JPH08164139A - Ultrasonic diagnostic system - Google Patents

Abstract

PURPOSE: To provide an ultrasonic diagnostic system capable of making the infarcted myocardium into an image characteristically by distinguishing from the normal myocardium. CONSTITUTION: This ultrasonic diagnostic system can obtain a reception signal of one frame repeatedly by scanning the two-dimensional area of an examinee by an ultrasonic wave. and generates the image by detecting the reception signal. Also, the system is equipped with a feature quantity image generating part 7 which generates the two-dimensional distribution of feature quantity representing similarity between the reception signal in the kernel ROI of a first frame and the reception signal in the object ROI of a second frame with scanning timing different from that of the first frame, and a display part 6 which displays such two-dimensional distribution as a feature quantity image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus for scanning a two-dimensional region of a subject with ultrasonic waves and detecting a received signal obtained to generate a tissue tomographic image. And a new technique for imaging infarcted myocardium.

[0002]

2. Description of the Related Art Ultrasonic waves propagate while being repeatedly reflected and refracted at the boundary between two media having different acoustic impedances. The reflection intensity depends on the difference between the acoustic impedances of the two media. In ultrasonic imaging, the amplitude of a reflected signal is converted into luminance and displayed. When the amplitude of the reflected signal is small, that is, the difference in acoustic impedance is small, the luminance change (concentration change) between the two media is small, so The accuracy of discriminating two media having a small difference in acoustic impedance on an ultrasonic tomographic image often depends on the knowledge and experience of a diagnostic doctor, and thus lacks objectivity.

Such a case is applicable to ultrasonic diagnosis of myocardial infarction, for example. That is, the difference in the acoustic impedance between the infarcted myocardium and the normal myocardium is small, and it is difficult to distinguish both on the ultrasonic tomographic image, and the objectivity is poor.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic diagnostic apparatus capable of characteristically imaging infarcted myocardium in distinction from normal myocardium.

[0005]

According to the present invention, a two-dimensional region of a subject is scanned with ultrasonic waves to obtain a reception signal for one frame repeatedly, and an image is generated by detecting the reception signal. In the ultrasonic diagnostic apparatus, a feature representing the similarity between the received signal in the first local area of the first frame and the received signal in the second local area of the second frame whose scanning timing is different from that of the first frame. A feature quantity two-dimensional distribution generation means for generating a two-dimensional distribution of quantities, and a display means for displaying the two-dimensional distribution as a feature quantity image.

[0006]

According to the present invention, the infarcted portion in which the position is not changed (metastatic) is simply changed according to the cyclic contraction of the normal myocardium, and the infarcted portion in the first local area of the first frame is The similarity with the received signal in the second local area of the frame can be regarded as high.

[0007]

An embodiment of the present invention will be described below with reference to the drawings. It should be noted that although a sector electronic scanning method with a narrow shallow visual field and a wide deep visual field, which is suitable for heart diagnosis, will be described here, a linear electronic scanning method or a linear electronic scanning method can be used if a two-dimensional region of a subject can be scanned. The convex electronic scanning method or another scanning method may be used. An ultrasonic probe 1 equipped with a transducer array for sector scanning, in which a plurality of transducers for reversibly converting acoustic signals and electric signals are arranged, is connected to a transmission system 2 at the time of transmission, and at the time of reception. It is connected to the receiving system 3. The transmission system 2 is composed of a clock generator, a rate pulse generator, a delay circuit provided for each transducer (each channel), and a pulser provided for each transducer (each channel). The clock pulse generated from the clock generator is divided into rate pulses of, for example, 5 KHz by the rate pulse generator. This rate pulse is distributed and sent to the pulsar via each delay circuit. Each delay circuit provides the rate pulse with the delay time necessary to focus the ultrasonic waves into a beam and determine the direction (called the scan line direction or azimuth direction) of the ultrasonic beam. The pulsar applies the pulse voltage to the corresponding vibrator at the timing of receiving the rate pulse. Thereby, the ultrasonic pulse is emitted from the probe 1 in the azimuth direction according to the delay time.
The reflected wave reflected at the boundary of the acoustic impedance inside the subject is converted into an electric signal by each transducer of the probe 1, and is captured by the receiver 3.

As the receiving system 3, Japanese Patent Publication No. 6-14934
The digital beam former method as shown in No. 1 is given as a good example, and is composed of a preamplifier, an analog-digital converter, a digital delay circuit and an adder. The analog received signal from each oscillator is amplified by the preamplifier, then converted to a digital signal by the analog-digital converter, and sent to the digital delay circuit. Is given a reverse delay time for each channel and further added by an adder.
This added digital signal is hereinafter referred to as an RF reception signal. By sequentially changing the delay time control at the time of transmission / reception described above for each repetition of the ultrasonic pulse, the two-dimensional area of the subject can be sector-scanned and the RF reception signal group for one frame can be obtained. Further, by repeating such sector scanning, the RF reception signal group can be repeatedly obtained.

The output from the receiving system 3 is detected by the signal processing unit 4 and is further subjected to logarithmic amplification which substantially expands the dynamic range. As a result, B-mode image (tissue tomographic image) data is generated. This B-mode image data is sent to the display 6 via the digital scan converter (DSC) 5, converted into analog, and then displayed as a light and shade as a visual B-mode image.

The output from the receiving system 3 is sent to the feature amount image generating section 7. The feature amount image generation unit 7 uses two frames of R having different scanning timings and different heartbeat time phases.
The F received signal group is used to generate a two-dimensional distribution (feature amount image) of feature amounts whose values change according to the degree of infarction of the myocardium. The feature amount image data is sent to the display unit 6, converted into analog, and then displayed in gray scale or color as a visual feature amount image.

FIG. 2 is a block diagram of the feature amount image generating section 7. The frame memory 11 has a capacity capable of storing RF reception signal groups for a plurality of temporally consecutive frames obtained by repeating a series of sector scans. Also,
The frame memory 11 is provided with two output ports. One of the output ports is loaded with the RF reception signal group of the first frame, and the other output port of the second frame whose heartbeat time phase is different from that of the first frame, for example, the second frame delayed by one frame from the first frame. A group of RF reception signals is loaded.

For example, an RF reception signal group for a plurality of frames is managed in frame units with a frame number n. The frame number n is added as a serial number according to the scanning order.
Similarly, the image is managed by the frame number N in the DSC 5. The frame number n and the frame number N are associated with each other. When the operator designates a specific image displayed on the display 6 via an input device (not shown), the RF reception signal group of the frame number n as the first frame corresponding to the frame number N of the specific image is one of The RF reception signal group of the frame number n + 1 as the second frame is loaded in the output port and is loaded in the other output port. In this way, the operator can specify the heartbeat time phase for creating the feature amount image by designating the image of the desired heartbeat time phase.

From one output port, a group of RF reception signals in a local area (called a kernel ROI) of a predetermined size, and from the other output port are the same size,
A local region near the kernel ROI (object ROI
The RF reception signal groups in the
Taken in 2. The feature amount calculation unit 12 calculates a feature amount indicating the similarity between the RF reception signal groups, for example, a cross-correlation coefficient. The feature amount calculator 12 repeats the calculation of the feature amount while transferring the position of the object ROI within the search ROI within a predetermined range while keeping the position of the kernel ROI fixed. As a result, a plurality of feature quantities are calculated for the kernel ROI at a certain position, and the feature quantity calculation unit 12 selects the maximum value (or the minimum value) from the plurality of feature quantities and selects the selected maximum value. The value is recognized as a feature amount corresponding to the kernel ROI. The feature amount calculation unit 12 repeats such feature amount calculation while changing the position of the kernel ROI. As a result, the two-dimensional distribution of the feature amount, that is, the feature amount image data is obtained. The feature amount image data is sent to the display 6 via the digital scan converter (DSC) 13, converted into analog, and then displayed in gray scale or color as a visual feature amount image.

The control system 10 can display the feature amount image when the generation process of the feature amount image data for one frame and the storage thereof in the DSC 13 are completed and the feature amount image can be displayed. It is preferable to display a message to the effect that the message is displayed on the display 6 via the DSC 13. After this message is displayed, when the operator gives an instruction to display the feature amount image via an input device (not shown), the control system 10 receives this instruction and the DSC 13
The feature amount image data is read out and displayed on the display 6.

FIG. 3 is a block diagram of the DSC 13. The characteristic amount image data obtained by the characteristic amount calculation unit 12 is sent to the display unit 6 as a digital video signal via the luminance conversion unit 14, the coordinate conversion unit 15, and the frame memory 16 at an appropriate timing specified by the operator. To be The brightness conversion unit 14 converts the feature amount into brightness data (or RGB hue data), and is composed of, for example, a ROM having an input as a feature amount and an output as brightness. The correspondence relationship (so-called setting) between the feature amount and the brightness is collected in the allocation table and stored in the brightness conversion unit 14. The brightness conversion unit 14 is preferably equipped with a plurality of types of tables having different settings as shown in FIG. 5, and is configured to be able to select an arbitrary table by the operator's designation. Figure 5
FIG. 5A shows the setting of luminance conversion, and FIG. 5B shows the setting of hue conversion. The coordinate conversion unit 15 converts the coordinate system (θ, d) expressing the feature amount into an appropriate coordinate system according to the display device 6, for example, an orthogonal coordinate system (x, y). θ
Is the swing angle of the ultrasonic beam, and d is the depth. It is preferable that the DSC 13 executes spatial interpolation of the feature amount.

FIG. 4 is a schematic explanatory view of the process of generating the feature amount image. As described above, the feature amount is a calculated value that is capable of differentiating the infarcted myocardium from the normal myocardium in which the degree of infarction of the myocardium is quantified. For example, the greater the feature amount, the stronger the infarct level,
It means that the smaller the characteristic amount, the closer to normal. By the way, the contraction rate of the infarcted myocardium is smaller than that of the normal myocardium, and the tissue in that portion is solidified (infarcted) regardless of the pulsation of the heart. Therefore, the infarcted portion simply changes its position (metastasis) according to the periodic contraction of normal myocardium. The present invention focuses on this point, that is, since the infarcted myocardial portion of the first frame and the infarcted myocardial portion of the second frame to which the portion has metastasized have little tissue change, RF reception within that portion The distributions of the signal groups are very similar (similar to each other) between both frames, and a numerical value indicating the similarity between the RF reception signal groups is given as a feature amount. However, the problem is that it is not known where the infarcted myocardial portion will metastasize. As will be described later, this problem is caused by the object R with the position of the kernel ROI fixed.
While transferring the position of the OI within the search ROI, the feature amount is calculated at each position, and the maximum value among the plurality of feature amounts is determined as the feature amount corresponding to the kernel ROI, that is, the infarcted myocardial portion is transferred. The problem is solved by moving the object ROI in a wide range and searching for the feature amount. The process of generating the feature amount image will be specifically described below.

As shown in FIG. 4A, two frames of RF reception signals having different scanning timings and different heartbeat time phases, preferably the frame number n designated by the operator while observing the B-mode image. R of the first frame
A feature amount image is generated from the F reception signal group and the RF reception signal group of the second frame of frame number n + 1 delayed by one frame from the first frame.

First, with reference to FIGS. 4B, 4C, and 4D, a procedure for obtaining the feature quantity of a certain kernel ROI (center point (xm, ym, n)) will be described. The RF reception signal group in the kernel ROI of the first frame is output from one output port of the frame memory 11, and the object RO of the second frame near the kernel ROI is output from the other output port.
The RF received signal group in I is taken in by the feature amount calculation unit 12. The similarity (feature amount) of the distribution of both RF reception signal groups is
For example, it is calculated as a cross-correlation coefficient. Details of the calculation method of the feature amount will be described later. The position of the object ROI is searched while keeping the position of this kernel ROI fixed.
It is transferred within and the feature quantity is calculated. Further, the position of the object ROI is transferred, and the feature amount is calculated in the same manner.
In this way, while transferring the object ROI in the search ROI, a plurality of feature quantities with the same position of the kernel ROI but different positions of the object ROI are obtained. The maximum value (or the minimum value) of the plurality of feature quantities is recognized as the feature quantity corresponding to the kernel ROI, and the position information of the center point of the kernel ROI is given to this maximum value.

Then, the kernel ROI is moved to, for example, the center point (xm + 1, ym + 1, n), and the feature quantity is similarly obtained. While changing the position of the kernel ROI, the feature amount is obtained at each position. As a result, the two-dimensional distribution of the feature amount, that is, the feature amount image is obtained.

The feature amount image thus obtained is the DSC.
The luminance conversion unit 14, the coordinate conversion unit 15, and the frame memory 16 of the display unit 13 are sequentially displayed as a digital video signal at a timing specified by an operator.
And is displayed in parallel with the B-mode image as shown in FIG. 6A or overlaid on the B-mode image as shown in FIG. 6B.

Next, a method of calculating the characteristic amount will be described. Two methods are provided as the method of calculating the feature amount. The feature amount calculation unit 12 may be configured to be capable of executing both types, and may be selectively used according to an operator's instruction, or one of the types may be fixedly used in advance. The first method is a method of calculating a cross-correlation coefficient as a feature amount, and the second method is a method of calculating a sum of absolute values of differences between the kernels of both frames and the ROI object ROI as a feature amount. .

Further, as the first method, the direct method and the two-dimensional Fourier transform method are provided. The direct method calculates based on the general formula (definition formula) of the cross-correlation coefficient,
In the two-dimensional Fourier transform method, the cross-correlation function is the inverse Fourier transform of the power spectrum of the original function.
It is calculated using Hinchin's theorem.

FIG. 7 is an explanatory diagram of the overall flow of the first method. c (x, y) is the cross-correlation coefficient distribution obtained. c (x, y)
Is a complex signal, so absolute value processing is required to finally image it. Here, the step of the calculation points X and Y loops (transition pitch of the kernel ROI) is 1/4 each with respect to the vertical and horizontal (rx, ry) of the size of the kernel ROI (same as the object ROI) shown in FIG. The degree is preferable from the viewpoint that the error of c (x, y) is within the allowable range and the calculation time is shortened. In this case, c (x, y) not calculated is interpolated.

FIG. 9 is an explanatory diagram of the calculation method of the direct method,
FIG. 10 is an explanatory diagram of the calculation procedure of the two-dimensional Fourier transform method. The prerequisite is defined as shown in FIG. ^* c
Is the complex conjugate of c, cc (τx, τy) is the cross-correlation coefficient, csum is the cross-correlation coefficient x = τx, y = τy element value, cc and csum
Is a complex signal.

FIG. 11 is an explanatory diagram of the second method. While moving the object ROI in the search ROI with respect to a certain kernel ROI (center point (x, y)), at each position, the absolute value ε (xi, yj) of the sum of the differences between the corresponding positions, and this ε
The ratio of (xi, yj) to the sum in the kernel ROI ε '(x
i, yj) is calculated, and the minimum value (or maximum value) of ε '(xi, yj) is set as the feature amount at the kernel ROI (center point (x, y)). By repeating such calculation while transferring the kernel ROI, a two-dimensional distribution of the feature amount is generated.

As described above, according to this embodiment, the degree of deformation of the myocardium is determined by using two frames having different cardiac time phases, the degree of similarity (feature amount) between the distributions of the RF reception signals in the local region of each frame. ), The infarcted myocardium can be objectively imaged. Moreover, since the similarity searches the search area, the infarcted myocardial metastasis can be followed.

This embodiment can be modified as follows,
In the above description, the similarity was observed based on the distribution of the RF reception signals between the two-dimensional local regions, but this was added to one dimension to develop the similarity between the three-dimensional local regions. It is a thing. This can be easily realized by adding depth information to the position information of the RF reception signal. That is, FIG.
1, a position detector 20 for detecting the position of the probe 1 is added to the configuration of FIG. 1, and the position information of the probe 1 is given to the feature amount image generation unit 7 as depth information, so that the probe 1 It is possible to handle the multi-layered RF reception signal group obtained while moving in parallel as one three-dimensional data. FIG. 13 shows an example of a three-dimensional feature amount image displayed in parallel with the B-mode image subjected to the three-dimensional image processing. According to this variant, 3 of unknown infarcted myocardium
It is possible to capture dimensional transitions. The present invention can be variously modified and implemented without departing from the scope of the invention. It should be noted that, in the above, it is also applicable to B mode and color flow mapping.

[0028]

Industrial Applicability The present invention is an ultrasonic diagnostic apparatus for repeatedly receiving a reception signal for one frame by scanning a two-dimensional region of a subject with ultrasonic waves and detecting the received signal to generate an image. In two dimensions, the two-dimensional feature quantity indicating the similarity between the received signal in the first local area of the first frame and the received signal in the second local area of the second frame whose scanning timing is different from that of the first frame. A feature quantity two-dimensional distribution generation means for generating a distribution and a display means for displaying the two-dimensional distribution as a feature quantity image are provided, and the position of the tissue is simply changed without deformation according to the periodic contraction of normal myocardium ( The infarcted portion that is transferred can be regarded as a high similarity between the received signal in the first local area of the first frame and the received signal in the second local area of the second frame, so that a normal myocardium is obtained. And the difference The infarcted myocardium can be provided an ultrasonic diagnostic apparatus capable of characteristically imaged.

[Brief description of drawings]

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

FIG. 2 is a block diagram of a feature amount image generation unit in FIG.

3 is a block diagram of the DSC of FIG.

FIG. 4 is a schematic explanatory diagram of a process of generating a feature amount image.

FIG. 5 is a diagram showing setting changes in luminance and hue conversion.

FIG. 6 is a diagram showing a display example of a feature amount image.

FIG. 7 is an explanatory diagram of a first method for obtaining a feature amount.

FIG. 8 is an explanatory diagram of parameters used in cross-correlation coefficient calculation.

FIG. 9 is an explanatory diagram of a calculation procedure of a direct method for calculating a cross correlation coefficient.

FIG. 10 is an explanatory diagram of a calculation procedure of a two-dimensional Fourier transform method for calculating a cross correlation coefficient.

FIG. 11 is an explanatory diagram of a second method for obtaining a feature amount.

FIG. 12 is a block diagram showing the configuration of a modified example of the ultrasonic diagnostic apparatus of the present invention.

FIG. 13 is a diagram showing a display example of a feature amount image according to a modified example.

[Explanation of symbols]

1 ... Ultrasonic probe, 2 ... Transmission system, 3 ... Reception system,
4 ... Signal processing unit, 5 ... DSC,
6 ... Display device, 7 ... Feature amount image generation unit.

Claims (6)

[Claims] 1. An ultrasonic diagnostic apparatus for generating an image by detecting a received signal for one frame repeatedly by scanning a two-dimensional region of a subject with ultrasonic waves, and detecting the received signal. A received signal in a first local area of a frame, and
The second of the second frame whose scanning timing is different from that of the frame
2 of the feature quantity that represents the similarity with the received signal in the local area
An ultrasonic diagnostic apparatus comprising: a feature quantity two-dimensional distribution generation means for generating a dimensional distribution; and a display means for displaying the two-dimensional distribution as a feature quantity image. 2. The feature quantity two-dimensional distribution generation means obtains a feature quantity for each of a plurality of second local areas spatially adjacent to one first local area, and determines the maximum value among the plurality of feature quantities. The ultrasonic diagnostic apparatus according to claim 1, wherein one of the value and the minimum value is set as the feature amount of the first local region. 3. The super-characteristic according to claim 1, wherein the characteristic amount is a cross-correlation coefficient between a received signal in the first local area and a received signal in the second local area. Sound wave diagnostic equipment. 4. The ultrasonic diagnosis according to claim 1, wherein the characteristic amount is a difference value between a received signal in the first local area and a received signal in the second local area. apparatus. 5. The ultrasonic diagnostic apparatus according to claim 1, wherein the display unit displays the two-dimensional distribution through one of a luminance conversion process and a hue conversion process. 6. A means for repeatedly receiving a reception signal relating to the three-dimensional area by repeatedly scanning a three-dimensional area of a subject with ultrasonic waves, and using a first reception signal and a second reception signal having different scanning timings. And a display unit for displaying the three-dimensional distribution as a three-dimensional feature amount image. And ultrasonic diagnostic equipment.