JP2742213B2 - Ultrasound image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic image processing apparatus, and more particularly to a correlation processing function for compensating for a temporary lack of ultrasonic image information in the ultrasonic image processing apparatus.

[0002]

2. Description of the Related Art In general, there is known an ultrasonic image processing apparatus for transmitting and receiving an ultrasonic beam to and from a subject, extracting ultrasonic image information from a received wave, and displaying the extracted information. As an ultrasound image,
For example, there are a Doppler image displaying the speed information of the motion of the subject, a tomographic image such as a B-mode displaying the tomographic information of the subject, and the like.

For example, when displaying a Doppler image,
A predetermined quadrature detection is performed on the obtained received wave to extract a Doppler signal. Then, auto-correlation processing and speed calculation processing are performed on the Doppler signal to obtain speed information of blood and the like, and the color information is displayed on a monitor as a Doppler image such as a two-dimensional speed distribution.

However, Doppler image information (speed information)
Is obtained by detecting the Doppler shift of an ultrasonic beam received when the ultrasonic beam is reflected by a moving body, and thus generally has a low S / N ratio. Therefore, in a Doppler image, local and temporary loss of image information is likely to occur in each pixel, and if the image is displayed on a monitor as it is, the image quality is low and a smooth image cannot be obtained. In the case of color display, since the resolution is lower than that of black and white, the image quality is significantly degraded due to lack of speed information.

Therefore, correlation processing has conventionally been performed on Doppler image information to compensate for the lack of displayed Doppler image information. Correlation processing means that when image information is lost in a specific pixel portion of the latest frame, the image information of the latest frame of the missing pixel portion is used at a fixed rate (correlation rate) with the image information of the past frame. This is the process of compensating for This correlation processing has been performed using a low-pass filter such as an IIR digital filter.

[0006] By performing such a correlation process, the lack of Doppler image information has been compensated.

[0007]

In order to compensate for the missing image information more strongly, the effect of the filter may be increased. However, enhancing the effect of the filter means increasing the correlation rate, that is, the utilization rate, with respect to the image information of the past frame.

Therefore, there is a problem that the image information of pixels without any information loss is correlated, uniformly affected strongly by the image information of the past frame, and an afterimage occurs in the Doppler image relating to the latest frame displayed. .

Further, when performing the correlation processing, the effect of the filter, that is, the correlation rate with respect to the image information of the past frame is always fixed. Therefore, even when the image information of the pixel is actually lost, the correlation process is executed as missing information, and the afterimage tends to occur for a longer period. As a result, there is a possibility that an image in which the blood flow exists in a place where the blood flow does not actually exist may be displayed, and there has been a problem that the reliability of diagnosis is reduced.

There is also a method of using an FIR type filter in order to suppress the influence of the afterimage and enhance the effect of the filter. However, in the case of the FIR type, it is necessary to provide a plurality of frame buffers corresponding to the number of taps of the filter, and there has been a problem that the cost of the apparatus increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a low-cost ultrasonic image processing apparatus capable of reducing occurrence of an afterimage in a correlation process for interpolating missing image information. Aim.

[0012]

In order to achieve the above object, an ultrasonic image processing apparatus according to the present invention has the following features.

An ultrasonic beam is transmitted / received to / from the subject, ultrasonic image information is extracted from the received wave, and a correlation process is performed based on the ultrasonic image information of the latest frame and the ultrasonic image information of the past frame in each pixel. An ultrasonic image processing apparatus for displaying an ultrasonic image, performing image information storage means for storing the ultrasonic image information for each frame, the ultrasonic image information of the latest frame, and the stored past frame. Based on the ultrasound image information, a correlation determination unit that determines whether or not to execute the correlation process for each pixel, a count unit that counts the number of continuous executions of the correlation process, and a count number of the number of continuous executions, A correlation ratio selection unit that selects a correlation ratio set according to the count number for each of the latest frame and the ultrasound image information related to the past frame, before the selection. A correlation calculation unit which performs the correlation process in the latest frame based on the correlation factor, and having a.

[0014] The correlation rate selection section is characterized by selecting a correlation rate that strongly reflects the ultrasonic image information of the latest frame as the count number increases.

The counting section sets the count number to 0 when the correlation processing is not executed continuously.

[0016] When the ultrasonic image information of the latest frame at the same pixel has a value smaller than the absolute value of the ultrasonic image information of the past frame,
It is characterized in that it is determined that the correlation processing is performed.

If the absolute value of the ultrasonic image information of the past frame and the ultrasonic image information of the latest frame at the same pixel is equal to or smaller than a predetermined value, the correlation judging unit judges that no correlation processing is performed. It is characterized by the following.

When the counted number is equal to or less than a predetermined number,
It is characterized in that it is determined not to perform the correlation processing.

[0019] The correlation determining unit determines that the correlation processing is not performed when the ultrasonic image information of the latest frame and the ultrasonic image information of the past frame in the same pixel are different in sign. And

[0020]

According to the ultrasonic image processing apparatus according to the present invention,
A correlation determining unit determines whether or not to execute a correlation process for each pixel based on the image information of the latest frame and the stored image information of the past frame. When performing the correlation processing, the counting unit counts the number of continuous executions of the correlation processing. Then, a predetermined correlation rate can be selected according to the count number.

Specifically, when the count number is small, a correlation rate that strongly reflects past image information is selected, and as the count number increases, the correlation rate that strongly reflects the latest (current) image information is selected. Selected. This makes it possible to always execute the correlation processing at the optimum correlation rate without using a complicated device configuration. For example, since information loss occurs intermittently in image information such as blood flow with high temporal continuity, a device capable of effectively interpolating this information loss by correlation processing can be realized.

On the other hand, in the Doppler image information (speed information), the moment the probe is moved and the breathing or pulsation, etc.
Noise having a small absolute value (low-speed motion information) and low temporal continuity is generated. If the correlation processing is also performed on this noise, unnecessary low-speed motion information is displayed in the Doppler image for a long period of time, which causes a deterioration in image quality and a misdiagnosis.

However, according to the present invention, the correlation determining unit determines the absolute value of the image information of the past frame and the image information of the latest frame,
Determine the number of counts, if these are less than the predetermined value,
Correlation processing is not substantially executed. Thus, the function of interpolating missing information by correlation processing is sufficiently exhibited for stationary motion information such as blood flow information. Then, for intermittent and low-speed motion information such as pulsation and respiration, a correlation rate that reflects 100% of the speed information of the latest frame is selected, and substantially no correlation processing is performed. . Therefore, according to the present invention, it is possible to improve the image quality of an ultrasonic image such as a Doppler image displayed on a monitor.

Further, the correlation determination section of the present invention determines the sign of the image information of the latest frame and the image information of the past frame relating to the same pixel, and does not perform the correlation processing if both codes are different. And

For example, in the case of a Doppler image, when the motion speed exceeds a predetermined speed and a waveform turnback occurs in the speed information, the sign differs between the speed information before the occurrence and the speed information after the occurrence. In this case, since the absolute values are almost the same, there is a possibility that if the speed information is correlated, the speed information obtained as a result of the correlation processing becomes zero. Therefore, in practice, a moving body moving at an extremely high speed is displayed as if it is moving at a low speed.

In the present invention, the sign of the speed information is determined as described above, and if the sign is different, the correlation processing is not performed. Therefore, completely different speed information is not displayed on the monitor, and the reliability of diagnosis is further improved. It is possible to improve.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic block diagram showing an ultrasonic image processing apparatus according to an embodiment of the present invention. Specifically, it is a schematic block diagram showing an ultrasonic Doppler diagnostic device that displays a Doppler image.

The transmission / reception unit 12 is a circuit for controlling transmission and reception of an ultrasonic beam by the probe 10. The Doppler operation unit 14 connected to the transmission / reception unit 12 is a circuit that performs predetermined quadrature detection, autocorrelation processing, and the like on the received signal and calculates speed information from the Doppler signal. On the output side of the Doppler calculation unit 14, a correlation determination unit 16 and a correlation calculation unit 26 are provided, and the obtained speed information of the latest frame is sequentially output to the correlation determination unit 16 and the correlation calculation unit 26.

A predetermined high-pass filter (high-pass filter) or the like is provided in the Doppler operation unit 14, and this filter extracts only a high-speed (high-frequency band) Doppler signal. If the subject is a blood vessel, the Doppler signal extracted by this high-pass filter is
This is a signal related to blood flow.

The correlation determining section 16 determines whether or not to execute the correlation processing. The correlation determining section 16 determines the latest frame speed information output from the Doppler operation section 14 and the previous frame speed information stored in the frame buffer 24. It is determined whether or not the speed information satisfies a predetermined condition for each pixel. If the condition is satisfied, it is determined whether or not the execution of the correlation process is "not". If the condition is not satisfied, it is determined whether or not the execution of the correlation process is "permitted".

The counting section 20 is a circuit connected to the output side of the correlation judging section 16 and counts the number of times the correlation processing has been continuously executed in each pixel. The count number is stored in the count buffer 22.

The correlation ratio selection section 18 is provided on the output side of the correlation determination section 16. Then, a predetermined correlation rate, which will be described later, is selected according to the result of the determination of “permitted” or “not” of the execution of the correlation processing by the correlation determination unit 16 and the count number of the correlation processing stored in the count buffer 22, and A selection unit that outputs to the correlation calculation unit 26.

The correlation operation unit 26 performs a correlation process on the speed information of the latest frame and the speed information of the immediately preceding frame supplied from the frame buffer 24 at a predetermined correlation rate selected for the speed information of each pixel. Is an arithmetic unit that performs the following.

Then, speed information after correlation processing (Result)
Are displayed as Doppler images on a monitor 30 such as a CRT connected via a DSC (digital scan converter) 28. Note that the frame buffer 24 is connected to the output side of the correlation operation unit 26 and stores the speed information after the correlation processing in one.
It is recorded for each frame, and is supplied to the input side of the correlation determination unit 16 and the correlation calculation unit 26 after one frame.

Next, the correlation processing procedure will be described with reference to FIGS.

When speed information is obtained by performing a predetermined operation on the ultrasonic signal reflected by the subject and received by the probe 10, the speed information is obtained for each frame by the Doppler operation unit 1.
4 to the correlation determining unit 16 and the correlation calculating unit 26.

A plurality of conditions are set in the correlation determination section 16 in advance in order to determine whether or not to perform a correlation process for each pixel on the obtained speed information. If the condition is not satisfied, a command to execute the correlation process “OK” is output to the correlation ratio selection unit 18 if the condition is satisfied.

As conditions, for example, there are the following three conditions.

(1) Whether the speed information of the latest frame related to the same pixel is larger than the absolute value of the speed information of the previous frame.

(2) Whether the sign of the speed information related to the same pixel is different between the latest frame and one frame before.

(3) Whether the absolute value of the speed information of the previous frame is smaller than a predetermined value and the absolute value of the speed information of the latest frame is almost 0. Furthermore, is the count number 1?

When each of the above three conditions is satisfied, the correlation judging unit 16 outputs a command to execute the correlation process “NO”. Upon receiving a "No" command, the correlation rate selection unit 1
8 is a correlation rate (a = 1.0: b = 0.0, a is a correlation rate with respect to the speed information of the latest frame, b is a correlation rate with respect to the speed information of the previous frame) at which the speed information of the latest frame is output at 100%. It is selected and output to the correlation calculator 26.
Therefore, when the command is “No”, the correlation operation unit 26 does not execute substantial correlation processing.

Here, the condition (1) is equivalent to the conventional condition. If the speed information is lost in the latest frame, the speed information of the pixel in the missing portion has the absolute value of the same pixel of the past speed information as the absolute value. This is based on the fact that it becomes smaller than the value. Therefore, when the speed information of the latest frame is smaller than the absolute value of the speed information of the previous frame, the correlation process is performed.

The condition (2) is that, when a waveform turnback unique to the ultrasonic Doppler diagnostic apparatus occurs in the speed information of the latest frame or one frame before, the two speed information have the same absolute value and the absolute value is almost the same. This is a condition noting that the signs are different from each other. When both the speed information are correlated, that is, integrated when the waveform folding occurs, the speed information obtained as a result of the correlation processing may become zero. As a result, a moving body that is actually moving at a very high speed is displayed as if it is moving at a low speed. Therefore, when the signs of both speed information are different depending on the condition (2), the correlation processing is not performed.

The condition (3) is that when diagnosing a high-speed moving body such as a blood flow, low-speed motion information relating to a low-speed moving body such as a blood vessel is displayed in a Doppler image as noise (such as wall motion noise). This is set in order to prevent the information from being deleted. When diagnosing a blood flow or the like, a Doppler signal in a high frequency band is selectively extracted by providing a high-pass filter in the Doppler operation unit 14 as described above. However, the energy of the movement of the living tissue is much larger than the energy of the blood flow, and there is a component that passes through the high-pass filter, so that the Doppler signal in the low frequency band cannot be completely removed.
If the correlation processing is performed on the low-speed motion information on the living tissue, the low-speed motion information is rather emphasized and displayed in the Doppler image, which causes an erroneous diagnosis.

Therefore, when the absolute value of the speed information of one frame before (the calculation result output from the correlation calculation unit) stored in the frame buffer 24 is equal to or smaller than a predetermined value, and the speed information of the latest frame is almost zero. Did not perform any substantial correlation processing. Further, in this case, it is determined whether or not the count number is 1 (= correlation processing has been performed only once before the previous time), and when the count number is 1 or less, the substantial correlation processing is not performed. .

According to the condition (3), when the speed information is low speed and intermittent, the correlation processing is not executed, so that the occurrence of an afterimage due to the correlation processing can be reduced. On the other hand, by performing the correlation processing at least once, the effect of the correlation processing can be expected for low-speed blood flow information near the blood vessel because the information is generally a steady flow.

It should be noted that the three conditions in the correlation judgment section 16 are not always three, and if no aliasing occurs, the condition (2) is not necessary, and if the performance of the high-pass filter is further improved (3 The condition of ()) may not be necessary. Further, other conditions may be further provided according to the purpose.

Next, a processing procedure when the above three conditions are not satisfied will be described.

First, since the condition is not satisfied, a command to execute the correlation processing “OK” is issued from the correlation determination section 16 to the correlation rate selection section 1.
8 and output to the counting section 20. The counting unit 20 counts the number of times the correlation processing has been continuously performed. If the correlation processing has not been performed last time, the count number is stored in the count buffer 22 as one. If the correlation processing has already been performed several times in succession, the count number is updated and stored in the count buffer 22.

The correlation rate selection section 18 selects a correlation rate according to the count number. As shown in FIG. 2, when the count number is small, the past speed information is strongly reflected, and as the count number increases, the correlation rate is selected by strongly reflecting the latest frame speed information. For example, when the count number is 0 (currently at the time of the first correlation processing), the correlation rate a = 0.2 with respect to the speed information of the latest frame,
The correlation ratio b = 0.8 with respect to the speed information of the past frame (one frame before) is selected and output to the correlation operation unit 26 (a + b = 1.0).

Here, in the present embodiment, the count number is from 0 to 3, and the correlation rate as shown in FIG. 2 is used, but these differ depending on the conditions. The count number may be larger than 3, and the correspondence between the correlation ratio a: b and the count number is not limited to this.

The count number is stored in the count buffer 22.
(3 in this embodiment). Then, when the count reaches the upper limit, the count is kept at the upper limit even if the correlation processing is further continuously executed. The count value is reset to 0 when the correlation determination unit 16 outputs a correlation processing “No” command and 100% of the latest frame speed information is reflected.

When the correlation rates a and b according to the conditions are selected and output to the correlation calculation section 26, the correlation calculation section 26 calculates the speed information of the latest frame and the frame buffer based on the correlation rates a and b. Correlation processing is performed on the speed information of one frame before supplied from 24 (Result = a * speed information of the latest frame + b * speed information of one frame before).

Speed information obtained as a result of calculation (Result)
Is displayed on the monitor 30 via the DSC. The speed information is sequentially stored in the frame buffer 24 for each frame, and is supplied to the input side of the correlation determination unit 16 and the correlation calculation unit 26 after one frame.

As described above, according to the configuration of the present embodiment, the correlation processing can always be executed at the optimum correlation rate without using a specially complicated device configuration, and the speed information with high temporal continuity can be obtained. Thus, the correlation processing can be performed effectively. On the other hand, when the probe is moved, or when the absolute value generated by respiration, pulsation, etc. is small and the temporal continuity is low (intermittent), no substantial correlation processing is performed, and an afterimage is generated. Will not occur.

This will be described with reference to FIG. FIG. 3 shows the result of the correlation processing when the speed information of the latest frame is the same for the present embodiment and the conventional correlation processing.

According to FIG. 3, in the correlation processing of this embodiment,
It is clear that the afterimage is reduced as compared with the conventional correlation processing. For example, the speed information of the latest frame is 0 for both frames 6 and 6 'and thereafter.

The result of the correlation processing is frame 8 in this embodiment.
At (count number 2, correlation ratio a0.8: b0.2), the speed information has already decreased to 1 and becomes 0 from the next frame. On the other hand, in the conventional example, the value is 4 in the frame 8 ', and the value does not become 0 even in the frame 10'.

In this embodiment, since the count number is small, the speed information one frame before is strongly reflected in the intermittent loss of the speed information such as the frames 3 and 3 ', and the correlation processing result is not obtained. It will be 20. On the other hand, the result of the conventional correlation processing is 16, and it is clear that the present embodiment is superior to the conventional correlation processing in terms of the interpolation function for intermittent loss of speed information.

In the present embodiment, the correlation processing has been described using Doppler image information as an example of ultrasonic image information. However, the ultrasonic image information is not limited to Doppler image information, and can be applied to tomographic image information that displays the reflection intensity of an ultrasonic beam of a subject as a tomographic image. If this is done, missing image information can be interpolated as in the present embodiment.

[0063]

As described above, according to the ultrasonic image processing apparatus of the present invention, the correlation judging section performs a pixel-by-pixel operation on the basis of the latest frame image information and the stored past speed information. It is determined whether or not the correlation processing can be executed. When performing the correlation process, the counting unit counts the number of continuous executions of the correlation process. Then, an optimum correlation rate is selected according to the count number.

Therefore, the correlation processing can always be executed at the optimum correlation rate, and it is effective against intermittent information loss occurring in speed information having high temporal continuity without using a specially complicated device configuration. Can be correlated. Therefore, an image with low display cost and high display quality can be obtained at low cost.

When the absolute value of the image information one frame before is less than a predetermined value, the speed information of the latest frame is extremely small, and the count number is less than a predetermined number, the correlation process is not substantially executed. And

As a result, since the correlation processing is not performed on the intermittent image information having a small absolute value, the occurrence of an afterimage due to the correlation processing can be reduced. On the other hand, at least one
By performing the correlation process each time, for example, even if the speed of the target moving body is low, the effect of the correlation process can be expected as long as the motion is stationary.

Therefore, when diagnosing a high-speed moving object, it is possible to prevent the speed information of the low-speed moving object from being displayed on the monitor for an unnecessarily long period of time due to an afterimage, and to reduce the image quality of the Doppler image displayed on the monitor. Can be improved.

Further, in the present invention, the correlation determination unit determines the sign of the image information of the latest frame and the image information of the past frame relating to the same pixel, and does not perform the correlation processing if both codes are different. And Therefore, image information having completely different values is not displayed on the monitor, and the reliability of diagnosis can be further improved.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing an ultrasonic Doppler diagnostic apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram for explaining a correlation processing procedure in the apparatus of FIG. 1;

FIG. 3 is a diagram for comparing the present embodiment with a conventional correlation process.

[Explanation of symbols]

 16 Correlation Judgment Unit 18 Correlation Rate Selection Unit 20 Count Unit 22 Count Buffer 24 Frame Buffer for Speed Information 26 Correlation Operation Unit

Claims (7)

(57) [Claims] 1. An ultrasonic beam is transmitted / received to / from a subject, ultrasonic image information is extracted from a received wave, and correlation is performed based on ultrasonic image information of a latest frame and ultrasonic image information of a past frame in each pixel. An ultrasonic image processing apparatus that performs processing and displays an ultrasonic image, comprising: an image information storage unit configured to store the ultrasonic image information for each frame; an ultrasonic image information of the latest frame; and the stored past. A correlation determining unit that determines whether or not to execute a correlation process for each pixel based on the ultrasonic image information of the frame; a counting unit that counts the number of continuous executions of the correlation process; A correlation rate selection unit that selects a correlation rate set according to the count number for each of the ultrasonic image information related to the latest frame and the past frame. Ultrasonic image processing apparatus characterized by having a correlation operation unit which performs the correlation process in the latest frame based on the correlation factor. 2. The ultrasonic image processing apparatus according to claim 1, wherein the correlation ratio selection unit selects a correlation ratio that strongly reflects the ultrasonic image information of the latest frame as the count number increases. Ultrasonic image processing device. 3. The ultrasonic image processing apparatus according to claim 2, wherein the counting unit sets the count number to 0 when the correlation processing is not performed continuously. Sound wave image processing device. 4. The ultrasonic image processing apparatus according to claim 1, wherein the correlation determination unit determines that the ultrasonic image information of the latest frame in the same pixel is an ultrasonic image of the past frame. An ultrasonic image processing apparatus characterized in that when it has a value smaller than the absolute value of the information, it is determined that a correlation process is to be performed. 5. The ultrasonic image processing device according to claim 1, wherein the correlation determination unit is configured to determine the ultrasonic image information of the past frame in the same pixel and the ultrasonic image information of the past frame. When the absolute value of the ultrasonic image information of the latest frame is equal to or smaller than a predetermined value, it is determined that the correlation process is not performed. 6. The ultrasonic image processing apparatus according to claim 5, wherein when the count number is equal to or less than a predetermined number, it is determined that the correlation processing is not performed. 7. The ultrasonic image processing apparatus according to claim 1, wherein the correlation determination unit determines the ultrasonic image information of the latest frame in the same pixel and the ultrasonic image information of the latest frame. An ultrasonic image processing apparatus characterized in that when the sign of the ultrasonic image information is different from the ultrasonic image information of the past frame, it is determined that the correlation processing is not performed.