WO2018208189A1

WO2018208189A1 - Method and device for producing high-intensity focused ultrasonic fields for non-invasive local destruction of biological tissues

Info

Publication number: WO2018208189A1
Application number: PCT/RU2018/050049
Authority: WO
Inventors: Павел Борисович РОСНИЦКИЙ; Вера Александровна ХОХЛОВА; Леонид Рафаилович ГАВРИЛОВ; Борис Александрович ВЫСОКАНОВ; Олег Анатольевич САПОЖНИКОВ
Priority date: 2017-05-11
Filing date: 2018-05-10
Publication date: 2018-11-15
Also published as: RU2662902C1

Abstract

The invention relates to the field of medicine and medical technology, more specifically to ultrasonic surgery. The method and device being proposed are intended for non-invasive local destruction of biological tissues with the aid of high-intensity focused ultrasound requiring the use of a maximum possible power and, consequently, a maximum permissible intensity on the surface of a focusing ultrasonic radiator, for example a phased array with a high density of filling with elements. The device being proposed is a phased array with a random arrangement of radiating elements in the form of polygons of identical area having a permissible deviation value of up to 1% and with a filling of at least 86% of the area of the surface of the array with elements when there are technological spaces between the elements (or 100% without such spaces). The method for manufacturing the device comprises forming a template of an array with a random arrangement of radiating elements of identical area by generating a computer model of said array with subsequent use of known methods for producing technological gaps between the elements and completion of the assembly of the device.

Description

METHOD AND DEVICE FOR CREATING HIGH-INTENSE FOCUSED ULTRASONIC FIELDS FOR NON-INVASIVE LOCAL DESTRUCTION OF BIOLOGICAL

FABRIC

The invention relates to the field of medicine and medical technology, and more particularly to ultrasound surgery. The proposed method and device are designed for non-invasive local destruction of biological tissues using high-intensity focused ultrasound, when it is necessary to use the maximum possible power and, therefore, the maximum permissible intensity on the surface of a focusing ultrasound emitter, for example, a phased array. The use of high power levels is necessary, for example, to achieve shock fronts in the focus of an ultrasonic emitter due to the effects of acoustic nonlinearity, which allows effective mechanical and thermal destruction of tissues. The power of the ultrasonic emitter needs to be further increased if it is necessary to compensate for the attenuation of the field intensity at the focus, which can be caused by strong absorption during irradiation of deeply located organs, aberrations caused by tissue inhomogeneities, and also strongly absorbing and reflecting obstacles, such as bones of the skull or chest.

State of the art

As you know, powerful focused ultrasound (the generally accepted HIFU abbreviation for High Intensity Focused Ultrasound) is used in medicine for local destruction of deeply located tissues of the body, in particular, tumors of the liver, breast, bones, kidneys, pancreas and uterus without damaging the tissues ultrasonic beam paths.

In recent years, very promising applications of HIFU have been developed, based on the use of non-linear pulsed-periodic irradiation regimes, when high-amplitude shock fronts are generated in the focus of an ultrasonic emitter [US Patent J JS2010 / 0069797 (A1), publication date March 18, 2010; US patent N ° US8,876,740 (B2), publication date 04/11/2014]. The use of such modes makes it possible to realize mechanical destruction of tissue in the focal region to subcellular fragments with virtually no thermal denaturation and side effects associated with tissue overheating in the near zone of the emitter [TD Khokhlova, MS Canney, VA Khokhlova, O. A. Sapozhnikov, LA Crum, and MR Bailey. Controlled tissue emulsification produced by high intensity focused ultrasound shock waves and millisecond boiling. J. Acoust. Soc. Amer., 2011, vol. 130, no. 5, pp. 3498-3510], thereby expanding the possibilities of practical applications of NGS [VA Khokhlova, JB Fowlkes, WW Roberts, GR Schade, Z. Xu, TD Khokhlova, TL Hall, A D. Maxwell, YN Wang, CA Cain. Histotripsy methods in mechanical disintegration of tissue: Towards clinical applications. Int. J. Hyperthermia, 2015 v. 31 (2), pp. 145-162], and also improves the speed and locality of the thermal effect of ultrasound on tissues [PV Yuldashev, SM Shmeleva, SA Ilyin, O. A. Sapozhnikov, LR Gavrilov, and VA Khokhlova. The role of acoustic nonlinearity in tissue heating behind a rib cage using high intensity focused ultrasound phased array. Phys. Med. Biol., 2013, vol. 58, no. 8, pp. 2537-2559].

To implement tissue destruction methods based on the use of nonlinear waves with high-amplitude shock fronts in focus, focusing systems with a very high acoustic power and, accordingly, with a very high intensity on the surface of the emitter are needed. The requirements for a high level of intensity are further enhanced when acoustic obstacles, such as, for example, the bones of the skull or chest, are encountered in the pathway of HIFU to the focus, as well as when exposed to deep organs, when there is a strong absorption of ultrasound and, in addition, can become significant aberrations caused by tissue heterogeneity. In many practically important cases, the intensity on the surface of an ultrasonic source, necessary for the implementation of nonlinear regimes of tissue irradiation, can exceed the maximum permissible level and lead to a loss of operability of the emitter.

In laboratory and clinical HIFU systems, the use of multi-element phased arrays as an emitter is becoming more common. They are a set of independently controlled radiating elements located on a flat or curved surface. Between the elements are technological gaps that define the density of the surface of the grating or the percentage of its active radiating area of the total surface area of the grating. Such multi-element emitters have a number of important advantages associated with the possibility of electronic control of the spatio-temporal structure of the ultrasonic field. This allows you to move the focus electronically, create multifocal configurations, compensate for aberrations arising from the propagation of ultrasound through inhomogeneous layers of tissue, and dynamically focus on a selected area of tissue that is displaced due to breathing. The use of gratings also allows for safer exposure when focusing through the ribs by turning off the elements behind the ribs [S. Bobkova, L. Gavrilov, V. Khokhlova, A. Shaw, and J. Hand. Focusing of high intensity ultrasound through the rib cage using a therapeutic random phased array. Ultrasound in Medicine & Biology, 2010, vol. 36, no. 6, pp. 888-906]. Thus, an extremely important task at present is the development of phased arrays that provide the maximum possible power of the ultrasonic beam.

The acoustic power of the grating can be increased by increasing the intensity of ultrasound on its elements. This method, however, is limited by the maximum permissible level of intensity, which in modern piezoelectric sources is about 30-40 W / cm ² with good cooling and short operating time [D. Cathignol. High intensity piezoelectric sources for medical applications: technical aspects. In: Nonlinear Acoustics at the Beginning of the 21st Century, ed. by OV Rudenko and OA Sapozhnikov (Faculty of Physics, MSU, Moscow, 2002), vol. 1, pp. 371-378; VA Khokhlova, PV Yuldashev, PB Rosnitskiy, AD Maxwell, W. Kreider, MR Bailey, and OA Sapozhnikov. Design of HIFU transducers to generate specific nonlinear ultrasound fields. Physics Procedia, 2016, vol. 87, pp. 132-138]. Exceeding the specified value may result in malfunction of the focusing device. Another way to increase power can be to increase the size of the grating and increase the number of its elements while maintaining the filling density. The large size of the source, however, leads to the need to increase the focal length of the emitter or its angular aperture, which complicates the design of the device, complicates acoustic matching with the object and visualization of the affected area. Therefore, almost the only reserve for increasing the power of the lattice is the dense arrangement of elements on its surface.

The density of the filling of the surface of the lattice with elements can be increased by their ordered arrangement [Gavrilov L.R. High intensity focused ultrasound in medicine. M: Phasis, 2013]. The main disadvantage of this arrangement is the appearance in the acoustic field of the lattice during electronic focus shifting of the side diffraction maxima (lattice lobes) with a relatively high intensity level, which can lead to undesirable overheating and even destruction of tissue outside the specified exposure area. It is known that in order to exclude the appearance of the petals of the lattice, the distance between the centers of its elements and, accordingly, the size of the elements themselves should be <λ / 2 [M. I. Skolnik, Introduction to Radar Systems. New York, NY: McGraw-Hill, 1962], where λ is the wavelength, that is, for example, less than 0.75 mm at a frequency of 1 MHz. In the case of such small elements, to create a phased array with a sufficiently large aperture and high acoustic power required for use in the above areas of ultrasound surgery, it is necessary to use an unrealistically large number of elements and electronic channels, estimated in the thousands and tens of thousands. In addition, this increases the total passive area of the gaps between the elements (technological gaps necessary to eliminate electrical and mechanical interaction between adjacent elements) and, thereby, reduces the active area of the grating.

The level of incident diffraction maxima in the field created by the lattice with elements having a size greater than the wavelength depends on the spatial periodicity of its structure. This periodicity (regularity) can be destroyed if you place the lattice elements on its surface in a non-periodic or random (randomized) way. It was shown that with the help of such randomized gratings, the level of side lobes can be significantly reduced and, thereby, the area of safe electronic focus movement can be expanded compared to regular gratings, without overheating of the structures outside the specified exposure area [SA Goss, LAFrizell, J. T. Kouzmanoff , JM Barich, and JM Yang, Sparse random ultrasound phased array for focal surgery. GEEEE Trans. Ultrason Ferroelect. Freq. Control., 1996, vol. 43, no. 6, pp. 1111-1121; LR Gavrilov and JW Hand, A theoretical assessment of the relative performance of spherical phased arrays for ultrasound surgery, ΓΕΕΕ Trans. Ultrason Ferroelect. Freq. Control., 2000, vol. 47, no. 1, pp. 125-139]. Known methods of spatial randomization of the arrangement of elements on the surface of the lattice lead to a relatively low, not more than 60%, filling density of its surface.

Thus, to implement the above HIFU applications, it is necessary to create gratings with a non-periodic (for example, random) arrangement of elements and with the highest possible fill factor in order to provide the maximum possible acoustic power at the minimum intensity of the secondary maxima outside the exposure area, as well as to provide the necessary parameters of dynamic focusing .

Known thinned antenna array with non-periodic arrangement of elements on the plane, consisting of a combination of smaller logarithmic spiral arrays and providing a relatively low level of the array petals [US Patent N ° 6,433,754 B1, publication date 08/13/2002]. Known thinned antenna array with non-periodic arrangement of elements on a spiral, designed for ultrasound diagnostics [US Patent N ° US 6,359,367 B1, publication date 03/19/2002]. Diagnostic arrays with a relatively small number of elements are known (128, 256), based on the use of Fermat spirals of various modifications, including multi-start ones [O. Martinez-Graullera, C. J. Martin, G. Godoy, L.J. Ullate. 2D array design based on Fermat spiral for ultrasound imaging. Ultrasonics, 2010, vol. 50, pp. 280-289]. All of these lattices are intended for visualization purposes, therefore, they consist of elements of a small wave size (less than the wavelength) located at a relatively large distance from each other and have a low filling density (not more than 10%).

A known design of an ultrasonic phased array, intended for ultrasound surgery and based on a random arrangement of elements of a sufficiently large wave size (at most 5 wavelengths) on the surface in the form of a spherical segment. The random nature of the arrangement of elements can significantly reduce the level of side lobes in the field created by the grating [Patent GB2347043, publication date 08/23/2000; US patent 6488630, publication date 12/03/2002; China Patent CN 1340184, Publication Date 08/16/2002; Hong Kong Patent PC 1045015, Date publication September 11, 2002]. The degree of filling of the surface of such gratings (in the presence of technological gaps between the elements) does not exceed 60%.

Known lattices with dense packing of elements based on the use of rectangular elements that are closely adjacent to each other, as well as elements having the shape of rhombuses and arranged in the form of a Penrose mosaic [B.I. Raju, C.S. Hall, and R. Seip. Ultrasound therapy transducers with space- filling non-periodic arrays. GEEEE Trans. Ultrason Ferroelectr. Freq. Contr., 2011, vol. 58, no. 5, pp. 944-954]. The maximum fill factor achieved with these gratings is 70% and 71%, respectively (in the absence of technological gaps between the elements in the grating design).

Phased arrays are known whose surface has the shape of a spherical segment with a circular hole in the center, and elements in the form of disks with a wave size of more than 5 wavelengths are located on an Archimedean spiral outward from the central axis of the lattice [K.R. Morrison, G.W. Keilman. Single Archimedean spiral close packed phased array HIFU. 2014 IEEE International Ultrasonics Symposium Proceedings. 2014, pp. 400-404]. The fill factor of such gratings does not exceed 60%.

A known method and device for non-invasive local destruction of biological tissue [RF Patent N ° 2589649, filing date 03/19/2015, publication date 07/10/2016]. In its technical essence, the device is an ultrasonic phased array with an arrangement of elements in the form of a dense single-pass or multiple-helix with various shapes of elements (round, square, in the form of trapezoid). This method allows to increase the degree of filling of the surface of the grating, for example, with round elements up to 70%, in the absence of technological gaps between the elements and up to 60% in the presence of such, and non-periodic arrangement of elements on the surface suppresses diffractive side lobes.

The disadvantage of all the above-described lattice designs with non-periodic arrangement of elements is the relatively low degree of filling and the fundamental impossibility of achieving 100% filling with elements of the surface of the lattice.

The closest analogue (prototype) of the invention is a phased array with radiating elements located on the surface of the array in a spiral Fermat, in which the elements are in the form of cells diagrams (mosaics) of Voronoi [M. Ries, M. De Greef, S. Bos. High intensity focused ultrasound apparatus. Patent WO 2016099279 Al. Publication date June 23, 2016. Priority date December 19, 2014; P. Ramaekers, M. Ries, ST. W. Moonen, and M. de Greef, Improved intercostal HIFU ablation using a phased array transducer based on Fermat's spiral and Voronoi tessellation: A numerical evaluation, Med. Phys., 2017, vol. 44, no.3, pp. 1071-1088]. A device for focusing high-intensity ultrasound and for delivering ultrasonic energy to an object is a base on which is a set of transducers of a given shape, a driver system for controlling the transducers, a controller for supplying signals to the driver system and HIFU generation, while the location of the transducers on the basis of the device according to a predetermined law. The proposed method involves the construction of a certain set of points S on a section of a flat surface and its subsequent division into cells in such a way that each cell is the set of points closest to one of the elements of the set S. If such a partition is applied to the set S of points located on a spiral The farm, the plane is divided into aperiodically located cells in the form of polygons. Projecting these cells onto a spherical bowl, we obtain a multi-element spiral grid with elements in the form of polygons (Fig. 1) and a surface filling density, in the absence of technological gaps between the elements, about 85%. As can be seen from FIG. 1, the limitation of the filling density is due to the fact that the region at the periphery of the lattice is not occupied by elements. The disadvantages of this method are the fundamental lack of the ability to achieve 100% filling of the lattice surface with elements and, as a consequence, the inability to provide the maximum possible lattice power at a given aperture and intensity on the surface of the elements. In addition, Voronoi’s mosaic on the plane does not provide equal cell areas, and the subsequent projection of elements onto the spherical shell of the lattice changes them and leads to even greater differences in the areas of the lattice elements. The inequality in the area of individual elements creates difficulties in the electrical matching of power amplifiers with different elements, and also worsens the quality of the field with electronic focus scanning. Finally, the arrangement of the elements in a Fermat spiral involves the creation of a round lattice without a hole in the center, whereas in practice both round and rectangular are required gratings with holes of various shapes for the installation of a diagnostic ultrasonic sensor.

Disclosure of invention

Modern devices for generating high-intensity focused ultrasound, as a rule, include several main units: a focusing emitter — a phased array, a digital unit that controls the frequency, amplitudes and phases on the array elements, a multi-channel power amplifier for supplying voltage to the array elements, an amplifier impedance matching unit power and lattice elements, computer, etc. In this application, the term "device" means a phased array.

The technical result of the present invention is that, for a given aperture of the lattice, the intensity on the surface of its elements and the random nature of the arrangement of the elements, the generation of an ultrasonic field with the maximum possible power required to form shock fronts in focus and increase the efficiency of tissue destruction is achieved by separation the surface of the lattice on the elements in the form of polygons of the same area with reaching the density of filling the lattice with elements up to 100% (in the absence of technology gaps between the elements).

The technical result is achieved due to the fact that the device for non-invasive local destruction of biological tissue is a phased array with a random arrangement of emitting elements in the form of polygons of the same area with an allowable deviation of up to 1% and with elements filling up to 100% of the surface of the array (in the absence of technological gaps between the elements), while each of the sides of the elements inside the lattice is adjacent to one of the sides of adjacent elements of the lattice.

Distinctive features of this device are the following. The surface of the lattice and its boundary can have an arbitrary shape. In particular, the surface of the grating may have a spherical or cylindrical shape; the boundary of the lattice may have a round or rectangular shape, or the shape of a polygon. The grill may include a central hole for installing an ultrasonic sensor to visualize the area of influence; however, the hole may have an arbitrary shape, for example, rectangular or round. It should be noted that in real gratings, 100% filling with elements is impossible due to the need to separate elements with technological gaps with a width of at least 0.1 - 0.2 mm. So, for example, if in the proposed phased array in the absence of gaps between the elements, the filling density is 100%, then with a characteristic radius of the elements 3.5 mm after the introduction of a technological gap 0.5 mm wide, the filling density will be 86%.

The random arrangement of radiating elements provides the possibility of electronic focus movement within a certain region, the boundary of which is set by the level of intensity reduction in the created focus by 50% compared to the maximum achievable intensity. With electronic focusing within the indicated region, the intensity level of side maxima does not exceed 10% of the intensity in the main maximum.

The present invention also includes a method for producing a phased array template with a random arrangement of radiating elements and a density of the surface of the array with elements up to 100% (in the absence of technological gaps between the elements) by forming its computer model, which includes the following sequence of operations: selecting the shape and boundary of the surface of the array; selection of the number of elements; drawing on the resulting surface according to the uniform distribution law of a random set of a large number of points, the number of which is determined by the number of lattice elements, with at least 1000 points being set on one element. Then all the points are randomly divided into groups according to the number of lattice elements. Next, all possible pairs of groups are sequentially sorted out, between which a pair exchange of points is carried out in order to form disjoint areas (cells). The process of pairwise separation of groups is continued until all groups are divided among themselves with the formation of disjoint cells. Then, for each cell, a convex hull with a minimum area is built, covering all points of the cell, forming a polygonal lattice element and providing elements with the same area. To form a technological gap between adjacent sides of the elements, each side of the element is parallelly transferred inside the element by half the size of the gap. Brief Description of the Drawings

The proposed method and device are illustrated by drawings.

FIG. 1. Sketch of the lattice with the arrangement of elements on the surface in the form of a Fermat spiral and Voronoi diagram (mosaic) [P. Ramaekers, M. Ries, ST. W. Moonen, and M. de Greef. Improved intercostal HIFU ablation using a phased array transducer based on Fermat's spiral and Voronoi tessellation: A numerical evaluation, Med. Phys., 2017, vol. 44, no. 3, pp. 1071-1088]. It is seen that the region on the periphery of the lattice inevitably turns out to be not occupied by elements, which reduces the fill factor of the lattice.

FIG. 2. a) A sketch of an existing 256-element lattice filled with 6 mm elements in the form of a 16-entry tight spiral [VA Khokhlova, PV Yuldashev, R. V. Rosnitskiy, AD Maxwell, W. Kreider, M. R. Bailey, and O. A. Sapozhnikov. Design of HIFU transducers to generate specific nonlinear ultrasound fields. Physics Procedia, 2016, vol. 87, pp. 132-138]; b) 364-element lattice with maximum filling with elements in the form of spherical polygons. The parameters of both gratings are as follows: frequency 1.5 MHz, aperture 144 mm, focal length 120 mm, element area 0.385 cm ² , diameter of the central hole for the diagnostic sensor 40 mm, minimum technological gap 0.5 mm. Only the number of elements, their shape and method of packaging differ.

FIG. 3. Illustration of the sequence of operations for the implementation of the maximum possible (up to 100%) filling the surface of the lattice with elements in the form of polygons with the same area. Five sets of points are represented, indicated by pluses, circles, crosses, dots and rhombs, a) the initial random distribution of points of different groups; b) the beginning of the process of pairwise separation of the sets of points of different groups; c) completion of the process of separation of sets of points and the formation of cells.

FIG. 4. Examples of focusing gratings of various shapes and different types of central holes. Left: a lattice in the form of a segment of a spherical surface of a rectangular shape with a round central hole. Right: a lattice in the form of a segment of a spherical surface of a round shape with a rectangular central hole.

FIG. 5. Explanation of the analytical method for calculating the far field of a polygonal element of the lattice, a) The partition of the polygon into a series of right-angled triangles. b) Scheme of analytical calculation of the field right triangle at a point with coordinates (x, y, z). c) Comparison of the sound pressure distributions along the axis of the element in the form of a right triangle. The solid line shows the results of numerical calculation of the field using the Rayleigh integral, the dashed line shows the results of analytical calculation in the far field approximation. Element parameters: sides of a right triangle a = 4 mm, b = 3 mm; frequency of 1 MHz.

FIG. 6. Two-dimensional distribution of the amplitude of sound pressure in the field of the existing lattice with 256 elements placed in the form of 16-zah one dense spiral. The results are normalized to the pressure on the surface of the element, a) Distributions in the plane along the axis of the lattice; the focus is in the center of the lattice curvature; b) the focus is electronically shifted 1 cm away from the axis; c), d) the corresponding distributions in the focal plane.

FIG. 7. Two-dimensional distribution of the amplitude of sound pressure in the field of the proposed lattice, consisting of 364 elements in the form of spherical polygons of equal area. The results are normalized to the pressure on the surface of the element, a) Distributions in the plane along the axis of the lattice; the focus is in the center of the lattice curvature; b) the focus is electronically shifted 1 cm away from the axis; c), d) the corresponding distributions in the focal plane.

FIG. 8. The contours of the areas of possible focus movement of the existing lattice with a spiral arrangement of elements (dashed curves) and the proposed lattice with elements in the form of spherical polygons of equal area (solid curves). Thin lines show the boundaries of focus movement with a decrease in intensity of no more than 10% of the maximum level (marked as 0.9) and 50% (shown as 0.5). Thick lines show the boundaries of the focus movement at which the levels of emerging side maxima do not exceed 10% of the intensity value at the main maximum (marked as 0.1).

The implementation of the invention

Below, as an example, confirming the operability of the proposed method and device for its implementation, the results of computer simulation of a lattice with a 100% density of filling its surface with elements in the form of polygons (in the absence of technological gaps between adjacent sides of adjacent elements) created by the proposed method. The quality of the intensity distributions in the field of the known lattice (Fig. 2a) with dense spiral packing of elements on the surface with a known minimum gap between the elements [VA Khokhlova, PV Yuldashev, R.V. Rosnitskiy, AD Maxwell, W. Kreider, M. R. Bailey, and O. A. Sapozhnikov. Design of HIFU transducers to generate specific nonlinear ultrasound fields. Physics Procedia, 2016, v. 87, pp. 132-138] and the developed lattice with the introduced technological gap between elements of the same size (red lines in Fig. 26).

The lattice parameters with dense spiral packing of elements on the surface (Fig. 2a) were as follows:

1.5 MHz frequency

Number of Elements 256

Diameter of elements 7 mm

Element area 38.5 mm ²

Value of the minimum

clearance between elements 0.5 mm

The number of visits tight spiral 16

Grating diameter 144 mm

Surface Curvature Radius: 120 mm

Diameter of the central hole 40 mm

The main parameters of the proposed lattice with elements in the form of polygons are chosen the same. Equal are the areas of the elements of the two gratings. Only the number and shape of the elements differ, as well as the way they are packaged. If there is a technological gap between the elements equal to 0.5 mm, the filling density of the spiral lattice is 60%, the filling density of the proposed lattice is 86%. In the absence of technological gaps between the elements, the filling density of the proposed lattice is 100%. Note that the indicated value of the minimum technological gap of 0.5 mm is usually considered sufficient to ensure reliable electrical safety of high power ultrasonic phased arrays.

Below is a description of the sequence of operations for the implementation of the maximum possible (up to 100%) filling the surface of the lattice with elements in the form of polygons with the same area and random the location of the elements on the surface of the lattice (Fig. 3). First, the continuous surface of the spherical shell of the lattice is replaced by a set of a large number of points that are randomly thrown at it according to the uniform distribution law. Each point is poured as follows: its x, y, and z coordinates are generated as standard normal random variables, and then the resulting radius vector (x, y, z) is normalized so that its end lies on the surface of a sphere containing a spherical shell of the lattice. If the point does not fall on the surface inside the boundaries of the lattice, it is discarded and the next one is thrown. Dots are drawn until a sufficient number of dots are scattered on the surface of the grating [Muller, M. E. A note on a method for generating points uniformly on N-dimensional spheres. Comm. Assoc. Comput. Mach. 2, 19-20, Apr. 1959]. Using this algorithm, a five-element lattice was formed in the form of a spherical segment with a round hole in the center. All sampling points were divided into N classes (according to the number of elements), each of which contained M points (Fig. 3a). In the case under consideration, N = 5, M = 128, the total number of points NM = 640. In FIG. Over the points of five different classes are shown with different icons: pluses, circles, crosses, dots and rhombs. The division of points into classes occurs randomly, in connection with which, the sets ("clouds") of points of various classes turn out to be completely mixed (Fig. 3a). Pairwise separation of the sets of points of different classes is implemented using the algorithm disclosed in [M. Balzer, T., Schlomer, T., O. Deussen. Capacity-constrained point distribution: A variant of Lloyd's method. 2009. ACM Trans, on Graphics (Proc. Of SIGGRAPH). vol. 28, no. 3, Article 86, 1-8]. Its essence is to conduct an iterative process of pairwise separation of sets of points belonging to different classes. At each iteration, all possible pairs of points of various classes are considered. For each pair of points, according to the mathematical rule described by Balzer et al. a decision is made on the exchange of points between classes (for example, the point ai belonging to the first class is assigned to the second class, a bj belonging to the second - the first). This rule implements the process of pairwise spatial separation of sets of points. After the first iteration, the points look much less mixed (Fig. 36), however traces of mixing are still observed. Therefore, iterations continue until full separation of sets of points (Fig. Sv). It is important to note that after separation, each of the N = 5 sets of points contains the same number M = 128 points, since the exchange of points between their sets always occurs in pairs. Finally, for the transition from a discrete representation of sets of points to a representation in the form of polygons, for each of the sets of points, a convex hull closures it is constructed (Fig. Sv). Obviously, as a result of this, polygons are formed, which are the elements of the lattice that absolutely densely fill its surface in the case of a large number of sampling points. Due to the fact that each cell contains the same number of M points scattered according to the uniform distribution law, the area of the cells is equal, since the fraction of points that fall into the element, up to a multiplicative constant, is a consistent unbiased estimate of its area.

Similarly, a 100% filling of the surface of the lattice with a more real one, i.e. with a significantly higher number of elements. So, with the above-mentioned lattice aperture (144 mm) instead of 256 elements located on a multi-helix, 364 elements in the form of polygons with the same area fit (see Fig. 26). In this case, M = 10240 points fall on each element. Note that when dividing the surface into cells, a large number of parameters affect the process of resorption of points: N = 364 sets of points, each of which consists of M = 10240 points randomly mixed. In this regard, the final arrangement of cells (lattice elements) is irregular and aperiodic, which provides good dynamic focusing capabilities.

To form a technological gap between adjacent sides of the elements, each side of the element is parallelly transferred inside the element by half the gap.

The proposed method allows you to create a lattice with an arbitrary surface shape, for example, spherical and cylindrical, and an arbitrary shape of the borders, for example, round or rectangular. When changing the shape of the surface from spherical to cylindrical, it is necessary to take into account the change in the metric, that is, the function that determines the distance between a pair of sampling points on the surface of the lattice. The grill may include a central hole, for example, rectangular or round, for installing a sensor to control the source of exposure (Fig. 4).

The calculation of the total acoustic field created by a lattice filled with polygons of equal area can be performed, for example, using the Rayleigh integral [N.T. O'Neil. Theory of focusing radiators. J. Acoust. Soc. Am. 1949, vol. 21, no 5, pp. 516-526] or the faster analytical method illustrated in FIG. 5. With this approach, each polygon element is divided into a set of right-angled triangles (Fig. 5 a), the acoustic field of which is calculated by the analytical method (Fig. 56), which in the far field gives results that are highly accurate with results based on the use of Rayleigh integral (Fig. 5c). The specified method for calculating the field of a multi-element ultrasonic emitter by summing the analytical solutions for the far field of each element was proposed earlier in [S. A. Ilyin, P.V. Yuldashev, V.A. Khokhlova, L.R. Gavrilov, P.B. Rosnitsky, O. A. Sapozhnikov. The use of the analytical method to assess the quality of acoustic fields during electronic focus shifting of multielement therapeutic gratings. Acoustics Zh., 2015, t. 61, N ° 1, p. 57-64]. In FIG. Figures 6 and 7 present the results of comparative calculations of two-dimensional distributions of the amplitude of sound pressure in the fields created by the two lattices under consideration: the existing lattice of 256 elements placed in the form of 16 zokes of one dense spiral, and the proposed lattice consisting of 364 elements in the form of spherical polygons of equal area . In both cases, the top shows the distributions in the plane along the axis of the lattice when the focus is in the center of curvature of the lattice. The distributions are shown below when the focus is electronically shifted 1 cm away from the axis. Figures c) and d) show the corresponding distributions in the focal plane.

Calculations show that the ultrasonic pressure at the focus of the proposed lattice, consisting of 364 elements in the form of spherical polygons of equal area, is 1.4 times higher than the pressure at the focus of the existing spiral lattice, which corresponds to the ratio of the filling densities of these lattices. The corresponding gain in intensity is 2.1 times, which is extremely important for the implementation of HIFU application modes with the maximum possible ultrasonic power at a given aperture of the emitter and the maximum permissible intensity on its surface.

The comparison of the quality of the acoustic fields of both gratings was carried out according to the method described in [S. A. Ilyin, P.V. Yuldashev, V.A. Khokhlova, L.R. Gavrilov, P.B. Rosnitsky, O. A. Sapozhnikov. The use of the analytical method to assess the quality of acoustic fields during electronic focus shifting of multielement therapeutic gratings. Acoustics Zh., 2015, t. 61, N ° 1, p. 57-64]. This method allows you to evaluate the ability of the lattice to perform dynamic focusing, i.e. determine the distance by which you can move the focus electronically with a given decrease in intensity (for example, to the level of 0.9, 0.7, 0.5, etc. from the maximum intensity level without moving the focus) without generating side maxima with an intensity exceeding 10% of the intensity mainly maximum.

The results (Fig. 8) are shown both in the axial plane (a) and in the focal plane. It is generally accepted that the effective focusing region is limited by the level of 0.5 decrease in intensity in the focus when it is shifted electronically. It can be seen that for this level 0.5, the difference between the contours for the existing and proposed gratings is less than 1 mm. In this case, the contours of the safe focus bias region, when focused inside which the level of side maxima does not exceed 10% of the intensity in the main maximum, are located outside the contours of the effective focusing region for both gratings. This allows us to consider the areas inside the effective focusing contours as the working areas of the dynamic focusing of the gratings. Thus, the proposed lattice with randomly located polygonal elements has the same dynamic focusing capabilities as a non-periodic spiral lattice with round elements.

In the considered example, the technological gap between the elements was equal to 0.5 mm, while the fill factor of the new lattice was 86%. Calculations show that with the same characteristic area of the elements, 38.5 mm ² , and a technological gap between them of 0.3 mm, the grating filling factor will be 91%, and with a gap of 0.2 mm - 94%. These values are in good agreement with an approximate analytical estimate of the maximum possible lattice fill factor 1 - h · ^ π / S, where h is the gap and S is the element area. Production of the device according to the phased array pattern obtained

(computer model) with a random arrangement of radiating elements can be implemented using methods known from the prior art [A. Khokhlova, P.V. Yuldashev, P.B. Rosnitskiy, A.D. Maxwell, W. Kreider, M.R. Bailey, and O. A. Sapozhnikov. Design of HIFU transducers to generate specific nonlinear ultrasound fields. Physics Procedia, 2016, vol. 87, pp. 132-138; Goland V.I., Kushkuley L.M. Strongly focusing multi-element therapeutic emitters for non-invasive ultrasonic adipose tissue ablation. Acoustics journal 2009.V. 55. N ° 4-5. S. 481-495; Hand J.W., Shaw A, Sadhoo N, Rajagopal S, Dickinson R.J., Gavrilov L.R. A random phased array device for delivery of high intensity focused ultrasound. Phys. Med. Biol. 2009. vol. 54. pp. 5675-5693; K.P. Morrison, G.W. Keilman. Single Archimedean spiral close packed phased array HIFU. 2014 GEEEE R7S Proceedings. 2014, pp. 400-404], based, for example, on the use of laser ablation of a conductive coating to create gaps between the elements [US5855049, publication date 01/05/1999].

In any case, for a given total area of the grating and a given value of the minimum gap between its elements, the proposed method and device can provide the maximum possible active area of the grating without deteriorating the field quality with an electronic focus shift characteristic of more sparse non-periodic gratings.

Claims

CLAIM

1. A device for creating high-intensity focused ultrasonic fields for non-invasive local destruction of biological tissue, which is a phased array with a random arrangement of emitting elements in the form of polygons, the areas of which differ up to 1% in the presence or absence of technological gaps between the elements, where each of the sides of the elements inside the lattice is adjacent to one of the sides of adjacent elements.

2. The device according to claim 1, characterized in that the radiating elements are arranged so that the focus can be moved electronically to a level of intensity reduction in focus by 50% compared to the maximum achievable intensity without generating side maxima with an intensity exceeding 10% of the intensity mainly maximum.

3. The device according to claim 1, characterized in that the technological gaps between the elements are not more than 0.5 mm.

4. The device according to claim 1, characterized in that the surface of the lattice and its boundary are arbitrary in shape.

5. The device according to claim 1, characterized in that the surface of the lattice has a spherical or cylindrical shape.

6. The device according to claim 1, characterized in that the boundary of the lattice has a circular shape, or a rectangular shape, or a polygon shape.

7. The device according to p. 1, characterized in that the grill includes a Central hole for installing a sensor to control the source of exposure.

8. The device according to p. 7, characterized in that the Central hole has a rectangular, round or oval shape.

9. The device according to p. 1, characterized in that in the absence of technological gaps between the elements, filling the surface of the lattice with the elements is up to 100% of its area.

10. A method of manufacturing a device according to claim 1, comprising obtaining a phased array pattern with a random arrangement of radiating elements by forming its computer model, followed by manufacturing the device according to the pattern obtained, in order to obtain a pattern: - the choice of the surface shape and the shape of the boundary of the lattice, as well as the number of its radiating elements,

- drawing on the resulting surface according to the uniform distribution law of a random set of points, the number of which is determined based on the number of lattice elements, at least 1000 points are set on one element, all points are randomly divided into groups according to the number of lattice elements,

- choose a pair of groups in which the pairwise replacement of points with the formation of disjoint areas, followed by enumerating the remaining pairs of groups,

- the process of pairwise separation of groups is continued until all groups are divided among themselves with the formation of disjoint cells,

- for each cell, a minimum convex hull is constructed, covering all points of the cell and forming a polygonal lattice element, with active elements of the same area being obtained, each side of the elements inside the lattice adjacent to one of the sides of adjacent elements.

11. The method according to claim 10, characterized in that the formation of technological gaps between adjacent sides of the elements is carried out, while each side of the element is simultaneously transferred inside the element by half the size of the technological gap.