range can be set and changed for each pixel in the image space or collectively.

[0032] The image forming unit 124, like the calculation unit 122, is composed of digital and / or analog circuits and is connected to a display device (not shown). The image forming unit 124 forms an ultrasonic image based on the pixel values ​​calculated by the calculation unit 122 in the fifth process and displays the ultrasonic image on the display device.

[0033] Figure 3 shows a flowchart of an ultrasonic image formation method according to one embodiment of the present invention. The ultrasonic image formation method according to this embodiment is performed using the ultrasonic diagnostic apparatus 100 as described above.

[0034] When an MRI image is acquired by the MRI device 200 with the array probe 110 attached to the subject 300, the markers 113 of the subject 300 and the array probe 110 are displayed in the MR image. The MRI device 200 transmits the acquired MR image to the ultrasound diagnostic device 100.

[0035] In the ultrasound diagnostic device 100 that receives the MR image, the calculation unit 122 calculates the three-dimensional coordinates of the transducer 112 from the MR image (S1). Step S1 corresponds to the first processing and the "first step" of the present invention.

[0036] Any method can be used to calculate the three-dimensional coordinates of the oscillator 112. In this embodiment, the calculation unit 122 calculates the three-dimensional coordinates of the marker 113 from the MR image. For the coordinate system of the three-dimensional coordinate space, the horizontal direction of the sliced ​​image obtained by slicing the MR image is the X-coordinate, the vertical direction of the sliced ​​image is the Y-coordinate, and the slicing direction is the Z-coordinate.

[0037] The calculation unit 122 pre-stores information necessary for calculating the three-dimensional coordinates of the oscillators 112, such as the size of the markers 113, the positional relationship between the markers 113 and the oscillators 112, and the spacing between the oscillators 112. Therefore, once the calculation unit 122 calculates the three-dimensional coordinates of the markers 113, it can calculate the three-dimensional coordinates of the oscillators 112 based on the three-dimensional coordinates of the markers 113.

[0038] Furthermore, the calculation unit 122 analyzes the image information (e.g., brightness) of the MR image to identify the biological tissue of the subject 300 displayed in the MR image. If the calculation unit 122 identifies, for example, that the MR image displays adipose tissue and muscle tissue of the subject 300, it determines the sound velocity C1 corresponding to the adipose tissue and the sound velocity C2 corresponding to the muscle tissue based on the stored sound velocity data, and calculates the three-dimensional coordinates of the boundary between the adipose tissue and the muscle tissue (the boundary between sound velocity C1 and sound velocity C2).

[0039] Next, the calculation unit 122 calculates the coordinates of the transducer 112 in the image space for forming an ultrasonic image and generates a sound velocity distribution in the image space (S2). Step S2 corresponds to the second processing and the "second step" of the present invention.

[0040] Specifically, the calculation unit 122 first sets up an image space for forming an ultrasonic image. Although an ultrasonic image is a two-dimensional image, the set up image space includes three-dimensional information. After setting up the image space, the calculation unit 122 performs a coordinate transformation on the three-dimensional coordinates of the transducer 112 and calculates the coordinates of the transducer 112 in the image space. The calculation unit 122 also performs a coordinate transformation on the three-dimensional coordinates of the sound velocity boundary line and calculates the coordinates of the boundary line in the image space to generate the sound velocity distribution in the image space.

[0041] Next, the calculation unit 122 calculates the propagation path of the ultrasonic echo that propagates from the pixel position to the coordinates of the transducer 112 based on the sound velocity distribution for each pixel constituting the image space (S3). Step S3 corresponds to the third processing and the "third step" of the present invention.

[0042] Figure 4 shows an example of a method for calculating the propagation path of an ultrasound echo. In Figure 4, the boundary line between the sound velocity C1 corresponding to adipose tissue and the sound velocity C2 corresponding to muscle tissue is located slightly above the center of the image space (towards the array probe 110). That is, the area above the boundary line corresponds to sound velocity C1, and the area below the boundary line corresponds to sound velocity C2.

[0043] In the sound velocity distribution described above, when multiple transducers 112 are driven simultaneously to transmit and receive ultrasonic pulses and ultrasonic echoes with pixel Pi, the multiple transducers 112 receive ultrasonic echoes (echo signals) returning from pixel Pi via a piecewise linear path. The calculation unit 122 calculates, for example, the propagation path (L1+L2) of the ultrasonic echo propagating from pixel Pi to the coordinates of transducer 112i based on the sound velocity distribution and Snell's law. Similarly, the calculation unit 122 calculates the propagation path from pixel Pi to all transducers 112, and then performs the same propagation path calculation for pixel Pi for all pixels that make up the image space of the ultrasonic image.

[0044] Next, the calculation unit 122 calculates the distance of the propagation path (propagation distance) and calculates the propagation time difference of the ultrasonic echo propagating along the propagation path (S4). Step S4 corresponds to the fourth process and the "fourth step" of the present invention.

[0045] In the case of Figure 4, the propagation distance is the sum of the distance along propagation path L1 and the distance along propagation path L2. For the sake of simplicity, in the following explanation, we will assume that the sound velocity distribution in image space is a single sound velocity.

[0046] Figure 5 shows an example of a method for calculating the propagation time difference of an ultrasonic echo. In Figure 5, transducer 112f is the reference transducer. The reference transducer is the transducer with the shortest propagation distance, and a reference transducer is set for each pixel. If the coordinates of transducer 112f are (Xf, Yf, Zf) and the coordinates of pixel Pi are (Px, Py, Pz), then the propagation distance Lf from pixel Pi to transducer 112f is expressed by the following equation.

number

[0047] The propagation distance Li from pixel Pi to transducer 112i can also be calculated similarly from the coordinates of transducer 112i and pixel Pi. The propagation time difference Ti between the ultrasonic echo received by transducer 112f and the ultrasonic echo received by transducer 112i is given by Ti = (Lf - Li) / C, where C is the single sound velocity in the sound velocity distribution.

[0048] The calculation unit 122 similarly calculates the propagation distance and propagation time difference for all transducers 112 from pixel Pi, and then performs the calculation of propagation distance and propagation time difference performed for pixel Pi for all pixels that make up the image space of the ultrasonic image.

[0049] Next, the extraction unit 123 extracts oscillators 112 whose propagation distance calculated by the calculation unit 122 falls within a preset distance range (S5). Step S5 corresponds to the "extraction step" of the present invention.

[0050] In this embodiment, the extraction unit 123 sets the propagation distance from the pixel to the reference transducer (shortest propagation distance) as the lower limit and the shortest propagation distance + 1% as the upper limit, and extracts transducers 112 whose propagation distance falls within the set distance range. The extraction unit 123 performs the same transducer 112 extraction for all pixels that make up the image space of the ultrasound image. That is, in step S5, a corresponding transducer 112 is extracted for each pixel.

[0051] Furthermore, since the propagation time of an ultrasonic echo propagating along a propagation path can be calculated from the propagation distance and the speed of sound, the propagation distance information is included. For this reason, the extraction unit 123 may extract transducers 112 whose ultrasonic echo propagation time falls within a preset time range.

[0052] Next, the calculation unit 122 performs an addition process to add the reflection time signals (time signals assumed to be reflected waves) extracted from each ultrasonic echo received by each transducer 112, and calculates the pixel value of the pixel based on the added value (S6). Step S6 corresponds to the fifth process and the "fifth step" of the present invention.

[0053] While known methods can be used to add the time signals assumed to be reflected waves from the pixels extracted from the ultrasonic echoes received by each transducer 112, in this embodiment, the addition process is performed only on the transducers 112 extracted in step S5. That is, the calculation unit 122 performs an addition process that adds only the ultrasonic echoes received by the transducers 112 extracted by the extraction unit 123, adding the time signals having a preset time width assumed to be reflected waves from the pixels, according to the propagation time difference calculated in step S4.

[0054] For example, as shown in Figure 6(A), if transducers 112f and 112i are extracted by the extraction unit 123, but transducers 112a, 112b, 112y, and 112z are not extracted by the extraction unit 123, the calculation unit 122 will add the instantaneous values ​​of the time signals of the ultrasonic echoes received by transducers 112f and 112i, but will not add the instantaneous values ​​of the time signals of the ultrasonic echoes received by transducers 112a, 112b, 112y, and 112z.

[0055] The time signal is a signal having a time width preset in the calculation unit 122, and the instantaneous value of the signal is proportional to the reflected wave (ultrasonic echo). In the addition process, when adding the instantaneous values ​​of each time signal, the time of the time signal is shifted according to the propagation time difference. For example, if the propagation time difference of time signal A extracted from ultrasonic echo A is TA, and the propagation time difference of time signal B extracted from ultrasonic echo B is TB, then in the addition process, the instantaneous value of time signal A at time (t+TA) and the instantaneous value of time signal B at time (t+TB) are added. Time (t) is any time included in the above time width.

[0056] After performing the above addition process, the calculation unit 122 extracts the signal of the required frequency by quadrature detection, takes the logarithm, and performs brightness modulation to obtain the brightness value, which is then used as the pixel value of pixel Pi. The calculation unit 122 performs the same series of processes, including addition, quadrature detection, and brightness modulation, that were performed on pixel Pi, for all pixels that make up the image space of the ultrasound image. As a result, the pixel value of all pixels is calculated.

[0057] Next, the image forming unit 124 forms an ultrasonic image based on the pixel values ​​of each pixel calculated by the calculation unit 122, and displays the ultrasonic image on the display device (S7). Step S7 corresponds to the "sixth step" of the present invention.

[0058] As described above, according to the ultrasound diagnostic apparatus 100 and the ultrasound image forming method using the ultrasound diagnostic apparatus 100 according to this embodiment, the deterioration of the ultrasound image quality can be reduced because the control device 120 forms the ultrasound image in step S7 after performing the processing in steps S1 to S6.

[0059] In particular, the calculation unit 122 determines the sound velocity inside the subject 300 from sound velocity data and MR images in the first process, generates a sound velocity distribution in image space in the second process, and calculates the propagation path based on the sound velocity distribution in the third process. As a result, the propagation distance and propagation time difference of the ultrasound echo can be calculated more accurately. Consequently, the degradation of the image quality of the ultrasound image can be further reduced.

[0060] Although embodiments of the ultrasonic image forming method and ultrasonic diagnostic apparatus according to the present invention have been described above, the present invention is not limited to the above embodiments.

[0061] [Example 1] In the ultrasound diagnostic apparatus 100 according to the above embodiment, the control device 120 may include a selection unit. The selection unit selects at least two transducers from the transducers 112 extracted by the extraction unit 123, and selects at least two groups of transducers, each consisting of multiple transducers 112 centered around the selected transducer. The selection unit that has selected the central transducer (central transducer) selects, for example, 128 transducers from 192 transducers 112, centered around the central transducer (for example, 64 transducers in order of proximity to the left of the central transducer, and 63 transducers in order of proximity to the right of the central transducer).

[0062] In this case, the calculation unit 122 performs an addition process that adds only the ultrasonic echoes received by the group of transducers selected by the selection unit, and only the time signals with a preset time width extracted for each pixel according to the propagation time difference calculated in step S4.

[0063] For example, as shown in Figure 6(B), if transducers 112f and 112i are extracted by the extraction unit 123, but transducers 112a, 112b, 112y, and 112z are not extracted by the extraction unit 123, the selection unit selects transducer 112f as the first central transducer and selects the first transducer group Tr1 (transducers 112b, 112f, and 112i) centered on transducer 112f. The selection unit also selects transducer 112i as the second central transducer and selects the second transducer group Tr2 (transducers 112f, 112i, and 112y) centered on transducer 112i. The calculation unit 122 adds the instantaneous values ​​of the time signals of the ultrasonic echoes received by the first transducer group Tr1, and then adds the instantaneous values ​​of the time signals of the ultrasonic echoes received by the second transducer group Tr2. The extraction unit 123, selection unit, and calculation unit 122 perform the same processing on pixel Pi for all pixels that make up the image space of the ultrasound image.

[0064] According to the modified ultrasound diagnostic apparatus and the ultrasound image forming method using the ultrasound diagnostic apparatus, the number of ultrasound echoes used to calculate the pixel value of each pixel is greater than in the above embodiment, thus reducing the degradation of the ultrasound image quality compared to the above embodiment.

[0065] [Differentiation 2] In the ultrasound diagnostic apparatus 100 according to the above embodiment, the calculation unit 122 can be configured to calculate the normals (normal vectors in modified example 2) of the multiple transducers 112 after calculating the coordinates of each transducer 112 in image space, before the fifth processing step. Any method can be used to calculate the normal vectors; for example, the tangents at each coordinate position may be calculated based on the coordinates of each transducer 112, and the normal vectors may be calculated based on the tangents.

[0066] Instead of extracting oscillators 112 whose propagation distance calculated by the calculation unit 122 falls within a predetermined distance range, the extraction unit 123 may extract oscillators 112 whose angle θ between the normal vector N and the propagation path L falls within a predetermined angle range. For example, as shown in Figure 7, the normal vector Nb of oscillator 112b is orthogonal to the line connecting oscillators 112a and 112f, and the angle between the normal vector Nb and the propagation path Lb is θb. The normal vector Nf of oscillator 112f is orthogonal to the line connecting oscillators 112b and 112i, and the angle between the normal vector Nf and the propagation path Lf is θf. The normal vector Ni of oscillator 112i is orthogonal to the line connecting oscillators 112f and 112y, and the angle between the normal vector Ni and the propagation path Li is θi. The normal vector Ny of oscillator 112y is assumed to be perpendicular to the line connecting oscillators 112i and 112z, and the angle between the normal vector Ny and the propagation path Ly is denoted as θy.

[0067] Note that the normal vector N is defined to be orthogonal to the line connecting the positions of the two oscillators 112 on either side of the oscillator 112 of interest. Since oscillators 112a and 112z do not have an oscillator 112 on one side, the normal vector N cannot be defined. For this reason, it is preferable to exclude oscillators 112a and 112z from the extraction targets of the extraction unit 123. However, the normal vector N of the end oscillators 112 (here, oscillators 112a and 112z) may be defined as follows. The normal vector Na of oscillator 112a is defined to be orthogonal to the line connecting oscillators 112a and 112b, and the angle between the normal vector Na and the propagation path La is θa. The normal vector Nz of oscillator 112z is defined to be orthogonal to the line connecting oscillators 112y and 112z, and the angle between the normal vector Nz and the propagation path Lz is θz. In the case of Figure 7, angles θb, θf, and θi are included in a preset angle range, while angles θa, θy, and θz are not included in that angle range. Therefore, the extraction unit 123 extracts a group of oscillators consisting of oscillators 112b, 112f, and 112i.

[0068] The calculation unit 122 performs an addition process on only the ultrasonic echoes received by the group of transducers extracted by the extraction unit 123, adding the instantaneous values ​​of the time signals according to the propagation time difference calculated in the fourth process. In the case of Figure 7, the calculation unit 122 adds the instantaneous values ​​of the time signals of the ultrasonic echoes received by transducers 112b, 112f, and 112i, but does not add the instantaneous values ​​of the time signals of the ultrasonic echoes received by transducers 112a, 112y, and 112z. The calculation unit 122 and the extraction unit 123 perform the same processing on pixel Pi for all pixels that make up the image space.

[0069] Figures 8(A) to 8(D) show examples of ultrasound images when the subject 300 is a graphite-containing agar phantom. Figure 8(A) is an ultrasound image obtained by applying a conventional method effective when the array shape is linear or arc-shaped to the ultrasound diagnostic apparatus described in Patent Document 1. Figure 8(B) is an ultrasound image obtained by the ultrasound image formation method according to Modification 1. Figures 8(C) and 8(D) are ultrasound images obtained by the ultrasound image formation method according to Modification 2, where (C) has an angular range of 0°≦θ≦5° and (D) has an angular range of 0°≦θ≦2°. θ is the angle between the normal vector of the transducer 112 and the propagation path.

[0070] A comparison of (A) and (B) in Figure 8 shows that the ultrasonic image obtained by the ultrasonic image formation method according to Modification 1 has a clearer phantom boundary and reduced image quality degradation compared to the ultrasonic image obtained by the conventional method. Furthermore, a comparison of (B) with (C) and (D) shows that limiting the extraction of the transducer 112 by angle rather than by distance improves the contrast of the ultrasonic image (contrast between the phantom and the non-phantom area). A comparison of (C) and (D) shows that reducing the upper limit of the angle range improves the contrast.

[0071] In the modified example 2, the extraction unit 123 extracts oscillators 112 whose propagation distance is within a predetermined distance range, but instead extracts oscillators 112 whose angle θ between the normal vector and the propagation path is within a predetermined angle range. However, oscillators 112 whose propagation distance is within a predetermined distance range and whose angle θ is within a predetermined angle range may also be extracted. The condition that the propagation distance is within a predetermined distance range can be replaced with the condition that the propagation time is within a predetermined time range. Furthermore, the above angle range may be changed for each pixel.

[0072] [Other variations] The ultrasonic image formation method according to the present invention is an ultrasonic image formation method using an ultrasonic diagnostic device, comprising: a first step of calculating the three-dimensional coordinates of a plurality of transducers arranged on an array probe from a three-dimensional image displayed of a subject and the array probe of the ultrasonic diagnostic device; a second step of setting an image space composed of a plurality of pixels for forming an ultrasonic image and calculating the coordinates of each of the plurality of transducers in the image space from the three-dimensional coordinates; a third step of calculating the propagation path of each ultrasonic echo that propagates from the position of a pixel to each coordinate of the plurality of transducers when ultrasonic pulses and ultrasonic echoes are transmitted and received by simultaneously driving a plurality of transducers; and the propagation time of the ultrasonic echo propagating along the propagation path. Alternatively, the process includes a fourth step of calculating the propagation distance and the propagation time difference of each ultrasound echo based on the propagation time or propagation distance; a fifth step of performing an addition process to calculate the pixel value of each pixel by adding time signals extracted from each ultrasound echo, which have a preset time width and are assumed to be reflected waves from the pixel, according to the propagation time difference; and a sixth step of forming an ultrasound image based on the pixel values ​​of multiple pixels. The configuration can be modified as appropriate if, before the third step, the sound velocity inside the subject is determined based on sound velocity data and a three-dimensional image, a sound velocity distribution in the image space is generated based on the sound velocity, and in the third step, the propagation path is calculated based on the sound velocity distribution.

[0073] In the ultrasonic image forming method according to the present invention, if the array shape changes after the formation of the ultrasonic image, for example, by changing the mounting position of the array probe, steps 1 to 6 may be performed again. On the other hand, if the array shape has not changed after the formation of the ultrasonic image, only steps 5 and 6 may be performed again.

[0074] Figure 9 shows an example of a specific processing flow after ultrasound image formation by the ultrasound diagnostic device 100. After the ultrasound diagnostic device 100 forms an ultrasound image (S11), it determines whether or not to continue the measurement (S12). For example, if the operator performs the operation to start the measurement again, the ultrasound diagnostic device 100 determines to continue the measurement (YES in S12), and if the operator performs the operation to end the measurement or if no operation is performed for a certain period of time, it determines not to continue the measurement (NO in S12).

[0075] If measurement is to be continued (YES in S12), the ultrasound diagnostic device 100 determines whether the array shape of the array probe 110 has changed since the previous ultrasound image formation (S13). This determination may be made by detecting the movement of the array probe 110 using a motion sensor or the like, or by an operator. In the latter case, the operator inputs the determination result into the ultrasound diagnostic device 100.

[0076] If the array shape of the array probe 110 changes (YES in S13), the ultrasound diagnostic device 100 performs steps 1 through 6 (S14). In this case, before step 3, the ultrasound diagnostic device 100 determines the sound velocity inside the subject 300 based on the sound velocity data and the three-dimensional image, generates a sound velocity distribution in the image space based on the sound velocity, and in step 3 calculates the propagation path based on the sound velocity distribution. On the other hand, if the array shape of the array probe 110 does not change (NO in S13), the ultrasound diagnostic device 100 performs only steps 5 and 6 (S15).

[0077] This forms a new ultrasound image (S11), and the ultrasound diagnostic device 100 determines whether or not to continue the measurement (S12). If the measurement is not to be continued (NO in S12), the ultrasound diagnostic device 100 terminates the ultrasound image formation process.

[0078] The ultrasound diagnostic apparatus according to the present invention comprises an array probe for transmitting and receiving ultrasound pulses and ultrasound echoes, and a control device for forming an ultrasound image, wherein the array probe comprises a main body that can change shape along the body, and a plurality of transducers arranged on the main body, and the control device comprises a drive unit for driving the plurality of transducers, a first process for calculating the three-dimensional coordinates of the plurality of transducers from a three-dimensional image showing the body and the array probe, a second process for setting an image space composed of a plurality of pixels for forming an ultrasound image and calculating the coordinates of each of the plurality of transducers in the image space from the three-dimensional coordinates, and each ultrasound that propagates from the pixel position to each coordinate of the plurality of transducers when the plurality of transducers are driven simultaneously to transmit and receive ultrasound pulses and ultrasound echoes. The system includes a calculation unit that performs a third process for calculating the propagation path of an echo, a fourth process for calculating the propagation time or distance of an ultrasonic echo propagating along the propagation path and calculating the propagation time difference of each ultrasonic echo based on the propagation time or distance, and a fifth process for calculating the pixel value of a pixel by performing an addition process in which a time signal extracted from each ultrasonic echo and having a preset time width assumed to be a reflected wave from the pixel, is added according to the propagation time difference, and an image forming unit that forms an ultrasonic image based on the pixel values ​​of multiple pixels. The calculation unit can be configured as appropriate if, before the third process, it determines the sound velocity inside the subject based on sound velocity data and a three-dimensional image and generates a sound velocity distribution in the image space, and in the third process, it calculates the propagation path based on the sound velocity distribution.

[0079] In the above embodiment, the ultrasound diagnostic device 100 acquires three-dimensional images from the MRI device 200, but it may also acquire three-dimensional images from a device other than the MRI device 200 (for example, an X-ray CT device or an optical CT device). [Explanation of symbols]

[0080] 100 Ultrasound diagnostic equipment 110 Array Probes 111 Main body 112 oscillator 113 Markers 120 Control device 121 Drive unit 122 Arithmetic section 123 Extraction part 124 Image forming unit 200 MRI machine 300 subjects

Claims

1. An ultrasound imaging method using an ultrasound diagnostic device, The first step is to calculate the three-dimensional coordinates of a plurality of transducers arranged on the array probe from a three-dimensional image displayed of the subject and the array probe of the ultrasound diagnostic device, A second step involves setting up an image space composed of multiple pixels for forming an ultrasonic image, and calculating the coordinates of each of the multiple transducers in the image space from the three-dimensional coordinates, A third step is to calculate the propagation path of each ultrasonic echo that propagates from the pixel position to each coordinate of the plurality of transducers when the plurality of transducers are driven simultaneously to transmit and receive ultrasonic pulses and ultrasonic echoes, A fourth step involves calculating the propagation time or propagation distance of the ultrasonic echo propagating along the propagation path, and calculating the propagation time difference of each ultrasonic echo based on the propagation time or propagation distance. A fifth step involves performing an addition process for each pixel, adding the time signals extracted from each ultrasonic echo, which are assumed to be reflected waves from the pixel and have a predetermined time width, according to the propagation time difference, in order to calculate the pixel value of the pixel. A sixth step of forming the ultrasonic image based on the pixel values ​​of the plurality of pixels, The extraction step includes, for each pixel, extracting a group of oscillators consisting of oscillators whose angle between the normal vector at each coordinate of the plurality of oscillators and the propagation path falls within a predetermined angular range, In the first step, multiple biological tissues of the subject are identified based on image information including the brightness of the three-dimensional image, the sound velocity corresponding to each of the multiple biological tissues is determined based on pre-stored sound velocity data, and the three-dimensional coordinates of the boundary lines of the multiple biological tissues are calculated. In the second step, the coordinates of the boundary line in the image space are calculated from the three-dimensional coordinates of the boundary line, and a sound velocity distribution in the image space is generated based on the coordinates of the boundary line and the sound velocity. In the third step described above, the propagation path is calculated based on the sound velocity distribution, Prior to the fifth step, based on the coordinates of the plurality of oscillators calculated in the second step, a straight line connecting the oscillators on both sides of the target oscillator is calculated as a tangent, and the normal is calculated as a vector perpendicular to the tangent. In the fifth step, the addition process is performed for each pixel only with respect to the ultrasonic echo received by the group of transducers. An ultrasonic image forming method characterized by the following:

2. The group of oscillators is further comprised of oscillators, for each pixel, whose propagation time or propagation distance falls within a predetermined time range or distance range. The ultrasonic image forming method according to feature 1.

3. In the extraction step, the time range or the distance range can be changed for each pixel. The ultrasonic image forming method according to feature 2.

4. The array probe is a flexible array probe whose array shape can be changed. If the array shape changes after the formation of the ultrasound image, steps 1 through 6 and the extraction step are repeated, If the array shape has not changed after the formation of the ultrasound image, only steps 5 and 6 are repeated. The ultrasonic image forming method according to feature 1.

5. An array probe that transmits and receives ultrasonic pulses and ultrasonic echoes, A control device for forming an ultrasound image, An ultrasound diagnostic device comprising, The aforementioned array probe is A main body that can change shape to conform to the subject, The main body comprises a plurality of vibrators arranged in the main body, The control device is A drive unit for driving the plurality of vibrators, A first process that calculates the three-dimensional coordinates of the plurality of oscillators from a three-dimensional image showing the subject and the array probe. A second process involves setting an image space composed of multiple pixels for forming the aforementioned ultrasonic image, and calculating the coordinates of each of the multiple transducers in the image space from the three-dimensional coordinates. A third process for calculating the propagation path of each ultrasonic echo that propagates from the pixel position to each coordinate of the plurality of transducers when the plurality of transducers are driven simultaneously to transmit and receive ultrasonic pulses and ultrasonic echoes, A fourth process which involves calculating the propagation time or propagation distance of the ultrasonic echo propagating along the propagation path, and calculating the propagation time difference of each ultrasonic echo based on the propagation time or propagation distance. A calculation unit performs a fifth process for each of the aforementioned pixels, which involves adding together time signals extracted from each of the aforementioned ultrasonic echoes, which are assumed to be reflected waves from the aforementioned pixels and have a predetermined time width, in accordance with the propagation time difference, thereby calculating the pixel value of the aforementioned pixel. An image forming unit that forms the ultrasonic image based on the pixel values ​​of the plurality of pixels, For each of the aforementioned pixels, an extraction unit extracts a group of oscillators consisting of oscillators whose angle between the normal vector at each coordinate of the plurality of oscillators and the propagation path falls within a predetermined angular range. Equipped with, The aforementioned arithmetic unit, In the first process, multiple biological tissues of the subject are identified based on image information including the brightness of the three-dimensional image, the sound velocity corresponding to each of the multiple biological tissues is determined based on pre-stored sound velocity data, and the three-dimensional coordinates of the boundary lines of the multiple biological tissues are calculated. In the second process described above, the coordinates of the boundary line in the image space are calculated from the three-dimensional coordinates of the boundary line, and a sound velocity distribution in the image space is generated based on the coordinates of the boundary line and the sound velocity. In the third process described above, the propagation path is calculated based on the sound velocity distribution, Before the fifth process, based on the coordinates of the plurality of oscillators calculated in the second process, a straight line connecting the oscillators on both sides of the target oscillator is calculated as a tangent, and the normal is calculated as a vector perpendicular to the tangent. In the fifth process, the addition process is performed for each pixel only with respect to the ultrasonic echo received by the group of transducers. An ultrasound diagnostic device characterized by the following features.

6. The group of oscillators is further comprised of oscillators, for each pixel, whose propagation time or propagation distance falls within a predetermined time range or distance range. The ultrasound diagnostic apparatus according to feature 5.

7. The extraction unit can change the time range or the distance range for each pixel. The ultrasound diagnostic apparatus according to feature 6.

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