JP7377016B2 - Ultrasonic image generation device and its control method - Google Patents

Description

The present invention relates to an ultrasound image generation device and a control method thereof.

An ultrasound diagnostic device is a device that non-invasively observes the internal state of the body by transmitting ultrasound waves into the body and observing the reflected waves. Ultrasonic diagnostic equipment has various modes for displaying images of the strength of reflected waves, changes in frequency, etc., and the user selects an appropriate mode depending on the area to be observed and the purpose of observation. For example, color Doppler mode (also called color mode, flow, CFM (Color Flow Mapping), etc.) is a typical mode used when observing blood vessels and blood flow.

Color Doppler mode uses the Doppler shift caused by the reflection of the ultrasound frequency by a moving body (blood) inside the body, and calculates the speed and direction of tissue movement at each position within the measurement range, as well as the strength of reflected waves. This mode displays an image (color Doppler image) that represents (power) etc. in color. In the color Doppler mode, since it is necessary to transmit and receive ultrasound multiple times for each scanning line, the frame rate is lower than in a mode such as B mode, which only requires transmitting and receiving ultrasound once for each scanning line.

In order to suppress the decrease in frame rate in color Doppler mode, it is known that the number of scanning lines per frame in color Doppler mode is reduced compared to B mode, and the resolution of the color Doppler image is increased by interpolation (Patent Document 1).

Japanese Patent Application Publication No. 10-165402

If the measured values used for interpolation have different signs, the absolute value of the interpolated value will be small. For example, an interpolated value that yields measured values with equal absolute values and different signs may be zero. Since a position with a value of 0 is displayed as being stationary, there is a possibility that the position may be mistaken for a blood vessel wall, etc., even though there should be blood flow there.

The present invention has been made in order to alleviate the problems of the prior art, and provides an ultrasound image generation device and a control method thereof that can improve the quality of color Doppler images generated by interpolation. is one purpose.

The above-mentioned purpose is an ultrasound image generation device that generates a color Doppler image based on measurement values obtained by the Doppler method, and interpolates measurement values at the positions of pixels forming the color Doppler image by interpolating multiple measurement values. an interpolation processing means that applies filter processing to the measured value at the pixel position obtained by the interpolation processing means, and pixel data of a color Doppler image according to the measured value processed by the filter processing means. , and the filtering means applies spatial filter processing to the measured value to be processed using the measured value to be processed and a plurality of measured values in the vicinity of the measured value to be processed. Among a plurality of nearby measured values, for each of the measured values to be processed and the measured values with different signs, it is determined whether the different signs are due to aliasing, and it is determined that the different signs are due to the aliasing phenomenon. If the measured values are of different signs, the measured values are corrected to the original sign values before being used for filter processing, and the interpolation processing means is used to correct the measured values to the original sign values. If it is not determined that the different signs are due to an aliasing phenomenon, interpolation processing is performed using the first interpolation method that does not have an interpolation position where the interpolation value becomes 0, and the opposite signs are determined to be due to an aliasing phenomenon. This is achieved by an ultrasonic image generation apparatus characterized in that, if it is determined that the interpolation value is correct, interpolation processing is performed using a second interpolation method having an interpolation position at which the interpolation value is folded back.

With such a configuration, the present invention can provide an ultrasound image generation device and a control method thereof that can improve the quality of a color Doppler image generated by interpolation.

1 is a block diagram showing an example of a functional configuration of an ultrasound diagnostic apparatus to which the present invention can be applied. FIG. 2 is a block diagram showing an example of a functional configuration of a Doppler processing section in FIG. 1. FIG. FIG. 2 is a block diagram showing an example of the functional configuration of the DSC in FIG. 1. FIG. FIG. 3 is a schematic diagram regarding interpolation processing in DSC. FIG. 3 is a schematic diagram regarding interpolation processing in DSC. It is a flowchart regarding spatial filter processing. FIG. 6 is a diagram illustrating an example of the effect of interpolation processing according to the embodiment. FIG. 6 is a diagram illustrating an example of the effect of spatial filter processing according to the embodiment.

Hereinafter, the present invention will be described in detail based on exemplary embodiments thereof with reference to the drawings. An embodiment in which the present invention is applied to an ultrasonic diagnostic apparatus as an example of an ultrasonic imaging biological apparatus will be described below. However, the present invention does not require a configuration related to transmitting and receiving ultrasonic waves, and can be implemented in any electronic device capable of generating color Doppler images.

Note that the embodiments described below do not limit the present invention in any way. Furthermore, not all of the configurations described in the embodiments are essential to the present invention. Furthermore, unless it is clearly impossible or denied, configurations included in different embodiments may be combined or replaced. Furthermore, in order to avoid redundant explanation, the same or similar components are designated by the same reference numerals throughout in the accompanying drawings.

●(First embodiment)
FIG. 1 is a block diagram showing a configuration example of an ultrasound diagnostic apparatus according to a first embodiment. The ultrasonic diagnostic apparatus 100 includes a main body 120 and an ultrasonic probe 130 that is detachable from the main body 120. The functions of the ultrasound diagnostic apparatus 100 are realized by the control section 101 controlling the operations of each section. The control unit 101 has, for example, a programmable processor, reads a program stored in the nonvolatile memory 102 into the system memory 103 and executes it, and controls the operation of each part of the ultrasound diagnostic apparatus 100. Note that the control unit 101 may use a hardware circuit such as an ASIC (Application Specific Integrated Circuit) or an ASSP (Application Specific Standard Product) for a part of the processing.

For example, the rewritable nonvolatile memory 102 stores programs to be executed by the control unit 101, GUI data, various setting values of the ultrasound diagnostic apparatus 100, and the like. Note that data (drive waveform pattern data) representing a waveform pattern for generating a pulsed voltage used by the drive circuit 104 to drive the transducer 105 of the ultrasound probe 130 is also stored in the nonvolatile memory 102. .

The system memory 103 is used by the control unit 101 to read and execute a program, and is used as a buffer for received signals.

The drive circuit 104 reads from the nonvolatile memory 102 the drive waveform pattern data selected by the control unit 101 from among the plurality of drive waveform pattern data stored in the nonvolatile memory 102 . The drive circuit 104 then generates a pulsed drive voltage based on the read drive waveform pattern data and applies it to the transducer 105 of the ultrasound probe 130 to drive the transducer 105.

The transducer 105 included in the ultrasound probe 130 includes a plurality of transducers arranged one-dimensionally or two-dimensionally. Each vibrator is an electromechanical transducer (eg a piezoelectric element). The vibrator 105 generates (transmits) ultrasonic waves using a voltage applied from the drive circuit 104 . Further, the vibrator 105 converts the received vibration into an electrical signal (observation signal) and outputs it. Note that the detailed explanation of the vibrator 105 will be omitted here for ease of explanation and understanding. The drive circuit 104 separately drives the plurality of transducers included in the transducer 105 at timings depending on the type of measurement, settings, scanning method, and the like.

The receiving circuit 106 performs processing such as noise reduction, amplification, A/D conversion, and addition on the observation signal output by the transducer 105 of the ultrasound probe 130, and stores the resultant signal in the system memory 103 as reflected wave data. Note that by controlling and adding the delay times of the received signals of each vibrator, the focus of the received signals can be improved.

The Doppler processing unit 107 processes the reflected wave data stored in the system memory 103 by applying Doppler methods such as continuous wave Doppler method, pulsed Doppler method, and color Doppler method (also called CFM (Color Flow Mapping)). Signal processing can be applied. Among the reflected wave data stored in the system memory, an address in which reflected wave data of a scanning line to be displayed based on the Doppler method is stored is given to the Doppler processing unit 107 from the control unit 101, for example. The Doppler processing unit 107 calculates the measured value at each measurement point on the scanning line of the object, and outputs the measured value data to the digital scan converter (DSC) 111.

The Doppler method is a method for detecting the speed of a moving object based on the Doppler shift of reflected waves. The color Doppler mode is a mode that displays an image in which the speed, direction, dispersion, and strength (power) of reflected waves of a detected moving object are expressed using colors. In the color Doppler mode, ultrasonic waves are intermittently transmitted and received at multiple measurement points on the same scanning line to detect the velocity of the object at each measurement point. Since ultrasonic waves are transmitted and received multiple times for the same scanning line, the frame rate of a color Doppler image is theoretically lower than the frame rate of a B-mode image. In order to increase the reliability of measurement values, when measurements are performed multiple times at the same measurement point, the frame rate further decreases. In order to improve the frame rate of color Doppler images, color Doppler images are generally generated only for a partial region called a region of interest (ROI) or a color window. The position and size of the partial region for generating a color Doppler image can be set and changed by the user.

When the color Doppler mode is set, the control unit 101 controls the drive circuit 104 to drive the ultrasound transducer with a drive pattern for generating a B-mode image and a color Doppler image.

The B-mode processing unit 109 can perform signal processing corresponding to B-mode (a mode in which the intensity of reflected waves is expressed by brightness) on the reflected wave data stored in the system memory 103. Among the reflected wave data stored in the system memory, an address where reflected wave data of a scanning line for display in B mode is stored is given to the B mode processing unit 109 from the control unit 101, for example. The B-mode processing unit 109 generates an image representing the relationship between the depth and the strength of the reflected wave for each scanning line of the target, and outputs it to the DSC 111. Although this embodiment describes only the B-mode processing unit 109 that generates a B-mode image that is generally combined with a color Doppler image, the ultrasonic diagnostic apparatus 100 can process other images such as an A-mode image and an M-mode image. It has a function to generate known ultrasound images.

The DSC 111 generates a Doppler image based on the measurement data output by the Doppler processing unit 107. The DSC 111 generates a Doppler image by obtaining measurement values for each pixel position of the Doppler image through interpolation processing. Details of the Doppler image generation process will be described later. The DSC 111 also performs coordinate conversion to display the one-dimensional image in the depth direction generated by the B-mode processing unit 109 in units of scanning lines as a two-dimensional image (B-mode image) on the raster scan display unit 112. . The DSC 111 outputs the Doppler image to the filter processing section 114 and the B-mode image to the synthesis section 115.

The filter processing unit 114 applies smoothing processing to the Doppler image output by the DSC 111. As will be described later, the filter processing unit 114 of this embodiment changes the filter processing depending on whether or not the values used for the smoothing processing are affected by the aliasing phenomenon. The filter processing unit 114 also generates a color Doppler image by generating pixel data representing a color according to the measured value after filter processing. The filter processing section 114 outputs the color Doppler image to the composition section 115.

The combining unit 115 combines the color Doppler image output by the filter processing unit 114 and the B-mode image output by the DSC 111, or selects and outputs one without combining. Whether or not to perform synthesis in the synthesis unit 115 and whether to select a Doppler image or a B-mode image when synthesis is not performed depends on the measurement mode, user settings, or user instructions through the operation unit 113. The control unit 101 controls.

The display unit 112 is a display (touch display) that can detect touch operations, and displays the ultrasound image output by the DSC 111. Further, a part of the display screen of the display unit 112 may be used as a display area for software keys. In this case, the ultrasound image output by the DSC 111 is displayed in an area other than the software key display area of the display screen.

The operation unit 113 is an input device for a user to input instructions to the ultrasound diagnostic apparatus 100. This includes physical switches and keys, software keys realized by the display unit 112, and the like.

(Doppler processing unit 107)
FIG. 2 is a block diagram showing an example of the functional configuration of the Doppler processing unit 107. The Doppler processing unit 107 includes a quadrature detection circuit 1071, an MTI filter 1072, an autocorrelation calculation circuit 1073, a velocity dispersion calculation circuit 1074, and a selection and blanking processing circuit 1075.

The quadrature detection circuit 1071 includes, for example, a pair of mixers that multiply a received signal (reflected wave) by a reference frequency signal having the same frequency but a phase difference of 90 degrees, and a pair of low-pass filters that are applied to the output signal of the mixer. The quadrature detection circuit 1071 extracts a pair of signals (I, Q) representing Doppler shift from the received signal (reflected wave).

An MTI (Moving Target Indicator) filter 1072 is applied to a pair of outputs (I, Q) of the quadrature detection circuit 1071, and is used to adjust the lower limit speed of movement to be displayed. The MTI filter 1072 is also called a wall filter and is realized by a high-pass filter. The cutoff frequency of MTI filter 1072 is user adjustable. A pair of outputs (MTII, MTIQ) of the MTI filter 1072 are output to an autocorrelation calculation circuit 1073.

ここで、自己相関を求めるｉはＭＴＩフィルタ１０７２が出力する信号を構成する時系列データのサンプル番号、Ｎは自己相関を求めるサンプル総数である。なお、ＤＥＮＯは速度ベクトルの実部、ＮＵＭＥは速度ベクトルの虚部に相当する。 The autocorrelation calculation circuit 1073 calculates and outputs the autocorrelation (DENO, NUME) and power (POWER) of the received signals (MTII, MTIQ) obtained at different times regarding the same measurement point as follows.

Here, i for which the autocorrelation is to be determined is the sample number of time series data that constitutes the signal output by the MTI filter 1072, and N is the total number of samples for which the autocorrelation is to be determined. Note that DENO corresponds to the real part of the velocity vector, and NUME corresponds to the imaginary part of the velocity vector.

Based on the autocorrelation and power determined by the autocorrelation calculation circuit 1073, the speed variance calculation circuit 1074 calculates and outputs the speed and variance as measured values as follows.
Speed = tan ^-1 (NUME/DENO)
Variance = 1 - (DENO ² +NUME ² ) ^1/2 / POWER
Note that since the method of determining the velocity based on the autocorrelation of received signals (reflected waves) obtained from the same measurement point is well known, further detailed explanation will be omitted.

The selection and blank processing circuit 1075 selects whether to output only the velocity or both velocity and dispersion as measured values. Furthermore, when the power corresponding to the measured value to be output is less than the threshold value, the selection and blanking processing circuit 1075 performs blanking processing to replace the measured value with a specific value (for example, 0). The threshold value used here is, for example, a value corresponding to a predetermined noise level. Since data whose corresponding power is less than the threshold value is considered to be unreliable, it is set to a specific value by blanking. Therefore, the power calculated by the autocorrelation calculation circuit 1073 can be used as the reliability of the measurement value calculated based on the autocorrelation (DEMO, NUME) calculated at the same timing.

(DSC111)
FIG. 3 is a block diagram showing an example of the functional configuration of the DSC 111. The DSC 111 has two frame memories 1111 and 1113, an interpolation calculation circuit 1112, a read address generation circuit 1114, an interpolation coefficient generation circuit 1115, and a write address generation circuit 1116.

The frame memory 1111 stores one frame of measured values and power output from the Doppler processing unit 107. Since the Doppler processing unit 107 outputs data in the order of measurement points, the frame memory 1111 stores measurement values and powers in the order of scanning lines.

The read address generation circuit 1114 generates an address for data to be read from the frame memory 1111 to the interpolation calculation circuit 1112, and supplies the address to the frame memory 1111. Specifically, the read address generation circuit 1114 generates an address for reading data at a plurality of measurement points necessary for generating pixel data in the interpolation calculation circuit 1112. The speed and dispersion data read from the frame memory 1111 are output to an interpolation calculation circuit 1112.

Note that measurement points necessary for obtaining measurement values for each pixel position constituting the Doppler image by interpolation can be known in advance. Therefore, when the interpolation calculation circuit 1112 generates pixel data in a predetermined order, the read addresses to be supplied to the frame memory 1111 and their order can also be known in advance. Therefore, the read address generation circuit 1114 may be configured to sequentially supply a predetermined set of read addresses to the frame memory 1111.

The interpolation coefficient generation circuit 1115 determines an interpolation coefficient to be used in the interpolation calculation in the interpolation calculation circuit 1112 based on the distance from the plurality of measurement points used in the interpolation to the position of the pixel to be interpolated. The interpolation coefficient generation circuit 1115 supplies the determined interpolation coefficient to the interpolation calculation circuit 1112. The interpolation coefficient controls the weight applied to the measurement value in interpolation processing based on weighted addition of measurement value data.

The interpolation calculation circuit 1112 performs an interpolation process using a plurality of measured values read from the frame memory 1111 and interpolation coefficients supplied from the interpolation coefficient generation circuit 1115 to perform measurement at the position of each pixel constituting the Doppler image. Find the value. The interpolation calculation circuit 1112 performs an aliasing judgment when the measured values used for correction have different signs, corrects the measured values according to the judgment result, and then performs interpolation, or corrects the obtained interpolated values. .

FIG. 4 is a diagram showing an example of interpolation processing in this embodiment.
FIG. 4(a) schematically shows the positional relationship between measurement points and pixels forming a Doppler image. The position of the measurement point by the Doppler method (circle in the figure) exists on a scanning line extending radially from the probe position. On the other hand, the coordinates (● in the figure) of pixels constituting the Doppler image are equal in the horizontal and vertical directions. Furthermore, the density of measurement points is lower than the density of pixels in the Doppler image. In this embodiment, the value of each pixel constituting the Doppler image is obtained by interpolating measurement values at measurement points existing around the pixel.

FIG. 4(b) shows an interpolation method for determining the value of one pixel P in FIG. 4(a). In this embodiment, the measured values at four measurement points forming the vertices of the smallest rectangle that includes the pixel position to be interpolated among the rectangles having the measurement points as vertices are used for interpolation. In the example of FIG. 4(b), the measured values at the four measurement points B[L,N], B[L+1,N], B[L,N+1], and B[L+1,N+1] are obtained by interpolating the pixel P. used for. Here, B[m, n] represents the m-th measurement point in the azimuth direction and the n-th measurement point in the depth direction of the measurement point, or a measurement value obtained at the measurement point.

In this embodiment, the measured value of the pixel position is obtained by performing interpolation processing in different directions using four measured values. Specifically, values at two points (★ in the figure) at the same depth as the pixel P are determined by interpolation in the scanning line direction (first interpolation process). Next, a measured value of the position of the pixel P is obtained by interpolation in the azimuth direction (second interpolation process) using the two values obtained in the first interpolation process. Note that the measured value of the position of the pixel P may be obtained by first performing interpolation in the azimuth direction and then performing interpolation in the depth direction.

Here, it is assumed that interpolation is performed using measured values at two points located on both sides of the pixel position on a straight line passing through the pixel position, as shown in FIG. 4(c). FIG. 4(c) shows a case where the measured values at the measurement points A and B are interpolated to obtain the measured value at the pixel position C. When the distance between measurement points A and B is 1, the distance from one measurement point (measurement point A here) to the pixel position C to be interpolated is x, and the interpolation coefficient is y (0≦y≦1) Then,
Measured value at pixel position C = Measured value at measurement point A x (1-y) + Measured value at measurement point B x y
The value of pixel position C can be obtained as follows. Note that here, the interpolation coefficient y is used as the weight of the measurement value of measurement point B, but even if the interpolation coefficient y is used as the weight of the measurement value of measurement point A and the weight of the measurement value of measurement point B is (1-y), good.

Furthermore, in the present embodiment, the interpolation calculation circuit 1112 performs aliasing determination when the signs of two measured values used for interpolation are different, corrects the measured value according to the aliasing determination result, and then performs interpolation. The aliasing determination is a process for determining whether or not the sign reversal is due to an aliasing phenomenon. The aliasing phenomenon is also called aliasing, and is a phenomenon in which a Doppler shift exceeding the maximum detected Doppler shift frequency appears as a Doppler shift of the opposite sign.

A measured value whose sign has been reversed due to the aliasing phenomenon is originally a value exceeding the maximum value of the opposite sign. Therefore, the interpolation calculation circuit 1112 corrects the measured value whose sign is determined to be reversed due to the aliasing phenomenon to the original value before using it for interpolation. On the other hand, conventionally, measured values for which it is determined that the sign reversal is not due to an aliasing phenomenon are used for interpolation without being corrected. At this time, the pair of measured values used for interpolation are values sandwiching 0, so the interpolated value approaches 0. Therefore, the problems mentioned above arise.

The interpolation calculation circuit 1112 in this embodiment performs an aliasing determination when two measured values used for interpolation have different signs, and corrects the measured values even when it is determined that the reversal of signs is not due to an aliasing phenomenon. Then perform interpolation. Specifically, the interpolation calculation circuit 1112 performs interpolation after correcting the measured value so that the absolute value of the interpolated value does not become zero.

The aliasing determination may be, for example, a determination that when the absolute values of two measured values exceed a threshold value, the signs have been reversed due to the influence of aliasing. For example, when the speed is determined as tan ⁻¹ (NUME/DEMO), the speed takes a value from −π to +π. If speed is expressed as a signed 8-bit value, it is expressed as a range of ±127. In this case, if the absolute values of measurement values A and B with opposite signs to be determined as aliasing are |A| and |B|, then if |A|+|B|>Th1 (Th1=127) is satisfied, the measurement value The fact that A and B have different signs can be determined to be due to an aliasing phenomenon.

FIG. 5 is a schematic diagram showing an interpolation method using opposite sign measurement values according to the conventional method and the present embodiment. Here, it is assumed that an interpolated value at a position x in a range of xa<x<xb is calculated using measured values A and B obtained at positions xa and xb. The absolute values of measured values A and B are represented by the size of the arrow, and the sign is represented by the direction of the arrow. Furthermore, a straight line extending from the tip of the arrow indicates the relationship between the interpolated value obtained from the two measured values and the interpolated position.

FIG. 5A shows a conventional interpolation method when it is determined that the sign reversal is not caused by an aliasing phenomenon (|A|+|B|≦Th1). Conventionally, when it is determined that the sign reversal is not due to an aliasing phenomenon (|A|+|B|≦Th1), linear interpolation is performed without correcting the measured value, so the interpolation position where the interpolated value becomes 0 is exist. Therefore, the position where the interpolated value is 0 and the vicinity thereof are displayed as a stationary part, and there is a possibility that the position may be mistaken for a blood vessel wall, etc., even though there is originally blood flow.

In this embodiment, as shown in FIG. 5(b), when it is determined that the sign reversal is not due to the aliasing phenomenon (|A|+|B|≦Th1), the interpolation position where the interpolation value becomes 0 is Interpolate as if it does not exist. Specifically, interpolation is performed such that the absolute value of the interpolated value changes linearly from the absolute value of one measured value to the absolute value of another measured value, depending on the interpolation position. Furthermore, the sign of the interpolated value is inverted at a specific interpolation position. Here, in a conventional interpolation method in which measured values are linearly interpolated, the sign of the interpolated value is inverted at the interpolation position where the absolute value of the interpolated value becomes 0.

In this case, as shown in FIG. 5(b), if interpolation is performed using the measured values A and B as they are as shown in FIG. 5(a), the interpolated value becomes 0 at position x0. Here, if xa<x<x0 is section 1 and x0≦x<xb is section 2, then
For section 1, interpolate by inverting the sign of B (linear interpolation between A and -B)
For section 2, interpolate by inverting the sign of A (linear interpolation between -A and B)
do. As a result, the interpolated value changes as shown by the solid line, and there is no position where it becomes 0. Note that other interpolation methods may be used as long as the change in the absolute value of the interpolation value is linear and there is no position where the interpolation value becomes 0.

Note that when it is determined that the sign reversal is due to an aliasing phenomenon (|A|+|B|>Th1), interpolation as shown in FIG. 5(c) is performed.
B<0: Correct B to (255-|B|) and perform linear interpolation (if interpolated value>127, interpolate value by -255)
A<0: Correct B to (-255+B) and perform linear interpolation (if interpolated value <-127, increase interpolated value by +255)
In this way, if it is determined that the sign reversal is due to a folding phenomenon, interpolation is performed to increase the absolute value, and from the interpolation position where the interpolated value reaches the maximum value, the interpolated value is folded back to the value of the opposite sign. Use methods. In this way, by using an interpolation method that has an interpolation position where the interpolation value is folded back, the absolute value of the interpolation value can be maintained at a large value.

The interpolation calculation circuit 1112 uses the four measurement values read from the frame memory 1111 and the two interpolation coefficients supplied from the interpolation coefficient generation circuit 1115 to obtain the measurement value at the pixel position by interpolation. For each of the first interpolation process and the second interpolation process, the interpolation calculation circuit 1112 performs aliasing determination when the measured values used for interpolation have different signs, and corrects the measured value and interpolated value based on the aliasing determination result. conduct.

When the measured values used for interpolation have the same sign, the interpolation coefficient y1 in the first interpolation process and the interpolation coefficient y2 in the second interpolation process, the interpolation calculation circuit 1112 calculates the pixel position P shown in FIG. 4(b). The measured value at
P = {B[L,N]×(1-y1)+B[L,N+1]×y1}×(1-y2)+{B[L+1,N]×(1-y1)+ B[L+1,N+1]×y1}×y2
Find it as. When the measured values used for interpolation have opposite signs, the correction of the measured values and interpolated values as described above is reflected.

Then, the interpolation calculation circuit 1112 outputs the value of P to the frame memory 1113. The write address generation circuit 1116 generates a write address and supplies it to the frame memory 1113 so that the speed data output by the interpolation calculation circuit 1112 is stored at the address in raster order on the display section 112.

Next, a description will be given of spatial filter processing that the filter processing unit 114 applies to the Doppler image stored in the frame memory 1113 in this embodiment. The filter processing unit 114 is a smoothing filter, and is used for purposes such as noise reduction. In this embodiment, in the spatial filter processing, aliasing determination processing is performed when the pixel of interest and the reference pixel have different signs, and the method of correcting the value of the reference pixel is varied depending on the aliasing determination result.

FIG. 6 is a flowchart regarding filter processing in this embodiment. The filter processing unit 114 in this embodiment sequentially applies spatial filter processing to each pixel constituting a Doppler image stored in the frame memory 1113 in which each pixel indicates a velocity, as a pixel of interest to be processed. Here, filter processing using the measured value of the pixel of interest and the measured values of a plurality of reference pixels in the vicinity of the pixel of interest is applied to the measured value of the pixel of interest. Here, n-point filter processing is applied to the reference pixels using the values of the same number of reference pixels arranged to the right and left of the pixel of interest. For example, n=5 or n=7. Here, the reason why pixels in the left and right directions of the pixel of interest are used in the filtering process is that the resolution of the measurement value that is the basis of the Doppler image is lower in the scanning direction than in the scan line direction (depth direction).

In S101, the filter processing unit 114 reads one-dimensional data of n pixels centered on the pixel of interest from the Doppler image data stored in the frame memory 1113, and extracts the value Vc of the pixel of interest. Here, if the one-dimensional pixel data of n points is V[i] (i=1 to n), Vc corresponds to V[(n\2+1)]. Here, \ is an integer division operator or a quotient operator, and the quotient (integer part) of the division result is obtained. Therefore, when n=5, Vc=V[3], and when n=7, Vc=V[4].

In S103, the filter processing unit 114 determines whether V[i] and Vc have different signs. If it is determined that they have different signs, the process proceeds to S105, and if not, the process proceeds to S117. In this way, when V[i] and Vc have the same sign, the processes of S105 to S111 are not applied.

In S105, the filter processing unit 114 performs a return determination. If the absolute value of the difference between V[i] and Vc exceeds the threshold Th2, the filter processing unit 114 determines that the sign reversal is due to aliasing. The aliasing here includes one due to the aliasing phenomenon and one due to the interpolation method shown in FIG. 5(c).

Note that here, since V[i] and Vc have different signs, the sum of the absolute value of V[i] and the absolute value of Vc is used instead of the absolute value of the difference between V[i] and Vc. It's okay. Note that the threshold value Th2 used in S105 is set to a value larger than the threshold value Th1 used for aliasing determination in the interpolation process. As a result, it is possible to perform correction only on pixels (velocities) in portions where there is a high possibility that the pixels (velocities) have been folded back to values of opposite signs with large absolute values.

As a result of the aliasing determination in S105, the filter processing unit 114 advances the process to S107 if it is determined that the reversal of the signs of V[i] and Vc is due to aliasing, and otherwise proceeds to S113.

In S107, the filter processing unit 114 determines whether V[i] is 0 or more, and if it is determined to be 0 or more, the process proceeds to S109; If so, the process advances to S111.

In S109, the filter processing unit 114 subtracts 255 from V[i] and advances the process to S113. This is because if V[i]≧0, the actual value is a negative value with a large absolute value.
In S111, the filter processing unit 114 adds 255 to V[i] and advances the process to S113. This is because if V[i]<0, the actual value is a positive value with a large absolute value.
Through the corrections in S109 and S111, the pixel value is returned to the original code value (value when not folded back).

In S113, the filter processing unit 114 increases i by 1.
In S115, the filter processing unit 114 determines whether or not the processes from S103 to S113 have been executed for all of the pixel data of n points. If the filter processing unit 114 determines that the process has been executed, the process proceeds to S117, and if it is not determined, the process returns to S103 and executes the process for the next V[i].

In S117, the filter processing unit 114 generates the filtered value Vout of the pixel of interest as follows.
Vout=Σ(|V[i]|)/n
Voutsign=Σ(V[i])/n
Vout=-Vout (if Voutsign<0)
Here, Σ() is the total value of n values obtained by sequentially substituting 1 to n for i in (). In other words, the value Vout of the pixel of interest after filter processing is a value whose absolute value is the average value of the sum of absolute values of V[i] (i=1 to n), and whose sign is the sign of the average value of V[i]. It is.

Next, in S119, the filter processing unit 114 makes the following correction in order to set the range of Vout to a range of ±127 when the absolute value of Vout exceeds 127, and ends the filter processing.
Vout=Vout-255 (when Vout>127)
Vout=255+Vout (when Vout<-127)
Note that if -127≦Vout≦127, no correction is made in S119.
The above spatial filter processing is executed for each pixel of the Doppler image stored in the frame memory 1113.

The filter processing unit 114 sequentially outputs pixel data having a color corresponding to the value of Vout after the filter processing to the synthesis unit 115. Note that in the case of the mode in which the color is determined by considering the dispersion, the filter processing unit 114 can refer to the frame memory 1113 to obtain the dispersion value, perform filter processing on the dispersion value, and determine the color of the pixel.

In this way, in this embodiment, among the reference pixels used for spatial filter processing, aliasing is determined for reference pixels that have a value with a different sign from the value of the pixel of interest (pixel to be filtered), and the reversal of the sign is determined by aliasing. Determine whether it is caused by For reference pixels that are determined to have reversed sign due to aliasing, the values are corrected to the original sign and used for spatial filter processing.

Thereby, it is possible to suppress reduction in the brightness of the portion where the sign is reversed due to folding due to the spatial filter processing. Therefore, compared to the case where filter processing is applied without performing aliasing determination, it is possible to realize smoothing processing of the Doppler image while maintaining the characteristics of the portion where the velocity is high.

FIG. 7(a) is a color Doppler image obtained by applying a conventional interpolation method using linear interpolation when it is determined that the sign reversal is not due to an aliasing phenomenon, and FIG. 7(b) is a color Doppler image obtained by applying the conventional interpolation method using linear Color Doppler images obtained using the same original data as in a) and using the interpolation method described in this embodiment that does not have an interpolation position where the interpolation value becomes 0 are shown. In the figure, the area surrounded by the white dotted line is the area where the sign is reversed due to the aliasing phenomenon (referred to as area A), and the area surrounded by the solid white line is the area where the sign is reversed not due to the aliasing phenomenon (referred to as area A). area B). Comparing FIGS. 7(a) and 7(b), it can be seen that there is no change in region A, and that in region B, the change in the edge portion is smooth.

Further, FIG. 8 shows the results of applying different spatial filters to the color Doppler image interpolated by the method of this embodiment. FIG. 8(a) shows the result of applying spatial filter processing without aliasing determination. FIG. 8(b) and FIG. 8(c) both show the results of applying the spatial filter of this embodiment with aliasing determination. FIGS. 8(b) and 8(c) differ in the value of the threshold Th2 used for aliasing determination in the spatial filter processing. FIG. 8B shows a case where the threshold Th2 is set equal to the threshold Th1 used for aliasing determination during interpolation (Th1=Th2=128). Further, FIG. 8(c) shows a case where the threshold Th2 is set larger than the threshold Th1 used for aliasing determination during interpolation (Th1=128, Th2=192).

Comparing FIG. 8(a) and FIG. 8(b), it can be seen that the area surrounded by a white circle and whose sign is reversed due to folding is brighter in FIG. 8(b). In other words, the characteristic parts with large speeds are easier to understand. Further, when comparing FIG. 8(b) and FIG. 8(c), it can be seen that unnecessary glare is suppressed in the portion surrounded by a black circle in FIG. 8(c). By making the threshold value Th2 larger than the threshold value Th1, only the portions where the sign is likely to be reversed due to aliasing are corrected to be brighter, and it is possible to suppress an increase in brighter portions than necessary.

As described above, according to the present embodiment, when generating a color Doppler image by interpolating measurement values obtained by the Doppler method, the measurement values used for interpolation have opposite signs, and the sign reversal is aliased. The interpolated value will no longer be 0 if it is not caused by a phenomenon. Therefore, it is possible to prevent a position where blood flow normally exists from being displayed as a blood vessel wall or the like. In addition, in the spatial filter processing applied after interpolation, if the sign reversal is due to aliasing for a reference pixel with a different sign from the pixel value to be processed, the value of the reference pixel is corrected to the value of the original sign. Spatial filter processing is now performed. Therefore, it is possible to suppress the characteristics of the folded portion from being smoothed by the spatial filter processing. Furthermore, by setting the threshold value for aliasing determination in spatial filter processing to be larger than the threshold value for aliasing determination during interpolation, it is possible to obtain a Doppler image that is visually more preferable and suppresses unnecessary glare.

The invention is not limited to the embodiments described above, and various modifications and changes can be made within the scope of the invention. For example, in the embodiment described above, interpolation processing using two values is performed twice to obtain a measured value for one pixel position. However, the measured value for one pixel position may be determined by one interpolation process using four measured values. In this case, a difference in weights depending on the difference in distance to the pixel position to be interpolated may be applied to the interpolation coefficients for the four measured values. Further, the spatial filter may be a two-dimensional filter.

Note that the ultrasound image generation device according to the present invention can also be realized by executing a program on a generally available electronic device (computer) that can execute a program, such as a personal computer, a smartphone, or a tablet terminal. . Therefore, a program for causing a computer to function as the ultrasonic image generation device according to the invention, and a storage medium storing such a program (an optical recording medium such as a CD-ROM or DVD-ROM, or a magnetic recording medium such as a magnetic disk) media, semiconductor memory cards, etc.) also constitute the invention.

DESCRIPTION OF SYMBOLS 100... Ultrasonic diagnostic apparatus, 101... Control part, 104... Drive circuit, 106... Receiving circuit, 107... Doppler processing part, 109... B mode processing part, 111... DSC, 112... Display part, 113... Operation part

Claims (10)

An ultrasound image generation device that generates a color Doppler image based on measurement values obtained by the Doppler method,
interpolation processing means for obtaining measurement values at the positions of pixels constituting the color Doppler image by interpolation processing for interpolating a plurality of measurement values;
filter processing means for applying filter processing to the measured value at the position of the pixel determined by the interpolation processing means;
generating means for generating pixel data of the color Doppler image according to the measurement values processed by the filter processing means,
The filter processing means includes:
Spatial filter processing using a measured value to be processed and a plurality of measured values in the vicinity of the measured value to be processed is applied to the measured value to be processed,
Among the plurality of measured values in the vicinity, determining whether the different signs are due to aliasing for each of the measured values to be processed and the measured values with different signs,
If it is determined that the different sign is due to an aliasing phenomenon, the measured value is corrected to the value of the original sign and then used in the filtering process,
The interpolation processing means
When the plurality of measured values have different signs, determining whether the different signs are due to an aliasing phenomenon,
If the different signs are not determined to be due to an aliasing phenomenon, perform the interpolation process using a first interpolation method that does not have an interpolation position where the interpolation value becomes 0,
If it is determined that the different signs are due to an aliasing phenomenon, performing the interpolation process using a second interpolation method having an interpolation position where the interpolated value is aliased;
An ultrasonic image generation device characterized by: 2. The interpolation processing means determines that the different signs are due to an aliasing phenomenon when the sum of the absolute values of the plurality of measured values exceeds a predetermined first threshold value. Ultrasonic image generation device. The first interpolation method is a method for determining the interpolated value such that the absolute value of the interpolated value linearly changes from one of the absolute values of the plurality of measured values to another one according to the interpolation position. The ultrasonic image generation device according to claim 1 or 2, characterized in that: 4. The ultrasound image generation apparatus according to claim 1, wherein the sign of the interpolated value determined by the first interpolation method changes at a specific interpolation position. 5. The ultrasound image generation apparatus according to claim 4, wherein the specific interpolation position is an interpolation position where an interpolation value becomes 0 when the plurality of measurement values having opposite signs are linearly interpolated. further comprising filter processing means for applying filter processing to the measured value at the position of the pixel determined by the interpolation processing means,
The generation means generates the pixel data according to the measurement value processed by the filter processing means,
The ultrasonic image generation device according to any one of claims 1 to 5. The filter processing means determines that the different signs are due to aliasing when the difference or the sum of absolute values between the measured value to be processed and neighboring measured values of opposite signs exceeds a predetermined second threshold. The ultrasonic image generation device according to claim 1 , wherein the ultrasonic image generation device makes a determination. The interpolation processing means determines that the different signs are due to an aliasing phenomenon when the sum of the absolute values of the plurality of measured values exceeds a predetermined first threshold;
The ultrasound image generation device according to claim 7 , wherein the second threshold is larger than the first threshold. A method for controlling an ultrasound image generation device that generates a color Doppler image based on measurement values obtained by the Doppler method, the method comprising:
an interpolation processing step of obtaining measurement values at the positions of pixels constituting the color Doppler image by interpolation processing of interpolating a plurality of measurement values;
a filter processing step of applying filter processing to the measured value at the pixel position obtained in the interpolation processing step;
a generation step of generating pixel data of the color Doppler image according to the measurement values processed in the filter processing step,
The filter processing step applies spatial filter processing to the measurement value to be processed using a measurement value to be processed and a plurality of measurement values in the vicinity of the measurement value to be processed,
In the filter processing step, it is determined whether or not the different signs are due to aliasing, for each of the measurement values to be processed and the measurement values with different signs among the plurality of measured values in the vicinity, and whether the different signs are due to an aliasing phenomenon. The measured value determined to be true is corrected to the original sign value and then used for the filter processing,
The interpolation processing step is
If the plurality of measured values have different signs, a determination step of determining whether the different signs are due to an aliasing phenomenon;
An interpolation process,
If the different signs are not determined to be due to an aliasing phenomenon in the determination step, performing the interpolation process using a first interpolation method that does not have an interpolation position where the interpolation value becomes 0;
If it is determined in the determination step that the different signs are due to an aliasing phenomenon, performing the interpolation process using a second interpolation method having an interpolation position at which the interpolated value is aliased;
A method for controlling an ultrasonic image generation device, comprising: an interpolation step. A program that causes a computer to function as the ultrasound image generation device according to any one of claims 1 to 8 .

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