Ultrasonic diagnostic apparatus, control method for ultrasonic diagnostic apparatus, and control program for ultrasonic diagnostic apparatus

Abstract

To provide an ultrasound diagnostic apparatus capable of generating a color Doppler image of high image quality without lowering a frame rate when a transmission / reception condition of an ultrasonic wave is changed by a user.SOLUTION: An ultrasound diagnostic apparatus causes an ultrasonic probe to perform a first ultrasonic scan related to a B mode and a second ultrasonic scan related to a C mode, and generates a color Doppler image with a blood flow image superimposed on a B mode image. When generating the blood flow image, an ensemble number acquired in one-time second ultrasonic scan is determined to be an ensemble number suited for performing a target frame rate on the basis of a transmission / reception condition of ultrasonic waves in the first ultrasonic scan and the second ultrasonic scan designed by a user, and a group of time serial reflection wave data which combine time-serial ensemble data obtained in a plurality of second ultrasonic scans in a temporal direction and increases the ensemble number.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to an ultrasonic diagnostic apparatus, a control method thereof, and a control program for an ultrasonic diagnostic apparatus.

Background Art

[0002] An ultrasonic diagnostic apparatus transmits ultrasonic waves into a subject by an ultrasonic probe, and receives ultrasonic reflected waves (echoes) generated by differences in acoustic impedance of the subject tissue. Further, based on the electrical signal obtained from this reception, an image showing the structure of the internal tissue of the subject is generated and displayed on a monitor. Since the ultrasonic diagnostic apparatus causes little invasion to the subject and can observe the state of the internal tissue in real time with a tomographic image or the like, it is widely used for morphological diagnosis of a living body.

[0003] The ultrasonic diagnostic apparatus is equipped with a Color Flow Mapping (CFM) method. In the CFM method, a Doppler shift (frequency shift) generated in an echo due to the movement of internal tissue such as blood flow is detected, and velocity information and power information are superimposed and displayed as a two-dimensional image on a two-dimensional tomographic image (that is, a B-mode image).

[0004] Generally, in the CFM method, imaging of information obtained from blood flow is performed. Therefore, as an extraction process of a component of blood flow information (hereinafter referred to as "blood flow component") included in an echo, a Moving Target Indicator (MTI) filter is used to remove a component of information (hereinafter referred to as "clutter component") obtained from the movement of tissue and stationary tissue from the echo.

[0005] As this MTI filter, for example, in addition to a FIR filter using the difference in average velocity between the blood flow component and the clutter component, an adaptive type MTI filter that changes coefficients according to an input signal is used. The adaptive type MTI filter obtains a signal in which the phase difference is canceled by obtaining the velocity of the tissue from the signal before the MTI filter input.

[0006] In recent years, as this type of adaptive MTI filter, principal component analysis is performed using a correlation matrix from the Doppler signal before the MTI filter input, and based on the principal components (i.e., eigenvectors) of each order, the blood flow component and the clutter component are identified, whereby an eigenvector type MTI filter that obtains a blood flow image with the clutter component removed has attracted attention (see, for example, Patent Document 1). The eigenvector type MTI filter is useful compared to an FIR filter or the like in that it can remove the clutter component even when the frequency bands of the blood flow component and the clutter component overlap.

[0007] FIG. 1 is a diagram for explaining the processing of a general eigenvector type MTI filter. In FIG. 1, blood flow images with only the eigenvectors of the 0th order component reduced, blood flow images with the eigenvectors of the 0th order to 1st order components reduced, blood flow images with the eigenvectors of the 0th order to 2nd order components reduced... blood flow images with the eigenvectors of the 0th order to nth order components (in FIG. 1, up to the 0th order to 13th order components) reduced are shown in order from the upper left to the lower right.

[0008] In this type of eigenvector type MTI filter, for example, a method is taken in which an appropriate rank cut order (eigenvectors to be reduced) is determined based on the eigenvalues of the eigenvectors (i.e., principal components) of each order obtained by principal component analysis, and a blood flow image with the clutter component removed is obtained.

[0009] Specifically, in this type of eigenvector-based MTI filter, for the plurality of eigenvectors calculated by principal component analysis, the order of the eigenvectors is set such that the order increases in descending order according to the magnitude of the eigenvalues. Usually, since the clutter signal has a greater signal intensity (i.e., eigenvalue) than the blood flow signal, the eigenvectors on the lower order side become the eigenvectors related to the clutter signal, and the eigenvectors on the higher order side become the eigenvectors related to the blood flow component, and the order is assigned to the eigenvectors. And in the eigenvector-based MTI filter, for example, for the eigenvectors of each order whose eigenvalue magnitude is equal to or greater than the threshold, they are regarded as clutter components, and the rank cut order is determined. For example, in FIG. 1, an aspect in which the 4th order component is determined as the rank cut order is shown, and here, a blood flow image obtained by reducing the eigenvectors of the 0th order component to the 4th order component is used as the blood flow image to be displayed.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] By the way, in this type of ultrasonic diagnostic apparatus, there is a demand for the user to be able to change the ultrasonic transmission and reception conditions when generating a color Doppler image in consideration of the inspection object and inspection conditions at that time.

[0012] Examples of such ultrasonic transmission and reception conditions include the transmission and reception line density and transmission and reception depth in ultrasonic scanning for generating a B-mode image (hereinafter referred to as "B-mode scanning" or "first ultrasonic scanning"), and the transmission and reception line density, transmission and reception depth, width of the region of interest (ROI), and flow velocity range in ultrasonic scanning for generating a blood flow image (hereinafter referred to as "C-mode scanning" or "second ultrasonic scanning").

[0013] However, when changing such ultrasonic transmission and reception conditions, there is a problem that the frame rate for generating a color Doppler image may unintentionally become slow for the user, or image quality deterioration may occur in the color Doppler image.

[0014] For example, the user may try to obtain a clearer C-mode image by increasing the transmission and reception line density during C-mode scanning. However, in this case, the transmission and reception time required for each C-mode scan becomes long, and as a result, the frame rate significantly decreases due to this being the bottleneck.

[0015] Also, for example, the user may set a small flow velocity range during C-mode scanning to observe low-flow blood. However, in this case as well, reducing the flow velocity range causes the pulse repetition frequency to decrease (i.e., the pulse repetition interval increases), so the transmission and reception time required for each C-mode scan becomes long, and as a result, the frame rate significantly decreases due to this being the bottleneck.

[0016] Such a decrease in the frame rate of the color Doppler image leads to a decrease in the visibility of the movement of tissues and blood flow, inhibiting accurate ultrasonic examination. That is, in this type of ultrasonic diagnostic apparatus, generally, the frame rate and the image quality are in a trade-off relationship, and depending on the user's settings, there is a risk that either the frame rate or the image quality of the color Doppler image will be sacrificed.

[0017] The present disclosure has been made in view of the above problems, and an object thereof is to provide an ultrasonic diagnostic apparatus, a control method for the ultrasonic diagnostic apparatus, and a control program for the ultrasonic diagnostic apparatus that can generate a high-quality color Doppler image without causing a decrease in the frame rate when the user changes the ultrasonic transmission and reception conditions.

Means for Solving the Problems

[0018] The main disclosure of the present invention for solving the above problems is an ultrasonic diagnostic apparatus that alternately executes a first ultrasonic scan related to the B mode and a second ultrasonic scan related to the C mode on an ultrasonic probe, and generates a color Doppler image in which a blood flow image is superimposed on a B mode image, wherein a C mode image generation unit that generates the blood flow image based on the transmission and reception conditions of ultrasonic waves in the first ultrasonic scan and the second ultrasonic scan specified by a user, determines the number of ensembles acquired in one second ultrasonic scan to a number of ensembles suitable for realizing a target frame rate, an ensemble number determination unit, an ensemble data combining unit that combines temporally consecutive ensemble data obtained by performing the second ultrasonic scan a plurality of times in the time direction to generate a time-series reflected wave data group with an increased number of ensembles, an MTI filter generation unit that performs principal component analysis on the time-series reflected wave data group and calculates filter coefficients of an MTI filter based on a plurality of eigenvectors obtained by the principal component analysis, an MTI filter processing unit that applies the MTI filter to the time-series reflected wave data group and extracts a blood flow signal for generating the blood flow image, and an ultrasonic diagnostic apparatus comprising the same.

[0019] In another aspect, a control method for an ultrasonic diagnostic apparatus that alternately executes a first ultrasonic scan related to the B mode and a second ultrasonic scan related to the C mode on an ultrasonic probe, and generates a color Doppler image in which a blood flow image is superimposed on a B mode image, when generating the blood flow image, based on the transmission and reception conditions of ultrasonic waves in the first ultrasonic scan and the second ultrasonic scan specified by a user, a first process of determining the number of ensembles acquired in one second ultrasonic scan to a number of ensembles suitable for realizing a target frame rate, a second process of combining temporally consecutive ensemble data obtained by performing the second ultrasonic scan a plurality of times in the time direction to generate a time-series reflected wave data group with an increased number of ensembles, Perform principal component analysis on the time-series reflected wave data group, and calculate the filter coefficients of the MTI filter based on a plurality of eigenvectors obtained by the principal component analysis. This is the third process. Apply the MTI filter to the time-series reflected wave data group, and extract a blood flow signal for generating the blood flow image. This is the fourth process. This is a control method for an ultrasonic diagnostic apparatus that executes the above processes.

[0020] In another aspect, A control program for an ultrasonic diagnostic apparatus that alternately executes a first ultrasonic scan related to the B mode and a second ultrasonic scan related to the C mode on an ultrasonic probe, and generates a color Doppler image in which a blood flow image is superimposed on a B mode image. When generating the blood flow image, Based on the transmission and reception conditions of ultrasonic waves in the first ultrasonic scan and the second ultrasonic scan specified by the user, determine the number of ensembles acquired in one second ultrasonic scan to be a number of ensembles suitable for realizing a target frame rate. This is the first process. Combine the temporally consecutive ensemble data obtained in multiple second ultrasonic scans in the time direction to generate a time-series reflected wave data group with an increased number of ensembles. This is the second process. Perform principal component analysis on the time-series reflected wave data group, and calculate the filter coefficients of the MTI filter based on a plurality of eigenvectors obtained by the principal component analysis. This is the third process. Apply the MTI filter to the time-series reflected wave data group, and extract a blood flow signal for generating the blood flow image. This is the fourth process. This is a control program for an ultrasonic diagnostic apparatus that executes the above processes.

Advantages of the Invention

[0021] According to the ultrasonic diagnostic apparatus according to the present disclosure, even when the transmission and reception conditions of ultrasonic waves are changed when the user generates a color Doppler image, it is possible to generate a high-quality color Doppler image without causing a decrease in the frame rate.

Brief Description of the Drawings

[0022]

Figure 1

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Figure 16

Embodiments for Carrying Out the Invention

[0023] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same function are denoted by the same reference numerals, and redundant description is omitted

[0024] [Overall Configuration of Ultrasonic Diagnostic Apparatus] First, with reference to FIGS. 2 to 4, the overall configuration of an ultrasonic diagnostic apparatus 1 according to an embodiment will be described

[0025] FIG. 2 is a schematic block diagram showing the configuration of the ultrasonic diagnostic apparatus 1 according to the present embodiment. FIG. 3 is a block diagram showing the functional configuration of the C - mode image generation unit 7 according to the present embodiment

[0026] The ultrasonic diagnostic apparatus 1 is installed in a medical institution such as a hospital, and is a device that generates ultrasonic images of a subject such as a living body of a patient who is an object to be measured. The ultrasonic diagnostic apparatus 1 is configured by connecting an ultrasonic probe 101 to an ultrasonic diagnostic apparatus main body 100

[0027] The ultrasonic diagnostic apparatus main body 100 includes an operation unit 2, a transmission unit 3, a reception unit 4, a B (Brightness) - mode image generation unit 5, an ROI (Region Of Interest) setting unit 6, a C - mode image generation unit 7, a display processing unit 8, a control unit 9, a storage unit 10, and a display unit 11

[0028] The ultrasonic probe 101 has a plurality of transducers (piezoelectric conversion elements) 101a arranged in a one-dimensional direction. Each transducer 101a converts a drive signal (transmission electrical signal) from a transmission unit 3 described later into ultrasonic waves to generate an ultrasonic beam. Therefore, the user can irradiate the inside of the subject with an ultrasonic beam by placing the ultrasonic probe 101 on the surface of the subject. Then, the ultrasonic probe 101 receives the reflected ultrasonic wave from the inside of the subject, converts the reflected ultrasonic wave into a received electrical signal by the plurality of transducers 101a, and supplies it to a reception unit 4 described later.

[0029] In the present embodiment, a linear ultrasonic probe 101 in which a plurality of transducers 101a are arranged in a one-dimensional direction will be described as an example, but the present invention is not limited thereto. For example, it is also possible to use an ultrasonic probe 101 such as a convex type or a sector type in which a plurality of transducers 101a are arranged in a one-dimensional direction, an ultrasonic probe 101 in which a plurality of transducers 101a are arranged two-dimensionally, or an ultrasonic probe 101 in which a plurality of transducers 101a arranged in a one-dimensional direction swing. Further, based on the control of the control unit 9, the transmission unit 3 selects the transducers 101a used by the ultrasonic probe 101, and controls the transmission depth position and the transmission direction of the ultrasonic beam transmitted by the ultrasonic probe 101 by individually changing the timing and the value of the voltage applied to the transducers 101a.

[0030] Further, the ultrasonic probe 101 may include some functions of a transmission unit 3 and a reception unit 4 described later. For example, the ultrasonic probe 101 generates a drive signal in the ultrasonic probe 101 based on a control signal (hereinafter referred to as a "transmission control signal") for generating a drive signal output from the transmission unit 3, converts the drive signal into ultrasonic waves by the transducers 101a, converts the received reflected ultrasonic wave into a received electrical signal, and generates a reception signal described later based on the received electrical signal in the ultrasonic probe 101.

[0031] Furthermore, although the ultrasonic probe 101 is generally configured to be electrically connected to the ultrasonic diagnostic apparatus main body 100 via a cable, it is not limited thereto. For example, the ultrasonic probe 101 may be configured to transmit and receive transmission signals and reception signals to and from the ultrasonic diagnostic apparatus main body 100 by wireless communication such as UWB (Ultra Wide Band). However, in such a case, it goes without saying that the ultrasonic diagnostic apparatus main body 100 and the ultrasonic probe 101 are configured to include communication units capable of wireless communication.

[0032] The operation unit 2 receives an input from the user and outputs a command based on the user's input to the control unit 9. The operation unit 2 enables the user to select either a mode in which an image (B-mode image) representing the amplitude of the reflected ultrasonic wave as brightness (luminance) is displayed, or a mode in which a color flow mode image (C-mode image) is superimposed and displayed on the B-mode image. Then, the operation unit 2 also includes a function of receiving a designation input of the position of the ROI for displaying the C-mode image on the B-mode image by the user. Further, as the C-mode image to be displayed, there are also C-mode images in display modes including a V-mode in which the flow velocity and direction of blood flow are color-displayed by the blood flow velocity V as a blood flow signal indicating the state of blood flow, a P-mode in which the power of blood flow is color-displayed by the power P of the blood flow as a blood flow signal, and a V-T mode in which the flow velocity and dispersion of blood flow are color-displayed by the blood flow velocity V and the dispersion T as a blood flow signal. The operation unit 2 is to receive an input of the display mode as well when receiving an input of the C-mode from the user. Note that the display modes of the C-mode image may include a T (dispersion) mode, a dP (directional power) mode, and the like. Thus, the C-mode includes a color Doppler mode (V-mode, V-T mode, etc.), a power Doppler mode (P-mode, etc.).

[0033] Further, the operation unit 2 may include a touch panel provided on the display screen of the display unit 11 and configured to receive a touch input from the user.

[0034] The transmission unit 3 performs a transmission process that generates at least a drive signal and causes the ultrasonic probe 101 to transmit an ultrasonic beam. As an example, the transmission unit 3 performs a transmission process of generating a drive signal for transmitting an ultrasonic beam from the ultrasonic probe 101 having the vibrator 101a, and supplies a high-voltage drive signal that occurs at a predetermined timing to the ultrasonic probe 101 based on this drive signal, thereby driving the vibrator 101a of the ultrasonic probe 101. Thereby, the ultrasonic probe 101 can irradiate the subject with an ultrasonic beam by converting the drive signal into ultrasonic waves.

[0035] According to the control of the control unit 9, when the color Doppler image display is turned on, the transmission unit 3 performs, in addition to the transmission process for displaying the B-mode image, the transmission process for the C-mode for displaying the blood flow image. At this time, the transmission unit 3 alternately performs, for example, B-mode scanning and C-mode scanning. In C-mode scanning, while repeatedly transmitting the ultrasonic beam in the same direction (the same line) n (n is, for example, a dozen times such as 16) times (this number of repetitions is referred to as the ensemble number), the ultrasonic beam is transmitted in all directions (all lines) of the ROI set by the ROI setting unit 6. Further, the transmission unit 3 designates additional information for the transmission process for the B-mode image or the transmission process for the C-mode image at the time of the transmission process, and supplies this additional information to the reception unit 4.

[0036] The reception unit 4 performs a reception process of generating a reception signal as an electrical RF (Radio Frequency) signal based on the reflected ultrasonic wave according to the control of the control unit 9. For example, the reception unit 4 receives the reflected ultrasonic wave with the ultrasonic probe 101, and generates a reception signal (beam data) by amplifying the received electrical signal, performing A / D conversion, and performing coherent addition on the received electrical signal converted based on the reflected ultrasonic wave.

[0037] The receiving unit 4 acquires additional information from the transmitting unit 3. If the acquired additional information is additional information for B-mode images, the received signal is supplied to the B-mode image generation unit 5. If the acquired additional information is additional information for C-mode images, the received signal is supplied to the C-mode image generation unit 7. Hereinafter, the received signal for B-mode image generation will be referred to as the "B-mode received signal", and the received signal for C-mode image generation will be referred to as the "C-mode received signal".

[0038] In this embodiment, the receiving unit 4 selects whether the received signal related to the generated image frame is for B-mode images or C-mode images and supplies it to each block. However, the present invention is not limited to this. For example, the received signal related to the generated image frame may be selected by each of the B-mode image generation unit 5 and the C-mode image generation unit 7.

[0039] The B-mode image generation unit 5 performs envelope detection, logarithmic compression, etc. on the B-mode received signal input from the receiving unit 4 according to the control of the control unit 9, adjusts the dynamic range and gain, and performs luminance conversion to generate B-mode image data and output it to the display processing unit 8.

[0040] The ROI setting unit 6 sets the region of interest (ROI) of the C-mode image in the transmitting unit 3 and the display processing unit 8 according to the designation information of the ROI input from the user via the operation unit 2 under the control of the control unit 9.

[0041] The C-mode image generation unit 7 generates C-mode image data according to the C-mode received signal input from the receiving unit 4 under the control of the control unit 9 and outputs it to the display processing unit 8.

[0042] The C-mode image generation unit 7 includes a quadrature detection circuit 71, a corner turn control unit 72, an MTI filter 73, a correlation operation unit 74, a data conversion unit 75, a noise removal spatial filter 76, an inter-frame filter 77, and a C-mode image conversion unit 78 (see FIG. 3).

[0043] The quadrature detection circuit 71 calculates the phase difference between the acquired C-mode reception signal and the reference signal by performing quadrature detection on the C-mode reception signal input from the reception unit 4 in accordance with the control of the control unit 9, and acquires the (complex) Doppler signals I and Q.

[0044] The corner turn control unit 72 arranges the Doppler signals I and Q input from the quadrature detection circuit 71 for each same acoustic line (line) in the depth direction from the ultrasonic probe 101 to the subject and in the ensemble direction of the number of repetitions n of ultrasonic transmission and reception (hereinafter abbreviated as "number of repetitions"), stores them in a memory (not shown), and reads out the Doppler signals I and Q in the ensemble direction for each depth.

[0045] In the received signal (Doppler signals I and Q), in addition to the signal components of the blood flow necessary for C-mode image generation, information on unnecessary blood vessel walls and tissues (clutter components) is also mixed. The MTI filter 73 filters the Doppler signals I and Q input from the corner turn control unit 72 to remove the clutter components in accordance with the control of the control unit 9.

[0046] Next, with reference to FIGS. 4 to 11, the internal configuration of the MTI filter 73 will be described. Note that the MTI filter 73 according to the present embodiment is the above-described eigenvector type MTI filter.

[0047] FIG. 4 is a diagram showing the internal configuration of the MTI filter 73 according to the present embodiment. FIG. 5 is a diagram showing the input / output relationship of the MTI filter 73. FIG. 6 is a diagram showing a method for calculating the MTI filter coefficients of the MTI filter 73. FIG. 7 is a diagram showing the data configuration of the ensemble data used to obtain one frame of the C-mode image.

[0048] The MTI filter 73 includes a principal component analysis execution unit 731, a filter coefficient calculation unit 732, a filtering processing unit 733, an ensemble data number determination unit 734, and an ensemble data combination unit 735. Note that the principal component analysis execution unit 731 and the filter coefficient calculation unit 732 correspond to the "MTI filter generation unit" of the present invention.

[0049] First, with reference to FIGS. 4 to 7, the basic processing of the MTI filter 73 will be described.

[0050] The basic processing of the MTI filter 73 is realized by a principal component analysis execution unit 731, a filter coefficient calculation unit 732, and a filtering processing unit 733. The basic operation methods themselves are the same as those of the MTI filter according to the prior art. However, the MTI filter 73 according to the present embodiment combines the ensemble data Sp obtained during one C-mode scan output from the corner turn control unit 72 by the ensemble data combining unit 735 into ensemble data with an increased number of ensembles by combining the ensemble data for a plurality of C-mode scans (described later with reference to FIG. 10). Using this ensemble data with an increased number of ensembles, the principal component analysis execution unit 731, the filter coefficient calculation unit 732, and the filtering processing unit 733 can execute processing (details will be described later).

[0051] Generally, in the color Doppler method, while performing ultrasonic transmission and reception in the same direction a plurality of times, the region of interest is scanned with ultrasonic waves, and a blood flow signal for generating a blood flow image is extracted from the time-series reflected wave data group received thereby. During one ultrasonic scan, the data sequence of the reflected wave signals (reflected wave data) obtained by ultrasonic transmission and reception performed in the same direction is called ensemble data. Also, the number of repetitions of ultrasonic transmission and reception performed in the same direction during one ultrasonic scan is called the number of ensembles. The number of ensembles in a general color Doppler method is about 5 to 16.

[0052] The Doppler signals I and Q with the number of repetitions n (number of ensembles n) output from the corner turn control unit 72 are used as the ensemble data Sp. At this time, the ensemble data Sp is represented as time-series n input data x(0), x(1),..., x(n - 1) obtained from the same position. It is assumed that x(0), x(1),..., x(n - 1) are arranged in the generated chronological order or the reverse order.

[0053] The corner turn control unit 72 outputs such ensemble data Sp to the ensemble data combining unit 735. Here, when the ensemble data combining unit 735 does not perform the data combining process described later, the ensemble data Sp input from the corner turn control unit 72 to the MTI filter 73 is directly sent to the principal component analysis execution unit 731 and the filtering process unit 733.

[0054] The input and output of the MTI filter 73 are represented by, for example, the following equation (1) (see FIG. 5). y = A reg × x …(1) However, y: an output vector indicating the ensemble data y(0), y(1), …, y(n - 1) output from the MTI filter, A reg : the MTI filter coefficient (an n×n filter matrix), x: an input vector indicating the input data x(0), x(1), …, x(n - 1).

[0055] The MTI filter 73 is represented by the MTI filter coefficient A reg (an n×n matrix filter matrix) as shown in the following equation (2) (see FIG. 6). A reg = b × G × b H …(2) However, b: an orthonormal basis (an n×n matrix), G: a gain matrix (an n×n matrix), b H : the orthonormal basis of b and the Hermitian transpose (an n×n matrix).

[0056] The orthonormal bases b, b H for calculating the MTI filter 73 consist of a plurality of eigenvectors obtained by principal component analysis. The orthonormal bases b, b H are represented such that the eigenvector with the largest eigenvalue is the 0th order, and the order increases in descending order according to the magnitude of the eigenvalue. That is, in the orthonormal basis b, the order increases as the column number increases. The orthonormal basis b H is such that the order increases as the row number increases.

[0057] The diagonal components G0, G1, …, G of the gain matrix G n-1 correspond to the clutter reduction rate of the MTI filter 73. When this diagonal component is 0, the reduction rate corresponds to 100%, and when the diagonal component is 1, the reduction rate corresponds to 0%. The diagonal components G0, G1, …, G n-1 are arranged in ascending order of eigenvalues according to the order. The diagonal components G0, G1, …, G n-1 are set to be divided into 0 and 1, for example, at the order of the boundary corresponding to the rank cut order. The larger the clutter reduction rate of the MTI filter 73, the more 0s there are in the diagonal components G0, G1, …, G n-1 . However, as the diagonal components G0, G1, …, G n-1 , in addition to 0 and 1, it may be configured to take a numerical value including a decimal point between 0 and 1.

[0058] In addition, the gain matrix G (diagonal components G0, G1, …, G n-1 ) is set based on the rank cut order specified by the user or the rank cut order set by the threshold processing of the control unit 9.

[0059] The principal component analysis execution unit 731, the filter coefficient calculation unit 732, and the filtering processing unit 733 execute the above arithmetic processing, for example.

[0060] The principal component analysis execution unit 731 performs principal component analysis on the time-series reflected wave data group in the region of interest obtained during C-mode scanning, and calculates a plurality of eigenvectors that constitute the orthonormal basis b, b H .

[0061] Specifically, the principal component analysis execution unit 731 first obtains, from the corner turn control unit 72, the data of the ensemble data (hereinafter referred to as "ensemble data group Sp1") of each observation point in the region of interest set in the ROI setting unit 6, and generates a matrix C related to the ensemble data group Sp1 (see the following formula (3)) and a matrix C of the Hermitian transpose of the matrix C H . The ensemble data group Sp1 includes input data x0, x1, …, x related to each observation point in the region of interest MIt contains the number of ensembles (i.e., the number of repetitions n), and the matrix C becomes an n×M matrix (see Figure 7). Incidentally, the ensemble data group Sp1 is grouped in frame units with the ensemble data of each observation point at the k-th time out of the n repetitions being F1(k - 1).

Number

[0062] Incidentally, the ensemble data group Sp1 referred to by the principal component analysis execution unit 731 is the ensemble data group obtained by one C-mode scan when the ensemble data combining unit 735 does not perform data combining processing. However, when the ensemble data combining unit 735 performs data combining processing, it is an ensemble data group in which the ensemble data groups obtained by a plurality of consecutive C-mode scans are combined in the time direction to increase the number of ensembles (described later with reference to Figure 10).

[0063] Next, the principal component analysis execution unit 731 calculates the covariance matrix R from the matrices C, C H by Equation (4). R = C × C H …(4)

[0064] Then, the principal component analysis execution unit 731 solves the eigenvalue problem related to the covariance matrix R (i.e., Rb = λb) to calculate the eigenvalues and eigenvectors (i.e., the orthonormal basis b, b H ). At this time, the principal component analysis execution unit 731 typically calculates the eigenvalues and eigenvectors for the n dimensions corresponding to the number of ensembles. Then, the principal component analysis execution unit 731 sends the calculated eigenvalues and eigenvectors to the MTI filter coefficient calculation unit 732.

[0065] At this time, the principal component analysis execution unit 731 sets the order of the eigenvectors such that, for the calculated plurality of eigenvectors, the eigenvector with the largest eigenvalue is set as the 0th order, and the order of the eigenvectors increases in descending order according to the magnitude of the eigenvalues. Usually, since the clutter signal has a larger signal intensity (i.e., eigenvalue) than the blood flow signal, the eigenvectors on the lower order side become the eigenvectors related to the clutter signal, and the eigenvectors on the higher order side become the eigenvectors related to the blood flow component, and the order is assigned to the eigenvectors.

[0066] The MTI filter coefficient calculation unit 732 calculates, for example, the filter coefficient of the MTI filter 73 (i.e., the MTI filter coefficient A Reg ) from a predetermined gain matrix G and the eigenvectors input from the principal component analysis execution unit 731 according to Equation (2).

[0067] Note that the gain matrix G referred to by the MTI filter coefficient calculation unit 732 is set based on, for example, the rank cut-off order specified by the user or the rank cut-off order calculated by threshold processing based on the eigenvalues, as described above. However, considering the existence of eigenvectors representing frequency components including both the clutter signal and the blood flow signal, the gain matrix G may be such that the reduction rate of the eigenvectors of each order (i.e., each diagonal component G0, G1,..., G n-1 ) is represented by a value that is 0 or more and 1 or less (including a decimal point).

[0068] The MTI filtering processing unit 733 applies, for example, the filter coefficient of the MTI filter 73 (i.e., the MTI filter coefficient A Reg ) input to itself to the ensemble data x input to itself, and calculates the ensemble data y after clutter signal removal (i.e., the Doppler signals I, Q related to the blood flow component after clutter signal removal) according to Equation (1). Then, the MTI filtering processing unit 733 outputs the calculated ensemble data y to the correlation calculation unit 74.

[0069] Here, the ensemble data x referred to by the MTI filtering unit 733 is the ensemble data obtained by one C-mode scan when the ensemble data combining unit 735 does not perform the data combining process described later. However, when the ensemble data combining unit 735 performs the data combining process described later, the ensemble data obtained by a plurality of consecutive C-mode scans in the time direction is combined in the time direction to obtain ensemble data with an increased number of ensembles (described later with reference to FIG. 10).

[0070] Next, with reference to FIGS. 8 to 16, the operation mode of the MTI filter 73 when the ensemble data combining unit 735 performs the data combining process will be described together with the configurations of the ensemble number determination unit 734 and the ensemble data combining unit 735.

[0071] FIG. 8 is a diagram for explaining the basic color Doppler image generation process in the ultrasonic diagnostic apparatus 1. In FIG. 8, the length of the bar in the time axis direction represents the time required for one B-mode scan or one C-mode scan.

[0072] FIG. 9 is a diagram for explaining the data combining process in the ensemble data combining unit 735. FIG. 10 is a diagram schematically showing the data combining process of FIG. 9. In FIG. 10, the fan mark with the "B" symbol represents one B-mode scan, and the fan mark with the "C" symbol represents one C-mode scan. Also, CF(t) represents the blood flow image obtained when one C-mode scan is performed, and CF(t + 1) represents the blood flow image obtained when the next C-mode scan is performed.

[0073] FIG. 11 is a diagram showing an overview of the operation of the ultrasonic diagnostic apparatus 1. Regarding the specific flowchart for executing the operation in FIG. 11, it will be described later with reference to FIG. 14.

[0074] The ultrasonic diagnostic apparatus 1 alternately executes B-mode scanning (ultrasonic scanning related to the B mode) and C-mode scanning (ultrasonic scanning related to the C mode) on the ultrasonic probe 101 under the control of the control unit 9, and generates a color Doppler image by superimposing the blood flow image obtained by the C-mode scanning on the B-mode image obtained by the B-mode scanning.

[0075] At this time, in the normal operation (that is, the operation when the data combining process by the ensemble data combining unit 735 is not performed), the ultrasonic diagnostic apparatus 1 generates a B-mode image from the reflected wave data group obtained by one B-mode scan, generates a blood flow image from the reflected wave data group obtained by one C-mode scan, and superimposes them to generate one color Doppler image. Note that one ultrasonic scan (B-mode scan, C-mode scan) means a scan in which the vibrators 101a on one end side of the ultrasonic probe 101 are sequentially driven from the vibrator 101a on one end side to the vibrator 101a on the other end side along the scanning direction, and refers to acquiring the reflected wave data for one frame by one ultrasonic scan.

[0076] As shown in FIG. 8, the frame rate of the color Doppler image in the ultrasonic diagnostic apparatus 1 is determined by the total time of the transmission and reception time of the ultrasonic wave required to execute one B-mode scan and the transmission and reception time of the ultrasonic wave required to execute one C-mode scan. Note that the transmission and reception time of the ultrasonic wave required for one B-mode scan is typically determined by the density of the transmission and reception lines and the display depth of the transmission and reception waves (meaning the depth of the measurement target in the subject; the same applies hereinafter) in the B-mode scan. Also, the transmission and reception time of the ultrasonic wave required for one C-mode scan is typically determined by the density of the transmission and reception lines, the display depth of the transmission and reception waves, the size of the region of interest, the flow velocity range of the observation target, and the ensemble number in the C-mode scan.

[0077] Still, since the density of the transmission / reception lines and the size of the region of interest define the number of times of ultrasonic transmission / reception performed in one ultrasonic scan, they affect the ultrasonic transmission / reception time for one ultrasonic scan. Also, since the display depth of the transmission / reception lines and the flow velocity range of the object to be observed define the pulse repetition frequency of the ultrasonic waves, they affect the ultrasonic transmission / reception time for one ultrasonic scan. Also, as described above, the number of ensembles defines the number of times of ultrasonic transmission / reception in the same direction during C-mode scanning, and thus affects the ultrasonic transmission / reception time for one ultrasonic scan.

[0078] Thus, generally in the ultrasonic diagnostic apparatus 1, when the user changes the density of the transmission / reception lines or the display depth of the transmitted / received waves in B-mode scanning, or the density of the transmission / reception lines, the display depth of the transmitted / received waves, the size of the region of interest, or the flow velocity range of the object to be observed, etc. in C-mode scanning, the frame rate of the color Doppler image will change accordingly (see FIG. 9). Still, at this time, when the user tries to capture a specific observation object more clearly and changes these ultrasonic transmission / reception conditions, usually, when the user specifies the ultrasonic transmission / reception conditions, the frame rate of the color Doppler image may decrease.

[0079] In the ultrasonic diagnostic apparatus 1 according to the present embodiment, in order to solve such a problem, the target frame rate is ensured by automatically adjusting the number of ensembles during C-mode scanning, and on top of that, in order to ensure the filter performance in the MTI filter 73 (that is, to suppress the deterioration of the image quality of the blood flow image due to the compression of the number of ensembles), the combining process of the ensemble data is performed. The ones performing such a process are the ensemble number determination unit 734 and the ensemble data combining unit 735.

[0080] In FIGS. 9 and 10, as an example, along with the operation of changing the transmission / reception conditions of ultrasonic waves by the user, the ensemble number determination unit 734 changes the setting of the number of ensembles acquired in one C-mode scan from 15 to 5, and the ensemble data combining unit 735 combines the ensemble data of three consecutive C-mode scans in the time direction, and shows a mode in which such combined ensemble data is used as the ensemble data for obtaining a blood flow image for one frame.

[0081] More specifically, the ensemble number determination unit 734 determines the number of ensembles acquired in one C-mode scan to be an ensemble number suitable for realizing the target frame rate based on the transmission / reception conditions of ultrasonic waves in the B-mode scan and the C-mode scan specified by the user.

[0082] As described above, since the number of ensembles acquired in one C-mode scan affects the transmission / reception time of ultrasonic waves for one C-mode scan, it is possible to increase the frame rate of the color Doppler image by decreasing the number of ensembles acquired in one C-mode scan. That is, the ensemble number determination unit 734 adjusts the number of ensembles acquired in one C-mode scan so that the frame rate of the color Doppler image determined by the sum of the first transmission / reception time required for performing one B-mode scan and the second transmission / reception time required for performing one C-mode scan approaches the target frame rate.

[0083] In the ultrasonic diagnostic apparatus 1, the user can specify the transmission and reception conditions of ultrasonic waves in B-mode scanning and the transmission and reception conditions of ultrasonic waves in C-mode scanning by using an input operation with the operation unit 2. Here, the transmission and reception conditions of ultrasonic waves in B-mode scanning are, for example, the density of transmission and reception lines and the display depth of transmitted and received waves. Also, the transmission and reception conditions of ultrasonic waves in C-mode scanning are typically the density of transmission and reception lines, the display depth of transmitted and received waves, the size of the region of interest, the flow velocity range of the observation target, and the number of ensembles. Note that, regarding the number of ensembles in C-mode scanning, the user cannot specify it as a parameter for the automatic setting change by the ensemble number determination unit 734.

[0084] The ensemble number determination unit 734 estimates, for example, the first transmission and reception time required to perform one B-mode scan from the transmission and reception conditions of ultrasonic waves in B-mode scanning by using a B-mode data table (not shown) obtained in advance through experiments or simulations. Also, the ensemble number determination unit 734 estimates, for example, the second transmission and reception time required to perform one C-mode scan from the transmission and reception conditions of ultrasonic waves in C-mode scanning by using a C-mode data table (not shown) obtained in advance through experiments or simulations. Then, the ensemble number determination unit 734 adds, for example, the first transmission and reception time and the second transmission and reception time, and calculates the reciprocal thereof as the frame rate of the color Doppler image.

[0085] Note that, in the present embodiment, in order to obtain a blood flow image for one frame, ensemble data for a plurality of C-mode scans is required. At this time, as shown in FIG. 10, the ensemble data combining unit 735 also uses the ensemble data obtained by the C-mode scan performed at a certain timing redundantly as the ensemble data for obtaining the blood flow image at the next timing. Therefore, the frame rate of the color Doppler image is defined by the sum of the first transmission and reception time required to perform one B-mode scan and the second transmission and reception time required to perform one C-mode scan.

[0086] At this time, the target frame rate referred to by the ensemble number determination unit 734 may be a value specified by the user, or may be an appropriate value set in advance. Further, such a target frame rate may be the frame rate set by the user before changing the setting of the ultrasonic transmission / reception conditions.

[0087] Incidentally, FIG. 12 is a diagram showing an example of a display screen of a user interface for the user to set the target frame rate. FIG. 12A shows an example of an icon R1 for switching between "ON" (i.e., set) and "OFF" (i.e., not set) of the user setting of "target frame rate". Further, FIG. 12B shows an example of an icon R2 for the user to set the "target frame rate". In the icon R2 of FIG. 12B, the user can set the "target frame rate" to a desired value by pressing the "+" symbol or the "-" symbol.

[0088] For example, as shown in FIG. 11, when the ultrasonic transmission / reception conditions of B-mode scanning or C-mode scanning are changed by the user, the ensemble number determination unit 734 updates the ensemble number. At this time, for example, the ensemble number determination unit 734 adjusts the ensemble number to the one that makes the estimated frame rate of the color Doppler image, which is determined by the sum of the first transmission / reception time required to execute one B-mode scan and the second transmission / reception time required to execute one C-mode scan among the ensemble numbers that can be changed in terms of device specifications, closest to the target frame rate so that the target frame rate before the change of the ultrasonic transmission / reception conditions is maintained. However, the determination method can be changed in various ways. For example, the ensemble number may be adjusted under the condition that the frame rate of the color Doppler image is greater than the target frame rate.

[0089] In this way, through the processing of the ensemble number determination unit 734, based on the ultrasonic transmission and reception conditions in the B-mode scan and the C-mode scan specified by the user, the number of ensembles acquired in one C-mode scan is automatically determined to be an ensemble number suitable for achieving the target frame rate.

[0090] However, reducing the number of ensembles acquired in one C-mode scan will cause a decrease in the filter performance of the MTI filter 73 and lead to image quality degradation of the blood flow image.

[0091] FIG. 13 is a diagram showing the relationship between the number of ensembles acquired in one C-mode scan and the filter performance (eigenvectors obtained by the MTI filter 73) of the MTI filter 73.

[0092] In the eigenvector type MTI filter 73, each eigenvector (i.e., each order eigenvector) is a spatio-temporal vector expressed on the eigen space obtained by principal component analysis, and is a composite vector of a plurality of frequency components representing characteristic frequency changes in the time direction. In such an MTI filter 73, the eigenvector is calculated by performing principal component analysis on the time series of reflected wave data groups obtained during the C-mode scan, as described with reference to FIG. 6. The number of eigenvectors that can be represented by the MTI filter 73 is typically the same as the number of ensembles acquired in one C-mode scan.

[0093] Therefore, as shown in FIG. 13, when the number of ensembles acquired in one C-mode scan is T, the number of eigenvectors that can be represented by the MTI filter 73 is T. At this time, the fewer the number of eigenvectors that can be represented by the MTI filter 73, the more a clutter component (i.e., the frequency band of the clutter component) and a blood flow component (i.e., the frequency band of the blood flow component) are mixed in one eigenvector. Therefore, it becomes difficult to completely separate the clutter component and the blood flow component with such an MTI filter 73.

[0094] From this perspective, the ensemble data combiner 735 combines the temporally consecutive ensemble data obtained from multiple C-mode scans in the time direction to increase the number of ensembles and generate a time-series reflected wave data group with an increased number of ensembles in order to ensure the number of ensembles necessary to achieve a predetermined filter performance with the MTI filter 73. That is, the ensemble data combiner 735 obtains a time-series reflected wave data group with an increased number of ensembles by combining the temporally consecutive ensemble data obtained from multiple C-mode scans with the B-mode scan in between (see FIG. 10).

[0095] Specifically, the ensemble data combiner 735 sequentially acquires the ensemble data (ensemble data group Sp1 shown in FIG. 7) of each observation point within the region of interest set in the ROI setting unit 6 from the corner turn controller 72. The ensemble data combiner 735 is configured to temporarily hold the ensemble data group Sp1 for several time instants (i.e., for several C-mode scans) acquired from the corner turn controller 72, and combines the past ensemble data group Sp1 corresponding to the number of data combinations determined by itself with the ensemble data group Sp1 obtained at the current time. The ensemble data combiner 735 thus sends the ensemble data group Sp1 with an increased number of ensembles to the principal component analysis execution unit 731 and the filtering processing unit 733. Then, each time the ensemble data combiner 735 acquires a new ensemble data group Sp1 from the corner turn controller 72, it executes such data combination processing.

[0096] In this way, by increasing the number of ensembles in the time-series reflected wave data group, the number of eigenvectors that can be represented by the MTI filter 73 also increases. In the examples of FIGS. 9 and 10, by combining the ensemble data of three C-mode scans, the number of eigenvectors that can be represented by the MTI filter 73 can be expanded from the number of ensembles "5" acquired in one C-mode scan to "15".

[0097] Here, the ensemble data combining unit 735 determines the number of combined ensemble data based on the number of ensembles acquired by C-mode scanning determined by the ensemble number determination unit 734 and the number of ensembles required to achieve a predetermined filter performance with the preset MTI filter 73.

[0098] At this time, for example, the ensemble data combining unit 735 determines the number of combined ensemble data such that the number of ensembles obtained by combining temporally consecutive ensemble data obtained by a plurality of C-mode scans is equal to or greater than the number of ensembles required to achieve a predetermined filter performance with the preset MTI filter 73. However, if the number of combined ensemble data is excessively increased, it becomes difficult to accurately extract the blood flow component due to the influence of the movement of the blood flow that changes moment by moment. Therefore, the number of combined ensemble data is preferably set to the minimum necessary such that the number of ensembles obtained by combining temporally consecutive ensemble data obtained by a plurality of C-mode scans is near the number of ensembles required to achieve a predetermined filter performance with the MTI filter 73.

[0099] In the examples of FIGS. 9 and 10, a mode is shown in which the number of ensembles required to achieve a predetermined filter performance with the MTI filter 73 is set to "15". Here, since the ensemble number determination unit 734 determines the number of ensembles acquired by one C-mode scan to be "5" in relation to the target frame rate, the ensemble data combining unit 735 determines the number of combined C-mode scan ensemble data to be "three times".

[0100] In addition, the number of ensembles required to achieve a predetermined filter performance with the MTI filter 73 is preferably, for example, 8 or more. However, the number of ensembles required to achieve a predetermined filter performance with the MTI filter 73 may be arbitrarily set by the user.

[0101] In the MTI filter 73 according to this embodiment, the above-described principal component analysis execution unit 731, filter coefficient calculation unit 732, and filtering processing unit 733 perform respective arithmetic processes using the time-series reflected wave data group combined by the ensemble data combining unit 735 in this way. As a result, when the transmission and reception conditions of ultrasonic waves are changed when a color Doppler image is generated by the user, it is possible to generate a high-quality color Doppler image in real time without causing a decrease in the frame rate.

[0102] Returning to FIG. 3, the processing of the C-mode image generation unit 7 (correlation calculation unit 74, data conversion unit 75, noise removal spatial filter 76, inter-frame filter 77, C-mode image conversion unit 78) following the processing of the MTI filter 73 will be described.

[0103] The correlation calculation unit 74 calculates the real part D and the imaginary part N of the average value S (average value of the phase difference vector) of the autocorrelation operation of the Doppler signal in the following equation (5) from the Doppler signals I and Q (complex Doppler signal z) filtered by the MTI filter 73 according to the control of the control unit 9.

Equation

[0104] The data conversion unit 75 calculates the blood flow velocity V, the power P, and the variance T from the Doppler signals I and Q filtered by the MTI filter 73 and the real part D and the imaginary part N of the average value S of the autocorrelation operation of the Doppler signal according to the control of the control unit 9. More specifically, the data conversion unit 75 calculates the blood flow velocity V from the real part D and the imaginary part N of the average value S of the autocorrelation operation of the Doppler signal by the following equation (6).

Equation

[0105] Further, the data conversion unit 75 calculates the power P as the average value of the intensity of the Doppler signal from the Doppler signals I and Q (complex Doppler signal z) by the following equation (7). [Number]

[0106] Further, the data conversion unit 75 calculates, according to the following formula (8), the variance T as the ratio of the magnitude of the phase difference vector to the power (where the magnitude is reversed by subtracting from 1) from the real part D and the imaginary part N of the average value S of the autocorrelation operation of the Doppler signal. [Number]

[0107] The noise removal spatial filter 76 filters the power P, the blood flow velocity V, and the variance T calculated by the data conversion unit 75. The noise removal spatial filter 76 has, for example, a keyhole filter and a spatial filter (both not shown).

[0108] The keyhole filter filters the power P, the blood flow velocity V, and the variance T that constitute the frame of the C-mode image to remove noise. In the V-mode and V-T mode, the keyhole filter filters the blood flow velocity V by removing the blood flow velocity V in the region to be removed set by the blood flow velocity V and the power P calculated by the data conversion unit 75. In the V-mode and V-T mode, the blood flow velocity V is used for image display (coloring). In the P-mode, the keyhole filter filters the power P by removing the power P in the region to be removed set by the blood flow velocity V and the power P calculated by the data conversion unit 75. In the P-mode, the power P is used for image display (coloring).

[0109] More specifically, in the V mode and the V-T mode, the keyhole filter regards the blood flow signals in the regions where the blood flow velocity V is smaller than a predetermined threshold as clutter noise, and regards the blood flow signals in the regions where the power P is smaller than a predetermined threshold as background noise, and removes the blood flow velocity V in these regions. Also, in the P mode, the keyhole filter regards the blood flow signals in the regions where the blood flow velocity V is smaller than a predetermined threshold as clutter noise, and regards the blood flow signals in the regions where the power P is smaller than a predetermined threshold as background noise, and removes the power P in these regions.

[0110] The spatial filter is a two-dimensional weighted average filter for smoothing the data of the blood flow velocity V, the power P, and the variance T that constitute the frame of the C-mode image. In the V mode or the V-T mode, the spatial filter filters the blood flow velocity V filtered by the keyhole filter and the variance T calculated by the data conversion unit 75. In the P mode, the spatial filter filters the power P filtered by the keyhole filter.

[0111] The inter-frame filter 77 smooths the changes between frames and filters to leave an afterimage for the blood flow components of each frame constituting the C-mode image corresponding to the display mode operationally input at the operation unit 2, among the blood flow velocity V, the power P, and the variance T filtered by the noise removal spatial filter 76.

[0112] The C-mode image conversion unit 78 performs color mapping on the blood flow velocity V, the power P, and the variance T filtered by the inter-frame filter 77, and converts them into C-mode image data for generation.

[0113] Returning to FIG. 2, the display processing unit 8 constructs display image data to be displayed on the display unit 11 and performs processing to cause the display unit 11 to display the display image data. In particular, when the B mode is selected, as an ultrasonic image, processing is performed to include the B mode image of the B mode image data generated by the B mode image generation unit 5 in the display image data. Further, when the C mode is selected, as an ultrasonic image, composite image data is generated by superimposing the C mode image of the C mode image data generated by the C mode image generation unit 7 on the position of the selected ROI on the B mode image generated by the B mode image generation unit 5, and processing is performed to include this in the display image data.

[0114] The control unit 9 is configured to include, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The control unit 9 reads out various processing programs such as system programs stored in the ROM and expands them in the RAM, and controls the operations of each part of the ultrasonic diagnostic apparatus 1 according to the expanded programs. The RAM forms a work area for temporarily storing various programs executed by the CPU and data related to these programs. The ROM is composed of a non-volatile memory such as a semiconductor, and stores system programs for the ultrasonic diagnostic apparatus 1, various processing programs executable on the system programs, and various data. These programs are stored in the form of computer-readable program codes, and the CPU sequentially executes operations according to the program codes.

[0115] The storage unit 10 is composed of a large-capacity recording medium such as an HDD (Hard Disk Drive), and stores ultrasonic image data (B mode image data, C mode image data, composite image data), gain matrix, frame rate, and the like.

[0116] The display unit 11 is a so-called monitor such as an LCD (Liquid Crystal Display) or an EL (Electro Luminescence) display that displays the image data output from the display processing unit 8.

[0117] Regarding each part of the ultrasonic diagnostic apparatus 1, some or all of the functions of each functional block can be realized as a hardware circuit such as an integrated circuit. The integrated circuit is, for example, an LSI (Large Scale Integration), and depending on the degree of integration, the LSI may also be referred to as an IC (Integrated Circuit), a system LSI, a super LSI, or an ultra LSI. Also, the method of integrating into a circuit is not limited to LSI, and it may be realized by a dedicated circuit or a general-purpose processor, or by using an FPGA (Field Programmable Gate Array) or a reconfigurable processor capable of reconfiguring the connection and setting of circuit cells inside the LSI. Further, some or all of the functions of each functional block may be executed by software. In this case, this software is stored in a storage medium such as one or more ROMs, an optical disk, or a hard disk, and this software is executed by an arithmetic processor.

[0118] [Update Processing of Ultrasonic Transmission / Reception Conditions in Ultrasonic Diagnostic Apparatus] FIG. 14 is a flowchart showing the update processing of the ultrasonic transmission / reception conditions in the ultrasonic diagnostic apparatus 1. Note that the operation flow shown in FIG. 14 is the processing executed by the ensemble number determination unit 734 and the ensemble data combination unit 735 when a change command for the ultrasonic transmission / reception conditions is input from the user.

[0119] In step Sa1, first, the ensemble number determination unit 734 determines whether a change command for the transmission / reception conditions of ultrasonic waves related to B-mode scanning or C-mode scanning has been input from the user. At this time, when a change command for the transmission / reception conditions of ultrasonic waves has been input from the user (step Sa1: YES), the processing proceeds to step Sa2. On the other hand, when a change command for the transmission / reception conditions of ultrasonic waves has not been input from the user (step Sa1: NO), without executing any particular processing, the processing of the series of flowcharts in FIG. 14 is terminated.

[0120] In step Sa2, the ensemble number determination unit 734 calculates the transmission / reception time required for one B-mode scan.

[0121] In step Sa3, the ensemble number determination unit 734 calculates the transmission / reception time required for one C-mode scan.

[0122] In step Sa4, the ensemble number determination unit 734 adds the transmission / reception time required for one B-mode scan calculated in step Sa2 and the transmission / reception time required for one C-mode scan calculated in step Sa3, and calculates the frame rate of the color Doppler image based on the total time.

[0123] In step Sa5, the ensemble number determination unit 734 compares the frame rate of the color Doppler image calculated in step Sa4 with the target frame rate, and determines whether the difference between the frame rate of the color Doppler image calculated in step Sa4 and the target frame rate is equal to or less than a first threshold value (where the first threshold value is a threshold value for determining whether the difference value of the frame rate is sufficiently small). At this time, when the difference between the frame rate of the color Doppler image calculated in step Sa4 and the target frame rate is equal to or less than the first threshold value (step Sa5: YES), the ensemble number determination unit 734 determines the ensemble number in C-mode scanning to be the currently set value, and proceeds to step Sa7. On the other hand, when the difference between the frame rate of the color Doppler image calculated in step Sa4 and the target frame rate is greater than the first threshold value (step Sa5: NO), the process proceeds to step Sa6 in order to change the ensemble number in C-mode scanning.

[0124] In step Sa6, the ensemble number determination unit 734 decrements the ensemble number in C-mode scanning by one from the current set value, returns to step Sa3, and calculates again the transmission / reception time required for one C-mode scanning under the said transmission / reception conditions.

[0125] In step Sa7, the ensemble data combining unit 735 determines whether the ensemble number in C-mode scanning determined in step Sa5 is equal to or less than a second threshold value (where the second threshold value is the ensemble number required to achieve a predetermined filter performance by the MTI filter 73). At this time, when the ensemble number in C-mode scanning determined in step Sa5 is equal to or less than the second threshold value (step Sa7: YES), the process proceeds to step Sa8. On the other hand, when the ensemble number in C-mode scanning determined in step Sa5 is greater than the second threshold value (step Sa7: NO), the process proceeds to step Sa9.

[0126] In step Sa8, the ensemble data combiner 735 calculates the necessary number of combined ensemble data to combine the ensemble data obtained by C-mode scanning multiple times. At this time, the ensemble data combiner 735 divides, for example, the number of ensembles required to achieve predetermined filter performance (e.g., 15) with the preset MTI filter 73 by the number of ensembles in the C-mode scanning determined in step Sa5 (e.g., 5) to calculate the number of combined ensemble data.

[0127] In step Sa9, the ensemble number determination unit 734 and the ensemble data combiner 735 transmit the information related to the determined ultrasonic transmission / reception conditions (i.e., the number of ensembles in C-mode scanning) to the control unit 9, and the transmission unit 3 changes the number of ensembles when performing C-mode scanning.

[0128] In the ultrasonic diagnostic apparatus 1 according to this embodiment, by such a series of processes, when reflecting the ultrasonic transmission / reception conditions at the time of B-mode scanning and the ultrasonic transmission / reception conditions at the time of C-mode scanning specified by the user, it is possible to provide a high-quality color Doppler image with highly suppressed clutter components while maintaining the target frame rate.

[0129] FIG. 15 is a diagram showing a comparison between a blood flow image (lower figure) obtained by performing filter processing in the MTI filter 73 using the ensemble data (here, the ensemble data obtained by C-mode scanning three times) combined by the ensemble data combiner 735 and a blood flow image (upper figure) obtained by performing filter processing in the MTI filter 73 using the ensemble data obtained by one-time C-mode scanning without data combination by the ensemble data combiner 735.

[0130] The upper figure (data combination not performed by the ensemble data combination unit 735) and the lower figure (data combination performed by the ensemble data combination unit 735) in FIG. 15 are blood flow images obtained after performing filter processing by the MTI filter 73 on the same ultrasonic image. Here, blood flow images obtained under the same conditions as in FIGS. 9 and 10 are shown, and the condition is that the number of ensembles in one C-mode scan is 5 times and the number of data combinations in the ensemble data combination unit 735 is 3 times (lower figure).

[0131] The images with "2 / 5", "3 / 5", and "4 / 5" attached to the upper figure in FIG. 15 correspond to the blood flow images when the rank cut order is set to "2", "3", and "4", respectively. In the upper figure of FIG. 15, since the filter processing in the MTI filter 73 is performed using the ensemble data obtained by one C-mode scan, there are only 5 eigenvectors.

[0132] The images with "7 / 15", "9 / 15", "11 / 15", "12 / 15", "13 / 15", and "14 / 15" attached to the lower figure in FIG. 15 correspond to the blood flow images when the rank cut order is set to "7", "9", "11", "12", "13", and "14", respectively. In the lower figure of FIG. 15, since the filter processing in the MTI filter 73 is performed using the combined data of the ensemble data obtained by three C-mode scans, there are 15 eigenvectors.

[0133] Comparing the lower diagram of Fig. 15 (data combination performed by the ensemble data combination unit 735) with the upper diagram of Fig. 15 (data combination not performed by the ensemble data combination unit 735), in the lower diagram of Fig. 15, the blood flow component and the clutter component can be more appropriately separated compared to the upper diagram of Fig. 15. As the rank cut order increases, it can be seen that the clutter component is selectively suppressed in the image and only the blood flow component remains. In other words, in the upper diagram of Fig. 15, since only 5 eigenvectors represent the blood flow component and the clutter component in the blood flow image, the blood flow component and the clutter component cannot be clearly separated, and it can be seen that both the blood flow component and the clutter component remain even as the rank cut order increases.

[0134] Also, in the lower diagram of Fig. 15, as a result of an increase in the number of samples in the time direction compared to the upper diagram of Fig. 15, an effect of noise smoothing can also be observed in the image. That is, in the blood flow image obtained by the ultrasonic diagnostic apparatus 1, for example, there is flickering caused by thermal noise of the electronic circuit, acoustic noise caused by scattering, multiple reflection, or reverberation in the subject, etc. By performing data combination by the ensemble data combination unit 735, this type of flickering can be reduced.

[0135] Fig. 16 is a diagram for explaining the general filter characteristics of the eigenvector type MTI filter. Fig. 16A shows the whole of a measurement signal (for example, the pixel value of a blood flow image) that changes moment by moment, Fig. 16B shows a continuous signal extracted from the measurement signal of Fig. 16A, and Fig. 16C shows a discontinuous signal extracted from the measurement signal of Fig. 16A.

[0136] As described above, the MTI filter 73 according to this embodiment performs filter processing using a time-series reflected wave data group in which the time-series continuous ensemble data obtained by a plurality of C-mode scans are combined in the time direction to increase the number of ensembles. Since such a time-series reflected wave data group is combined data of the ensemble data of each C-mode scan obtained when B-mode scanning and C-mode scanning are alternately performed, a temporally discontinuous portion occurs in the combined portion in such a time-series reflected wave data group (see the R3 region in FIG. 16C).

[0137] MTI filters such as HPF generally used in the prior art decompose a measurement signal into each frequency component to remove clutter. Such an MTI filter functions normally for frequency decomposition when the measurement signal is a continuous signal (FIG. 16B), and can remove clutter with high accuracy. However, when the measurement signal is a discontinuous signal obtained by combining a plurality of continuous signals (FIG. 16C), such an MTI filter decomposes and represents the discontinuous combined portion into each frequency component, so noise is mixed into each frequency component representing the measurement signal, and a lot of noise is also mixed into the blood flow signal after clutter removal.

[0138] On the other hand, unlike a frequency filter, a eigenvector type MTI filter generally represents a measurement signal by eigenvectors (synthetic vectors of a plurality of frequency components representing characteristic frequency changes in the time direction) expressed on an eigen space obtained by principal component analysis. Therefore, even when the measurement signal is a discontinuous signal obtained by combining a plurality of continuous signals (FIG. 16C), the eigenvector type MTI filter can extract the measurement signal as a component corresponding to the signal change of the discontinuous combined portion in addition to the blood flow component and the clutter component. As a result, the eigenvector type MTI filter can prevent the blood flow signal after filter processing from including noise caused by the discontinuous portion.

[0139] In the MTI filter 73 according to this embodiment, based on such filter characteristics, an eigenvector type MTI filter is applied. That is, in the MTI filter 73 according to this embodiment, regardless of the presence of discontinuous portions in the combined portions of the ensemble data of each C-mode scan, it is possible to generate a high-quality blood flow image that does not include noise components.

[0140] As described above, according to the ultrasonic diagnostic apparatus 1 according to this embodiment, even when the transmission and reception conditions of ultrasonic waves are changed when a color Doppler image is generated by the user, a high-quality color Doppler image with highly suppressed clutter components can be generated in real time without reducing the frame rate.

[0141] As described above, although specific examples of the present invention have been described in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

Industrial Applicability

[0142] According to the ultrasonic diagnostic apparatus according to the present disclosure, even when the transmission and reception conditions of ultrasonic waves are changed when a color Doppler image is generated by the user, it is possible to generate a high-quality color Doppler image without causing a reduction in the frame rate.

Explanation of Reference Numerals

[0143] 1 Ultrasonic diagnostic apparatus 2 Operation unit 3 Transmission unit 4 Reception unit 5 B-mode image generation unit 6 ROI setting unit 7 C-mode image generation unit 8 Display processing unit 9 Control unit 10 Storage unit 71 Quadrature detection circuit 72 Corner turn control unit 73 MTI filter 731 Principal component analysis execution unit 732 Filter coefficient calculation unit 733 Filtering processing unit 734 Ensemble number determination unit 735 Ensemble data combining unit 74 Correlation operation unit 75 Data conversion unit 76 Noise removal spatial filter 77 Inter-frame filter 78 C-mode image conversion unit 100 Ultrasonic diagnostic apparatus main body 101 Ultrasonic probe 101a Vibrator

Claims

1. An ultrasonic diagnostic apparatus that alternately executes a first ultrasonic scan related to the B mode and a second ultrasonic scan related to the C mode on an ultrasonic probe, and generates a color Doppler image in which a blood flow image is superimposed on a B mode image, wherein a C mode image generation unit that generates the blood flow image, an ensemble number determination unit that determines, based on transmission / reception conditions of ultrasonic waves in the first ultrasonic scan and the second ultrasonic scan specified by a user, an ensemble number acquired in one execution of the second ultrasonic scan to an ensemble number suitable for realizing a target frame rate; an ensemble data combining unit that combines temporally consecutive ensemble data obtained by a plurality of executions of the second ultrasonic scan in the time direction to generate a time-series reflected wave data group with an increased ensemble number; an MTI filter generation unit that performs principal component analysis on the time-series reflected wave data group and calculates filter coefficients of an MTI filter based on a plurality of eigenvectors obtained by the principal component analysis; an MTI filter processing unit that applies the MTI filter to the time-series reflected wave data group and extracts a blood flow signal for generating the blood flow image; and is provided with The ensemble data combining unit determines the number of combinations of the temporally consecutive ensemble data so as to secure an ensemble number necessary for realizing predetermined filter performance by the MTI filter, based on the ensemble number acquired in one execution of the second ultrasonic scan determined by the ensemble number determination unit. Ultrasonic diagnostic apparatus.

2. The ensemble number determination unit estimates the frame rate of the color Doppler image from the total time of a first transmission / reception time required to execute one first ultrasonic scan and a second transmission / reception time required to execute one second ultrasonic scan, based on the transmission / reception conditions of ultrasonic waves in the first ultrasonic scan and the second ultrasonic scan, and determines the ensemble number acquired in one execution of the second ultrasonic scan so that the frame rate of the color Doppler image approaches the target frame rate. The ultrasonic diagnostic apparatus according to claim 1.

3. When the number of ensembles determination unit is changed by the user, the transmission and reception conditions of the ultrasonic wave in the first ultrasonic scan or the transmission and reception conditions of the ultrasonic wave in the second ultrasonic scan, the target frame rate before the change is maintained. Update the number of ensembles acquired in one second ultrasonic scan. The ultrasonic diagnostic apparatus according to claim 1 or 2.

4. The transmission and reception conditions of the ultrasonic wave in the first ultrasonic scan referred to by the number of ensembles determination unit include the transmission and reception line density and the transmission and reception depth in the first ultrasonic scan. The ultrasonic diagnostic apparatus according to any one of claims 1 to 3.

5. The transmission and reception conditions of the ultrasonic wave in the second ultrasonic scan referred to by the number of ensembles determination unit include the transmission and reception line density, the transmission and reception depth, the size of the region of interest, and the flow velocity range of the observation target in the second ultrasonic scan. The ultrasonic diagnostic apparatus according to any one of claims 1 to 4.

6. It has a setting unit that accepts the designation of the target frame rate by the user. The ultrasonic diagnostic apparatus according to any one of claims 1 to 5.

7. A control method for an ultrasonic diagnostic apparatus that alternately executes a first ultrasonic scan related to the B mode and a second ultrasonic scan related to the C mode on an ultrasonic probe, and generates a color Doppler image in which a blood flow image is superimposed on a B mode image. There is, When generating the blood flow image, based on the transmission and reception conditions of the ultrasonic wave in the first ultrasonic scan and the second ultrasonic scan specified by the user, the number of ensembles acquired in one second ultrasonic scan is determined to be an ensemble suitable for realizing the target frame rate. A first process of determining the number, A second process of generating a time-series reflected wave data group with an increased number of ensembles by combining temporally continuous ensemble data obtained by a plurality of second ultrasonic scans in the time direction, A third process of performing principal component analysis on the time-series reflected wave data group and calculating filter coefficients of an MTI filter based on a plurality of eigenvectors obtained by the principal component analysis, A fourth process of applying the MTI filter to the time-series reflected wave data group and extracting a blood flow signal for generating the blood flow image, Execute, The second process is a control method for an ultrasonic diagnostic apparatus that determines the number of combined ensemble data that are temporally continuous in order to secure the number of ensembles necessary to achieve a predetermined filter performance with the MTI filter, based on the number of ensembles acquired in one second ultrasonic scan determined in the first process.

8. A control program for an ultrasonic diagnostic apparatus that alternately executes a first ultrasonic scan related to the B mode and a second ultrasonic scan related to the C mode on an ultrasonic probe, and generates a color Doppler image in which a blood flow image is superimposed on a B mode image, when generating the blood flow image, a first process of determining the number of ensembles acquired in one second ultrasonic scan to a number of ensembles suitable for achieving a target frame rate, based on the ultrasonic transmission / reception conditions in the first ultrasonic scan and the second ultrasonic scan specified by a user; a second process of generating a time-series reflected wave data group with an increased number of ensembles by combining temporally continuous ensemble data obtained in a plurality of second ultrasonic scans in the time direction; a third process of performing principal component analysis on the time-series reflected wave data group and calculating filter coefficients of an MTI filter based on a plurality of eigenvectors obtained by the principal component analysis; a fourth process of applying the MTI filter to the time-series reflected wave data group and extracting a blood flow signal for generating the blood flow image; is executed, wherein the second process determines the number of combined ensemble data that are temporally continuous in order to secure the number of ensembles necessary to achieve a predetermined filter performance with the MTI filter, based on the number of ensembles acquired in one second ultrasonic scan determined in the first process. A control program for an ultrasonic diagnostic apparatus.

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