JP2003061964A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic diagnostic apparatus having analysis algorithm capable of observing the state of not only cirrhosis but small abnormal lesion in a homogeneous tissue structure by using a statistical property of a speckle pattern to smooth an image and extracting a micro-structure. SOLUTION: In this ultrasonic diagnostic apparatus, an ultrasonic pulse is applied to a patient to obtain a tomographic image. The apparatus is provided with analysis operating means 23, 24, 26 for extracting a specified signal by using the intensity of an echo signal generated from a region P of the patient or statistical property of amplitude information, and a display means 14 for displaying the result extracted from the analysis operating means.

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 obtaining an ultrasonic image in a subject based on an echo signal resulting from the ultrasonic waves applied to the subject. The present invention relates to an ultrasonic diagnostic apparatus having a function of extracting a minute structure in a living organ in a specimen.

[0002]

2. Description of the Related Art There are various medical applications of ultrasonic signals, and an ultrasonic diagnostic apparatus is one of them.

The mainstream of this ultrasonic diagnostic apparatus is a type that obtains a tomographic image of a soft tissue of a living body by using an ultrasonic pulse reflection method. This imaging method can non-invasively obtain a tomographic image of a tissue, and can display in real time as compared with other medical modalities such as an X-ray diagnostic apparatus, an X-ray CT scanner, an MRI apparatus, and a nuclear medicine diagnostic apparatus. The device has many advantages such as a small size and relatively low cost, no exposure to X-rays, and blood flow imaging based on the ultrasonic Doppler method. Therefore, it is widely used in the diagnosis of cardiovascular (heart), abdomen (liver, kidney, etc.), mammary gland, thyroid gland, urology, obstetrics and gynecology. In particular, the heart beat and fetal movement can be observed in real time by a simple operation of applying an ultrasonic probe to the body surface, and there is no worry of X-ray exposure, so repeated inspections can be performed, and further, It is preferred that the ultrasonic diagnostic apparatus can be moved to the bedside for easy inspection.

Further, the ultrasonic diagnostic apparatus currently in use usually has various measuring functions. “Measurement” here is to quantify a physical event in the subject, and the measurement result is presented as a numerical value itself and / or converted into an amount such as color or brightness corresponding to the numerical value. It

The main measurement functions installed in the conventional ultrasonic diagnostic apparatus are listed below. 1. Shape measurement: With this shape measurement function, for example, the size of the liver tumor, the wall thickness of the myocardium, the size of the fetus, and the like are measured. 2. Velocity measurement: This velocity measurement function includes, for example, blood flow velocity of the artery using the Doppler method and blood flow velocity mapping of blood vessels in the liver using the color Doppler method. 3. Measurement of volume, flow rate, etc .: With this measurement function, for example, volume estimation of the heart chamber based on several lengths in the heart chamber, measurement of blood flow from changes in signal intensity of the contrast agent over time can be performed. Done.

Of course, many of the measured values obtained by such measurement are useful information for evaluating the severity of disease. For example, information such as tumor size and the degree of regurgitation in blood vessels immediately indicates the degree of need for treatment.

[0007] On the other hand, there is a lot of measurement information that is not directly for evaluating the disease but indirectly useful for diagnosing the health condition of the subject. Rather, this is more common as a familiar everyday measurement. For example, the height, weight, blood pressure of the subject, or various numerical values obtained by a blood test fall into this category.

[0008] Further, as a matter that sets it apart from such various measuring functions, there is a diagnosis close to quantification based on the empirical judgment of the doctor. This valuable diagnosis can be found everywhere in the medical setting. For example, one such diagnosis is the diagnosis of cirrhosis of the liver.

Cirrhosis means that fibrotic tissue increases in the liver due to repeated destruction and regeneration of hepatocytes, the number of hepatocytes gradually decreases, and the liver becomes hard and shrunk. At the initial stage of liver cirrhosis, there is no subjective symptom of the patient, and it is difficult to visually recognize the minute fibrotic structure in the ultrasound diagnostic image. However, as the degree of liver cirrhosis becomes higher, the nonuniformity of the speckle pattern of the liver parenchyma becomes visible, so this is used as a standard for judging the degree of liver cirrhosis by visually observing this nonuniformity in the medical field. .

The speckle pattern appearing in this ultrasonic diagnostic image is a portion where the echo signal intensity is high due to the innumerable superposition of scattered waves when innumerable scatterers are distributed with fineness less than the resolution of ultrasonic waves. Is a phenomenon that occurs with the lower part. It is well known that this is a physical phenomenon close to what is called an interference fringe, and the pattern itself does not directly reflect the structure of an organ. Also in the above observation of cirrhosis, the speckle pattern does not directly reflect the state of the structure of the fibrotic tissue. However, as the severity of cirrhosis increases, this speckle pattern exhibits a characteristic visual pattern, which is used for diagnosis.

For example, FIGS. 15 (a) and 15 (b) schematically show tomographic images of the liver which are referred to when observing the above-mentioned liver cirrhosis. FIG. 7A is a tomographic image of a normal person without abnormal liver, and a pattern called liver speckle pattern looks relatively uniform. On the other hand, FIG. 7B schematically shows a tomographic image of an abnormal liver having a disease, and the speckle pattern thereof is not uniform as compared with the image of FIG. It can be confirmed that

Therefore, when the ultrasonic diagnostic image of the liver is presented, the "uniformity" of the speckle pattern is visually observed, and if the unevenness is strong, the abnormal liver of cirrhosis is suspected. It is diagnosed as being present.

However, so far, "nonuniformity of speckle pattern", that is, "abnormality" in this example.
There was no case that was quantified, and the diagnosis was based on the empirical judgment of the doctor.

Only in recent years, the question of what kind of human recognition pattern the above-mentioned doctor's empirical judgment makes is objectively and scientifically investigated. Studies have begun to clarify. For example: 1, Yamaguchi T, Hachiya H,
"Modeling of the Cirrrhoti
c Liver Considering the L
iver Llobule Structure ", Jp
n, J. App ;. Phys. Vol. 38 (199
9) pp. 3382-3392; 2, Otsuka, Yamaguchi, Hachiya: "Simulation study of ultrasonic B-mode images of lesioned liver", IEICE Technical Report, US9.
6-16 (1996-06), pp. 15-22: 3, Tsuneo Kikuchi, Toshihiro Nakazawa, et al., "Development of quantitative diagnostic technique for inter-disease by using echo waveform spectrum shape of ultrasonic diagnostic equipment", Nissho Medical Basic Technology Research Group, BT-2000-31,
pp. 9-15 (2001); etc.

According to these documents, the reason why the speckle pattern of the tomographic image of the liver changes with the progress of liver cirrhosis (see FIGS. 15 (a) and 15 (b)) occurs with the progress of liver cirrhosis. When the nodules and fibrotic tissues that grow into the structure become recognized as a structure to the ultrasonic pulse in the process of increasing in size as they progress, information on the structure gradually appears in the speckle pattern. However, it is considered that this aspect will gradually change as the number increases.

[0016] Also, in the prior arts disclosed so far, some attempts have been made to quantify the degree of progression of this cirrhosis. For example, Japanese Patent Application 2000-
In 054201, there is an invention which is “a method for quantitative analysis of tissue normality using an ultrasonic diagnostic apparatus and ultrasonic waves”.

The invention described in this Japanese Patent Application No. 2000-054201 is based on the statistical properties of the speckle pattern as shown below.

A curve 51 in FIG. 16A shows a probability density distribution of brightness values of echo signals reflected from a normal liver. From the perspective of probability / statistics, if the scatterers are randomly distributed, the probability density distribution P (x) of the amplitude value that is the intensity of the echo signal reflected from these scatterers.
Is P (x) = (x / σ ² ) exp (−x ² / 2σ ² ).
Will follow the Rayleigh distribution. Where σ ²
Represents the variance and is standardized as 0 on average.

When the liver is normal, it can be assumed that many scatterers (excluding trivial structures such as blood vessels) are randomly present in the liver. Therefore, the echo signal intensity (amplitude) representing the liver is obtained. 16 has a Rayleigh distribution as a curve 51 shown in FIG. However, if the above-mentioned fibrotic structure increases in the liver, the speckle pattern will reflect the structure, and it cannot be said that it is random. As a result, the luminance probability density function deviates from the Rayleigh distribution as shown by the curve 52 in FIG.

As described above, it is possible to judge whether the liver is normal or abnormal by observing the outline of the probability density distribution curve of the echo signal intensity. That is, the error between the probability density distribution obtained by the actual measurement and the Rayleigh distribution as the theoretical value is used as the evaluation criterion.

However, the resolution of the ultrasonic diagnostic image is determined by the transmission frequency, the transmission wave number, the transmission aperture, and the like, and the minute fibrous structure existing in the initial fibrotic structure or tissue in the liver cirrhosis as described above. (Lesions near or below the resolution limit of a general diagnosis)
At present, the images are either buried in the speckle pattern and invisible, or are visualized in a state that is difficult to distinguish from the speckle pattern. For the diagnosis of liver cirrhosis, it is ideal to be able to make a diagnosis based on images at the initial stage when the subjective symptoms of the patient do not appear much, but because of the above-mentioned characteristics of ultrasonic diagnosis, speckle Finding and quantifying microstructures in it has been very difficult.

[0022]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to smooth the image of the speckle portion by using the statistical property of the speckle pattern. To provide an ultrasonic diagnostic apparatus equipped with an analysis algorithm capable of observing minute abnormal lesions in a homogeneous tissue structure, including the degree of progression of liver cirrhosis by performing and extracting minute structures. It is in.

[0023]

In order to solve the above-mentioned problems, the invention according to claim 1 is an ultrasonic diagnostic apparatus for obtaining a tomographic image by irradiating a subject with ultrasonic pulses, wherein the subject region is It is characterized by further comprising: an analysis calculation means for extracting a specific signal by using the statistical property of the intensity or amplitude information of the echo signal generated from the display; and a display means for displaying the result extracted by the analysis calculation means. .

In order to solve the above-mentioned problems, the invention according to claim 13 is an ultrasonic diagnostic apparatus for obtaining a tomographic image by irradiating a subject with an ultrasonic pulse, starting from a sample area having an echo signal of the pulse. The means for calculating the first statistic, the means for searching a region having a statistic in which the amplitude value of the echo signal follows the Rayleigh distribution from another echo signal existing in the vicinity of the sample to be calculated, and the searching. Means for calculating a second statistic from the region, and means for performing a test process for testing the hypothesis that the echo signal of the sample region follows a Rayleigh distribution by using the first and second statistics. , Means for determining the severity of the tissue property of the sample area using the result obtained by the assay, and displaying the determined result as an image or numerical value on the display unit And characterized by including a capability.

In order to solve the above-mentioned problems, the present invention according to claim 14 is an ultrasonic diagnostic apparatus for obtaining a tomographic image by irradiating a subject with an ultrasonic pulse, from a sample region having an echo signal of the pulse. The means for calculating the first statistic, the means for searching a region having a statistic in which the amplitude value of the echo signal follows the Rayleigh distribution from another echo signal existing in the vicinity of the sample to be calculated, and the searching. Means for computing a second statistic from a region and a CFAR for the sample region using the second statistic
It is characterized in that it comprises an arithmetic means for performing processing and a display means for displaying the result of the CFAR processing.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the control configuration of the ultrasonic diagnostic apparatus according to this embodiment.

Although the present invention can be applied to various diagnostic apparatuses, this embodiment will be described with respect to an ultrasonic diagnostic apparatus. Further, the diagnosis site can be applied to the liver, pancreas, myocardium, etc., which have a relatively homogeneous tissue structure in the normal state, but in this example, the case of diagnosing the liver cirrhosis severity will be described.

[Description of Structure] As shown in FIG. 1, the ultrasonic diagnostic apparatus according to this embodiment drives the ultrasonic probe 12 and an ultrasonic probe 12 that transmits and receives ultrasonic signals to and from a subject. In addition, the apparatus main body 11 for processing the reception signal of the ultrasonic probe 12, the input device 13 connected to the apparatus main body 11 and capable of inputting instruction information from the operator to the apparatus main body 11, and the monitor 14 are provided. The input device 13 includes a button, a keyboard, a trackball, etc. capable of controlling the diagnostic device and setting various image quality conditions.

The apparatus main body 11 is the ultrasonic transmission unit 2
1, ultrasonic examination unit 22, B mode processing unit 2
3, a Doppler processing unit 24, an image generation circuit 25, a signal analysis unit 26 (main in the present invention), a control processor (CPU) 27, a storage medium 28, and other interfaces 29. These may be composed of hardware such as an integrated circuit, but may be software programs modularized in software.

The ultrasonic wave transmission unit 21 is not shown in the figure.
The ultrasonic diagnosis unit 22 is composed of a transmission circuit such as a delay circuit and a pulsar circuit, and the ultrasonic diagnosis unit 22 is an A / D converter,
It is composed of a receiving circuit such as an adder, generates pulsed ultrasonic waves and sends them to the vibrating element of the probe 12, and the probe 12 receives the echo signal scattered by the tissue in the subject again to obtain a received signal.

The output from the ultrasonic examination unit 22 is B
It is sent to the mode processing unit 23. Here, logarithmic amplification of the echo signal, envelope detection processing, and the like are performed, and the signal strength becomes data represented by brightness of brightness. The Doppler processing unit 24 frequency-analyzes velocity information from the echo signal,
The analysis result is sent to the image generation circuit 25.

In the image generation circuit 25, the scanning line signal sequence of ultrasonic scanning is converted into the scanning line signal sequence of a general video format typified by a television, and character information and scales of various setting parameters are converted. And the like, and is output to the monitor 14 as a video signal. Thus, a tomographic image showing the shape of the subject's tissue is displayed on the monitor 14. Further, the image generation circuit 25 is equipped with a storage memory for storing image data, and can be called by an operator after diagnosis, for example.

The control processor 27 has a function as an information processing device (computer) and is a control means for controlling the operation of the ultrasonic diagnostic apparatus main body. Also in the signal analysis of the present invention, a command to transfer the necessary programs and data from the storage medium 28 to the signal analysis unit 26 is sent.

The storage medium 28 stores the diagnostic images and also stores the various analysis software programs described above (details will be described later).

The signal analysis unit 26 outputs the output signal (radio frequency) immediately after the ultrasonic wave reception unit 22.
cy (RF) signal) or the image brightness signal after passing through the B-mode processing unit 23, the analysis process of the present invention described later is performed, and the result is obtained by the image processing unit 25.
Is displayed on the display unit via the, or stored in the storage medium 28, or transferred to an external PC, printer, etc. via the network interface 29.

[Explanation of Analysis Method] Next, an analysis method in the signal analysis unit 26 will be described with reference to FIG.

First, the echo signal to be analyzed is
Selected by the operator. Since this signal is preferably an echo signal obtained from the liver parenchyma even when an RF signal is used, a region 41 (hereinafter referred to as ROI 41) is designated in the image as shown in FIG. By that,
Echo data spatially corresponding to the signal analysis unit 2
It is designed to be taken in by 6. In this example, RO
The shape of I41 is a square, but it is also possible to specify a circle (oval) or a free closed curve. Also, multiple ROIs
It is also possible to specify 41.

Next, the following processing is performed on the signal in the ROI 41. Here, it is assumed that the RF signals or image brightness signals in the ROI 41 are numbered in a two-dimensional array spatially corresponding to the diagnostic image. For example, as shown in FIG. 3, it is assumed that the ROI 41 has Nx data in the x direction and Ny data in the y direction, that is, Nx × Ny data in total.
Further, the coordinates of the point P in the ROI 41 are (x, y) (where 1 ≦ x ≦ Nx, 1 ≦ y ≦ Ny).

Each point P (x, y) in the ROI 41 is subjected to the arithmetic processing described below.

First, as shown in FIG. 4, a region near P (x, y) is secured. It is more ideal if this neighboring region is circular with the point P as the center, but for simplicity, here, as shown in FIG. 4, ± a in the x direction and ± a in the y direction.
Let us consider a rectangular area such that b. (Note: the neighborhood area in FIG. 4 is included in the ROI 41 in FIG. 3 and is generally sufficiently smaller than the ROI 41 shown in FIG. 3.) Here, points in this neighborhood area are denoted by Q (i ，
j), the signal strength values at points P and Q are Ip,
Let Iq.

Next, smoothing processing is performed on the above-mentioned neighborhood area from the viewpoint of "similarity". The general description of the smoothing process will be given below, followed by a specific description of the smoothing process according to the present invention.

<A: General Description> The smoothing process is a process for obtaining a so-called “blurring” effect by somewhat weighting the information (value) of a nearby point to the value of a certain point. Is. In the conventional general smoothing process, weighting is often performed in correlation with the distance between two points (that is, the weighting coefficient of the near point is large and the weighting coefficient of the far point is small).

<B: Specific Description of Smoothing Processing According to the Present Invention> On the other hand, the weighting coefficient according to the method of the present invention is irrelevant to the distance between the two points and whether or not the two points are statistically similar. Is determined from the viewpoint of "similarity". When the degree of similarity of the point Q near the point P is high, the value of the point Q is weighted to the point P by a coefficient close to 1, for example, and when the degree of similarity is low, the coefficient close to 0, for example. The value of the point Q is weighted to the point P by. The process smoothed by the degree of similarity in this way is called a "coherent filter" process.

An example of the coherent filter processing will be described below.

First, the following evaluation function W is defined: W = D- | Iq-Ip | / [sigma] (1) where [sigma] is a standard obtained from the probability density distribution of the echo signal intensity in the ROI 41. Is a deviation, and D is a threshold value set separately (see FIG. 5). If W <0 (that is, the second term on the right side is larger than the threshold value D),
The point Q is judged to be “not similar” to the point P, and is excluded from the weighting target (this is a method called statistical test,
(This corresponds to the case where the rejection area is selected as D). If W> 0, the amplitude value Iq at the point Q is weighted by Ip. However, the weighting coefficient Cw (i, j) at that time is a function of the difference in intensity as follows: Cw (i, j) = [1-{(Iq-Ip) / [sigma] D} ² ].
^Two .

This weighting factor is obtained for all points in the neighborhood area and added to the point P to obtain the value Ip of the point P after calculation.
′: Ip ′ = Ip + {Σ (Cw (i, j) × Iq (i,
j))} / Ctot where Ctot is the total addition amount of Cw.

The rejection area D can be designated and changed by the operator, but it goes without saying that optimum conditions are stored in advance in the ultrasonic diagnostic apparatus. As described above, since the amplitude of the echo signal has a statistical property that follows the Rayleigh distribution, the rejection area D is determined from the probability density function of the Rayleigh distribution.

FIG. 6 shows the result of the image processing obtained by this method. However, (A) is an original image, and although the target is a normal liver, it is an example in which a structure is confirmed such as a boundary in the upper part of the liver and a cross section of a relatively large blood vessel in the liver. And (B) is the image after the calculation. Here, as the standard deviation σ, a value calculated based on the statistic of a relatively homogeneous portion in the liver parenchyma in this data was used.

Generally, when a simple smoothing process is performed, so-called "edge blurring" occurs, the spatial resolution of the image is impaired, and the entire image is blurred. However, looking at the result (B) obtained by this method, since the luminance of the real part is a speckle pattern according to the Rayleigh distribution, similarities are recognized, and as a result, a very large smoothing process is performed. There is. On the other hand, since the structures of the liver boundary wall and the blood vessel wall do not follow the statistical distribution of the parenchyma of the liver, they are not subjected to smoothing processing and are depicted as they are.
As described above, the image processing result obtained by this method is characterized in that the boundary of the structure is extremely steep as compared with the normal smoothing processing.

Next, the flow of the procedure of the operator will be described with reference to FIG.

First, the operator scans the liver of the subject and selects a cross section to be analyzed (S71). Next, the ROI to be analyzed is designated (S72). Next, the standard deviation σ required for the evaluation function is obtained. At this time, the operator separately specifies the ROI for obtaining the standard deviation σ (S73), and calculates the standard deviation σ in advance from the echo signal of the entire image at that time and from the data in the ROI to be analyzed, It is possible to select the method (S74) in which this value is called. Next, an actual analysis is performed (S7
5), the analysis result is displayed on the display unit (S76).
At this time, the threshold value D takes an arbitrary value, but by changing the threshold value D, it is not similar to the speckle pattern,
That is, since the degree of recognition as a structure changes, the value of the threshold D is changed according to the analysis result, and recalculation is performed (S77). As a result of the repeated calculation, the analysis ends when the desired image is obtained (S78).

<Various Ideas for Improving Accuracy ... No. 1> Next, a first method for improving the accuracy of the present analytical calculation will be described.

When performing the main analysis, the operator inputs to the system that the analysis is to be started, so that the ultrasonic diagnostic apparatus of the present invention changes to a dedicated transmission / reception condition. This is to achieve the following objects: [1] Improvement of analysis accuracy by increasing the number of samples of acquired data ... Since analysis uses statistical properties, it is better that the number of samples of echo data is large. However, simply increasing the number of transmissions and receptions only takes echo signals having the same information, and does not substantially increase the amount of information. To achieve this object, the scan line density of transmission and reception is higher than that at the time of normal diagnosis, for example, 2 times or 4 times. Or
Ultrasonic transmission / reception is performed a plurality of times on the same scanning line under transmission conditions of different frequencies.

Since the above-mentioned processing leads to a reduction in the real-time observation ability due to a decrease in the frame rate, the system operates under normal scanning line conditions until just before the analysis, and at the timing of the analysis start (instructed by the operator, etc.). , The transmission / reception conditions are changed.

[2] Improvement of S / N ratio in high frequency band ... Due to the basic property of ultrasonic waves, it can be said that transmitting and receiving in a high frequency band has a higher resolution and a larger amount of spatial information. On the other hand, at a high frequency, the sound wave is greatly attenuated, which causes a problem that the received signal cannot be acquired up to the deep region. In order to solve this, the same number of transmissions and receptions on the same scanning line is increased, and the averaging process is performed at the RF signal level. For example, when the averaging process of the same received RF data is performed twice, random noise is reduced and the steady echo signal amplitude level is increased by about 6 dB. In this method as well, as in [1] above, an increase in scanning line density leads to a decrease in real-time observation capability due to a decrease in frame rate. Therefore, until immediately before analysis, the system operates under normal scanning line conditions and the timing of analysis start The transmission / reception conditions are changed (by an instruction from the operator).

[3] Avoiding signal saturation ... In the presence of a medium having a large scattering coefficient, the received signal may be saturated. If the operator makes an error in setting the gain on the device, the received signal will be saturated similarly. When the signal is saturated, there is a risk that the statistical amount of the signal changes and an incorrect analysis result is presented. In the present system, the signal analysis unit 26 shown in FIG. 1 monitors the signal level of the ultrasonic receiving unit 22 based on the information of the maximum value that the received signal can take, and when a signal reaching the maximum value is generated ( Alternatively, when a value close to that occurs, the analysis is stopped and a message prompting the operator to re-measure is displayed.

[4] Analysis of a plurality of frames ... The signal analysis unit 26 is provided with a memory for storing RF data of a plurality of frames, and as shown in FIG.
In addition to y), it is also possible to perform the above-described analysis processing (coherent filter processing) on a three-dimensional neighborhood by taking into account information in the z direction of a plurality of frames. In this case, in order to increase the amount of information of the signal in the z direction, it is desirable to change the scan plane in the living body with time by moving the probe, but in our study, even if the probe is not intentionally moved, In addition, it is confirmed that the information of the echo signal changes with time due to a minute movement of the operator or a movement of the subject such as heartbeat and respiration, and the analysis accuracy of the present method is improved by the analysis by the plurality of frames.

<Other functions> [5] Display / non-display of analysis area ... In the analysis result image, the feature amount of the structure is extracted from the speckle pattern, and is used as new information for diagnosis. However,
Even so, there are situations where it is desired to reconfirm the echo image before analysis. The information of the diagnostic image before analysis is retained by being stored in the signal analysis unit 26 of FIG. 1 or once being recorded in the storage medium 28. Even after the analysis, the information of the operator using the input device is retained. Monitor 14 by calling command
It is possible to display in. As a display form at that time, it is possible to perform a parallel display, a superimposed display, or a display that is alternately switched by button input or the like.

[6] Enlargement of analysis area ... In the ultrasonic diagnostic apparatus of the present invention, the ROI portion designated as the analysis area can be enlarged and displayed before analysis, during analysis, or after analysis. ing. Generally, the information of the diagnostic image processed by the image generation circuit is larger than the number of pixels displayed in the television format on the display unit. Therefore, unlike the case of simply enlarging a photograph or the like, the enlarged display in this case results in an increase in the amount of information itself displayed in the ROI. Further, as described above, in the transmission / reception control method (idea [1]) according to the present invention, the scanning line density is denser than that in the conventional method. Be advantageous.

<Various Ideas for Improving Accuracy ... No. 2> Next, a second method for improving the accuracy of the present analytical calculation will be described.

In order to quantify the tissue property from a diagnostic image, it is common to analyze a local region of the image as a "sample". This is because the diagnostic image includes blood vessels, organ boundaries, gallbladder, and the like in addition to the tissue region, and analysis with these included results in a large error.

Thus, a limited part of the image (sample)
A statistical method called "test" is well known as a method for estimating the population from the. This is done by making one hypothesis about the properties of the population and examining the properties of the sample,
This is a method of determining whether or not to reject this hypothesis.

Taking the tissue diagnosis of the liver as an example, it is as follows.

First, it is hypothesized that the liver (population) is normal. It is known that the set of amplitudes of echo signals obtained from a normal liver follows the Rayleigh distribution as described above. Therefore, a method called a test determines whether or not this hypothesis applies to the sample taken out.

Generally, χ ² test, t test, F
There are various methods such as an assay, but the method itself is already widely known, and therefore its details are omitted here.

However, if these tests are used for the above-mentioned normal tissue diagnosis, the following problems will occur.

That is, in the above-mentioned normal tissue diagnosis, the statistic of "normal tissue" corresponding to the population cannot be directly obtained. This statistic means "mean or variance of cases where the liver cirrhosis patient had normal liver", and it is not possible to obtain this value from the liver cirrhosis patient (patient suspected of having liver cirrhosis). It is possible. In addition, this value does not make sense as an average value or a dispersion value obtained from an echo signal of another subject (human body) having a normal liver. This is because these statistics change depending on the irradiation sound pressure of ultrasonic waves and the gain setting. This problem cannot be solved even if the setting of the diagnostic device is the same, because the value changes due to the difference in the biological attenuation of the subject.

Therefore, in the present invention, a local area suitable as a statistic of "normal tissue" is extracted from the subject being diagnosed at present, and the statistic of the population (variance value σ ² ,
The standard deviation σ) is used.

This method will be described below.

FIG. 9 shows the analysis result of the liver showing the variance value σ ² calculated from the spatial arrangement (see FIG. 8) similar to the diagnostic image based on the echo signal of the liver diagnosed as cirrhosis. Is. The method of analyzing the curves A and B in the figure will be described below.

A: First, as shown in FIG. 10, a small region R01 of a fixed size for taking a sample is set, and its position is gradually shifted, and its average value μ and variance σ ₁ ^{2 are set.}
And the dispersion value σ ₁ ² is displayed is the curve A shown in FIG. B: Next, the curve B is obtained by substituting the above average value μ into the following equation to obtain the variance σ ₂ ² . σ ₂ ² = (4 / π−1) μ (1) The above formula (1) is valid only when the assumption that the probability density distribution of the sample “follows the Rayleigh distribution” holds. Therefore, if the sample has a non-Rayleigh distribution, this equation (1) does not hold.

As is apparent from FIG. 9, the values of both are almost the same in the range of section (1) in FIG. From this, it can be predicted that in the section (1), the variance value σ ₂ ² calculated using the equation (1) and the actually obtained variance value σ ₁ ² will be substantially the same. Therefore, in this section (1), it can be determined that the probability density distribution of the sample substantially follows the Rayleigh distribution.

On the other hand, in the range of the section (2), the two values are greatly different. This indicates that the formula (1) does not hold. Therefore, in this section (2), it can be determined that the probability density distribution of the sample is highly likely to be the non-Rayleigh distribution.

What is important here is the fact that a range such as section (1) can be found locally. As described above, even in a tissue region diagnosed as cirrhosis, it is possible to find a small region according to the Rayleigh distribution by searching while changing the position of the sample.

In the present invention, a sample having a variance value similar to the Rayleigh distribution is searched for by the above method (see FIG. 11), this variance value is taken as the variance σ ₀ ^{2 of the} population, and the analysis region in the vicinity thereof is used. The variance value is set to σ ₁ ^2, and the test is performed from both values. As described above, the characteristic of the present invention is to obtain the "pseudo population variance" by the search.

As described above, the test method itself goes
There are several types, and since it is a widely used method,
The description will be omitted here. Also here
Broadly construed, the "test" of
-Whether it shows a distribution or not "
It is not necessary to use a strict verification method. For example, above σ ₁
^TwoAnd σ_Two ^TwoIf the ratio with
It may be a method.

In any case, as a result of the test, if the hypothesis is rejected, the area is judged to be "non-Rayleigh".

<Application to CFAR> The method of the present invention is a so-called Constant False Alarm.
It can also be applied to Rate processing (CFAR processing). The CFAR is a method well known in the radar technology whose principle is similar to that of the ultrasonic diagnostic apparatus.

The principle will be briefly described below.

FIG. 12 shows a signal displayed on the radar as an example (the CFAR processing performed on the video luminance signal in this way is called LOG / CFAR processing, but is simply referred to herein as CFAR processing). . In this example,
Three signals typified by airplanes are included in the scattering objects typified by clouds.

In this example, the points to be extracted are clear, but when they are displayed as luminance information, this extract may be difficult to see due to the influence of the above-mentioned scatterers. Therefore, in order to remove the scattered matter, so-called gain adjustment is performed so that a certain threshold value or less is not displayed.

However, in the case of this example, if T1 shown in the same figure is used as the threshold value, the point C will not be extracted. Further, when T2 shown in the figure is used as a threshold value, the point C is displayed, but instead, the scattered matter near the point A is visually recognized. So in this case,
Further, CFAR processing will be performed.

In this CFAR processing, with respect to a certain point X, the average value of signals in the vicinity excluding the point itself is taken as the point X.
Is subtracted from, and then the threshold value for display is set again.

When this CFAR processing is applied to the signal displayed on the radar shown in FIG. 12, the result shown in FIG. 13 is obtained. As is clear from the figure, by performing this CFAR processing, the inclination of the entire scatterer is removed, and the threshold value T3 for extracting the points A to C can be easily set.

What has been described above is the so-called CFAR processing.

Although there has already been a paper report that the lesion site of the liver could be extracted relatively well using this CFAR,
CFAR can be performed well when the points to be extracted are sparsely present, and when the points to be extracted are densely present, that is, when advanced cirrhosis is assumed,
I know that it doesn't work theoretically. Because
Since the above “neighborhood average value” includes not only the scattered matter but also adjacent extraction points, the non-Rayleigh property is no longer exhibited (see FIG. 14). Therefore, in such a case, the subtraction result is an underestimate.

Therefore, in such a case, by using the present method, a region having a Rayleigh distribution in the vicinity is searched, and the average value obtained from the region is used to obtain the same degree as in the case where the extract is sparse. The accuracy of can be maintained.

<Method of Presenting Judgment Result> It is highly possible that the part rejected by the above judgment method is not a normal tissue. Therefore, in this example, a tomographic image of this portion is displayed, and a portion that is not rejected is displayed in black with a brightness value of 0, for example. By such a method, it is possible to emphasize and display a part that may be a diseased part.

As a modification of this, for example, in a B-mode black-and-white luminance image, a highlighted display method in which the rejected area is color-displayed in red or the like can be considered.

Further, if the original B-mode tomographic image can be observed even after the highlighted image of the above-mentioned diseases is obtained, it is convenient to confirm the analysis result and the original tissue property.

Therefore, in the present invention, the highlighted image as the analysis result and the original B-mode tomographic image can be switched and displayed by an operator's instruction (for example, button operation). It is also possible to display them in parallel on one screen at the same time.

<Display of Statistics> In the present invention, the variance value σ ₀ ² of the population obtained by the above method, the variance value σ ₁ ^{2 of} the region of interest, or its square root (standard deviation),
Further, the average value μ is configured to be displayed on the display unit.

<Display of Probability Density Curve> In the present invention, it goes without saying that the sample data of each area such as the average value and the variance value obtained by the above-mentioned analysis is displayed in the probability density distribution as shown in FIG. Shall be. Furthermore, in the present invention, it is also possible to display the probability density curve for one point or a local area on the image designated by the operator after the analysis on another screen.

[0094]

As described above, according to the ultrasonic diagnostic apparatus and the analysis method thereof according to the present invention, it is difficult to visually distinguish an ultrasonic pulse from a speckle pattern during ultrasonic diagnosis. By extracting the existence of a structure close to the limit of resolution using statistical properties and generating an image that is easy to visually recognize, it becomes possible to more easily diagnose the severity of cirrhosis.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of a case where an analysis region is designated in the ultrasonic diagnostic apparatus according to the present invention.

FIG. 3 is a conceptual diagram showing an arrangement of data in an analysis region in the ultrasonic diagnostic apparatus according to the present invention.

FIG. 4 is a diagram showing an area used for smoothing processing for one point in the analysis area in the ultrasonic diagnostic apparatus according to the present invention.

FIG. 5 is a conceptual diagram for explaining a relationship between signal intensities at two points on which smoothing processing is performed.

FIG. 6 is an example of an image obtained by the ultrasonic diagnostic apparatus and the analysis method thereof according to the present invention.

FIG. 7 is a flowchart showing the procedure of the operator when performing the analysis of the present invention.

FIG. 8 is a conceptual diagram when performing smoothing processing on one point in the analysis region of the present invention using a plurality of frames.

FIG. 9 is based on an echo signal of the liver diagnosed as cirrhosis,
9 is an analysis result of the liver showing a variance value σ ² calculated from a spatial arrangement similar to that of the diagnostic image shown in FIG. 8.

10 is an explanatory diagram for explaining a sample acquisition method for drawing the curve A shown in FIG.

11 is a conceptual diagram showing a process of searching for a sample having a variance value similar to a Rayleigh distribution by the method shown in FIG.

FIG. 12 is an explanatory diagram showing an example of a signal displayed on a radar.

FIG. 13 is a diagram showing a result of performing CFAR processing on the explanatory diagram shown in FIG. 12;

FIG. 14 is a diagram showing a difference between the average value of the conventional method and the average value after the Rayleigh part search when there are densely extracted points, that is, when advanced cirrhosis is assumed.

FIG. 15 is a schematic diagram showing a difference in appearance of diagnostic images between a normal liver and a cirrhotic liver.

FIG. 16 is a schematic diagram showing the difference in probability density distribution of signal intensity between normal liver and cirrhotic liver.

[Explanation of symbols]

11 ... Device body 12 ... Ultrasonic probe 13 ... Input device 14 ... Monitor 21 ... Ultrasonic transmission unit 22 ... Ultrasonic reception unit 23 ... B mode processing unit 24 ... Doppler processing unit 25 ... Image reproduction circuit image memory 26 ... Signal analysis Unit 27 ... Control processor (CPU) 28 ... Storage medium 29 ... Other interface 41 ... Area 51 ... Probability density distribution 52 of brightness value of echo signal reflected from normal liver ... Reflected from liver with increased fibrotic structure Probability density distribution P of the brightness value of the echo signal that is to be measured P ... Object T1 ... Threshold value T2 ... Threshold value T3 ...

Continued front page    F-term (reference) 4C301 AA02 CC02 DD02 DD30 EE20                       HH31 HH52 JB03 JB11 JB29                       JB34 JC07 JC16 JC20 KK08                       KK25 KK30 KK31 LL02 LL03                       LL04 LL20                 4C601 DD30 DE01 EE30 JB01 JB11                       JB19 JB21 JB22 JB34 JB45                       JB49 JB55 JC04 JC15 JC20                       JC37 KK10 KK12 KK28 KK29                       KK31 KK33 LL01 LL02 LL04                       LL40                 5B057 AA07 BA05 CA02 CA08 CA13                       CA16 CB08 CB12 CB13 CB16                       CE11 DB02 DB09 DC30

Claims (17)

[Claims] 1. An ultrasonic diagnostic apparatus for obtaining a tomographic image by irradiating a subject with an ultrasonic pulse, wherein a specific signal is obtained using statistical properties of intensity or amplitude information of an echo signal generated from the subject region. An ultrasonic diagnostic apparatus comprising: an analysis / calculation means for extracting the data; and a display means for displaying a result extracted by the analysis / calculation means. 2. The analysis calculation means is provided with a determination means for determining a similarity between a first signal amplitude value and a second signal amplitude value in the echo signal to be analyzed by a test. The ultrasonic diagnostic apparatus according to claim 1. 3. The analyzing and calculating means digitizes weights determined by the similarity between the first signal amplitude value and the second signal amplitude value, and the digitized weights,
The ultrasonic diagnostic apparatus according to claim 2, further comprising an averaging unit that weights and averages the first signal amplitude value and the second signal amplitude value. 4. The ultrasonic diagnostic apparatus according to claim 3, wherein the averaging means obtains a new numerical value regarding the first signal amplitude value by weighted averaging. 5. The averaging means multiplies the second signal amplitude by a large weighting factor when the similarity between the first signal amplitude value and the second signal amplitude value is high, and the first signal amplitude value. And the second signal amplitude value has a low degree of similarity, the second signal amplitude is multiplied by a small weighting coefficient, and the weighted average of the weighted first and second signal amplitudes is calculated. 4. The ultrasonic diagnostic apparatus according to 4. 6. The analysis calculation means comprises data acquisition means for acquiring the data before the echo signal is converted into image data and using the data for the analysis calculation. The ultrasonic diagnostic apparatus according to claim 5. 7. The display device further comprises display means for reconstructing and displaying the result of the weighted average so as to spatially correspond to the tomographic plane of the subject.
The ultrasonic diagnostic apparatus according to any one of 1. 8. The display means comprises means for displaying the result of the weighted average reconstructed so as to spatially correspond to the tomographic plane of the subject, in parallel with the diagnostic image before analysis, or in an overlapping display. The ultrasonic diagnostic apparatus according to claim 7, characterized in that 9. The similarity test is performed by using a hypothesis that follows a probability density distribution in which a probability density distribution of signal amplitudes is a theoretical value that follows a Rayleigh distribution. The ultrasonic diagnostic apparatus according to 1 above. 10. The ultrasonic diagnostic apparatus according to claim 1, further comprising means capable of setting a rejection area for the test by an operator. 11. The ultrasonic diagnostic apparatus includes transmitting / receiving means for transmitting / receiving ultrasonic waves to / from an area to be analyzed by the analyzing means, wherein the transmitting / receiving means is different from the area to be analyzed. The device according to claim 1, wherein the device is configured to perform transmission / reception under transmission / reception conditions.
The ultrasonic diagnostic apparatus according to any one of 0. 12. A monitoring means for monitoring a saturated state of signal intensity when calculating the intensity of the echo signal, and a re-instructing means for instructing re-measurement when the saturated state occurs. The ultrasonic diagnostic apparatus according to any one of claims 1 to 11. 13. In an ultrasonic diagnostic apparatus for obtaining a tomographic image by irradiating a subject with an ultrasonic pulse, a means for calculating a first statistic from a sample region having an echo signal of the pulse, and the calculation. From another echo signal existing in the vicinity of the sample, means for searching a region where the amplitude value of the echo signal has a statistic according to a Rayleigh distribution,
A means for calculating a second statistic from the searched area, and a test process for testing the hypothesis that the echo signal of the sample area follows a Rayleigh distribution by using the first and second statistics. Means for performing, using the results obtained by the assay, means for determining the severity of the tissue properties of the sample area, and a function of displaying the results of the determination on the display unit as an image or numerical value. Characteristic ultrasonic diagnostic equipment. 14. In an ultrasonic diagnostic apparatus for obtaining a tomographic image by irradiating a subject with an ultrasonic pulse, a means for calculating a first statistic from a sample area having an echo signal of the pulse, and the calculation. From another echo signal existing in the vicinity of the sample, means for searching a region where the amplitude value of the echo signal has a statistic according to a Rayleigh distribution,
Means for computing a second statistic from the searched area,
The CF is applied to the sample area by using the second statistic.
An ultrasonic diagnostic apparatus comprising: an arithmetic unit that performs an AR process; and a display unit that displays a result of the CFAR process. 15. Existence in the vicinity of the sample to be calculated
The amplitude value of the echo signal from another echo signal
-A means for searching a region having a distribution-based statistic is
The average value μ obtained from the echo signal samples near
Variance value σ calculated assuming Rayleigh distribution_Two ^TwoAnd before
Variance value σ calculated directly from the sample_Two ^TwoCompare both
It is a means to search for a sample whose ratio is close to 1.
The ultrasonic diagnostic apparatus according to claim 14. 16. The ultrasonic diagnostic apparatus according to claim 15, further comprising display means for displaying respective values of σ ₁ ² and σ ₂ ² on a display unit. 17. An ultrasonic diagnostic apparatus for obtaining a tomographic image by irradiating a subject with ultrasonic pulses, the function of allowing a user to specify an analysis region in a displayed diagnostic image, and a statistical amount of the analysis region. A calculation function that calculates
The ultrasonic diagnostic apparatus according to claim 15, further comprising a function of displaying the respective values of σ ₁ and σ ₂ corresponding to the analysis region on a display unit.