WO2020018000A1

WO2020018000A1 - Method for producing 3d ultrasonic tomograms and device for carrying out said method

Info

Publication number: WO2020018000A1
Application number: PCT/RU2019/000508
Authority: WO
Inventors: Антон Александрович ГОНЧАРСКИЙ; Александр Владимирович ГОНЧАРСКИЙ; Святослав Радомирович ДУРЛЕВИЧ; Сергей Львович ОВЧИННИКОВ; Сергей Юрьевич РОМАНОВ; Сергей Юрьевич СЕРЁЖНИКОВ; Алексей Васильевич ЧЕРНЫШЁВ
Original assignee: Антон Александрович ГОНЧАРСКИЙ; Александр Владимирович ГОНЧАРСКИЙ; Святослав Радомирович ДУРЛЕВИЧ; Сергей Львович ОВЧИННИКОВ; Сергей Юрьевич РОМАНОВ; Сергей Юрьевич СЕРЁЖНИКОВ; Алексей Васильевич ЧЕРНЫШЁВ
Priority date: 2018-07-18
Filing date: 2019-07-16
Publication date: 2020-01-23
Also published as: EA036092B1; EA201800474A1

Abstract

A method and a device, claimed as the invention, for producing three-dimensional tomograms of the internal structure of a mammary gland in medicine relate to the field of non-invasive medical diagnostics. According to the claims, a method is described for producing three-dimensional tomograms of the internal structure of a mammary gland using low-frequency ultrasonic sources. In order to carry out the method, transmitted and reflected ultrasonic waves are recorded by a linear array of receivers arranged on a rotational adjustment appliance. A three-dimensional velocity profile is reconstructed using a GPU cluster incorporated into an ultrasonic tomograph.

Description

A method of obtaining 3d ultrasound tomographic images and a device for its implementation

Tomographic research methods are widely used at present in areas such as non-destructive testing of industrial products, process control, etc. Modern medicine is unthinkable without the use of tomographic diagnostic methods, such as magnetic resonance imaging (MRI), electron-positron tomography, x-ray tomography. In medicine, X-ray tomographs are the most widely used. The spatial resolution of modern X-ray tomographs is 1 - 2 mm, and the density resolution is about 1%. The disadvantages of all tomographs include their high price. Despite all its advantages, X-ray tomographs cannot be used for regular examinations due to high radiation exposure. The current trend in medicine is the rejection of the use of ionizing radiation.

In this regard, the development of ultrasound tomographs, which are currently intensively conducted in the USA, Europe, Japan, and Russia, is of great interest. Intensive research in this area has been conducted for over 10 years. There are currently no commercial ultrasound tomographs. Most of the developments are devoted to the diagnosis of breast cancer. Developments are being investigated on prototypes and prototypes (N. Duric, P. Littmp, L. Poulo, A. Babkin, R. Pevzner, E. Holsapple, O. Rama, C. Glide, Detection of breast cancer with ultrasound tomography : First results with the Computed Ultrasound Risk Evaluation (CURE) prototype, Med. Phys. 34 (2007) 773-785, J. Wiskin, DT Borup, SA Johnson, M. Berggren, Non-linear inverse scattering: High resolution quantitative breast tissue tomography, J. Acoust. Soc. Am. 131 (2012) 3802-3813; H. Gemmeke, A. Menshikov, D. Tchemikovski, L. Berger, G. Gobel, M. Birk, M. Zapf, NV Ruiter, Hardware Setup for the Next Generation of 3D Ultrasound Computer Tomography, IEEE NSS MIC 2010). The development of ultrasound tomographs is fraught with a number of difficulties. Compared to x-ray tomography, the inverse tasks of ultrasound tomography are much more complex. X-ray radiation is unique because the refractive index of x-ray radiation in any material is practically equal to unity, which means the absence of refraction. The inverse problems of x-ray tomography can be considered as two-dimensional and to study three-dimensional objects in layers. This means that the study of a three-dimensional object in x-ray tomography is reduced to a set of independent two-dimensional inverse problems in each layer. The inverse problems that arise are linear, the development of algorithms for solving linear two-dimensional problems is not a problem, the algorithms are easily implemented on a personal computer. In ultrasound imaging, the situation is much more complicated. The mathematical model should take into account such effects as diffraction, refraction, wave re-reflection, etc. The inverse problems of ultrasound tomography in such models are nonlinear.

Existing ultrasound diagnostic devices in medicine are not tomographic. They register a reflection signal. In reflection schemes, only the boundaries of inhomogeneities can be determined. It is impossible to obtain data on the distribution of the speed of sound inside an object necessary for characterizing tissues in reflection schemes (Goncharsky A.V., Romanov S.Yu., Seryozhnikov S.Yu. Wave tomography problems with an incomplete data range // Computational methods and programming : New Computing Technologies, 2014, vol. 15, N ° 2, pp. 274-285). Currently designed ultrasound tomographs using both reflected and transmitted radiation allow the characterization of soft tissues.

The primary concern in medicine is the development of ultrasound tomographs for the differential diagnosis of breast cancer. Mortality among the female half of humanity from this disease is in first place among all oncological diseases. Progress in Cancer Treatment the mammary gland is directly related to early diagnosis, which can be provided with regular examinations. Ultrasound radiation is harmless to humans. That is why the development of ultrasound tomographs for soft tissue research in medicine is an urgent task. The present invention is primarily focused on the development of ultrasound scanners for the early diagnosis of breast cancer.

The development of ultrasound tomographs for the diagnosis of breast cancer uses both wave and beam models. In the beam model, the time of arrival of the ultrasonic wave to the detector is recorded. Reconstruction of a high-speed section, as a rule, is carried out in a layered version, similar to how it is done in x-ray tomographs. The problems are that the wavelength in the ultrasound tomograph is 10 ⁵ times longer than in the x-ray. The main disadvantage of beam models is that such models are not adequate to reality, since they do not describe phenomena such as diffraction, wave re-reflection, etc. However, in various cases, beam models are used both in ultrasound diagnostic methods and in in devices for tomographic studies. Almost all patents related to radiation methods of ultrasound tomographic diagnostics describe layered methods.

US20080275344A1 proposes a method and device for the layered diagnosis of breast passage. The method of reconstruction of the velocity section is based on the beam model. Patent RU2526424C2 proposes an ultrasound tomograph for layer-by-layer examination of the mammary gland. For the reconstruction of layered images, a two-stage method is used. The inverse problem is solved in the wave approximation and consists in the search for sources of ultrasonic vibrations. To solve the inverse problem, a linearized approximation is used.

US5673697A proposes a device and a 3D ultrasound tomography method in which reconstruction of 3D ultrasound images is carried out in two stages. At the first stage, using the signal arrival time at passing, in the radiation model, the velocity section is restored. At the second stage, using the obtained velocity section, the image for reflection is calculated by the method of coherent summation.

US6786868B2 proposes a device for ultrasound imaging of the mammary gland, consisting of a container with a large number of transducers fixed on its surface, which are both sources and receivers of ultrasonic signals. The velocity section is restored in the beam model using the arrival time of the signal for passage. The patent discusses a device for reconstructing a 3D high-speed section in the framework of a beam model using the arrival time of the signal for passage.

In the patent US8366617B2 proposed ultrasonic tomographic device that allows for layered examination of the mammary gland. Sources and receivers are located in the horizontal plane on the support, which rotates around the axis of the cylindrical tank with the object under study, and can also move vertically along the axis. To examine the patient, you need to scan in many horizontal planes. Such a scheme automatically involves the study of a 3D object in layers. Passing waves are recorded separately and are used to reconstruct the velocity section, which is subsequently used to correct the data obtained for reflection. The disadvantages of such a device include low spatial resolution along the vertical axis.

US6005916A proposes a method and apparatus for reconstructing tomographic images using wave sources of probe radiation. In the proposed method, the inverse problem is solved in the parabolic approximation for the Helmholtz equation for a small set of frequencies. This approximation is adequate to reality only for propagation at small scattering angles. In essence, this means that the velocity section is restored in narrow layers. The resulting velocity section is used to reconstruct inhomogeneities in reflected waves. Decision algorithms inverse tasks are focused on the use of personal computers. The disadvantages of the method and device proposed in the patent US6005916A, also include insufficient resolution along the vertical axis. The latter is connected both with the location of sources and receivers in the registration scheme, and with the use of the parabolic approximation, which is adequate to reality only in a small range of angles.

The present invention is to provide a device and method for obtaining three-dimensional tomographic images of the internal structure of the mammary gland based on measurements of scattered by the object ultrasonic waves. An ultrasound tomographic image is a three-dimensional distribution of the speed of propagation of ultrasound within the object under study. In accepted terminology, the three-dimensional distribution of the speed of propagation of ultrasound is called a velocity section. In this patent application, a velocity cross section is reconstructed from all experimental data measured both for transmission and reflection. At the same time, a technical result is achieved, which consists in improving the quality of reconstructed 3D images of the internal structure of the investigated object, increasing the resolution of the ultrasound tomograph and reducing the time of examination of the patient.

The problem is to ensure the achievement of the specified technical result is solved in the method of obtaining three-dimensional tomographic images of the internal structure of the mammary gland in medicine according to claim 1 by the fact that the test object is placed in a tank filled with water. For sounding, use N, N <50, mounted on the internal container surfaces of the same type of ultrasonic wave sources with a working frequency range of 50 - 600 kHz. To register the reflected and transmitted through the studied object ultrasonic waves, a linear array of receivers fixed on a rotational slide is used. The vertical spacing of the receivers in the array is from 1.5 to 2.5 mm. For one revolution of the rotational movement, the experimental data are recorded (φ 0. which are signals from the / -th source, i = \, .. JSfi, at the j-th receiver, j = \, ..., M, at the time /, 0 <t <T at the angular position of the rotational shift fk , k = \, ..., K. Parameters K and T are set. The reconstruction of a three-dimensional high-speed section c (g) is performed in two stages. At the first stage, the registered signals are digitally filtered by a low-pass filter with a bandwidth of up to 200 kHz; at the second stage, all recorded data in the frequency range 50 - 600 kHz is used. At each stage, the reconstruction of the velocity section is carried out using an iterative process of gradient minimization of the mean square error between the experimental data

(fc, i) and a numerically calculated wave field. At the first stage, c ₀ (r) = const is taken as the initial approximation of the velocity section, and at the second stage, the velocity section obtained by minimizing the mean-square error at the first stage is used as the initial approximation. The calculation of the wave field for each of the sources is carried out by a separate graphics processor.

Claim 2 describes a device for obtaining three-dimensional tomographic images of the internal structure of the mammary gland in medicine according to claim 1, comprising a cylindrical container filled with water, on the inner surface of which Ni of the same type of ultrasonic wave sources with an operating frequency range of 50 - 600 kHz are fixed . A linear array of receivers or an assembly of two linear arrays of receivers is fixed on a rotational slide rotating around the axis of the cylinder, in which one of the linear arrays is located vertically parallel to the axis of the cylinder and the second at an angle g, 30 ° <g <60 ° to the axis of the cylinder. The vertical spacing of the receivers is from 1.5 to 2.5 mm. The device contains an optical sensor of the rotation angle of the rotational shift, a probe pulse generator, preliminary amplifiers of the signals of the receivers, an analog-to-digital processing unit of the signals of the receivers, a computing device based on graphic processors (GPU cluster), containing N _} graphic processors. In the method of obtaining three-dimensional tomographic images of the internal structure of the mammary gland in medicine according to claim 3 of the claims, the test object is placed in a container filled with water. For sounding, two types of ultrasonic sources fixed on the inner surface of the tank are used, Ni sources of the first type with an operating frequency range of 200 - 600 kHz and - / V _? ultrasonic sources of the second type with an operating frequency range of 50 - 200 kHz. The total number of sources N = N _j --N ₂ does not exceed 50. The number of sources of the second type

less than N _t . To register the reflected and transmitted through the studied object ultrasonic waves, a linear array of receivers mounted on a rotational slide is used. The vertical spacing of the receivers in the array is from 1.5 to 2.5 mm. For one revolution of the rotational movement, the experimental data C / ^E) are recorded _for (f *, t), which are pulses from the z-th source,

on the j-th receiver

at time времени, 0 <t <T, with the angular position of the rotational movement cp _k , k = \, ..., K. Parameters K and T are set. The reconstruction of the velocity section c (d) is performed in two stages. At the first stage, data is used only from sources of the second type with an operating frequency range of 50 - 200 kHz, at the second stage, data is only used from sources of the first type with an operating frequency range of 200 - 600 kHz. At each stage, the reconstruction of the velocity section is carried out using an iterative process of gradient minimization of the mean square error between the experimental data

(f *, t) and a numerically calculated wave field. At the first stage, c ₀ (r) = const is taken as the initial approximation of the velocity section, and at the second stage, the velocity section obtained by minimizing the mean-square error at the first stage is used as the initial approximation. The calculation of the wave field for each of the sources is carried out by a separate graphics processor.

Paragraph 4 of the claims describes a device for obtaining three-dimensional tomographic images of the internal structure of the mammary gland in medicine according to paragraph 3 of the claims, containing a cylindrical container filled with water, mounted on the inner surface of the container ultrasonic sources of two types, N _j sources of the first type with an operating frequency range of 200 - 600 kHz and N2 ultrasonic sources of the second type with an operating frequency range of 50 - 200 kHz. The number of sources of the second type N _{2 is} less than N _/ . The total number of sources N = N _J + N ₂ does not exceed 50. A linear array of receivers or an assembly of two linear arrays of receivers in which one of the linear arrays is located vertically parallel to the axis of the cylinder and the other at an angle g, 30 ° <g <60 ° to the axis of the cylinder. The vertical spacing of the receivers d is from 1.5 to 2.5 mm. The device contains an optical sensor of the rotation angle of the rotational shift, a probe pulse generator, preliminary amplifiers of the signals of the receivers, an analog-digital processing unit of the signals of the receivers, a computing device based on graphic processors (GPU cluster) containing N _j graphic processors.

Claim 5 describes a variant of the device according to claim 2 or claim 4, characterized in that the receiving elements in the linear array of receivers are arranged in two rows in a checkerboard pattern. The vertical spacing of the receivers is from 1.5 to 2.5 mm, the distance between the rows is from 2 to 8 mm.

Claim 6 describes a variant of the device according to claim 2 or claim 4, characterized in that for the rotation of the ruler, a motorized rotary table located under the bottom of the tank is used to control the angular position of the ruler using an optical sensor.

The claimed invention uses low-frequency sources of ultrasonic waves with frequencies not exceeding 600 kHz, which distinguishes this application from most patents for ultrasound tomographs for the diagnosis of breast, in which frequencies of at least 1 - 1.5 MHz are used (US5673697A). Ultrasonic sources emit short probe pulses with a duration of not more than 15 μs. Broadband sources are used to generate such pulses. The use of low-frequency ultrasonic waves as probing radiation in the frequency range up to 600 kHz allows detailed recording of the wave field using a small number of receivers. To register the wave field, use one rotating linear array of receivers, or an assembly of two such arrays. A linear array of receivers rotating vertically around the axis of the vessel, located vertically, registers the wave field on the cylindrical surface surrounding the object. The vertical spacing of the receivers can be 1.5 - 2.5 mm. The size of the receivers in a linear array can also be 1.5 - 2.5 mm. For the frequency range from 50 to 600 kHz, the center frequency is about 300 kHz. This frequency corresponds to a wavelength of ultrasonic radiation l = 5 mm. Thus, the sizes of the receivers and the distances between them during the registration of the wave field do not exceed l / 2. The selected parameters provide a precise measurement of the wave field. Precise registration of the wave field allows reconstructing a three-dimensional high-speed section with a high resolution, of the order of 2 mm, using a small number of probing radiation sources. For a qualitative reconstruction of the internal structure of the mammary gland, 30 to 50 sources are sufficient.

A small number of sources, not more than 50, significantly reduces the computational complexity of the inverse problem of reconstructing a three-dimensional high-speed section and allows you to effectively parallelize calculations using a GPU cluster as a computing tool. GPUs are ideal for calculating the propagation of ultrasonic waves in an inhomogeneous medium. Using a graphics card increases the performance of calculations in such tasks by tens of times. The composition of the device according to claim 2 or claim 4 of the claims includes a computing device based on graphic processors (GPU cluster), the number of graphic processors in which coincides with the number of sources (N _] ). With the number of sources N _{/ of the} order of 30-50, the use of the GPU cluster allows you to speed up calculations by 1000 or more times compared to a PC. Relatively few sources allows the use of compact GPU clusters as computing tools as part of a tomographic complex.

The invention is illustrated by graphic material, where figure 1 shows the location of the investigated object inside a tank filled with water; in FIG. 2 shows the shape and frequency spectrum of a broadband probe pulse; FIG. 3 shows a layout of sources and receivers in a variant of the device according to claim 2 of the claims with one linear array of receivers; in FIG. 4 shows a layout of sources and receivers in a variant of the device according to claim 2 of the claims with an assembly of two linear arrays of receivers; in FIG. 5 shows the arrangement of measuring points of the wave field on a cylindrical surface; FIG. 6 shows a layout of sources and receivers in a variant of the device according to claim 4 of the claims with one linear array of receivers; in FIG. 7 shows the arrangement of sources and receivers in a variant of the device according to claim 4 of the claims with an assembly of two linear arrays of receivers, FIG. 8 shows a receiver arrangement in embodiments of the device according to claim 2 or claim 4 of the claims, FIG. 9 shows the location of the receivers in the embodiment of the device according to claim 5, FIG. 10 shows a block diagram of a device for obtaining three-dimensional tomographic images; in FIG. 11 is a diagram of a rotary device of an array of receivers in a device according to claim 6; in FIG. 12 shows the shape and frequency spectrum of the probe pulse of the first type of sources; in FIG. 13 shows the shape and frequency spectrum of the probe pulse of the second type of sources; in FIG. Figure 14 shows the horizontal and vertical cross-sectional views of a 3D phantom used in model calculations; in FIG. 15 shows a horizontal and vertical velocity section reconstructed in a model problem at the first stage of reconstruction; FIG. 16 shows a horizontal and vertical velocity section reconstructed in a model problem at the second stage of reconstruction; FIG. 17 shows the signals measured for transmission and reflection, in FIG. Figure 18 shows a horizontal phantom velocity section and a velocity section reconstructed from experimental data. FIG. 1-1 1 illustrate devices for obtaining three-dimensional tomographic images of the internal structure of the mammary gland in medicine according to claim 2, claim 4 and claim 5 of the claims.

In FIG. 1 shows a tomographic diagram of a study of the mammary gland. The investigated object 2 is placed in a cylindrical tank 1. The tank is filled with water 3. For probing the mammary gland, the inventive device uses broadband sources of ultrasonic radiation, which make it possible to form short probe pulses. The device according to claim 2 of the claims uses the same type of broadband ultrasonic sources with an operating frequency range of 50 - 600 kHz. In FIG. 2 (a) shows an example of a real probe pulse, in FIG. 2 (6) shows the frequency spectrum of this pulse. As can be seen from the figure, the operating frequency range of the source at a level of -15 dB is 40 -600 kHz. A level of -15 dB means a signal attenuation of 5 times.

In FIG. 3 shows a layout of sources and receivers in the device according to claim 2. Sources of ultrasonic radiation 4 are fixed on the inner surface of the tank and have a wide radiation pattern that overlaps the object under study. A vertical linear array of receivers 6, consisting of identical elements, is fixed on the rotary slide 5. The vertical spacing of the receivers is from 1.5 to 2.5 mm, which does not exceed half the wavelength of the probe radiation. Such a step of the arrangement of the receivers provides a precise registration of the wave field. The receivers are located between the test object and the surface of the cylindrical tank. The length of the array of receivers exceeds the dimensions of the investigated object vertically. In the FIG. In version 3 of the device, one linear array of receivers is used.

In FIG. Figure 4 shows the arrangement of sources and receivers in the device according to claim 2 in the embodiment where an assembly of two linear arrays of receivers is used 6. One of the linear arrays in the assembly is located vertically parallel to the axis of the cylinder, and the second at an angle g, 30 ° <g <60 ° to the vertical. The total height of the assembly exceeds the dimensions of the investigated object vertically.

Data collection is carried out in one revolution of the rotational movement 5. In the process of data collection, the array of receivers rotates around the vertical axis of the tank and registers the wave field on the cylindrical surface surrounding the object. The position of the array of receivers during each measurement is controlled using an optical sensor for the angle of rotation of the rotational movement. In FIG. Figure 5 shows the arrangement of the points of measurement of the wave field on a cylindrical surface. At each angular position of the array of receivers f *, k = \, ..., K, all sources in turn emit sounding pulses. Acoustic signals registered by receivers are digitized and stored. All experimental data necessary for the reconstruction of the velocity section are collected in one revolution of the rotational movement.

In FIG. 6 shows a layout of sources and receivers in a variant of the device according to claim 4 of the claims. In this embodiment of the device, two types of low-frequency ultrasonic sources are used. The number 7 shows the sources of the first type with an operating frequency range of 200 - 600 kHz, the figure 8 shows the sources of the second type with an operating frequency range of 50 - 200 kHz. The number of sources of the second type is less than the number of sources of the first type. In the FIG. In version 6 of the device, one linear array of receivers is used.

In FIG. 7 shows the arrangement of sources and receivers in the embodiment of the device according to claim 4, where an assembly of two linear arrays of receivers is used 6. One of the linear arrays in the assembly is located vertically parallel to the axis of the cylinder, and the second at an angle g, 30 ° < g <60 ° to the vertical. The total height of the assembly exceeds the dimensions of the investigated object vertically. In FIG. Figure 8 shows the arrangement of receivers in a linear array of receivers in devices according to claim 2 and claim 4 of the claims. The vertical spacing of the receivers d is from 1.5 to 2.5 mm. In FIG. 9 shows the location of the receivers in a linear array in a variant of the device according to claim 5. The receivers are arranged in two rows in a checkerboard pattern. The vertical spacing of the receivers d is from 1.5 to 2.5 mm. The distance between the rows / can be from 2 to 8 mm. Such an arrangement of receivers allows minimizing ultrasound reflections between receivers at a given step of recording the wave field d.

In FIG. 10 shows a block diagram of the inventive device for obtaining three-dimensional tomographic images. The control computer 9 issues commands to set the preset position of the rotational movement of the receivers 5 and to generate sounding pulses by the pulse forming unit 10. The generated electrical pulses are sent to ultrasonic sources. In a variant of the device according to claim 4, two types of ultrasound sources with different frequency ranges are used. In a variant of the device according to claim 2, the same type of broadband ultrasonic sources are used. The ultrasonic waves transmitted through the object under investigation and reflected from the object are recorded by an array of receivers 6. The receivers are mounted on a rotary slide 5, the position of which is controlled by an optical angle sensor 11. At each position of the rotational move, the receivers record ultrasonic signals from all sources emitting sounding pulses in turn . Using the sensor 11, the exact position of the rotational movement during each measurement is transmitted to the control computer. The recorded signal from the receivers 6 is amplified by a block of pre-amplifiers 12 and digitized by a block of analog-to-digital converters (ADC) 13. The digitized data is transmitted to the control computer 9. The reconstruction of a three-dimensional high-speed section is carried out using a GPU cluster 14. The number of graphic processors in the cluster corresponds to the number of ultrasonic sources N _j . The calculation of the wave field for each source is carried out by a separate graphics processor.

A specific problem in the design of ultrasound tomographs for examining the mammary gland in water is the sealing of the tank when the rotary mechanisms are located outside the tank. One of the solutions to this problem is given in paragraph 6 of the claims. In FIG. 11 is a diagram of a rotary device array of receivers in the device according to claim 6. The rotary device is located under the bottom of the tank with water. The rotation of the array of receivers is provided by a motorized rotary table 15, which transmits torque to the hollow shaft 16. The angular position of the receiver line is controlled by an optical rotation sensor 17. The hollow shaft is mounted on bearings 18 in the sleeve 19. To ensure tightness, the internal space between the shaft and the sleeve is filled with oil. Seals and gaskets also provide tightness of the structure 20. The holder of the receiver array is attached to the upper part of the hollow shaft located inside the tank with water. Through the space inside the shaft, wires are removed from the receivers. After wiring, this space is sealed. The proposed option solves the problem of sealing the tank.

In this application, two variants of the method for obtaining three-dimensional tomographic images of the internal structure of the mammary gland in medicine are proposed. In claim 1 of the claims describes a preferred variant of the method of obtaining 3D tomographic images. The studied object is placed in a tank filled with water, on the walls of which sources of probe pulses are fixed. In a preferred embodiment of the method, broadband sources with an operating frequency range of 50-600 kHz are used. Ultrasonic waves transmitted through the object and reflected from the object are recorded using an array of receivers located in a vertical plane passing through the axis of the cylindrical container. The array consists of the same type of elements located in increments of 1.5 to 2.5 mm vertically, which does not exceed half the wavelength of the probe radiation. Array receivers rotate around the axis of the tank using a rotary movement. At each angular position of the rotational movement f *, k = 1, ..., all sources in turn emit sounding pulses. The wave field 1 ^e) (f *, t) at the jth receiver during pulse emission by the ith source, i = \, ..., N, is recorded as a function of time /, 0 <t <T. The value of T represents the time required to register each pulse is 200 to 400 μs. The receiver bandwidth includes a frequency range of 50 - 600 kHz. All data is recorded per revolution of the rotational movement, so that the angle sr * varies from 0 to 360 °. The number of angular positions K is chosen so that the distance between adjacent measurement points on the circle described by rotation of each receiver (Fig. 5) does not exceed half the wavelength of the probe radiation.

Paragraph 3 of the claims describes a variant of the method for obtaining 3D tomographic images, in which two types of ultrasound sources are used for generating probe pulses, N _j sources of the first type with an operating frequency range of 200 - 600

sources of the second type with an operating frequency range of 50 - 200 kHz. Two sets of sources provide sounding of the test object with ultrasonic waves in the range of 50 - 600 kHz to obtain high-quality tomographic images. The number of sources of the second type N _{2 is} less than N _j . The total number of sources N ^ N _/ + N ₂ does not exceed 50. The duration of the probe pulses does not exceed 15 μs. In FIG. 12 (a) gives an example of the shape of the probe pulse of the first type of sources. The abscissa axis represents time in microseconds; the ordinate axis represents the acoustic pressure generated by the source. In FIG. 12 (6) shows the frequency spectrum of this pulse. In FIG. 13 (a), an example of the shape of the probe pulse for sources of the second type is given. In FIG. 13 (6) shows the frequency spectrum of this pulse.

The reconstruction of a three-dimensional velocity section in the method according to claim 1 or claim 3 of the claims is carried out in the framework of a scalar wave model describing the phenomena of diffraction, refraction, and re-reflection of ultrasound in heterogeneous environment. The wave field in the scalar wave model is related to the propagation velocity of ultrasound by the hyperbolic equation

where u (r, i) is the acoustic pressure at the point r at time t, c (r) is the distribution of the speed of sound in the object under study, r is the three-dimensional vector r = {x, y zj, r ₀ is the given point at which is the source of ultrasonic radiation, d (g) is the Dirac delta function, f (i) is a function that defines the shape of the probe pulse. The inverse problem is to reconstruct the velocity section c (r) from the measured wave field U (r, t) on the surface surrounding the object (Fig. 5). The reconstruction of the high-speed section is carried out according to all recorded data - both for reflection and for passage.

The reconstruction of a three-dimensional velocity section is carried out using an iterative process of gradient minimization of the residual functional

The residual functional is the standard deviation of the experimental data at the receivers ί / ^, - _j (f *, from the numerically calculated data lf ^c) i _j (<р t). Function

(f *, ή is a wave field calculated by solving the direct problem of ultrasonic wave propagation from each / -th source for a given velocity section c (d). In formula (2), summation over / is performed over all sources used, summation over j is carried out on all receivers,

summation over k is carried out over all angles of rotation of the rotational movement f *, k - 1, ..., integration over time t is carried out in the range 0 <t <T, where T is the given signal recording time. For a given speed section c (g), the value of the functional f (c) is a number. If the velocity section c (r) coincides with the actual distribution of the speed of sound in the object under study, then Φ (c) = 0. The approximate value of the velocity section is constructed in the iterative process of minimizing the residual functional Φ (s), starting from a given initial approximation from ₀ (r). To minimize the residual functional, various methods of minimizing the functional can be used. In the claimed methods for obtaining three-dimensional tomographic images according to claim 1 and claim 3 of the claims, gradient methods of minimizing the functional are used, which are most effective for practical implementation on GPU clusters. The exact expression for the gradient of the residual functional is known (AVGoncharsky, SY Romanov, Iterative methods for solving coefficient inverse problems of wave tomography in models with attenuation, Inverse Problems 33 (2017), 025003). The gradient F '(c) of the residual functional Φ (c) uniquely determines the direction of the maximum decrease of the functional Φ (c). At each nth iteration of the gradient iterative process, the one-dimensional minimization of the functional Φ (c) is carried out in the direction of the maximum decrease of the functional. The resulting minimum point is taken as the nth approximation of the velocity section with _n (r).

The reconstruction of a three-dimensional high-speed section c (r) is performed in two stages. At the first stage, the initial approximation of the velocity section in the iterative process is taken with ₀ (r) = const. To calculate the wave field at the first stage, data with a limited frequency band are used. In the embodiment of the method according to claim 1, at the first stage, digitally filter all registered signals using a low-pass filter with a bandwidth of up to 200 kHz. In the embodiment of the method according to claim 3 of the claims, at the first stage, only data obtained from sources of the second type with an operating frequency range of 50-200 kHz is used.

At the second stage, as the initial approximation of the velocity section c (d), the velocity section obtained by minimizing the residual functional in the first stage is used. To calculate the wave field at the second stage, data with a wide frequency band are used. In a variant of the method according to claim 1, all registered data in the frequency range 50 - 600 kHz. In the embodiment of the method according to claim 3 of the claims, in the second stage only data from sources of the first type with an operating frequency range of 200 - 600 kHz are used.

The wave field is calculated using a GPU cluster, the number of processors in which corresponds to the number of ultrasonic sources (N _j ). The wave field calculation for each of the sources is carried out on a separate graphics processor. Since the differentiation operation is linear, the value of the gradient of the residual functional (2) can be represented as the sum of the gradients of the residual functional for each source, which can be calculated independently. The use of a GPU cluster consisting of N _j graphic processors allows efficient parallelization of gradient calculation for all sources. The use of such a cluster as part of the diagnostic complex allows you to accelerate the calculations in comparison with a personal computer more than 1000 times.

The use of a high-performance GPU cluster makes it possible to use a scalar wave model for reconstructing a three-dimensional high-speed section, which describes well the effects of diffraction, refraction, and re-reflection of ultrasonic waves. The inverse problem of reconstructing a three-dimensional velocity section in the wave model is non-linear and very complex. Such tasks cannot be solved on a personal computer. The use of personal computers as part of tomographic systems necessitates the use of simplified mathematical models that do not fully describe real physical processes.

The effectiveness of the proposed method for obtaining three-dimensional tomographic images of the internal structure of the mammary gland is illustrated by model calculations. FIG. 14-16 illustrate a computational experiment to restore a three-dimensional high-speed section using the proposed method according to claim 3 of the claims using probing radiation sources of two different types. In FIG. Figure 14 shows an image of a phantom with a given velocity distribution. propagation of ultrasound with (g). In FIG. 14 (a) shows a horizontal section X - Y of the three-dimensional distribution of the speed of sound c (x, y, z), in FIG. 14 (6) - vertical section X - Z. Light areas correspond to a higher speed of sound, dark areas to a lower one. In FIG. 15 (a, b) shows the horizontal and vertical sections of the approximate solution obtained at the first stage of the reconstruction of the high-speed section using low-frequency probe pulses (Fig. 13). In FIG. 16 (a, b) shows the horizontal and vertical sections obtained at the second stage of the reconstruction of the high-speed section using high-frequency probe pulses (Fig. 12). As an initial approximation in the second stage, we used the approximate solution obtained in the first stage (Fig. 14). In a numerical experiment, a spatial resolution of the order of 2 mm was obtained both in the horizontal section and along the vertical axis. This resolution is quite acceptable for the diagnosis of soft tissue in medicine.

Model calculations showed that for practical examinations it is necessary to solve a three-dimensional inverse problem with a dimension of about 500 for each of the spatial coordinates X, Y, Z. The number of unknowns in the inverse problem of reconstruction of a velocity section is about 60 million. To solve such problems on a GPU cluster you can use graphics processors with a built-in memory of 6 - 12 GB, the RAM capacity of each computing node is 16 - 32 GB and the bandwidth of the communication network between nodes 200 - 500 MB / s

Currently, devices that satisfy this requirement are widespread, and on their basis a GPU cluster can be assembled, which in its parameters may well be part of a tomographic diagnostic complex. Such a GPU cluster can be located within the same rack and have a power consumption of less than 10 kW. Thus, the infrastructure requirements imposed by the tomographic complex on the basis of the proposed device options for obtaining tomographic images are no higher than that of the widely used x-ray and magnetic resonance imaging. With the development of computer technology, infrastructure requirements will decrease, and the calculation time will be reduced.

Thus, the main differences of the proposed method and device for obtaining three-dimensional tomographic images of the internal structure of the mammary gland in medicine from known patents are as follows:

1. The fundamental point in the inventive devices and method is the use of a relatively small number (not more than 50) of probing radiation sources in an ultrasound tomograph. For comparison, US5673697A uses a tomographic scheme in which the number of sources is tens of times greater than the number of sources in this patent application. The number of sources in the device proposed in this application determines the number of graphic processors in the GPU cluster, which is part of the ultrasound tomograph. A cluster containing no more than 50 GPUs does not impose strict requirements on the infrastructure of the diagnostic complex. If the number of processors in the cluster is more than 50, additional liquid cooling is required for the cluster, high infrastructure requirements are imposed, which significantly increases the cost of the tomographic complex.

2. The most important characteristic of any tomograph is spatial resolution. When the number of sources is less than 50, to ensure a high spatial resolution of the tomograph, it is necessary to ensure precise registration of the wave field. The parameters that are given in this application (frequency ranges, receiver sizes and distances between them) provide a wave field measurement with high accuracy. For precision recording of the wave field, you can use receivers located in steps of less than half the wavelength, which is 1.5 - 2.5 mm. Such receivers exist and are widespread. 3. The choice of the low-frequency range in which the frequencies of the probe radiation do not exceed 600 kHz is also important for the following reason. Ultrasound absorption in soft tissues is highly dependent on frequency. With a typical ultrasound absorption coefficient in soft tissues of 1 - 2 dB / cm / MHz, the attenuation of the signal at frequencies of 0.5 and 1.5 MHz may differ by 10 or more times. The use of low frequencies in the claimed invention allows for higher accuracy of experimental data.

4. In the claimed invention, to increase the efficiency of reconstruction of a three-dimensional high-speed section, two types of sources are used, operating in different frequency ranges. The use of probe pulses with a lower central frequency allows an approximate low-resolution velocity section. The reconstruction of a high-speed section with a low resolution takes several times less time than the reconstruction of a high-speed section with a high resolution, which significantly reduces the total time of reconstruction of a high-speed section. An increase in the resolution of the tomographic image is achieved at the second stage of the reconstruction process using probing pulses with a higher central frequency. It was shown in experiments that the proposed technical solutions provide a spatial resolution of at least 2 mm.

5. The technical solutions proposed in this patent application can reduce the examination time of the patient to several minutes. The use in the proposed device of a vertical array of a small number of receivers, rotating around the axis of the tank, allows you to collect all the experimental data necessary for obtaining a three-dimensional tomographic image in one revolution of the rotational movement. Due to the use of rotational movement, the total number of receivers in the claimed devices does not exceed 100. This number of elements is tens of times smaller than in the scheme for registering ultrasonic radiation in US6786868B2. The scheme proposed in this application provides sufficient wave field accuracy for obtaining high-quality three-dimensional tomographic images.

6. Unlike existing patents, in which the reconstruction of tomographic images is carried out by layers (US8366617B2, US6005916A), in this application, the reconstruction result is a three-dimensional tomographic image obtained using all experimental data. This approach provides high resolution both in the horizontal X - Y plane and along the vertical Z axis.

7. The reconstruction of a three-dimensional high-speed section in the claimed invention is carried out using a GPU cluster, the number of graphic processors in which does not exceed 50. Most of the existing designs of ultrasound tomographs are focused on the use of personal computers, which forces us to use simplified mathematical models for calculations that do not fully describe physical processes . The use of the GPU cluster allows us to solve the nonlinear inverse problem of reconstructing a three-dimensional velocity section as a coefficient inverse problem for the wave equation in a mathematical model that takes into account the effects of diffraction, refraction, and re-reflection of ultrasound without simplifications. An important point is that the structure of the cluster, consisting of N _t GPUs, in terms of the number of sources, allows you to efficiently parallelize the calculations, which provides an acceleration of calculations by 1000 or more times compared to a PC. Currently, such a cluster can be assembled on the basis of generally available components and, by its parameters, may well be part of the tomographic diagnostic complex.

The effectiveness of the patented invention is demonstrated by the following example.

Example.

To demonstrate the effectiveness of the technical solutions proposed in this application, a stand for low-frequency ultrasound was assembled tomographic studies, in which the source and receiver independently moved both around the object being studied, and vertically. The angular position of the source and receiver was controlled by optical sensors. The stand used a broadband source of low-frequency ultrasonic vibrations with a central frequency of 300 kHz and an operating frequency range of 50 - 600 kHz. The source conversion coefficient was 5 Pa · meter / Volt, operating voltage ± 80 V. A hydrophone with a diameter of the receiving element of 2.5 mm and a passband of 10 - 800 kHz was used as a receiver. The sensitivity of the receiver was -228 dB with respect to 1 V / μPa. The signals were amplified by a preamplifier with a gain of 32 dB.

The experiments were carried out at 24 positions of the source. At each position of the source, experimental data were collected on a cylindrical surface in increments of 0.5 ° around the circumference and 2.5 mm vertically. The distance between adjacent measurement points on the circumference was 0.8 mm. The received signals were digitized using an ADC module with a sampling frequency of 5 MHz and a resolution of 14 bits. This configuration of the stand allows you to obtain experimental data for implementing the method according to claim 1 of the claims. In FIG. Figure 2 shows the form (a) and the frequency spectrum (b) of a broadband probe pulse, experimentally measured on a bench in a homogeneous medium. In FIG. 17 shows the measured signals from transmitted through the object (a) and reflected from the object (b) of ultrasonic waves.

The experiments were carried out on phantoms with acoustic parameters close to the parameters of human soft tissues. As a phantom, we used a silicone cylinder with a diameter of 56 mm containing inhomogeneities in which the speed of propagation of ultrasound varied from 1400 to 1800 m / s. The phantom velocity section is shown in FIG. 18 (a). The bright areas in FIG. 18 correspond to a high speed of propagation of ultrasonic waves in the phantom, dark to low. In FIG. 18 (6) shows a velocity section reconstructed from experimental data obtained in the same section. Spatial resolution of the reconstructed velocity section was no worse than 2 mm. The calculations were performed on a GPU cluster as part of the Lomonosov-2 supercomputer at Moscow State University.

The experiments performed showed the high efficiency of the technical solutions proposed in the patent application.

Claims

Claim

1. A method of obtaining three-dimensional tomographic images of the internal structure of the mammary gland in medicine, which consists in placing the test object in a container filled with water, for sensing using N _j , iV _/ <50, mounted on the inner surface of the tank of the same type of ultrasonic wave sources with a working range frequencies of 50 - 600 kHz, for registration of reflected and transmitted through the studied object ultrasonic waves, a linear array of receivers fixed on a rotational slide is used with an arrangement step of vertical receivers from 1.5 to 2.5 mm, for one revolution of the rotational movement register experimental data l ³⁾ i _j (f *, t), which are signals from the r ^' source, / = l, .. , V _/ , on the jth receiver, j = \, ..., M, at time t, 0 <t <T for the angular position of the rotational movement of the receivers f *, k = 1, ..., K, reconstruction a three-dimensional high-speed section with (g) is performed in two stages, at the first stage, the registered signals are digitally filtered by a low-pass filter with a passband of up to 200 kg c, at the second stage, all the registers are used data in the frequency range 50 - 600 kHz, at each stage, the reconstruction of the velocity section is carried out using an iterative process of gradient minimization of the mean square error between the experimental data l / ³⁾ _j (f *,) and the numerically calculated wave field, while at the first stage the initial approximation of the velocity section is taken c ₀ (r) = const, and at the second stage, the velocity section obtained by minimizing the mean square error in the first stage is used as the initial approximation, the calculation in The wave field for each of the sources is carried out by a separate graphics processor.

2. A device for obtaining three-dimensional tomographic images of the internal structure of the mammary gland in medicine according to claim 1 of the invention, containing a cylindrical container filled with water, mounted on the inner surface of the tank N _/ , N _/ <50, of the same type of ultrasonic wave sources with an operating frequency range of 50 - 600 kHz rotating around the cylinder axis there is a rotational movement, on which a linear array of receivers is fixed or an assembly of two linear arrays of receivers, the vertical spacing of the receivers is from 1.5 to 2.5 mm, an optical sensor for the rotation angle of the rotational movement, a probe pulse generator, preliminary signal amplifiers receivers, an analog-to-digital signal processing unit for receivers, a computing device based on graphic processors (GPU cluster), containing N _j graphic processors.

3. A method for obtaining three-dimensional tomographic images of the internal structure of the mammary gland in medicine, which consists in placing the test object in a container filled with water, for probing, two types of ultrasonic sources, N 1 sources of the first type, with a working frequency range of 200, are mounted on the internal surface of the tank - 600 kHz and N ₂ of the second type of ultrasonic sources operating frequency range 50 - 200 kHz, the total number of sources N = N _I + N ₂ <50, N ₂ <N, for registration of the reflected and transmitted through issl object under investigation using ultrasonic waves fitted on the rotary motions the linear array of receivers with the accommodation step receivers vertically from 1.5 to 2.5 mm, in one rotational motions turnover recorded experimental data 1 ^{e ^)} q (f *, t), which are signals from the / -th source, / —I ,. ., N, on the jth receiver,

at time t, 0 <t <T, with the angular position of the rotational movement cp _k ,

reconstruction of a three-dimensional velocity section c (d) is performed in two stages, at the first stage, data are used only from sources of the second type, at the second stage, data are used only from sources of the first type, at each stage, reconstruction of the velocity section is carried out using an iterative process of gradient minimization of the mean square error between the experimental data of 1 ^e) q (f *, /) and the numerically calculated wave field, in this case, at the first stage, c ₀ (r) = const, and for W In the second stage, the velocity section obtained as a result of minimizing the mean-square error at the first stage is used as the initial approximation; the wave field for each of the sources is carried out by a separate graphics processor.

4. A device for obtaining three-dimensional tomographic images of the internal structure of the mammary gland in medicine according to claim 3 of the claims, containing a cylindrical container filled with water, two types of ultrasonic sources fixed to the internal surface of the vessel, N1 sources of the first type with an operating frequency range of 200 - 600 kHz and N2 ultrasonic sources of the second type with the working frequency range 50 - 200 kHz, the total number of sources N = Ni + N ₂ <50, N ₂ <Ni, rotating around the cylinder axis of the rotary motions, which fasten a linear array of receivers or an assembly of two linear arrays of receivers, the vertical spacing of the receivers is from 1.5 to 2.5 mm, an optical sensor for the rotation angle of the rotational movement, a probe pulse generator, preliminary amplifiers of the signals of the receivers, an analog-to-digital signal processing unit receivers, a computing device based on GPUs (GPU cluster) containing N _] GPUs.

5. The device according to claim 2 or claim 4 of the claims, characterized in that the receiving elements in the linear array of receivers are arranged in two staggered rows, the vertical spacing of the receivers is from 1, 5 to 2.5 mm, the distance between ranks from 2 to 8 mm.

6. The device according to claim 2 or claim 4 of the claims, characterized in that for the rotation of the array of receivers, a motorized rotary table located under the bottom of the tank is used to control the angular position of the ruler using an optical sensor.