WO2019088169A1 - Ultrasonic diagnosis system and ultrasonic diagnosis method - Google Patents

Ultrasonic diagnosis system and ultrasonic diagnosis method Download PDF

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Publication number
WO2019088169A1
WO2019088169A1 PCT/JP2018/040506 JP2018040506W WO2019088169A1 WO 2019088169 A1 WO2019088169 A1 WO 2019088169A1 JP 2018040506 W JP2018040506 W JP 2018040506W WO 2019088169 A1 WO2019088169 A1 WO 2019088169A1
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WIPO (PCT)
Prior art keywords
distribution image
sound velocity
velocity distribution
scatterer
measurement data
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PCT/JP2018/040506
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French (fr)
Japanese (ja)
Inventor
東　隆
大佑 近藤
宏翔 林
周 ▲高▼木
直輝 富井
弘文 中村
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株式会社Ｌｉｌｙ ＭｅｄＴｅｃｈ
国立大学法人東京大学
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Priority to JP2019550454A priority Critical patent/JP6933262B2/en
Publication of WO2019088169A1 publication Critical patent/WO2019088169A1/en

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/13—Tomography
    • A61B8/14—Echo-tomography
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/13—Tomography
    • A61B8/15—Transmission-tomography

Definitions

  • the present invention relates to an ultrasonic diagnostic system and an ultrasonic diagnostic method for producing a tomographic image of a subject by irradiating ultrasonic waves.
  • a noninvasive ultrasound diagnostic system is widely used in the medical field as a technique for diagnosing information inside a subject, since there is no need for a surgical operation to directly incise and observe a living body.
  • Ultrasonic CT (Computed Tomography), which is a method of ultrasonic diagnosis, irradiates an ultrasonic wave to a subject, and creates a tomographic image of the subject using reflected ultrasonic waves and transmitted ultrasonic waves. Studies have shown that it has utility in the detection of breast cancer.
  • Ultrasonic CT uses, for example, a ring-type array transducer in which a large number of elements for transmitting and receiving ultrasonic waves are arranged in a ring to create a tomogram.
  • ultrasonic CT a method of measuring the attenuation amount of ultrasonic waves and displaying the attenuation factor distribution of the fault plane, and a method of measuring the propagation time of the ultrasonic waves and displaying the sound velocity distribution of the fault plane are known. There is. In order to make ultrasound CT a clinically more effective diagnostic method, it is required to image physical quantities other than the attenuation rate distribution and the sound velocity distribution.
  • the present invention has been made in view of the above-described conventional situation, and an object thereof is to provide an ultrasonic diagnostic system and an ultrasonic diagnostic method capable of generating a density distribution image of a tomographic plane of a subject.
  • a plurality of elements disposed around the subject and performing at least one of transmission and reception of ultrasonic waves, and any one of the plurality of elements transmit ultrasonic waves.
  • Data collection unit for collecting actual measurement data, and the sound velocity distribution of the subject is estimated using the actual measurement data, and the element is received when ultrasonic waves propagate through a region having the estimated sound velocity distribution
  • Calculate virtual measurement data calculate a difference waveform between the actual measurement data and the virtual measurement data, and obtain from the difference waveform a component used to calculate a sound velocity distribution image or a component used to calculate a scatterer distribution image
  • the component used for the calculation of the sound velocity distribution image is a forward scattered wave component which is a component of a scattered wave scattered to the side other than the side of the element transmitting the ultrasonic wave
  • the component used for calculation of the body distribution image is a backscattered wave component that is a component of a scattered wave scattered to the side of the element that has transmitted the ultrasonic wave.
  • the plurality of elements are arranged at equal intervals in a ring shape
  • the calculation unit is an element located on one half side of the ring circumference centering on the element that has transmitted the ultrasonic wave.
  • the corresponding differential waveform is classified into the backscattered wave component, and the differential waveform corresponding to the element located on the other half side of the ring circumference is classified into the forward scattered wave component.
  • the calculation unit calculates a sound velocity distribution image and a scatterer distribution image for each of the transmission elements that transmitted the ultrasonic wave, adds the sound velocity distribution images for each of the transmission elements, and the transmission element
  • the image processing apparatus further includes an image generation unit that performs addition of each scatterer distribution image.
  • the image creating unit creates a density distribution image from the sound velocity distribution image and the scatterer distribution image.
  • the calculation of the sound velocity distribution image includes back propagation of the differential waveform of the forward scattered wave component
  • the calculation of the scatterer distribution image includes back propagation of the differential waveform of the back scattered wave component.
  • the estimated sound velocity distribution is updated using the scatterer distribution image, and the calculation of the difference waveform, the calculation of the sound velocity distribution image, or the calculation of the sound velocity distribution image using the updated sound velocity distribution. Calculation of scatterer distribution image is performed.
  • the plurality of elements are arranged in a ring shape, and a scatterer distribution image is reconstructed by back propagation of the differential waveform from part of elements on the ring circumference.
  • the ultrasonic diagnostic method transmits ultrasonic waves from any one of a plurality of elements arranged around a subject, and receives scattered waves by at least a part of the plurality of elements.
  • Switching the element transmitting the sound wave in order collecting measurement data which is data obtained from the element receiving the scattered wave, and estimating the sound velocity distribution of the subject using the actual measurement data
  • Calculating an estimated measurement data received by each element by propagating ultrasonic waves through a region having the estimated sound velocity distribution Calculating a differential waveform between the actual measurement data and the estimated measurement data for each element
  • a step of classifying the differential waveform of each element into a forward scattered wave component and a backward scattered wave component, a step of calculating a sound velocity distribution image using the differential waveform of the forward scattered wave component, and the backward scattered wave Component difference wave A step of calculating the scatterer distribution image with those with a.
  • FIG. 5 a is a scatterer distribution image
  • FIG. 5 b is a graph showing the brightness of the point scatterer.
  • FIG. 6 a is a scatterer distribution image
  • FIG. 6 b is a graph showing the brightness of the point scatterer.
  • FIG. 7 a is a sound velocity distribution image
  • FIG. 7 b is a graph showing the brightness of the point scatterer.
  • FIG. 8 a is a sound velocity distribution image
  • 8 b is a graph showing the brightness of the point scatterer. It is a flowchart explaining the tomogram creation method by a modification. 10a and 10b show simulation models, FIG. 10c shows a backscattered image and FIG. 10d shows a forward scatter image. It is a figure which shows the element which receives a forward scattered wave component, and the element which receives a backscattered wave component.
  • An ultrasonic diagnostic system irradiates an ultrasonic wave to an object such as a human body and creates a tomogram of the object using the received signal.
  • the doctor can diagnose a lesion such as a malignant tumor by confirming the created tomogram.
  • the ultrasound diagnostic system 10 includes a ring array R, a switch circuit 110, a transmission / reception circuit 120, an arithmetic unit 130, and an image display unit 140.
  • the ring array R is a ring-shaped transducer preferably having a diameter of 80 to 500 mm, more preferably 100 to 300 mm, which is configured by combining a plurality of transducers.
  • the ring array R can also be configured to have a variable diameter.
  • a ring-shaped vibrator in which four concave vibrators P01 to P04 are combined is used.
  • each of the concave vibrators P01 to P04 has 256 strip-shaped piezoelectric elements E (hereinafter, also simply referred to as "elements E")
  • the ring array R is composed of 1024 elements E. become.
  • the number of elements E provided in the concave transducers P01 to P04 is not limited, and is preferably 1 to 1000, more preferably 100 to 500.
  • Each element E has a function of mutually converting an electrical signal and an ultrasonic signal.
  • the element E transmits an ultrasonic wave to the subject T, receives a scattered wave scattered by the subject T, and forms an electrical signal as measurement data.
  • the scattered waves include forward scattered waves, backward scattered waves (like scattered waves other than forward scattered waves, including side scattered waves), and the like.
  • each element E is described as having both the transmission and reception functions of ultrasonic waves, but is not limited thereto.
  • a plurality of transmitting elements and a plurality of receiving elements may be arranged in a ring using a transmitting element or a receiving element having only one of an ultrasonic wave transmitting function and a receiving function.
  • an element having both transmission and reception functions, a transmission element, and a reception element may be mixed.
  • FIG. 2 is a cross-sectional view taken along line AA of FIG.
  • the ring array R is placed under the perforated bed so that the bed holes and the insertion portion SP overlap.
  • the subject inserts a body part (subject T, for example, a breast) to be imaged into the insertion part SP from the hole in the bed.
  • An insertion portion SP for inserting the subject T is provided at the center of the ring array R.
  • the plurality of elements E of the ring array R are provided at equal intervals around the insertion portion SP along the ring.
  • a convex lens called an acoustic lens is attached to the surface.
  • the elements E are arranged in a ring at equal intervals, but the shape of the ring array R is not limited to a circle, for example, an arbitrary polygon such as a hexagon, a square, or a triangle, at least a part of The shape may be a shape including a curve or arc, or any other shape, or a part of these shapes (for example, a semicircle or arc). That is, the ring array R can be generalized to the array R.
  • the ring array R is connected to the transmission / reception circuit 120 via the switch circuit 110.
  • the transmission / reception circuit 120 (control unit) transmits a control signal (electrical signal) to the element E of the ring array R to control transmission / reception of ultrasonic waves.
  • the transmission / reception circuit 120 instructs the element E the frequency and size of the ultrasonic wave to be transmitted, the type of wave (continuous wave, pulse wave, and the like), and the like.
  • the switch circuit 110 is connected to each of the plurality of elements E of the ring array R, transmits the signal from the transmission / reception circuit 120 to an arbitrary element E, drives the element E, and performs signal transmission / reception. For example, the switch circuit 110 performs control to switch the element E that supplies the control signal from the transmission / reception circuit 120, thereby causing any one of the plurality of elements E to function as a transmission element that transmits ultrasonic waves. The scattered wave is received by the element E of (for example, all).
  • All elements E may be driven simultaneously to collect measurement data, or plural elements E of the ring array R may be divided into several groups and measurement data may be collected sequentially in groups.
  • the measurement data can be collected almost in real time by switching the group in several microseconds or less.
  • the ring array R is vertically movably installed by a stepping motor or the like.
  • the ring array R is moved up and down to collect data of the entire subject T.
  • the arithmetic unit 130 is configured by, for example, a computer including a CPU, a storage unit (RAM, ROM, hard disk, etc.), a communication unit, and the like. By executing the program stored in the storage unit, the functions of the transmission element determination unit 131, the data collection unit 132, the calculation unit 133, the image creation unit 134, etc. as shown in FIG. 3 are realized, and calculation results are stored.
  • the area 135 and the measurement data storage area 136 are secured in the storage unit. The processing by each unit will be described later.
  • the ring array R is provided with 256 elements E 1 to E 256 .
  • the elements E 1 to E 256 are arranged at equal intervals on the circumference in this order.
  • a state in which the subject T is not inserted into the insertion portion SP (any state may be used as long as the subject T is not present, for example, a case in which the subject T is inserted or a state in which water is present)
  • ultrasonic waves are transmitted while switching the transmission elements, and received by a plurality of elements (step S1).
  • ultrasonic waves are transmitted from the element E 1, to receive the transmission waves in all elements E 1 ⁇ E 256. While switching sequentially the transmission element from the element E 1 to the element E 256, to receive the transmission waves in all elements E 1 ⁇ E 256.
  • the transmission element determination unit 131 instructs the transmission / reception circuit 120 to transmit ultrasonic waves in order from the elements E 1 to E 256 .
  • the data collection unit 132 collects (includes or receives) measurement data (reception data) which is data obtained by the elements E 1 to E 256 through the switch circuit 110 and the transmission / reception circuit 120.
  • the measurement data (transmission wave data) is stored in the measurement data storage area 136.
  • the measurement of transmitted wave data may be performed in advance.
  • ultrasonic waves are transmitted while switching the transmission elements, and the scattered waves are received by a plurality of elements (step S2).
  • ultrasonic waves are transmitted from the element E 1, and receives the scattered wave in all elements E 1 ⁇ E 256. All elements E 1 to E 256 receive scattered waves while sequentially switching the transmission elements from element E 1 to element E 256 .
  • Actual measurement data which is data obtained by the elements E 1 to E 256 is stored in the measurement data storage area 136.
  • the measurement data obtained in steps S1 and S2 are three-dimensional data in which the first axis is the receiving element number, the second axis is the signal arrival time, and the third axis is the transmitting element number.
  • the calculation unit 133 calculates an estimated value of the sound velocity distribution of the imaging region using the actual measurement data acquired in step S2 (step S3). For example, using the actual measurement data acquired in step S2, a tomogram is generated by the aperture synthesis method, and the contour of the subject T is extracted. Then, the average sound velocity in the subject T is calculated from the signal arrival time of the transmitted wave. Alternatively, the sound velocity distribution is calculated using a known ray-base sound velocity distribution reconstruction method. The calculation result is stored in the calculation result storage area 135.
  • the calculation unit 133 calculates virtual measurement data (emulation data) received by each element when the ultrasonic wave is transmitted from the element selected in step S4 using the estimated value of the sound velocity distribution calculated in step S3. (Step S5).
  • the calculation unit 133 solves the wave equation and the Helmholtz equation numerically, calculates the behavior of the ultrasonic wave propagating in the region having the sound velocity distribution calculated in step S3, and obtains virtual measurement data received by each element .
  • the calculation unit 133 extracts, from the measurement data storage area 136, data in which the transmission element is the element selected in step S4 out of the actual measurement data acquired in step S2.
  • the calculation unit 133 subtracts the virtual measurement data calculated in step S5 from the extracted actual measurement data for each receiving element to calculate a differential waveform (step S6).
  • the actual measurement data obtained in step S2 includes the first wave scattered from the large structure of the sound velocity distribution, and the second wave scattered by the fine structure of the sound velocity distribution and the structure of density change.
  • the virtual measurement data calculated in step S5 is a wave scattered from the large structure related to the sound velocity distribution calculated in step S3, and corresponds to the above-mentioned first wave. Therefore, by subtracting the virtual measurement data from the actual measurement data, the component of the first wave is canceled, and the component of the wave containing the component of the second wave as the main component remains.
  • the calculation unit 133 classifies the differential waveform for each receiving element into, for example, a backscattered wave component and a forward scattered wave component, into a component used for calculating the sound velocity distribution image and a component used for calculating the scatterer distribution image (step S7).
  • the forward scattered wave component is the component of the scattered wave scattered to the side other than the side of the element that transmitted the ultrasonic wave
  • the backward scattered wave component is the component of the scattered wave scattered to the side of the element transmitted the ultrasonic wave (See Figure 11).
  • the differential waveform of the receiving element located on one half side of the ring array R centering on the transmitting element is classified into the backscattered wave component.
  • the differential waveform of the receiving element located on the other half side of the ring array R is classified into forward scattered wave components.
  • the differential waveform of the element E 193 ⁇ E 256, E 1 ⁇ E 64 located on one half side of the ring array R around the element E 1 is classified into backscattered wave component Ru. Further, the differential waveform of the elements E 65 to E 192 located on the other half side of the ring array R is classified into forward scattered wave components.
  • the calculation unit 133 calculates a sound velocity distribution image from the forward scattered wave component (step S8).
  • the wave equation is calculated by an algorithm such as time-domain finite difference method by rearranging the differential waveform classified as the forward scattered wave component in the opposite direction from the receiving element position toward the transmitting element, that is, the space and time are discretized.
  • a sound velocity distribution image is calculated using a so-called back propagation method in which the scattering position to be focused is detected by solving and propagating waves in the ring array R.
  • the calculation unit 133 calculates a scatterer distribution image from the backscattered wave component (step S9).
  • the calculation of the scatterer distribution image can use the same method as step S8 described above.
  • steps S5 to S9 are performed for all the transmission elements (step S10).
  • the same number for example, 256
  • sound velocity distribution images and scatterer distribution images as the transmission elements can be obtained.
  • the image creating unit 134 adds the obtained sound velocity distribution images to generate a final sound velocity distribution image (step S11). Further, the image creating unit 134 adds all scatterer distribution images to generate a final scatterer distribution image.
  • RF data may be added, or absolute value data or data after envelope detection may be added.
  • the image creating unit 134 compares the sound velocity distribution image and the scatterer distribution image, and for example, generates a density distribution image by subtracting the sound velocity distribution image from the scatterer distribution image (step S12).
  • the image generated by the image generation unit 134 is displayed on the image display device 140.
  • the forward scattered wave component and the backward scattered wave component are classified, and after the influence of the transmitted wave (forward scattered wave) having a larger amplitude than the backward scattered wave is separated, the backward scattered wave is obtained. Reversing the time of time and revising. Therefore, the density distribution and the sound velocity distribution can be independently evaluated. By imaging the density distribution, ultrasound CT can be a clinically more useful diagnostic technique.
  • the density was increased stepwise by 10 kg / m 3 in the counterclockwise direction from the position of 12 o'clock.
  • FIG. 5a shows a scatterer distribution image.
  • FIG. 5 b is a graph showing the brightness of the point scatterer.
  • the numbers 1 to 8 on the horizontal axis in FIG. 5b correspond to point scatterers arranged in order counterclockwise from the 12 o'clock position.
  • FIG. 6a shows a scatterer distribution image.
  • FIG. 6 b is a graph showing the brightness of the point scatterer.
  • FIG. 7a shows a sound velocity distribution image.
  • FIG. 7 b is a graph showing the brightness of the point scatterer.
  • FIG. 8a shows a sound velocity distribution image.
  • FIG. 8 b is a graph showing the brightness of the point scatterer.
  • the luminance was proportional to the sound velocity.
  • the brightness also depends on the size of the scatterer.
  • the scatterer model with different density and the scatterer model with different sound velocity are respectively examined in separate simulations.
  • the shape of the scatterer is circular, which is very different from the structure in an actual living body.
  • FIG. 10 shows the result of examination in a model in which the sound velocity distribution and the density distribution are simultaneously provided.
  • the sound velocity distribution was subjected to segmentation of the tissue according to the brightness of the image from the clinical image by MRI to model a structure that could be practically present as an object.
  • segmentation is performed based on the brightness and the determination of the inside and outside of the contour on four tissues of water (outside the breast area), skin, mammary gland tissue, and fat, and the speed of sound is 1500, 1640, 1550, 1450 m / s, respectively. (See Figure 10a).
  • the sound velocity of the point scatterer is the same as the ambient sound velocity, and the density is 1100 kg / m 3 . All other tissues have a density of 1000 kg / m 3 .
  • the echo data are calculated, and the results of image reconstruction are shown in FIG. 10 c as a backscattered image and in FIG. 10d as a forward scatter image.
  • the estimated value of the initial sound velocity distribution corresponding to step S3 does not exceed the true value at the spatial resolution (resolution limit in imaging).
  • a model obtained by applying a low pass filter in the spatial direction to the set model was used as an initial sound velocity distribution estimated value in step S3.
  • the sound velocity distribution and the density distribution are given simultaneously in one model, but the backscattered image shown in FIG. 10c is an image reflecting the sound velocity distribution, and the forward scattering image shown in FIG. 10d is an image reflecting the density distribution. It can be confirmed that it is imaged.
  • step S3 was a method of constructing the final image in the state already set by the known method.
  • the sound velocity distribution in step S3 is updated based on the calculation result in step S11, and step S4 and subsequent steps are repeated. It is possible.
  • step S11 since the absolute value of the difference between the true value and the sound velocity distribution image in step S3 is determined, strictly speaking, the code information of "true value-estimated value in step S3" is lost. Therefore, the sound velocity distribution in step S3 is updated so that the predetermined cost function is minimized while taking into consideration that there is a possibility of both positive and negative as the sign of the information in step S11.
  • the cost function for example, the sum of absolute differences between adjacent pixels is assumed.
  • the update of the sound velocity distribution in step S3 is effective as follows.
  • the difference ⁇ T T 1 ⁇ T 2 of the pulse propagation time T 2 estimated as the actual pulse propagation time T 1 becomes larger than the pulse width PW when calculating the differential waveform in step S 6, the difference The waveform is separated on the time axis from the actual received pulse and the emulated received pulse. As a result, the accuracy of focusing to the scatterer source in back propagation decreases. Therefore, by updating the sound velocity distribution of step S3 using the sound velocity distribution information newly obtained in step S11 and performing the reconstruction process again, it is possible to expect improvement in calculation accuracy.
  • the loop is updated from step S13 to step S3 using the condition that the pulse width PW is long (using a low frequency pulse or a pulse with a long cycle number). Each time, the pulse width PW is shortened. In this case, more accurately, the loop returns from step S13 to step S2, and the transmission waveform of step S2 is also changed to perform transmission and imaging again.

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Abstract

The purpose of the present invention is to generate a density distribution image of the cross-sectional surface of an object. In the ultrasonic diagnosis system according to an embodiment of the present invention, an ultrasonic wave is transmitted and a scattered wave that has been scattered in the object is received using a plurality of elements. The ultrasonic diagnosis system includes: a data collecting unit 132 that collects actual measurement data, which is data obtained from the elements having received the scattered wave; and a calculation unit 133 that estimates a sound velocity distribution of the object using the actual measurement data, calculates virtual measurement data obtained by the elements having received an ultrasonic wave that has propagated through an area having the estimated sound velocity distribution, calculates a differential waveform between the actual measurement data and the virtual measurement data, and calculates a sound velocity distribution image and a scattering body distribution image using the differential waveform.

Description

超音波診断システム及び超音波診断方法Ultrasound diagnostic system and ultrasound diagnostic method
　本発明は、超音波を照射して被検体の断層画像を作成する超音波診断システム及び超音波診断方法に関する。 The present invention relates to an ultrasonic diagnostic system and an ultrasonic diagnostic method for producing a tomographic image of a subject by irradiating ultrasonic waves.
　非侵襲性である超音波による診断システムは、生体を直接切開して観察する外科手術の必要がないため、被検体内部の情報を診断する技術として医療分野で広く用いられている。 A noninvasive ultrasound diagnostic system is widely used in the medical field as a technique for diagnosing information inside a subject, since there is no need for a surgical operation to directly incise and observe a living body.
　超音波診断の一手法である超音波ＣＴ（Computed　Tomography）は、超音波を被検体に照射し、反射超音波や透過超音波を用いて被検体の断層画像を作成するものであり、近年の研究により、乳がんの検出に有用性があることが示されている。超音波ＣＴは、例えば、超音波の送受信を行う多数の素子をリング状に配置したリング型アレイトランスデューサを使用し、断層像を作成する。 Ultrasonic CT (Computed Tomography), which is a method of ultrasonic diagnosis, irradiates an ultrasonic wave to a subject, and creates a tomographic image of the subject using reflected ultrasonic waves and transmitted ultrasonic waves, Studies have shown that it has utility in the detection of breast cancer. Ultrasonic CT uses, for example, a ring-type array transducer in which a large number of elements for transmitting and receiving ultrasonic waves are arranged in a ring to create a tomogram.
　超音波ＣＴでは、超音波の減衰量を測定して、断層面の減衰率分布を表示する手法と、超音波の伝搬時間を測定し、断層面の音速分布を表示する手法とが知られている。超音波ＣＴを臨床的にさらに有効な診断手法とするために、減衰率分布や音速分布以外の物理量を画像化することが求められている。 In ultrasonic CT, a method of measuring the attenuation amount of ultrasonic waves and displaying the attenuation factor distribution of the fault plane, and a method of measuring the propagation time of the ultrasonic waves and displaying the sound velocity distribution of the fault plane are known. There is. In order to make ultrasound CT a clinically more effective diagnostic method, it is required to image physical quantities other than the attenuation rate distribution and the sound velocity distribution.
国際公開第２０１７／０５１９０３号International Publication No. 2017/051903
　本発明は、上記従来の実状に鑑みてなされたものであり、被検体の断層面の密度分布像を生成することができる超音波診断システム及び超音波診断方法を提供することを目的とする。 The present invention has been made in view of the above-described conventional situation, and an object thereof is to provide an ultrasonic diagnostic system and an ultrasonic diagnostic method capable of generating a density distribution image of a tomographic plane of a subject.
　本発明による超音波診断システムは、被検体の周囲に配置され、超音波の送信及び受信の少なくともいずれか一方を行う複数の素子と、前記複数の素子のいずれか１つが超音波を送信し、前記複数の素子の少なくとも一部が、前記超音波が前記被検体で散乱した散乱波を受信するように、前記複数の素子を制御する制御部と、前記散乱波を受信した素子から得たデータである実測定データを収集するデータ収集部と、前記実測定データを用いて前記被検体の音速分布を推定し、推定した音速分布を有する領域を超音波が伝搬した場合に素子で受信される仮想測定データを計算し、前記実測定データと前記仮想測定データとの差分波形を計算し、前記差分波形から音速分布像の計算に用いる成分又は散乱体分布像の計算に用いる成分を取得し、前記音速分布像の計算に用いる成分の差分波形を用いた音速分布像の計算、又は前記散乱体分布像の計算に用いる成分の差分波形を用いた散乱体分布像の計算を行う計算部と、を備えるものである。 In the ultrasonic diagnostic system according to the present invention, a plurality of elements disposed around the subject and performing at least one of transmission and reception of ultrasonic waves, and any one of the plurality of elements transmit ultrasonic waves. Data obtained from a control unit that controls the plurality of elements such that at least a part of the plurality of elements receives the scattered wave in which the ultrasonic wave is scattered by the object; and data obtained from the element that received the scattered wave Data collection unit for collecting actual measurement data, and the sound velocity distribution of the subject is estimated using the actual measurement data, and the element is received when ultrasonic waves propagate through a region having the estimated sound velocity distribution Calculate virtual measurement data, calculate a difference waveform between the actual measurement data and the virtual measurement data, and obtain from the difference waveform a component used to calculate a sound velocity distribution image or a component used to calculate a scatterer distribution image A calculation unit for calculating a sound velocity distribution image using a difference waveform of components used for the calculation of the sound velocity distribution image, or calculating a scatterer distribution image using a difference waveform for the components used for calculating the scatterer distribution image; Is provided.
　本発明の一態様によれば、前記音速分布像の計算に用いる成分は、前記超音波を送信した素子の側以外の側に散乱する散乱波の成分である前方散乱波成分であり、前記散乱体分布像の計算に用いる成分は、前記超音波を送信した素子の側に散乱する散乱波の成分である後方散乱波成分である According to one aspect of the present invention, the component used for the calculation of the sound velocity distribution image is a forward scattered wave component which is a component of a scattered wave scattered to the side other than the side of the element transmitting the ultrasonic wave, The component used for calculation of the body distribution image is a backscattered wave component that is a component of a scattered wave scattered to the side of the element that has transmitted the ultrasonic wave.
　本発明の一態様によれば、前記複数の素子はリング状に等間隔に配置されており、前記計算部は、超音波を送信した素子を中心にリング円周の一半側に位置する素子に対応する差分波形を前記後方散乱波成分に分類し、リング円周の他半側に位置する素子に対応する差分波形を前記前方散乱波成分に分類する。 According to one aspect of the present invention, the plurality of elements are arranged at equal intervals in a ring shape, and the calculation unit is an element located on one half side of the ring circumference centering on the element that has transmitted the ultrasonic wave. The corresponding differential waveform is classified into the backscattered wave component, and the differential waveform corresponding to the element located on the other half side of the ring circumference is classified into the forward scattered wave component.
　本発明の一態様によれば、前記計算部は、超音波を送信した送信素子毎の音速分布像及び散乱体分布像を計算し、前記送信素子毎の音速分布像の加算、及び前記送信素子毎の散乱体分布像の加算を行う画像作成部をさらに備える。 According to one aspect of the present invention, the calculation unit calculates a sound velocity distribution image and a scatterer distribution image for each of the transmission elements that transmitted the ultrasonic wave, adds the sound velocity distribution images for each of the transmission elements, and the transmission element The image processing apparatus further includes an image generation unit that performs addition of each scatterer distribution image.
　本発明の一態様によれば、前記画像作成部は、前記音速分布像と前記散乱体分布像とから密度分布像を作成する。 According to one aspect of the present invention, the image creating unit creates a density distribution image from the sound velocity distribution image and the scatterer distribution image.
　本発明の一態様によれば、前記音速分布像の計算は前記前方散乱波成分の差分波形の逆伝搬を含み、前記散乱体分布像の計算は前記後方散乱波成分の差分波形の逆伝搬を含む。 According to one aspect of the present invention, the calculation of the sound velocity distribution image includes back propagation of the differential waveform of the forward scattered wave component, and the calculation of the scatterer distribution image includes back propagation of the differential waveform of the back scattered wave component. Including.
　本発明の一態様によれば、前記散乱体分布像を用いて前記推定した音速分布を更新し、更新後の音速分布を用いて、前記差分波形の計算と、前記音速分布像の計算又は前記散乱体分布像の計算とを行う。 According to one aspect of the present invention, the estimated sound velocity distribution is updated using the scatterer distribution image, and the calculation of the difference waveform, the calculation of the sound velocity distribution image, or the calculation of the sound velocity distribution image using the updated sound velocity distribution. Calculation of scatterer distribution image is performed.
　本発明の一態様によれば、前記複数の素子はリング状に配置されており、リング円周上の一部の素子からの前記差分波形の逆伝搬により散乱体分布像を再構成する。 According to one aspect of the present invention, the plurality of elements are arranged in a ring shape, and a scatterer distribution image is reconstructed by back propagation of the differential waveform from part of elements on the ring circumference.
　本発明による超音波診断方法は、被検体の周囲に配置された複数の素子のいずれか１つから超音波を送信し、前記複数の素子の少なくとも一部で散乱波を受信する処理を、超音波を送信する素子を順に切り替えて行う工程と、前記散乱波を受信した素子から得たデータである測定データを収集する工程と、前記実測定データを用いて前記被検体の音速分布を推定する工程と、推定した音速分布を有する領域を超音波が伝搬して各素子で受信される仮想測定データを計算する工程と、素子毎の前記実測定データと前記仮想測定データとの差分波形を計算する工程と、素子毎の差分波形を前方散乱波成分と後方散乱波成分とに分類する工程と、前記前方散乱波成分の差分波形を用いて音速分布像を計算する工程と、前記後方散乱波成分の差分波形を用いて散乱体分布像を計算する工程と、を備えるものである。 The ultrasonic diagnostic method according to the present invention transmits ultrasonic waves from any one of a plurality of elements arranged around a subject, and receives scattered waves by at least a part of the plurality of elements. Switching the element transmitting the sound wave in order, collecting measurement data which is data obtained from the element receiving the scattered wave, and estimating the sound velocity distribution of the subject using the actual measurement data Calculating an estimated measurement data received by each element by propagating ultrasonic waves through a region having the estimated sound velocity distribution; calculating a differential waveform between the actual measurement data and the estimated measurement data for each element A step of classifying the differential waveform of each element into a forward scattered wave component and a backward scattered wave component, a step of calculating a sound velocity distribution image using the differential waveform of the forward scattered wave component, and the backward scattered wave Component difference wave A step of calculating the scatterer distribution image with those with a.
　本発明によれば、被検体の断層面の密度分布像を生成することができる。 According to the present invention, it is possible to generate a density distribution image of a cross section of a subject.
本発明の実施形態における超音波診断システムの概略構成図である。It is a schematic block diagram of the ultrasound diagnostic system in the embodiment of the present invention. 図１のＡ－Ａ線断面図である。It is the sectional view on the AA line of FIG. 演算装置の機能ブロック図である。It is a functional block diagram of an arithmetic unit. 同実施形態による断層像作成方法を説明するフローチャートである。It is a flowchart explaining the tomogram production method by the embodiment. 図５ａは散乱体分布像であり、図５ｂは点散乱体の輝度を示すグラフである。FIG. 5 a is a scatterer distribution image, and FIG. 5 b is a graph showing the brightness of the point scatterer. 図６ａは散乱体分布像であり、図６ｂは点散乱体の輝度を示すグラフである。FIG. 6 a is a scatterer distribution image, and FIG. 6 b is a graph showing the brightness of the point scatterer. 図７ａは音速分布像であり、図７ｂは点散乱体の輝度を示すグラフである。FIG. 7 a is a sound velocity distribution image, and FIG. 7 b is a graph showing the brightness of the point scatterer. 図８ａは音速分布像であり、図８ｂは点散乱体の輝度を示すグラフである。FIG. 8 a is a sound velocity distribution image, and FIG. 8 b is a graph showing the brightness of the point scatterer. 変形例による断層像作成方法を説明するフローチャートである。It is a flowchart explaining the tomogram creation method by a modification. 図１０ａ，１０ｂはシミュレーションモデルを示す図であり、図１０ｃは後方散乱画像を示し、図１０ｄは前方散乱画像を示す。10a and 10b show simulation models, FIG. 10c shows a backscattered image and FIG. 10d shows a forward scatter image. 前方散乱波成分を受信する素子及び後方散乱波成分を受信する素子を示す図である。It is a figure which shows the element which receives a forward scattered wave component, and the element which receives a backscattered wave component.
　以下、図面を参照して本発明についてさらに詳細に説明する。本発明の実施形態に係る超音波診断システムは、人体等の被検体に超音波を照射し、受信した信号を用いて被検体の断層像を作成する。医師は、作成された断層像を確認することで、悪性腫瘍等の病変を診断することができる。 Hereinafter, the present invention will be described in more detail with reference to the drawings. An ultrasonic diagnostic system according to an embodiment of the present invention irradiates an ultrasonic wave to an object such as a human body and creates a tomogram of the object using the received signal. The doctor can diagnose a lesion such as a malignant tumor by confirming the created tomogram.
　図１に示すように、本実施形態に係る超音波診断システム１０は、リングアレイＲと、スイッチ回路１１０と、送受信回路１２０と、演算装置１３０と、画像表示装置１４０とを備えている。 As shown in FIG. 1, the ultrasound diagnostic system 10 according to the present embodiment includes a ring array R, a switch circuit 110, a transmission / reception circuit 120, an arithmetic unit 130, and an image display unit 140.
　リングアレイＲは、複数の振動子が組み合わさって構成される、好ましくは直径８０～５００ｍｍ、より好ましくは直径１００～３００ｍｍのリング型形状の振動子である。また、リングアレイＲは、直径を可変とする構成をとることもできる。本実施形態では一例として、４つの凹面型振動子Ｐ０１～Ｐ０４を組み合わせたリング形状の振動子を用いる。 The ring array R is a ring-shaped transducer preferably having a diameter of 80 to 500 mm, more preferably 100 to 300 mm, which is configured by combining a plurality of transducers. The ring array R can also be configured to have a variable diameter. In this embodiment, as an example, a ring-shaped vibrator in which four concave vibrators P01 to P04 are combined is used.
　例えば、凹面型振動子Ｐ０１～Ｐ０４が、それぞれ２５６個の短冊形圧電素子Ｅ（以下、単に「素子Ｅ」とも呼ぶ。）を有する場合、リングアレイＲは１０２４個の素子Ｅから構成されることになる。凹面型振動子Ｐ０１～Ｐ０４に設けられる素子Ｅの数は限定されず、好ましくは１～１０００個、より好ましくは１００～５００個である。 For example, in the case where each of the concave vibrators P01 to P04 has 256 strip-shaped piezoelectric elements E (hereinafter, also simply referred to as "elements E"), the ring array R is composed of 1024 elements E. become. The number of elements E provided in the concave transducers P01 to P04 is not limited, and is preferably 1 to 1000, more preferably 100 to 500.
　各素子Ｅは、電気的信号と超音波信号とを相互変換する機能を有する。素子Ｅは被検体Ｔに超音波を送信し、被検体Ｔで散乱される散乱波を受信し、電気的信号を測定データとして形成する。散乱波は、前方散乱波、後方散乱波（前方散乱波以外の散乱波をいい、側方散乱波を含む）等を含む。 Each element E has a function of mutually converting an electrical signal and an ultrasonic signal. The element E transmits an ultrasonic wave to the subject T, receives a scattered wave scattered by the subject T, and forms an electrical signal as measurement data. The scattered waves include forward scattered waves, backward scattered waves (like scattered waves other than forward scattered waves, including side scattered waves), and the like.
　本実施形態では、各素子Ｅが、超音波の送信及び受信の両方の機能を備えるものとして説明するが、これに限定されない。例えば、超音波の送信機能及び受信機能のうちいずれか一方のみを有する送信素子又は受信素子を使用し、複数の送信素子及び複数の受信素子をリング状に配置してもよい。また、送信及び受信の両方の機能を備える素子と、送信素子と、受信素子とが混在する構成であってもよい。 In the present embodiment, each element E is described as having both the transmission and reception functions of ultrasonic waves, but is not limited thereto. For example, a plurality of transmitting elements and a plurality of receiving elements may be arranged in a ring using a transmitting element or a receiving element having only one of an ultrasonic wave transmitting function and a receiving function. In addition, an element having both transmission and reception functions, a transmission element, and a reception element may be mixed.
　図２は、図１のＡ－Ａ線断面図である。例えば、リングアレイＲは、穴の開いたベッドの下に、ベッドの穴と挿入部ＳＰとが重畳するように設置される。被験者はベッドの穴から、撮像対象となる身体の部位（被検体Ｔ、例えば***）を挿入部ＳＰに挿入する。 FIG. 2 is a cross-sectional view taken along line AA of FIG. For example, the ring array R is placed under the perforated bed so that the bed holes and the insertion portion SP overlap. The subject inserts a body part (subject T, for example, a breast) to be imaged into the insertion part SP from the hole in the bed.
　被検体Ｔを挿入するための挿入部ＳＰは、リングアレイＲの中央に設けられている。リングアレイＲの複数の素子Ｅは、リングに沿って挿入部ＳＰの周囲に等間隔で設けられている。リングアレイＲの内周側には、音響レンズと呼ばれる凸面レンズが表面に取り付けられている。このような表面加工をリングアレイＲの内周側に施すことで、各素子Ｅが送信する超音波を、リングアレイＲを含む平面内に収束させることができる。リングアレイＲと被検体Ｔとの間は、例えば水で満たされている。 An insertion portion SP for inserting the subject T is provided at the center of the ring array R. The plurality of elements E of the ring array R are provided at equal intervals around the insertion portion SP along the ring. On the inner circumferential side of the ring array R, a convex lens called an acoustic lens is attached to the surface. By applying such surface processing to the inner peripheral side of the ring array R, the ultrasonic waves transmitted by the respective elements E can be converged in a plane including the ring array R. The space between the ring array R and the subject T is filled with, for example, water.
　本実施形態では、各素子Ｅを等間隔にリング状に配置しているが、リングアレイＲの形状は円形に限定されず、例えば、六角形、正方形、三角形など任意の多角形、少なくとも一部に曲線や円弧を含む形状、その他任意の形状、または、これらの形状の一部（例えば、半円や円弧）であってもよい。すなわち、リングアレイＲは、アレイＲと一般化することができる。 In the present embodiment, the elements E are arranged in a ring at equal intervals, but the shape of the ring array R is not limited to a circle, for example, an arbitrary polygon such as a hexagon, a square, or a triangle, at least a part of The shape may be a shape including a curve or arc, or any other shape, or a part of these shapes (for example, a semicircle or arc). That is, the ring array R can be generalized to the array R.
　リングアレイＲはスイッチ回路１１０を介して送受信回路１２０に接続されている。送受信回路１２０（制御部）は、リングアレイＲの素子Ｅに制御信号（電気的信号）を送信し、超音波の送受信を制御する。例えば、送受信回路１２０は、素子Ｅに対して、送信する超音波の周波数や大きさ、波の種類（連続波やパルス波等）等を指示する。 The ring array R is connected to the transmission / reception circuit 120 via the switch circuit 110. The transmission / reception circuit 120 (control unit) transmits a control signal (electrical signal) to the element E of the ring array R to control transmission / reception of ultrasonic waves. For example, the transmission / reception circuit 120 instructs the element E the frequency and size of the ultrasonic wave to be transmitted, the type of wave (continuous wave, pulse wave, and the like), and the like.
　スイッチ回路１１０は、リングアレイＲの複数の素子Ｅの各々に接続されており、送受信回路１２０からの信号を任意の素子Ｅに伝達し、素子Ｅを駆動させ、信号の送受信を行わせる。例えば、スイッチ回路１１０が、送受信回路１２０からの制御信号を供給する素子Ｅを切り替える制御を行うことで、複数の素子Ｅのいずれか１つを、超音波を送信する送信素子として機能させ、複数（例えば全て）の素子Ｅで散乱波を受信させる。 The switch circuit 110 is connected to each of the plurality of elements E of the ring array R, transmits the signal from the transmission / reception circuit 120 to an arbitrary element E, drives the element E, and performs signal transmission / reception. For example, the switch circuit 110 performs control to switch the element E that supplies the control signal from the transmission / reception circuit 120, thereby causing any one of the plurality of elements E to function as a transmission element that transmits ultrasonic waves. The scattered wave is received by the element E of (for example, all).
　全ての素子Ｅを同時に駆動して測定データを収集してもよいし、リングアレイＲの複数の素子Ｅをいくつかのグループに分けて、グループ単位で順に測定データを収集してもよい。グループの切り替えを数μｓ～ｍｓオーダ以下で行うことで、ほぼリアルタイムに測定データの収集を行うことができる。 All elements E may be driven simultaneously to collect measurement data, or plural elements E of the ring array R may be divided into several groups and measurement data may be collected sequentially in groups. The measurement data can be collected almost in real time by switching the group in several microseconds or less.
　リングアレイＲは、ステッピングモータ等により上下動可能に設置されている。リングアレイＲを上下動させて、被検体Ｔの全体のデータ収集が行われる。 The ring array R is vertically movably installed by a stepping motor or the like. The ring array R is moved up and down to collect data of the entire subject T.
　演算装置１３０は、例えばＣＰＵ、記憶部（ＲＡＭ、ＲＯＭ、ハードディスク等）、通信部等を備えたコンピュータにより構成されている。記憶部に格納されたプログラムが実行されることで、図３に示すような、送信素子決定部１３１、データ収集部１３２、計算部１３３、画像作成部１３４等の機能が実現され、計算結果格納領域１３５及び測定データ格納領域１３６が記憶部に確保される。各部による処理については後述する。 The arithmetic unit 130 is configured by, for example, a computer including a CPU, a storage unit (RAM, ROM, hard disk, etc.), a communication unit, and the like. By executing the program stored in the storage unit, the functions of the transmission element determination unit 131, the data collection unit 132, the calculation unit 133, the image creation unit 134, etc. as shown in FIG. 3 are realized, and calculation results are stored. The area 135 and the measurement data storage area 136 are secured in the storage unit. The processing by each unit will be described later.
　次に、本実施形態による断層像作成方法を図４に示すフローチャートを用いて説明する。以下の説明では、リングアレイＲは、２５６個の素子Ｅ１～Ｅ２５６が設けられているものとする。素子Ｅ１～Ｅ２５６はこの順番で円周上に等間隔に配置されている。 Next, a tomogram creation method according to the present embodiment will be described using the flowchart shown in FIG. In the following description, it is assumed that the ring array R is provided with 256 elements E 1 to E 256 . The elements E 1 to E 256 are arranged at equal intervals on the circumference in this order.
　まず、被検体Ｔを挿入部ＳＰに挿入していない状態（被検体Ｔがない状態であれば、いかなる状態でもよく、例えば、被検体Ｔを挿入する筐体や水が存在する状態でもよい）で、送信素子を切り替えながら超音波を送信し、複数の素子で受信する（ステップＳ１）。例えば、素子Ｅ１から超音波を送信し、全ての素子Ｅ１～Ｅ２５６で透過波の受信を行う。送信素子を素子Ｅ１から素子Ｅ２５６まで順に切り替えながら、全ての素子Ｅ１～Ｅ２５６で透過波の受信を行う。 First, a state in which the subject T is not inserted into the insertion portion SP (any state may be used as long as the subject T is not present, for example, a case in which the subject T is inserted or a state in which water is present) Then, ultrasonic waves are transmitted while switching the transmission elements, and received by a plurality of elements (step S1). For example, ultrasonic waves are transmitted from the element E 1, to receive the transmission waves in all elements E 1 ~ E 256. While switching sequentially the transmission element from the element E 1 to the element E 256, to receive the transmission waves in all elements E 1 ~ E 256.
　送信素子決定部１３１は、素子Ｅ１～Ｅ２５６から順に超音波が送信されるように、送受信回路１２０に指示する。データ収集部１３２は、スイッチ回路１１０及び送受信回路１２０を介して、素子Ｅ１～Ｅ２５６により得られたデータである測定データ（受信データ）を収集（受信又は取得することを含む）する。測定データ（透過波データ）は、測定データ格納領域１３６に格納される。 The transmission element determination unit 131 instructs the transmission / reception circuit 120 to transmit ultrasonic waves in order from the elements E 1 to E 256 . The data collection unit 132 collects (includes or receives) measurement data (reception data) which is data obtained by the elements E 1 to E 256 through the switch circuit 110 and the transmission / reception circuit 120. The measurement data (transmission wave data) is stored in the measurement data storage area 136.
　透過波データの測定は事前に行っておいてもよい。 The measurement of transmitted wave data may be performed in advance.
　次に、挿入部ＳＰから被検体Ｔを挿入した状態で、送信素子を切り替えながら超音波を送信し、複数の素子で散乱波を受信する（ステップＳ２）。例えば、素子Ｅ１から超音波を送信し、全ての素子Ｅ１～Ｅ２５６で散乱波の受信を行う。送信素子を素子Ｅ１から素子Ｅ２５６まで順に切り替えながら、全ての素子Ｅ１～Ｅ２５６で散乱波の受信を行う。 Next, in a state in which the subject T is inserted from the insertion unit SP, ultrasonic waves are transmitted while switching the transmission elements, and the scattered waves are received by a plurality of elements (step S2). For example, ultrasonic waves are transmitted from the element E 1, and receives the scattered wave in all elements E 1 ~ E 256. All elements E 1 to E 256 receive scattered waves while sequentially switching the transmission elements from element E 1 to element E 256 .
　素子Ｅ１～Ｅ２５６により得られたデータである実測定データ（散乱波データ）は、測定データ格納領域１３６に格納される。 Actual measurement data (scattered wave data) which is data obtained by the elements E 1 to E 256 is stored in the measurement data storage area 136.
　ステップＳ１，Ｓ２で得られる測定データは、第１軸が受信素子番号、第２軸が信号到達時間、第３軸が送信素子番号となる３次元データである。 The measurement data obtained in steps S1 and S2 are three-dimensional data in which the first axis is the receiving element number, the second axis is the signal arrival time, and the third axis is the transmitting element number.
　計算部１３３が、ステップＳ２で取得した実測定データを用いて、撮像領域の音速分布の推定値を計算する（ステップＳ３）。例えば、ステップＳ２で取得した実測定データを用いて開口合成法による断層像を生成し、被検体Ｔの輪郭を抽出する。そして、透過波の信号到達時間から、被検体Ｔ内の平均音速を計算する。あるいはまた、公知のｒａｙ－ｂａｓｅの音速分布再構成法を用いて音速分布を計算する。計算結果は、計算結果格納領域１３５に格納される。 The calculation unit 133 calculates an estimated value of the sound velocity distribution of the imaging region using the actual measurement data acquired in step S2 (step S3). For example, using the actual measurement data acquired in step S2, a tomogram is generated by the aperture synthesis method, and the contour of the subject T is extracted. Then, the average sound velocity in the subject T is calculated from the signal arrival time of the transmitted wave. Alternatively, the sound velocity distribution is calculated using a known ray-base sound velocity distribution reconstruction method. The calculation result is stored in the calculation result storage area 135.
　素子Ｅ１～Ｅ２５６のうち未選択の素子を１つ選択する（ステップＳ４）。計算部１３３が、ステップＳ３で算出した音速分布の推定値を用いて、ステップＳ４で選択した素子から超音波を送信した場合に、各素子で受信される仮想測定データ（エミュレートデータ）を算出する（ステップＳ５）。 One of the elements E 1 to E 256 which is not selected is selected (step S 4). The calculation unit 133 calculates virtual measurement data (emulation data) received by each element when the ultrasonic wave is transmitted from the element selected in step S4 using the estimated value of the sound velocity distribution calculated in step S3. (Step S5).
　例えば、計算部１３３は、波動方程式やヘルムホルツ方程式を数値的に解き、ステップＳ３で算出した音速分布を有する領域を伝搬する超音波の挙動を計算し、各素子で受信される仮想測定データを求める。 For example, the calculation unit 133 solves the wave equation and the Helmholtz equation numerically, calculates the behavior of the ultrasonic wave propagating in the region having the sound velocity distribution calculated in step S3, and obtains virtual measurement data received by each element .
　計算部１３３が、測定データ格納領域１３６から、ステップＳ２で取得した実測定データのうち、送信素子がステップＳ４で選択した素子であるデータを取り出す。計算部１３３は、受信素子毎に、取り出した実測定データから、ステップＳ５で計算した仮想測定データを減算し、差分波形を算出する（ステップＳ６）。 The calculation unit 133 extracts, from the measurement data storage area 136, data in which the transmission element is the element selected in step S4 out of the actual measurement data acquired in step S2. The calculation unit 133 subtracts the virtual measurement data calculated in step S5 from the extracted actual measurement data for each receiving element to calculate a differential waveform (step S6).
　ステップＳ２で取得した実測定データは、音速分布に関する大きな構造から散乱された第１の波と、音速分布に関する微細構造及び密度変化の構造で散乱された第２の波を含む。一方、ステップＳ５で算出した仮想測定データは、ステップＳ３で算出した音速分布に関する大きな構造から散乱された波であり、上述の第１の波に相当する。従って、実測定データから仮想測定データを減じることで、第１の波の成分がキャンセルされ、上述の第２の波の成分を主成分とする波の成分が残る。 The actual measurement data obtained in step S2 includes the first wave scattered from the large structure of the sound velocity distribution, and the second wave scattered by the fine structure of the sound velocity distribution and the structure of density change. On the other hand, the virtual measurement data calculated in step S5 is a wave scattered from the large structure related to the sound velocity distribution calculated in step S3, and corresponds to the above-mentioned first wave. Therefore, by subtracting the virtual measurement data from the actual measurement data, the component of the first wave is canceled, and the component of the wave containing the component of the second wave as the main component remains.
　計算部１３３が、受信素子毎の差分波形を、音速分布像の計算に用いる成分と散乱体分布像の計算に用いる成分に、例えば、後方散乱波成分と前方散乱波成分とに分類する（ステップＳ７）。前方散乱波成分は、超音波を送信した素子の側以外の側に散乱する散乱波の成分であり、後方散乱波成分は、超音波を送信した素子の側に散乱する散乱波の成分である（図１１参照）。例えば、送信素子を中心にリングアレイＲの一半側に位置する受信素子の差分波形を、後方散乱波成分に分類する。リングアレイＲの他半側に位置する受信素子の差分波形を、前方散乱波成分に分類する。 The calculation unit 133 classifies the differential waveform for each receiving element into, for example, a backscattered wave component and a forward scattered wave component, into a component used for calculating the sound velocity distribution image and a component used for calculating the scatterer distribution image (step S7). The forward scattered wave component is the component of the scattered wave scattered to the side other than the side of the element that transmitted the ultrasonic wave, and the backward scattered wave component is the component of the scattered wave scattered to the side of the element transmitted the ultrasonic wave (See Figure 11). For example, the differential waveform of the receiving element located on one half side of the ring array R centering on the transmitting element is classified into the backscattered wave component. The differential waveform of the receiving element located on the other half side of the ring array R is classified into forward scattered wave components.
　例えば、素子Ｅ１が送信素子である場合、素子Ｅ１を中心にリングアレイＲの一半側に位置する素子Ｅ１９３～Ｅ２５６、Ｅ１～Ｅ６４の差分波形が後方散乱波成分に分類される。また、リングアレイＲの他半側に位置する素子Ｅ６５～Ｅ１９２の差分波形が前方散乱波成分に分類される。 For example, when the element E 1 is the transmission device, the differential waveform of the element E 193 ~ E 256, E 1 ~ E 64 located on one half side of the ring array R around the element E 1 is classified into backscattered wave component Ru. Further, the differential waveform of the elements E 65 to E 192 located on the other half side of the ring array R is classified into forward scattered wave components.
　計算部１３３が、前方散乱波成分から音速分布像を計算する（ステップＳ８）。前方散乱波成分として分類された差分波形を、受信素子位置から送信素子に向かって逆向きに打ち直すことによって、つまり、空間と時間を離散化して、時間領域有限差分法などのアルゴリズムにより波動方程式を解き、波をリングアレイＲ内に伝搬させることによって、集束する散乱位置を検出する、いわゆるバックプロパゲーション法を用いて音速分布像を計算する。 The calculation unit 133 calculates a sound velocity distribution image from the forward scattered wave component (step S8). The wave equation is calculated by an algorithm such as time-domain finite difference method by rearranging the differential waveform classified as the forward scattered wave component in the opposite direction from the receiving element position toward the transmitting element, that is, the space and time are discretized. A sound velocity distribution image is calculated using a so-called back propagation method in which the scattering position to be focused is detected by solving and propagating waves in the ring array R.
　計算部１３３が、後方散乱波成分から散乱体分布像を計算する（ステップＳ９）。散乱体分布像の計算は、上述したステップＳ８と同様の手法を用いることができる。 The calculation unit 133 calculates a scatterer distribution image from the backscattered wave component (step S9). The calculation of the scatterer distribution image can use the same method as step S8 described above.
　ステップＳ５～Ｓ９の処理を、全ての送信素子について行う（ステップＳ１０）。これにより、送信素子と同数（例えば２５６個）の音速分布像及び散乱体分布像が得られる。 The processes of steps S5 to S9 are performed for all the transmission elements (step S10). As a result, the same number (for example, 256) of sound velocity distribution images and scatterer distribution images as the transmission elements can be obtained.
　画像作成部１３４が、得られた音速分布像を加算し、最終的な音速分布像を生成する（ステップＳ１１）。また、画像作成部１３４が、全ての散乱体分布像を加算し、最終的な散乱体分布像を生成する。ＲＦデータを加算してもよく、絶対値データや包絡線検波後のデータを加算してもよい。 The image creating unit 134 adds the obtained sound velocity distribution images to generate a final sound velocity distribution image (step S11). Further, the image creating unit 134 adds all scatterer distribution images to generate a final scatterer distribution image. RF data may be added, or absolute value data or data after envelope detection may be added.
　散乱は音響インピーダンスＺ＝ρｃ（ρ：密度、ｃ：音速）の空間微分であり、散乱体分布像は、音速分布及び密度分布を含む。画像作成部１３４は、音速分布像及び散乱体分布像を比較し、例えば散乱体分布像から音速分布像を減じることで、密度分布像を生成する（ステップＳ１２）。画像作成部１３４により生成された画像は、画像表示装置１４０に表示される。 Scattering is a spatial derivative of acoustic impedance Z = ρc (ρ: density, c: speed of sound), and the scatterer distribution image includes sound speed distribution and density distribution. The image creating unit 134 compares the sound velocity distribution image and the scatterer distribution image, and for example, generates a density distribution image by subtracting the sound velocity distribution image from the scatterer distribution image (step S12). The image generated by the image generation unit 134 is displayed on the image display device 140.
　このように本実施形態によれば、前方散乱波成分と後方散乱波成分とを分類し、後方散乱波よりも振幅の大きい透過波（前方散乱波）の影響を分離した上で、後方散乱波成分を時間反転して打ち直す。そのため、密度分布と音速分布とをそれぞれ独立して評価することができる。密度分布を画像化することで、超音波ＣＴを臨床的にさらに有効な診断手法にすることができる。 As described above, according to the present embodiment, the forward scattered wave component and the backward scattered wave component are classified, and after the influence of the transmitted wave (forward scattered wave) having a larger amplitude than the backward scattered wave is separated, the backward scattered wave is obtained. Reversing the time of time and revising. Therefore, the density distribution and the sound velocity distribution can be independently evaluated. By imaging the density distribution, ultrasound CT can be a clinically more useful diagnostic technique.
　シミュレーション
　上記実施形態による断層像作成方法を用いて、後方散乱波成分に基づく散乱体分布像の有効性をシミュレーションによって実証する。 Simulation The effectiveness of the scatterer distribution image based on the backscattered wave component is demonstrated by simulation using the tomogram creation method according to the above embodiment.
＜シミュレーション１＞
　リングアレイの径方向内側に、８個の点散乱体を同心円の円周上に等間隔に配置した。上記実施形態による方法で計算を行い、後方散乱波成分に基づく散乱体分布像を作成した。シミュレーション条件は以下の通りである。下記の５つの条件は、シミュレーション１～４において共通である。
リングアレイ素子数：２５６個
リングアレイ半径：５０ｍｍ
サンプリング周波数：５ＭＨｚ
励起：単位インパルス
リングアレイの中心から８個の点散乱体までの距離：７．５ｍｍ <Simulation 1>
Eight point scatterers were equally spaced on the circumference of a concentric circle radially inward of the ring array. Calculations were performed by the method according to the above embodiment to create a scatterer distribution image based on the backscattered wave component. The simulation conditions are as follows. The following five conditions are common to simulations 1 to 4.
Number of ring array elements: 256 Ring array radius: 50 mm
Sampling frequency: 5 MHz
Excitation: Distance from center of unit impulse ring array to eight point scatterers: 7.5 mm
　点散乱体は、１２時の位置から反時計回りに、密度を１０ｋｇ／ｍ３ずつ段階的に増やした。 In the point scatterer, the density was increased stepwise by 10 kg / m 3 in the counterclockwise direction from the position of 12 o'clock.
　結果を図５ａ，５ｂに示す。図５ａは散乱体分布像を示す。図５ｂは点散乱体の輝度を示すグラフである。図５ｂの横軸の番号１～８は、１２時の位置から反時計回りに順に配置された点散乱体に相当する。 The results are shown in Figures 5a, 5b. FIG. 5a shows a scatterer distribution image. FIG. 5 b is a graph showing the brightness of the point scatterer. The numbers 1 to 8 on the horizontal axis in FIG. 5b correspond to point scatterers arranged in order counterclockwise from the 12 o'clock position.
＜シミュレーション２＞
　８個の点散乱体の密度を、それぞれ、シミュレーション１よりも１０ｋｇ／ｍ３増加させた。また、点散乱体のサイズ（半径）を、１２時の位置から反時計回りに、１／８ｍｍから１ｍｍまで１／８ｍｍずつ段階的に増加させた。その他の条件はシミュレーション１と同じとした。 <Simulation 2>
The densities of the eight point scatterers were each increased by 10 kg / m 3 over Simulation 1. In addition, the size (radius) of the point scatterer was gradually increased by 1/8 mm from 1/8 mm to 1 mm counterclockwise from the 12 o'clock position. Other conditions were the same as in simulation 1.
　結果を図６ａ，６ｂに示す。図６ａは散乱体分布像を示す。図６ｂは点散乱体の輝度を示すグラフである。 The results are shown in Figures 6a, 6b. FIG. 6a shows a scatterer distribution image. FIG. 6 b is a graph showing the brightness of the point scatterer.
＜シミュレーション３＞
　８個の点散乱体の音速を、１２時の位置から反時計回りに２ｍ／ｓずつ段階的に増やした。その他の条件はシミュレーション１と同じとし、前方散乱波成分に基づく音速分布像を作成した。 <Simulation 3>
The sound speeds of the eight point scatterers were gradually increased by 2 m / s counterclockwise from the position of 12 o'clock. The other conditions were the same as in simulation 1, and a sound velocity distribution image based on the forward scattered wave component was created.
　結果を図７ａ，７ｂに示す。図７ａは音速分布像を示す。図７ｂは点散乱体の輝度を示すグラフである。 The results are shown in Figures 7a, 7b. FIG. 7a shows a sound velocity distribution image. FIG. 7 b is a graph showing the brightness of the point scatterer.
＜シミュレーション４＞
　８個の点散乱体の音速を、それぞれ、シミュレーション３よりも１０ｍ／ｓ増加させた。また、シミュレーション２と同様に、点散乱体のサイズ（半径）を、１２時の位置から反時計回りに、１／８ｍｍから１ｍｍまで１／８ｍｍずつ段階的に増加させた。その他の条件はシミュレーション３と同じとした。 <Simulation 4>
The sound speeds of the eight point scatterers were each increased by 10 m / s over Simulation 3. Further, as in the simulation 2, the size (radius) of the point scatterer was gradually increased by 1/8 mm from 1/8 mm to 1 mm counterclockwise from the position of 12 o'clock. Other conditions were the same as in simulation 3.
　結果を図８ａ，８ｂに示す。図８ａは音速分布像を示す。図８ｂは点散乱体の輝度を示すグラフである。 The results are shown in Figures 8a, 8b. FIG. 8a shows a sound velocity distribution image. FIG. 8 b is a graph showing the brightness of the point scatterer.
　図７ａ，７ｂに示すように、音速分布像は、輝度が音速に比例した。また、図８ａ，８ｂに示すように、音速分布像では、輝度が散乱体サイズにも依存した。 As shown in FIGS. 7a and 7b, in the sound velocity distribution image, the luminance was proportional to the sound velocity. Further, as shown in FIGS. 8a and 8b, in the sound velocity distribution image, the brightness also depends on the size of the scatterer.
　一方、図５ａ，５ｂ、図６ａ，６ｂに示すように、散乱体分布像は、輝度が密度に比例するが、輝度の散乱体サイズ依存性は小さいことが確認された。 On the other hand, as shown in FIGS. 5a and 5b and FIGS. 6a and 6b, in the scatterer distribution image, it was confirmed that although the luminance is proportional to the density, the scatterer size dependency of the luminance is small.
　ここまで図５から図８では、密度を変えた散乱体モデルと音速を変えた散乱体モデル、それぞれを別々のシミュレーションで検討した。また散乱体の形状が円形であり、実際の生体中の構造と大きく異なる。 So far, in FIGS. 5 to 8, the scatterer model with different density and the scatterer model with different sound velocity are respectively examined in separate simulations. In addition, the shape of the scatterer is circular, which is very different from the structure in an actual living body.
　図１０に、音速分布と密度分布を同時に持たせたモデルにおける検討の結果を示す。音速分布はＭＲＩによる臨床画像から、画像の輝度に応じた組織のセグメンテーションを行い、現実的に対象として存在しうる構造をモデル化した。 FIG. 10 shows the result of examination in a model in which the sound velocity distribution and the density distribution are simultaneously provided. The sound velocity distribution was subjected to segmentation of the tissue according to the brightness of the image from the clinical image by MRI to model a structure that could be practically present as an object.
　具体的には、水（***領域の外部）、皮膚、乳腺組織、脂肪の４組織に、輝度と、輪郭の内外の判定からセグメンテーションを行い、それぞれの音速は１５００，１６４０，１５５０，１４５０ｍ／ｓとした（図１０ａ参照）。これに図１０ｂに示した密度を変更した点散乱体を重畳したモデルを作成した。 Specifically, segmentation is performed based on the brightness and the determination of the inside and outside of the contour on four tissues of water (outside the breast area), skin, mammary gland tissue, and fat, and the speed of sound is 1500, 1640, 1550, 1450 m / s, respectively. (See Figure 10a). The model which superimposed the point scatterer which changed the density shown to FIG. 10 b to this was created.
　点散乱体の音速は周囲音速と同一であり、密度は１１００ｋｇ／ｍ３である。それ以外の組織は全て密度が１０００ｋｇ／ｍ３である。エコーデータを計算し、画像再構成した結果を、それぞれ図１０ｃに示す後方散乱画像、図１０ｄに示す前方散乱画像である。 The sound velocity of the point scatterer is the same as the ambient sound velocity, and the density is 1100 kg / m 3 . All other tissues have a density of 1000 kg / m 3 . The echo data are calculated, and the results of image reconstruction are shown in FIG. 10 c as a backscattered image and in FIG. 10d as a forward scatter image.
　一般に、ステップＳ３に相当する初期音速分布の推定値は、空間解像度においては、真値を上回ることはない（撮像における解像度の限界）。今回の計算の中では、設定したモデルに対して空間方向にローパスフィルタを与えたモデルをステップＳ３における初期音速分布推定値として用いた。 Generally, the estimated value of the initial sound velocity distribution corresponding to step S3 does not exceed the true value at the spatial resolution (resolution limit in imaging). In the calculation this time, a model obtained by applying a low pass filter in the spatial direction to the set model was used as an initial sound velocity distribution estimated value in step S3.
　１つのモデル内で音速分布と密度分布とを同時に与えているが、図１０ｃに示す後方散乱像は音速分布を反映した画像、図１０ｄに示す前方散乱像は密度分布を反映した画像として、それぞれ画像化されていることが確認できる。 The sound velocity distribution and the density distribution are given simultaneously in one model, but the backscattered image shown in FIG. 10c is an image reflecting the sound velocity distribution, and the forward scattering image shown in FIG. 10d is an image reflecting the density distribution. It can be confirmed that it is imaged.
　また、別の実施例として、図９に示す方法を説明する。図４に示す実施方法では、ステップＳ３は公知の方法によって既に設定された状態で最終画像を構築する方法であった。ステップＳ１１にて、ステップＳ３より高精度な音速分布像が求まった時に、これを活用する方法として、ステップＳ１１の計算結果を踏まえ、ステップＳ３の音速分布を更新し、ステップＳ４以降を繰り返すことも可能である。 As another embodiment, the method shown in FIG. 9 will be described. In the implementation shown in FIG. 4, step S3 was a method of constructing the final image in the state already set by the known method. When the sound velocity distribution image with high accuracy is obtained from step S3 in step S11, the sound velocity distribution in step S3 is updated based on the calculation result in step S11, and step S4 and subsequent steps are repeated. It is possible.
　この時、ステップＳ１１では、真値とステップＳ３の音速分布像との差分の絶対値が求まるので、厳密には「真値－ステップＳ３での推定値」の符号情報が失われている。そこでステップＳ１１の情報の符号として正負両方の可能性があることを考慮しながら、予め定めたコスト関数が最小化するようにステップＳ３の音速分布を更新する。コスト関数としては、例えば隣接画素間の差分絶対値の総和などが想定される。 At this time, in step S11, since the absolute value of the difference between the true value and the sound velocity distribution image in step S3 is determined, strictly speaking, the code information of "true value-estimated value in step S3" is lost. Therefore, the sound velocity distribution in step S3 is updated so that the predetermined cost function is minimized while taking into consideration that there is a possibility of both positive and negative as the sign of the information in step S11. As the cost function, for example, the sum of absolute differences between adjacent pixels is assumed.
　このようなステップＳ３の音速分布の更新が有効なのは以下の観点による。ステップＳ６において差分波形を計算する際に、実際のパルス伝搬時間Ｔ１と推定されたパルス伝搬時間Ｔ２の差ΔＴ＝Ｔ１－Ｔ２がパルス幅ＰＷより大きくなってしまった場合に、差分波形が実際の受信パルスとエミュレートされた受信パルスが時間軸上で分離してしまう。この結果、逆伝搬における散乱体源へ集束の精度が低下してしまう。そのため、ステップＳ１１で新たに求めた音速分布情報を用いて、ステップＳ３の音速分布を更新し、再構成処理を改めて行うことで、演算精度の向上を見込むことで出来る。 The update of the sound velocity distribution in step S3 is effective as follows. When the difference ΔT = T 1 −T 2 of the pulse propagation time T 2 estimated as the actual pulse propagation time T 1 becomes larger than the pulse width PW when calculating the differential waveform in step S 6, the difference The waveform is separated on the time axis from the actual received pulse and the emulated received pulse. As a result, the accuracy of focusing to the scatterer source in back propagation decreases. Therefore, by updating the sound velocity distribution of step S3 using the sound velocity distribution information newly obtained in step S11 and performing the reconstruction process again, it is possible to expect improvement in calculation accuracy.
　この時、精度が確保できていない段階では、パルス幅ＰＷが長い条件を用いて（低周波のパルスを用いることや、サイクル数の長いパルスを用いる）、ステップＳ１３からステップＳ３にループが更新される都度、パルス幅ＰＷを短くしていくという構成をとる。この場合、より正確にはステップＳ１３からステップＳ２にループが戻り、ステップＳ２の送信波形も変更して、送信、撮像を再度行う。 At this time, at the stage where the accuracy can not be ensured, the loop is updated from step S13 to step S3 using the condition that the pulse width PW is long (using a low frequency pulse or a pulse with a long cycle number). Each time, the pulse width PW is shortened. In this case, more accurately, the loop returns from step S13 to step S2, and the transmission waveform of step S2 is also changed to perform transmission and imaging again.
　本発明を特定の態様を用いて詳細に説明したが、本発明の意図と範囲を離れることなく様々な変更が可能であることは当業者に明らかである。
　本出願は、２０１７年１０月３１日付で出願された日本特許出願２０１７－２１０７３７に基づいており、その全体が引用により援用される。 Although the invention has been described in detail with particular embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application 2017-210737 filed on October 31, 2017, which is incorporated by reference in its entirety.
　１０　超音波診断システム
　１１０　スイッチ回路
　１２０　送受信回路
　１３０　演算装置
　１４０　画像表示装置 Reference Signs List 10 ultrasonic diagnostic system 110 switch circuit 120 transmission / reception circuit 130 arithmetic device 140 image display device

Claims (9)

  1. 　被検体の周囲に配置され、超音波の送信及び受信の少なくともいずれか一方を行う複数の素子と、
    　前記複数の素子のいずれか１つが超音波を送信し、前記複数の素子の少なくとも一部が、前記超音波が前記被検体で散乱した散乱波を受信するように、前記複数の素子を制御する制御部と、
    　前記散乱波を受信した素子から得たデータである実測定データを収集するデータ収集部と、
    　前記実測定データを用いて前記被検体の音速分布を推定し、推定した音速分布を有する領域を超音波が伝搬した場合に素子で受信される仮想測定データを計算し、前記実測定データと前記仮想測定データとの差分波形を計算し、前記差分波形から音速分布像の計算に用いる成分又は散乱体分布像の計算に用いる成分を取得し、前記音速分布像の計算に用いる成分の差分波形を用いた音速分布像の計算、又は前記散乱体分布像の計算に用いる成分の差分波形を用いた散乱体分布像の計算を行う計算部と、
    　を備える超音波診断システム。     A plurality of elements disposed around the subject and performing at least one of ultrasound transmission and reception;
    Any one of the plurality of elements transmits an ultrasonic wave, and at least a part of the plurality of elements controls the plurality of elements so that the scattered wave in which the ultrasonic wave is scattered by the subject is received A control unit,
    A data collection unit for collecting actual measurement data which is data obtained from an element that has received the scattered wave;
    The sound velocity distribution of the subject is estimated using the actual measurement data, virtual measurement data received by the element is calculated when an ultrasonic wave propagates in a region having the estimated sound velocity distribution, and the actual measurement data and The difference waveform with the virtual measurement data is calculated, the component used for calculating the sound velocity distribution image or the component used for calculating the scatterer distribution image is obtained from the difference waveform, and the difference waveform of the component used for calculating the sound velocity distribution image A calculation unit for calculating a scatterer distribution image using the calculation of the sound velocity distribution image used or the difference waveform of the components used for the calculation of the scatterer distribution image;
    An ultrasound diagnostic system comprising:
  2. 　前記音速分布像の計算に用いる成分は、前記超音波を送信した素子の側以外の側に散乱する散乱波の成分である前方散乱波成分であり、前記散乱体分布像の計算に用いる成分は、前記超音波を送信した素子の側に散乱する散乱波の成分である後方散乱波成分であることを特徴とする請求項１に記載の超音波診断システム。 The component used for the calculation of the sound velocity distribution image is a forward scattered wave component which is a component of the scattered wave scattered to the side other than the side of the element transmitting the ultrasonic wave, and the component used for the calculation of the scatterer distribution image is The ultrasound diagnostic system according to claim 1, wherein the ultrasound diagnostic system is a backscattered wave component that is a component of a scattered wave that is scattered to the side of the element that has transmitted the ultrasonic wave.
  3. 　前記複数の素子はリング状に等間隔に配置されており、
    　前記計算部は、超音波を送信した素子を中心にリング円周の一半側に位置する素子に対応する差分波形を前記後方散乱波成分に分類し、リング円周の他半側に位置する素子に対応する差分波形を前記前方散乱波成分に分類することを特徴とする請求項２に記載の超音波診断システム。     The plurality of elements are arranged at equal intervals in a ring shape,
    The calculation unit classifies a differential waveform corresponding to an element located on one half side of the ring circumference centering on the element that has transmitted the ultrasonic wave into the backscattered wave component, and an element located on the other half side of the ring circumference 3. The ultrasonic diagnostic system according to claim 2, wherein a differential waveform corresponding to is classified into the forward scattered wave component.
  4. 　前記計算部は、超音波を送信した送信素子毎の音速分布像及び散乱体分布像を計算し、
    　前記送信素子毎の音速分布像の加算、及び前記送信素子毎の散乱体分布像の加算を行う画像作成部をさらに備えることを特徴とする請求項１乃至３のいずれかに記載の超音波診断システム。     The calculation unit calculates an acoustic velocity distribution image and a scatterer distribution image for each of the transmission elements that have transmitted the ultrasonic waves,
    The ultrasound diagnosis according to any one of claims 1 to 3, further comprising an image creation unit that performs addition of the sound velocity distribution image for each transmission element and addition of a scatterer distribution image for each transmission element. system.
  5. 　前記画像作成部は、前記音速分布像と前記散乱体分布像とから密度分布像を作成することを特徴とする請求項４に記載の超音波診断システム。 The ultrasound diagnostic system according to claim 4, wherein the image creation unit creates a density distribution image from the sound velocity distribution image and the scatterer distribution image.
  6. 　前記音速分布像の計算は前記前方散乱波成分の差分波形の逆伝搬を含み、前記散乱体分布像の計算は前記後方散乱波成分の差分波形の逆伝搬を含むことを特徴とする請求項１乃至５のいずれかに記載の超音波診断システム。 The calculation of the sound velocity distribution image includes back propagation of the differential waveform of the forward scattered wave component, and the calculation of the scatterer distribution image includes back propagation of the differential waveform of the back scattered wave component. The ultrasound diagnostic system according to any one of to 5.
  7. 　前記散乱体分布像を用いて前記推定した音速分布を更新し、更新後の音速分布を用いて、前記差分波形の計算と、前記音速分布像の計算又は前記散乱体分布像の計算とを行うことを特徴とする請求項２乃至６のいずれかに記載の超音波診断システム。 The calculated sound velocity distribution is updated using the scatterer distribution image, and the calculation of the difference waveform and the calculation of the sound velocity distribution image or the calculation of the scatterer distribution image are performed using the updated sound velocity distribution. The ultrasound diagnostic system according to any one of claims 2 to 6, wherein
  8. 　前記複数の素子はリング状に配置されており、
    　リング円周上の一部の素子からの前記差分波形の逆伝搬により散乱体分布像を再構成することを特徴とする請求項１に記載の超音波診断システム。     The plurality of elements are arranged in a ring shape,
    The ultrasound diagnostic system according to claim 1, wherein a scatterer distribution image is reconstructed by back propagation of the differential waveform from part of elements on the ring circumference.
  9. 　被検体の周囲に配置された複数の素子のいずれか１つから超音波を送信し、前記複数の素子の少なくとも一部で散乱波を受信する処理を行う工程と、
    　前記散乱波を受信した素子から得たデータである測定データを収集する工程と、
    　前記実測定データを用いて前記被検体の音速分布を推定する工程と、
    　推定した音速分布を有する領域を超音波が伝搬して各素子で受信される仮想測定データを計算する工程と、
    　前記実測定データと前記仮想測定データとの差分波形を計算する工程と、
    　前記差分波形から音速分布像の計算に用いる成分又は散乱体分布像の計算に用いる成分を取得する工程と、
    　前記音速分布像の計算に用いる成分の差分波形を用いて音速分布像を計算する工程と、
    　前記散乱体分布像の計算に用いる成分の差分波形を用いて散乱体分布像を計算する工程と、
    　を備える超音波診断方法。     Transmitting an ultrasonic wave from any one of a plurality of elements disposed around the subject, and receiving a scattered wave by at least a part of the plurality of elements;
    Collecting measurement data which is data obtained from an element that has received the scattered wave;
    Estimating the sound velocity distribution of the subject using the actual measurement data;
    Calculating the virtual measurement data that ultrasonic waves propagate through the area having the estimated sound velocity distribution and are received by each element;
    Calculating a differential waveform between the actual measurement data and the virtual measurement data;
    Acquiring from the difference waveform a component used to calculate a sound velocity distribution image or a component used to calculate a scatterer distribution image;
    Calculating an acoustic velocity distribution image using a difference waveform of components used for calculating the acoustic velocity distribution image;
    Calculating a scatterer distribution image using a differential waveform of components used for calculating the scatterer distribution image;
    Method of ultrasound diagnosis.
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