Patent Application
20150141821
The present invention relates to an ultrasonic diagnostic apparatus. In particular, it relates to a technology for evaluating elasticity of a living body, utilizing acoustic radiation force.
An image display device for medical use represented by ultrasonic imaging, MRI (Magnetic Resonance Imaging) and X-ray CT (Computed Tomography) is widely utilized as a device that presents information in the living body that cannot be visually observed in the form of a numerical value or an image. Above all, the image display device utilizing an ultrasonic wave is provided with a high time resolution in comparison with other devices and has such a performance that the beating heart can be imaged with no bleeding.
The ultrasonic wave that propagates in the living body is broadly divided into a longitudinal wave and a transverse wave and many technologies (a technology for visualizing a tissue form and a technology for measuring a blood flow velocity) loaded on products mainly utilize information of the longitudinal wave (about 1540 m/s in sound velocity).
In recent years, a technology for evaluating a modulus of elasticity of a tissue by utilizing the transverse wave (hereinafter, a shear wave) attracts notice and clinical use thereof is being promoted for mammary tumors and chronic liver diseases. In this technology, the shear wave is generated in the tissue to be served as a measurement object and the elasticity is evaluated from a propagation velocity thereof. A technique for generating the shear wave is broadly divided into a mechanical system and a radiation pressure system. The mechanical system is a system for generating the shear wave by applying a vibration of about 1 kHz onto the body surface by utilizing a vibrator and so forth and requires a drive device serving as a vibration source. On the other hand, in the radiation pressure system, the acoustic radiation pressure is applied into the living body by utilizing focused ultrasound that makes ultrasonic waves concentrate onto a local part in the tissue and the shear wave is generated by tissue displacement in association therewith. Either system is a technology for measuring the tissue displacement in association with propagation of the generated shear wave by utilizing the ultrasonic wave and evaluating information relevant to the hardness of the tissue.
As a prior art literature related to them, there exists, for example, Patent Literature 1 that relates to a technique for elasticity evaluation utilizing the acoustic radiation pressure.
PTL 1: U.S. Pat. No. 8,118,744 B2
In the technique described in Patent Literature 1, the radiation force is generated in the tissue by utilizing the focused ultrasound so as to make the shear wave propagate in the tissue. Then, a plurality of measurement spots for performing ultrasonic wave transmission and reception are provided in a propagation direction to measure a time variation of the tissue displacement. Then, an arrival time of the shear wave at each measurement spot is measured by utilizing a result of measurement of the displacement. Then, a propagation time of the shear wave between the respective measurement spots is calculated by utilizing the arrival time at each measurement spot to measure a velocity.
However, in the technique described in the above-mentioned Patent Literature 1, in a case where there exist tissue structures such as a blood vessel, a fibrous tissue and so forth on a propagation path of the shear wave, the wave front scatters by being influenced by diffraction and refraction and the form of the wave front is disturbed. In the present technique for estimating the shear wave velocity by utilizing an amount of displacement of the tissue in association with propagation, disturbance of the wave front becomes a major cause of an increase in error in elasticity evaluation.
An object of the present invention is to provide ultrasonic diagnostic apparatus and method making highly reliable elasticity evaluation possible by reducing the influence of scattering of the wave front caused by the tissue structure.
In order to attain the above-mentioned object, in the present invention, there is provided an ultrasonic diagnostic apparatus, the ultrasonic diagnostic apparatus including a probe that transmits and receives an ultrasonic wave and a processing unit that transmits and receives the ultrasonic wave from the probe to an inspection object and processes reception data obtained from the inspection object, wherein the processing unit detects a tissue structure of the inspection object from reception data obtained by transmitting and receiving a first ultrasonic wave from the probe to the inspection object, determines a measurement region for detecting a shear wave velocity on the basis of the tissue structure detected, transmits a second ultrasonic wave to the measurement region to make it generate a shear wave, and
calculates the shear wave velocity from reception data obtained by transmitting and receiving a third ultrasonic wave to the measurement region.
In addition, in order to attain the above-mentioned object, in the present invention, there is provided an elasticity evaluation method, the elasticity evaluation method of detecting a tissue structure of an inspection object from reception data obtained by transmitting and receiving a first ultrasonic wave from a probe that transmits and receives an ultrasonic wave to the inspection object, determining a measurement region for detecting a shear wave velocity on the basis of the detected tissue structure, transmitting a second ultrasonic wave to the measurement region to make it generate a shear wave and calculating the shear wave velocity from reception data obtained by transmitting and receiving a third ultrasonic wave to the measurement region.
According to the present invention, the highly reliable tissue elasticity evaluation can be implemented by suppressing the wave front disturbance caused by the tissue structure.
In the following, embodiments of the present invention will be described in accordance with the drawings. Incidentally, in the present specification, it is supposed that elasticity information of the tissue refers to physical property values in general of the tissue such as a strain, a shear wave velocity, a longitudinal wave velocity, a Young's modulus, a modulus of rigidity, a volume elastic modulus, a Poisson's ratio, a coefficient of viscosity and so forth. In addition, structural objects such as a blood vessel, a local fibrous tissue, a cyst and so forth that are inspection objects for measuring the shear wave velocity by the ultrasonic diagnostic apparatus according to the present invention will be referred to as the tissue structures or the structural objects.
The first embodiment is an embodiment of an ultrasonic diagnostic apparatus provided with a probe that transmits and receives an ultrasonic wave and a processing unit that transmits and receives the ultrasonic wave from the probe to an inspection object and processes reception data obtained from the inspection object, wherein the processing unit detects a tissue structure of the inspection object from reception data obtained by transmitting and receiving a first ultrasonic wave from the probe to the inspection object, determines a measurement region for detecting a shear wave velocity on the basis of the detected tissue structure, transmits a second ultrasonic wave to the measurement region to make it generate a shear wave and calculates the shear wave velocity from reception data obtained by transmitting and receiving a third ultrasonic wave to the measurement region.
In addition, the first embodiment is an embodiment of an elasticity evaluation method, the elasticity evaluation method of detecting a tissue structure of an inspection object from reception data obtained by transmitting and receiving a first ultrasonic wave from a probe that transmits and receives an ultrasonic wave to the inspection object, determining a measurement region for detecting a shear wave velocity on the basis of the detected tissue structure, transmitting a second ultrasonic wave to the measurement region to make it generate a shear wave and calculating the shear wave velocity from reception data obtained by transmitting and receiving a third ultrasonic wave to the measurement region. Here, on the basis of the detected tissue structure is, for example, in a region except the detected tissue structure and so forth.
A shear wave velocity measuring method and a configuration example of the ultrasonic diagnostic apparatus that are the first embodiment will be described using a block diagram in
First, a configuration relevant to generation of RF data and image data to be utilized in the present embodiment will be described. An electric signal for transmission pulse is sent from a transmission beam former (a transmission BF) 13 for generating an ultrasonic signal for a probe 11 that has been set on the body surface of the inspection object described in
The acoustic signal that has been reflected in the course of propagation in the inspection object is received again by the probe 11, is converted into the electric signal reversely to that upon transmission and is sent to a reception beam former (a reception BF) 14 that generates complex RF data from the received ultrasonic signal via an analog/digital (A/D) converter illustration of which has been omitted as reception data. Change-over between transmission and reception is conducted by a transmission/reception change-over SW 12 on the basis of control of the control unit 15 that is the processing unit. In the reception BF 14, after addition processing (phasing addition) that the time delay that has been afforded upon transmission has been taken into account has been conducted on signals received by the plurality of elements and processing such as attenuation correction and so forth has been conducted thereon, they are sent to a Doppler image generation unit 16 that generates a Doppler image indicative of a velocity and a direction of a blood flow or a B-image generation unit 17 that generates a brightness-mode(B) image indicative of form information of the tissue from the RF data in the signal processing unit 24 that is the processing unit as the complex RF data.
The RF data that is the reception data that the signal processing unit 24 has received becomes element data of a specific one line along an ultrasonic wave transmission and reception direction in image data to be finally displayed on a display unit 20. The RF data is acquired as all pieces of reception data that become constitutional elements of the image data by performing transmission and reception of the ultrasonic wave relative to the inspection object by sequentially switching them in an array direction of the ceramic elements that configure the probe 11.
Image generation processing that is generally used in prevalent ultrasonic diagnostic apparatus such as gain control, logarithmic compression, envelope detection and so forth is performed on the RF data that is the acquired reception data in the B-image generation unit 17 of the signal processing unit 24 and the B-image indicative of the form information in the inspection object is generated.
On the other hand, in the Doppler image generation unit 16 of the signal processing unit 24, blood flow information (the velocity and the direction) is calculated by correlation arithmetic operation and the Doppler image is generated. Incidentally, although an ultrasonic wave transmission and reception sequence is different from that of the system of the B-image in regard to generation of the Doppler image, the technical contents thereof are generally known contents and therefore detailed description thereof is omitted. The B-image and the Doppler image are stored into a cone memory 18. Coordinate transformation and pixel interpolation according to the kind of the probe are conducted on the generated B-image and Doppler image by a scan converter 19 and they are displayed on the display unit 20 that displays these images, evaluated images and numerical values.
As shown in
In the structure detection unit 21 of the signal processing unit 24, the tissue structure that influences scattering of the shear wave is detected by utilizing the reception data from the reception BF 14 and a structure map that the tissue structure has been emphasized is generated. That is, the structure detection unit 21 of the signal processing unit 24 creates the structure map indicative of the position and the size of the tissue structure. The created structure map is displayed on the display unit 20 to be served as support information when a practitioner designates a region for measuring the shear wave.
Incidentally, although in the configuration of the ultrasonic diagnostic apparatus shown in
The measurement region adjustment unit 22 of the signal processing unit 24 automatically decides a region that is reduced in influence of the tissue structure by utilizing the information of the generated structure map. In a case where the measurement region includes the tissue structure, it discriminates the region that is reduced in influence of the tissue structure from the measurement region and limits a range for measuring tissue displacement.
The elasticity evaluation unit 23 of the signal processing unit 24 conducts burst wave transmission and track pulse transmission and reception in the measurement region decided by the measurement region adjustment unit 22 and evaluates information relevant to the tissue elasticity.
In the configurations of the ultrasonic diagnostic apparatus of the present embodiment shown in
Next, details of the elasticity evaluation unit 23 of the signal processing unit 24 in the configurations of the present embodiment will be described by utilizing a function explanatory diagram in
As shown in the same drawing, the elasticity evaluation unit 23 is provided with a second ultrasonic wave control function 25 that settles acoustic parameters and so forth required for wave transmission such as a focusing position, a transmission angle, a burst length, a voltage, a frequency, a number of driver elements and so forth that are wave transmission conditions of a ultrasonic burst wave for generating a radiation pressure in the measurement region that has been settled in the aforementioned measurement region control, a third ultrasonic wave control function 26 that settles acoustic parameters and so forth required for wave transmission such as the focusing position, the transmission angle, a wave number, the voltage, the frequency, a transmission and reception frequency, the number of driver elements and so forth that are the wave transmission conditions of an ultrasonic pulse wave (a track pulse) for measuring the displacement of the tissue on the basis of coordinate information, a displacement measurement function 27 that measures the displacement of the tissue by utilizing the RF data output from an ultrasonic wave transmission and reception unit, a velocity measurement function 28 that measures the shear wave velocity by utilizing a result of the displacement measurement function, and an elasticity evaluation function 29 that evaluates elasticity information (here, it refers the physical property values in general relevant to deformation and flow of a substance such as the strain, the shear wave velocity, the compressional wave velocity, the Young's modulus, the modulus of rigidity, the volume elastic modulus, the Poisson's ratio, the coefficient of viscosity and so forth) of the tissue by utilizing a result of the velocity measurement function. Incidentally, an arrival time of the shear wave can be calculated from a time variation of the displacement that has been measured by the displacement measurement function 27 by utilizing a maximum value, a minimum value, an intermediate value between the maximum value and the minimum value and so forth.
In the same drawing, first, the wave transmission conditions of a push pulse are settled on the basis of position coordinates of the designated measurement region by the second ultrasonic wave control function 25. As the wave transmission conditions for effectively generating the shear wave with no influence on the living body, a focusing condition of a substantially F-number=1-2 (a value that the width of the aperture has been divided by a focal depth) is appropriate and as an intensity and the burst length, ranges of 0.1-1 kW/cm2 in intensity and 100-1000 μs in burst length are suited.
Here, the width of the aperture is a range of the ceramic elements to be driven in reality and takes a discrete value of an inter-element spacing. Then, in order to form an ideal focal region, aperture weight (apodization) is added to the voltage to be applied to each element. Disturbance of the focal region due to the influence of diffraction is suppressed by gradually reducing the weight from the center of the aperture toward a corner. However, since the aperture weight has a drawback of reducing the intensity, in a case where an evaluation position is located on a deep part and the influence of attenuation is large, the intensity is taken in preference to region formation and the aperture weight is reduced in some cases. In addition, it is effective to set the transmission frequency in the vicinity of a center frequency of a sensitivity bandwidth of the probe 11. The transmission conditions of the push pulse are immediately sent to the transmission BF 13 via the control unit 15 and it is radiated from the probe 11 into the living body.
Then, the wave transmission conditions of the track pulse are settled by the third ultrasonic wave control function 26. The acoustic parameters such as the frequency, the wave number, the F-number and so forth become almost the same as those of the conditions when generating the image data. In a case where the inspection object is the abdominal region, the conditions of 1-5 MHz in frequency, 1-3 waves in wave number and 1-2 in F-number are utilized.
A reflected signal from the living body acquired by transmission of the track pulse is sent to the reception BF 14 via the probe 11 and the complex RF data is generated. The RF data is input into the displacement measurement function 27 and the tissue displacement in association with propagation of the shear wave is measured. The displacement measurement function 27 is performed by complex correlation arithmetic operation between pieces of the RF data acquired at time intervals of a pulse repetition time (PRT). In this case, in the present embodiment, a particle velocity is calculated as the displacement in unit time. Although there also exists a system of calculating an absolute value of the displacement using the RF data before wave transmission of the push pulse as a standard, the particle velocity has an effect of removing a low frequency component in association with swing of the probe and natural movement of a biological tissue and measuring the shear wave highly sensitively.
The arithmetic operation in the displacement measurement function 27 is conducted on all of the acquired RF signals and the shear wave velocity is measured by the velocity measurement function 28 on the basis of calculated displacement information.
Finally, the elasticity information (here, it refers to the physical property values in general of the tissue such as the strain, the shear wave velocity, the compressional wave velocity, the Young's modulus, the modulus of rigidity, the volume elastic modulus, the Poisson's ratio, the coefficient of viscosity and so forth) of the tissue is evaluated on the basis of the measured velocity of the shear wave by the elasticity evaluation function 29.
Next, detailed contents ranging from generation of the structure map to automatic control of the measurement region by the structure detection unit 21 and the measurement region adjustment unit 22 of the signal processing unit 24 of the device of the present embodiment will be described on the basis of a flowchart in
In the same drawing, in step 31, the B-image is acquired by transmission and reception of a first ultrasonic wave (the pulse signal) and the practitioner searches for an imaging plane suited for observation of a whole image of the inspection object and elasticity evaluation and measurement, for example, a plane that the tissue structure that obviously influences measurement such as a great blood vessel of about 1 cm and so forth is not included.
In step 32, the tissue structure that will cause disturbance of the wave front form of the shear wave is detected.
In calculation of the velocity of the shear wave, a time taken until the wave front arrives at a spatially set measurement spot is utilized. That is, in a case where the wave front form is disturbed, the arrival time is varied depending on the location of the wave front and it strongly influences the error in velocity measurement. Although as the tissue structure to be an object of detection in tissue structure detection step 32, the blood vessel through which the wave does not pass is set as a main object in characteristics of the shear wave, the local fibrous tissues and cysts are also included in the object in addition thereto. Here, for simplicity, description will be continuously made by giving the blood vessel as an example of the tissue structure.
In the following, first to fourth methods for detection of the tissue structure and structure maps obtained as a result thereof will be described. The first method is a method of utilizing human visual effects and utilizes a reverse image that the brightness (black-and-white gradation in gray scale) of the B-image generated by the B-image generation unit 17 has been reversed on the basis of the reception data obtained by transmitting and receiving the first ultrasonic wave to the inspection object as the structure map. In a case where the image data is 8-bit one, the reverse image is configured by processing of a numerical formula 1 in
Examples of a B-image and a reverse image used in the first method are shown in
In addition, in this first method, it is also possible to use a color image that the tissue structure has been colored as the structure map in place of the reverse image 74. Although
Since the first method for tissue structure detection that has been described hereinabove utilizes the signal before or after scan conversion that is the B-image stored in the cine memory 18 and generated by the B-image generation unit 17, the previously described configuration corresponding to
The second method for tissue structure detection utilizes the Doppler image generated by the Doppler image generation unit 16 as the structure map. Although it is the most direct approach in detecting the blood vessel, there are such problems that the sensitivity to a low-velocity blood flow is low and a time is required for acquisition of the image. The problem of the time is important, there is the possibility of already shifting to another imaging plane at the stage of setting the measurement region when the time is taken to display the structure map, and the object of setting the measurement region by avoiding the blood vessel cannot be attained. In a case where the aforementioned problems are solved owing to development of the imaging technology, the usability thereof as the structure map is increased. That is, it is the one that a B-image 91 on the left side of
Since this second method utilizes the Doppler image that has been output from the Doppler image generation unit 16 and stored into the cine memory 18, the apparatus configuration becomes the configuration corresponding to
Beside this, many display forms showing the tissue structures are provided on the ultrasonic diagnostic apparatus and utilization of this display as the structure map is also included in the present embodiment. For example, a function (elastography) that a pressure is applied to the tissue from the outside and a strain that is a response thereto is measured to display a color map is also widely known. A display image relevant to the tissue elasticity and a harmonic image that only a nonlinear signal has been extracted are also useful information in evaluation for homogeneity as the tissue and serve as structure maps useful for automatic selection of the measurement region like this.
The third method for tissue structure detection utilizes filtering. This method is the one that the structure map is created by filtering having a mask modeling on the shape of the tissue structure.
This mask 103 has a ring-like shape that one central pixel and pixels separated therefrom with equal distances are set to 1 and pixel values of others are set to 0. As characteristics of the present filtering method, as shown in (b) on the middle of
A concrete processing flow of the third method will be described by utilizing
Integration of mutual components of the reverse image 114 and the first mask 115, and the reverse image 114 and the second mask 116 is performed in accordance with a numerical formula 2 and a numerical formula 3 in
The structure map of the third method is formed by performing the foregoing processing on all of the pixels of the B-image 111 and two-dimensionally plotting the representative value of the ROI to be set. The structure map has intense brightness on the circular blood vessel of the radius D and makes it possible to readily decide the blood vessel position in comparison with a case of directly utilizing the B-image.
Although, in the above-mentioned description, the content is such that detection of the blood vessel has been specialized, it is also applicable to detection of the tumor, fibrillization and calcification in a sense that a tissue structural object that is a specific tissue structure is extracted by utilizing information on brightness and form. Incidentally, since the tumor, fibrillization and calcification exhibit high brightness on the image contrary to the blood vessel, reverse processing for reversing the brightness is not needed in the processing flow shown in
A form 121 that the central pixel of the mask has been widened is shown on the left side of
Incidentally, the shape of the mask can be optionally changed, and a line-shaped structure can be detected from a B-image 151 on the left side of
The fourth method for tissue structure detection utilizes correlation arithmetic operation. This method is the one that the structure map is calculated by correlation arithmetic operation by utilizing a plurality of pieces of the aforementioned reception data to be acquired at spatially different positions or a plurality of pieces of reception data to be acquired at the spatially same position and at different times.
As shown on the upper left side of
As another method, the same result is also obtained by a system of conducting correlation arithmetic operation by performing transmission and reception of the ultrasonic signal two times at the same position by changing the time as shown on the upper right side of
In this fourth method, the structure map showing the blood vessel position is formed by displaying a correlation value map that a position that is low in correlation value has been emphasized in superimposition on the B-image. The fourth method copes with the data formats of both of the RF data and the video data similarly to the third method. Therefore, the apparatus configuration corresponds to those in
Incidentally, in step 34 of the flowchart in
Incidentally, the practitioner can finely adjust the set measurement region freely by a generally known external input function such as a pointer and so forth. It has a function of making the practitioner recognize it as an alert in a sensibly recognizable form such as the color of the measurement region, blinking and a sound in a case where a structural object to be originally avoided has been included in the measurement region as a result of performance of fine adjustment. The practitioner can freely select information to be utilized by structure-mapping it, and in a case where a blood vessel extracted image such as, for example, the Doppler image and so forth and an elasticity image have been selected, as a region to be automatically recognized as a homogeneous region, a region that has no blood vessel structure and is homogeneous in strain distribution is selected. In association therewith, the alert by fine adjustment is, for example, multi-staged. A structure map 205 on which a blood vessel image 201 and a strain image 203 have been superimposed is shown in, for example,
One example of the form when setting a measurement region by the apparatus of the present embodiment is shown in
As described above, the region setting button 174 is provided on the display screen 171 in
The correctness of the measurement region is made to be visually recognized by changing coloring, the density, the transparency and so forth of the measurement regions 181 and 182 to be displayed respectively in a case of not including the structural object in this measurement region 175 as shown in (a) of
Returning to the flowchart in
A second adjustment method is a method of shifting the measurement region. On the right side of
Then, in step 36 in
As above, the wave front disturbance caused by the tissue structure is suppressed and highly reliable tissue elasticity evaluation is implemented by the various embodiments described so far. As a result, a reduction in inspection time of the ultrasonic diagnostic apparatus, a reduction in load on practitioners and patients and an improvement in accuracy rate of diagnosis can be expected.
Incidentally, the present invention is not limited to the above-mentioned embodiments and includes various modified examples. For example, the above-mentioned embodiments have been described in detail for better understanding of the present invention and it is not necessarily limited to those provided with all of the configurations described above. In addition, a part of a configuration of one embodiment can be replaced with a configuration of another embodiment and a configuration of another embodiment can be added to a configuration of one embodiment. For example, a signal processing unit that has the configuration in
Further, although the above-mentioned respective configurations, functions, processing units and so forth have been described with a focus on the example that the program for implementing some or all parts thereof is created, it goes without saying that, for example, the scan converter and so forth may be implemented by hardware by designing some or all parts thereof by, for example, an integrated circuit.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-077701 | Apr 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/058806 | 3/27/2014 | WO | 00 |
