WO2016099279A1

WO2016099279A1 - High intensity focused ultrasound apparatus

Info

Publication number: WO2016099279A1
Application number: PCT/NL2015/050896
Authority: WO
Inventors: Mario Günter RIES; Martijn DE GREEF; Clemens Bos
Original assignee: UMC Utrecht Holding BV
Current assignee: UMC Utrecht Holding BV
Priority date: 2014-12-19
Filing date: 2015-12-21
Publication date: 2016-06-23
Anticipated expiration: 2017-06-19
Also published as: NL2014025B1

Abstract

The invention relates to High energy focused ultrasound, HIFU,apparatus for delivering high energy focused ultrasound to an object. For example a human body. The apparatus can be applied in ablasive procedures. The apparatus comprises a base and multiple transducers of a predetermined shape, wherein the transducers of a predetermined shape are arranged on the base, a driver system for driving the multiple transducers and a controller for generating signals to the driver system to generate the high energy focused ultrasound wherein the geometrical arrangement is obtained by a seed curve of which consecutive generating points correspond to locations of the respective transducers on the base surface.

Description

High intensity focused ultrasound apparatus

Background of the invention

The invention relates to a high intensity focused ultrasound apparatus.

TECHNICAL FIELD

The high intensity focused ultrasound apparatus can be used in a variety of applications and implementations, e.g., as a high intensity focused ultrasound apparatus that is adapted for therapeutic purposes, such as hyperthermia or drug delivery in humans or in minimally-invasive thermal tumor ablation techniques in a human body, for example the upper abdomen. These techniques are becoming more important for curative treatment of malignant cancer. In particular, magnetic resonance-guided high intensity focused ultrasound and ultrasound guided high intensity focused ultrasound become increasingly important. In these combinations high intensity focused ultrasound enables non-invasive and precise tumor ablation, while image modalities provide simultaneous guidance.

A high intensity focused ultrasound apparatus is known from international patent publication WO2008135956. That document discloses an apparatus that comprises an array of transducers that exhibit space- filling, aperiodic placement.

Another example of a high intensity focused ultrasound apparatus comprises a sparse phased array transducer. Such a sparse phased array transducer is known from "A random phased array device for delivery of high intensity focused ultrasound" by J.W. Hand et al, PHYSICS IN MEDICINE AND BIOLOGY, Phys. Med. Biol. 54 (2009) 5675-5693. That document discloses a high intensity focused ultrasound apparatus comprising a randomized sparse phased array which can offer electronic steering of a single focus and simultaneous multiple foci concomitant with low levels of secondary maxima and can be applied as sources of high intensity focused ultrasound.

A disadvantage of the conventional high intensity focused ultrasound apparatus is that multiple undesired side lobes or multiple foci may occur and near field energy of the ultrasound waves is relatively high. So, only a small focal volume can be obtained in a target volume. When these sparse phased array transducers are applied in high intensity focused ultrasound therapy mechanical translations of the transducer with respect to the body are required to heat a target volume in the body in order to avoid tissue damage at the surface of the body. This is time consuming and may lead to clinical usage of impractically long duration.

A further drawback of the conventional high intensity focused ultrasound apparatus comprising a sparse phased array combining electronic and geometric focusing is that it is difficult to obtain, for example a good on-axis focusing and off- axis focusing while maintaining moderate element numbers, since complexity and costs increase with the amount of channels corresponding to the elements.

A further drawback is that the design of the high intensity focused ultrasound apparatus requires numerous computer simulations to determine an optimal

arrangement of the transducer elements with respect to design parameters such as size, power, location, aperture focal length, on-axis focusing and off-axis focusing and frequency. For example, a change in the design to a larger diameter of the ultra high power ultra sonic transducer may lead to a larger element number and a different arrangement of elements in the sparse phased array and may lead to different on-axis and off-axis focusing.

SUMMARY OF THE INVENTION

It is an object of the invention to mitigate the above mentioned drawbacks and to provide an ultrasound apparatus with improved focus performance at relatively low near field densities.

According to a first aspect of the invention this object is achieved by a high energy focused ultrasound apparatus for delivering high energy focused ultrasound to an object. The apparatus comprises a base and multiple transducers of a predetermined shape, wherein the transducers are arranged on a base. The apparatus further comprises a driver system arranged to drive the multiple transducers and a controller to generate signals to the driver system to generate the high energy focused ultrasound wherein the arrangement is determined by generating a seed curve of which consecutive points correspond to locations of the respective transducers on the base.

The transducers can be circular and have a diameter of e.g. 5 mm, because the element size is larger than the wavelength of the ultrasound waves, typically about 2 mm, a so-called "real" phased array is not possible because of the Huygens's principle of waves and this type of arrangement of transducers is known as a sparse phased array. The selection of the seed curve enables a low near field density, high focus energy and good focal beam steering.

The generating of the seed curve provides a distribution of a finite set of elements over a spherical cap, based on the following acoustic considerations:

1) the formation of side lobes in the focal-plane should be limited as much as possible and

2) in pre-focal planes parallel to the focal plane the acoustic field should present optimal homogeneous acoustic intensity.

The seed curve realizes a point placement that, in favor of 1) avoids point symmetries in the placement elements, and thus suppresses constructive interference, and a relatively homogeneous point distribution (in a Voronoi sense), in favor of point 2)

In an embodiment the seed-curve is a Fermat spiral, that "supports" a set of seeds, the Fermat spiral is mathematically defined as (in polar coordinates) r = ±αφ¹'² (1)

Wherein r is the radial coordinate, φ is the azimuthal angle/coordinate and a is a scaling factor. The angles at which the seed points are actually placed are incremented by the golden angle, such that point symmetries are avoided. The seeds are placed at angular positions φ_η = 2πηδ, where φ_η is the azimuthal angle of the n-t seed placed and δ = g², with g = - V5 - 1, such that 2πδ « 137.5°

An arrangement on a spherical base can be obtained by substituting the n and φ of a polar coordinate system by azimuthal angle and polar angle of a spherical coordinate system wherein a radial distance is constant.

The inventors have recognized that this arrangement of transducers is asymmetric which is advantageous for reduction of side lobes of the generated high energy focused ultra sound beam and that this arrangement enables the highest package density of the uniform transducers for different diameters of the base. Furthermore, the arrangement of transducers according to the invention enables a scalable design of the base, so that an arrangement and the number of the transducers for different diameters of the base of the transducers can be determined in a more similar way for different diameters of the base of each design while maintaining main characteristics with respect to on-axis focusing and off-axis focusing. Furthermore, this arrangement enables a closed solution of the ultrasonic transducers that is asymmetric with a maximum active surface, the higher density of transducers and more uniform near field density.

In a further embodiment of the apparatus according to the invention the start point of the seed curve is at a center of the base surface. This position of the starting point provides the best solution with respect to asymmetry of the arrangement of the transducers.

In a further embodiment of the apparatus according to the invention the areas of the multiple transducers on the base surface are substantially uniform. Uniform shapes of the transducer enables an easy positioning of the transducers along the seed curves. Furthermore, uniform shapes of the transducers lead to equal capacitance of the transducers which enables a simple adjustment of the power of individual channels of the driver system of the high energy focused ultrasound apparatus. For example, the shape of the transducers can be circular.

In a further embodiment of the apparatus according to the invention the base surface is a spherical surface. In a spherical base provides a good starting point for focus position.

In a still further embodiment of the apparatus according to the invention the respective shape of the respective areas of the transducers are conforming convex polygons comprising the respective generating points, determined such that a point in one of the convex polygons is closer to the generating point of the one polygon than to any other generating points of the other convex polygons. This arrangement of the polygons is known as Verenoi tiling. In this arrangement the surfaces of the different transducers are about equal, while the whole inner surface of the base can be covered by the respective elements with a convex polygon shape. An advantage of this arrangement is that a larger area of the base can be used to generate ultrasonic waves than with respect to a base with identical transducers and that a near field density can be more uniform and reduced compared to the intensity of the main focus and also maintaining good beam steering characteristics. In a further embodiment of the apparatus according to the invention the transducers comprises a first and second electrode and a piezo-electric material, for example, lead zirconium titanate (PZT) provided between the first and second electrode. This type of transducer enables manufacturing of the array of transducers.

In a still further embodiment of the apparatus according to the invention the first electrode of the transducers is integrated in a common electrode provided in the base surface.

This arrangement provides a further integration of the transducers in the base and a large active surface area with no gaps between elements can be obtained. The common electrode can be positioned in the inner side of the convex surface. The material of the common electrode is for example copper.

In a still further embodiment of the apparatus according to the invention the second electrodes of the respective transducers are arranged to define the areas of the respective transducers. The second electrodes can be arranged at the outer side of the spherical surface of the base.

In a different embodiment of the apparatus according to the invention the controller of the HIFU apparatus is further arranged to generate signals for the driver system to generate amplitudes and phases of driving signals to the ultra-sound transducers to generate ultra-sound waves for imaging the part of the body to be subjected to the HIFU ultrasound waves and to receive reflected ultrasound waves and to convert the received acoustic waves into image signals and to display the obtained ultrasound signals on the LCD monitor for guidance of the HIFU beams and the ablation procedure. In this arrangement the ultrasound transducers are operated alternatively in a transmitting mode and a receive mode in order to obtain ultrasound images for guidance of the HIFU ultrasound waves in for example an ablation procedure.

In a different embodiment of the apparatus according to the invention the high energy ultrasound apparatus comprises an ultrasound imaging transducer arranged at the base. The ultrasound imaging transducer can be integrated, for example, at the center of the base the high energy focused ultrasound apparatus and enables non- invasive and precisely targeted tumor ablation by simultaneous guidance with ultrasound imaging.

BRIEF DESCRIPTION OF THE DRAWING The above and other, more detailed aspects of the invention will be elucidated and described hereinafter, by way of example, with reference to the accompanying drawing.

Therein:

Fig. 1 shows an high energy focused ultrasound, HIFU, apparatus;

Fig. 2 shows a cross-section of a part of base and integrated transducers;

Fig. 3 shows an arrangement 30 of a conventional sparse phase array transducer;

Fig. 4 shows an example of an arrangement of transducers in an HIFU apparatus;

Fig. 5 shows an arrangement of the transducers in a first embodiment of the HIFU apparatus according to the invention;

Fig. 6 shows an arrangement 60 of the transducers in a second embodiment of an HIFU apparatus according to the invention;

Fig.7 shows pressure distribution diagrams for comparison of the performance of the HIFU apparatus according to a second embodiment of the invention and a conventional HIFU apparatus; and

Fig. 8 shows temperature distribution diagrams for comparison of the performance of the HIFU apparatus according to a second embodiment of the invention and a conventional HIFU apparatus.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Fig. 1 shows a high energy focused ultrasound, HIFU, apparatus 1 for radiating high energy focused ultrasound to an object 2 on an object table 3. The object 2 can be a part of a human body and the apparatus can be used for example in non-invasive and precisely target tumor ablation. The HIFU apparatus 1 comprises a base 4 and multiple, for example 256 transducers 5 arranged on the base 4. The shape of the base 4 can be convex or spherical. Instead of 256 any number of transducers can be used between 64 and 4096. The transducers 5 operate in a frequency range of 1.2 - 1.45 MHZ.

The HIFU apparatus 1 further comprises a driver system 6 provided with a number of channels equal to the number of transducers 5, so in this example 256. The channels can be electrically connected to respective transducers 5. Furthermore, the HIFU apparatus comprises a controller 7 arranged to generate signals to the driver system 6. The driver system 6 is further arranged to control the amplitude and phase of the channels connected to the respective transducers 5 according to the signals received from the controller 7 and the transducers 5 can generate the high energy focused ultrasound waves to a focus volume in the part of the human body. The driver system 6 can be obtained for example from Verasonics in the USA. The driver system 6 may comprises a communication unit for communication with the controller 7 and a power converter for each ultrasound channel, for example a power converter may comprise an 8-bit driver for amplitude and phase adjustment for each channel.

The HIFU apparatus may further comprise a display device 8, for example an LCD-monitor, input means, for example, a key board 9 and a memory 10 for storage of data and user programs. The controller 7 can be connected to the internet and can be further arranged to provide a user interface for a person controlling the ablation procedure or other procedures.

The controller 7 can be a general purpose computer arranged to generate information related to focus patterns, power level operation time and mode and to send the information to the multi-channel ultrasound driver 6.

The controller 7 is a well-known devices or can be designed and implemented by a person skilled in the art.

In this embodiment the 256 transducers 5 can be arranged at an inner side on a spherical section of the base 4, each transducer 5 is electrically connected to the respective channels of the driver system 6.

In operation, the controller 7 is arranged to generate signals for the driver system 6 to generate amplitudes and phase of driving signals to the ultrasound transducers 5 to generate ultrasound waves with a predetermined focus pattern and amplitude for non-invasive ultrasound surgery of the human body. In this way, for example, single on- and off axial focus, multiple on- and off foci, half sub array focus patterns can be obtained.

The HIFU apparatus 1 can be further provided with an ultrasound imaging transducer 11 arranged at the base 4. The controller 7 and the ultrasound imaging transducer are further arranged to obtain images of the part of the body subjected or to be subjected to the HIFU ultrasound waves and to display the obtained ultrasound images on the LCD monitor for guidance of the HIFU beams and the ablation procedure. Alternatively, an MRI apparatus can be used for imaging and guidance of the HIFU beams and the ablation procedure.

Fig. 2 shows a cross-section of a part of base of integrated transducers. The ultra-sound transducers 5 comprise a first integrated electrode 20 and second electrode 21 and a piezo-electric material 22 provided between the first and second electrode. The first electrodes of the transducers can be a common electrode provided at surface of the base 4. The second electrodes 21 of the ultra-sound transducers are separated from each other and define the shape of the transducers. The first electrode 20 can be electrically connected to a common output of the multi-channel ultrasound driver and the second electrodes 21 can be respectively connected to the respective channels of the driver system 6.

In general, characteristics of a HIFU apparatus comprising a sparse phased array ultrasound transducer are

High possible focal point pressure/intensity;

Good Side lob-suppression on axis;

A beam steering range larger then ± 10 mm, comparable with a conventional sparse phased array ultrasound transducer;

Side-lobe suppression off-axis; and

simultaneously a low near-field pressure/ intensity.

The size and shape of the multiple ultrasound transducers and the geometrical arrangement contribute for a large part to these characteristics. Computer simulations can be used to determine an optimal design of the sparse phased array transducer. An example of a conventional arrangement is a pseudo-random sparse phase array. In the pseudo-random sparse phased array the transducer can have a circular shape and are pseudo-randomly arranged on the base.

Fig.3 shows an arrangement 30 of a conventional pseudo random sparse phase array transducer with a high density arrangement of the multiple ultrasound

transducers. However, even in HIFU apparatus provided with these sparse phase array unwished foci may still occur. Furthermore, for different diameters of the base new different higher density arrangements of the multiple ultrasound transducer on the disk surface have to be determined. Fig. 3 shows a high density arrangement at the center 31 of the base and a less dense arrangement 32 of the transducers at the edges of the circle.

The design of a sparse phased array involves an optimization problem for aperture, focal length, frequency, number n of transducers, position n_x, n_y of the transducers, power and size and shape of the transducers. So, a 6 + n_x, n_y degree of freedom exists. Practically, aperture and focal length are restricted by anatomy of the body and mechanical integration. The number of transducers is restricted to the available channels of the driver, for example 256. The shape of the transducers can be a circular shape. Even with this restriction the optimization involves 2 + n_x, n_y degrees of freedom and requires a lot of effort to solve.

The inventers have found that an arrangement comprising multiple transducers wherein the transducers are arranged in a sparse array arrangement on a base, wherein the arrangement is obtained by a seed curve of which consecutive generating points correspond to locations and area of the respective transducers on the base surface, provides an optimal solution. So, arrangements of the multiple ultrasound devices for different diameters and shape of the base can be determined that provide optimal characteristics.

In an embodiment the seed curve is defined by a Fermat spiral, as defined in (1) and the respective locations of the respective ultrasound transducers correspond to consecutive generating point of the Fermat spiral. It appears that the thus obtained geometric arrangement does not exhibit any point symmetry which is advantageous for reducing unwished multi-foci and appears that this arrangement also provides the highest density mathematically possible as stated by Fermat.

The seed point in Cartesian coordinate's x_n, y_n of point n in an X, Y plane can be derived from the formula (1) by x_n = α\/2πη<5 cos 2πηδ ~Vn cos 2π η δ (2)

y_n = α\/2πη<5 sin 2πηδ ~ Vn sin 2π n (5 (3)

Wherein n G [1, n_elem n_elem is the number of total number of elements for which for each a single seed is placed.

In order to find the location of the transducer elements on a spherical surface the n and φ of a polar coordinate system are substituted by azimuthal angle and polar angle in a spherical coordinate system wherein a radial distance is constant so that the transducers are located on the spherical surface. A generator function for a point set of size N is defined by

r„ = Vn(AP72)/VN (4)

Zn = FL cos(^n), (9)

where AP' is the arc length going from a point on the edge of the spherical cap, through the origin, to the edge of the cap on the opposite side, i.e. AP' = 2FL

sm^~l{{API2.0)IFL) with AP the aperture diameter and FL the focal length of the transducer. r_n is an arc length.

Fig. 4 shows as illustration an arrangement of transducers on a flat surface, obtained via a Fermat spiral method. As illustrated in Fig. 4 a transducer corresponds to a circle 41 with a radius r. A starting position of a first transducer is selected at a first axis 40 in a plane of the circle 41 wherein the origin of the axis coincides with a point of the circle. Next, a position of a second transducer can be determined by rotating the axis 40 with respect to the origin in the plane of the first circle with an angle co, the golden angle or Fibonacci angle, ~ 137,5° and determining a point of tangency of the first circle 41 and a second circle 42 with its centre located on the rotated axis. The center of the second circle 42 corresponding to the tangency of the first and second circle 42, 42 is then the position of the second transducer. These steps can be repeated to determine the positions of subsequent circles 43, 44, 45.

Fig. 5 shows an arrangement 50 of the transducers in a first embodiment of the HIFU apparatus according to the invention. The arrangement is a dense packaging obtained via the above described Fermat' s spiral method, wherein a start point of the seed curve, in particular the Fermat spiral, is at a center of the base surface. The areas of the multiple transducers on the base surface are substantially uniform and have an identical circular shape. The transducer can be arranged at a spherical surface. It is remarked that this arrangement does not exhibit point-symmetry which is advantageous in the reduction of side foci.

Fig. 6 shows an arrangement 60 of the transducers in a second embodiment of an HIFU apparatus according to the invention. In this arrangement the respective shape and area of the transducers is further enlarged into convex polygons comprising the respective generating points of the Fermat spiral, where a shape of one the convex polygons is d such that a point in that one of the convex polygons is closer to the generating point of that one polygon than to any other generating points of the other convex polygons. This arrangement of transducers increases the active area of the transducers in order to deliver a higher energy to a focus point at a relatively low near field intensity. This arrangement is a so-called Voronoi tiling of the respective ultrasound transducers. Voronoi tiling as such is known from. Voronoi, Georgy (1908). "Nouvelles applications des parametres continus a la theorie des formes quadratiques". Journal fur die Reine und Angewandte Mathematik 133 (133): 97-178. In a Voronoi tiling a plane is partitioned into convex polygons 61 such that each polygon contains only one generating point and every point in a polygon is closer to the generating point of that polygon than a generating point of any other polygon. This Voronoi diagram is also known as Dirichlet tessellation.

The advantage of this arrangement of the ultrasound transducers with such a Voronoi tiling is that a large active area of the transducers, about 80% of the surface of the base, can be obtained. This arrangement further contributes to a low Near Field Density of the ultrasound waves. Furthermore, a closed solution for any diameter and number of ultrasound transducer elements is possible in computer simulation of the design using the Rayleigh equations.

A further advantage is that transducers can have a substantially equal size. The substantially equal size has advantages in operating the transducers as the respective transducers elements have about the same capacitance and adjustments for each of the multi-channel ultrasound driver can be about the same.

In a further embodiment of the HIFU apparatus the controller of the HIFU apparatus generate signals for the driver system 6 to generate amplitudes and phase of driving signals to the ultra-sound transducers 5 to generate and receive ultra-sound waves for imaging the part of the body to be subjected to the HIFU ultrasound waves and to display the obtained ultrasound images on the LCD monitor for guidance of the HIFU beams and the ablation procedure.

Fig. 7 shows pressure distribution diagram 71, 72 for comparison between the performance of the HIFU apparatus according to the second embodiment and a conventional HIFU apparatus. Fig 7 shows an X-Z pressure distribution diagram 71 of a sample object, for example, an 8 mm ablation cell, in an X, Z plane perpendicular to the Y-axis and with its origin coinciding with the focus of ultrasound waves generated by the conventional HIFU apparatus. Furthermore, Fig 7 shows an X, Z pressure distribution diagram 72 of a sample object, for example, an 8 mm ablation cell, in the X, Z plane and with its origin coinciding with the focus of ultrasound waves generated by the HIFU apparatus according to the second embodiment of the invention.

A comparison between the pressure distribution diagrams 71,72 shows that the pressure distribution diagram 72 generated by the HIFU apparatus according to the second embodiments shows reduced local pressure maxima outside the focus, whereas the pressure distribution diagram 71 of the conventional apparatus shows multiple local maxima left and right from the focus area.

Fig. 8 shows temperature distribution diagrams 81,82,83,84 for comparison between the performance of the HIFU apparatus according to the second embodiment of the invention and conventional HIFU apparatus. Fig. 8 shows an X, Z-temperature distribution diagram 81 of a sample object, for example, an 8 mm ablation cell, in the X, Z plane perpendicular to the Y-axis and with its origin coinciding with the focus of ultrasound waves generated by the conventional HIFU apparatus. Furthermore, Fig 8 shows an X, Z-temperature distribution diagram 82 of a sample object, for example, an 8 mm ablation cell, in the X, Z plane and with its origin coinciding with the focus of ultrasound waves generated by the HIFU apparatus according to the second

embodiment of the invention.

Furthermore, Fig. 8 shows an X, Y temperature distribution diagram 83 of an 8 mm ablation cell in the X, Y plane perpendicular to the focal axis and with its origin at the focus of the ultrasound waves generated by the conventional HIFU apparatus.

Fig8 also shows an X, Y temperature distribution diagram 84 of a similar object in an X, Y plane perpendicular to the focal axis and with its origin on the focus generated by ultrasound waves generated by the HIFU apparatus according to the second embodiment for the same object.

When the X, Z temperature distribution diagrams 81 and 82 are compared the temperature distribution in a focal volume near the focus generated by the different HIFU apparatus are rather uniform and about the same size, however the temperature distribution generated by the HIFU apparatus according to second embodiment of the invention shows an improved uniformity outside the focus area. When the X, Y temperature distribution diagrams 83 and 84 are compared, the temperature distribution of the ablation cell obtained with the HIFU-apparatus according to the second embodiment is more uniform and does not show large variations compared with the temperature distribution of the ablation cell obtained with the conventional HIFU-apparatus. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims, In the claims the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

The invention is summarized as a High energy focused ultrasound, HIFU, apparatus for delivering high energy focused ultrasound to an object. For example a human body. The apparatus can be applied in ablasive procedures. The apparatus comprises a base and multiple transducers of a predetermined shape, wherein the transducers of a predetermined shape are arranged on the base, a driver system for driving the multiple transducers and a controller for generating signals to the driver system to generate the high energy focused ultrasound wherein the geometrical arrangement is obtained by a seed curve of which consecutive generating points correspond to locations of the respective transducers on the base surface.

The mere fact that certain measures are recited in mutually difference dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

High energy focused ultrasound apparatus for delivering high energy focused ultrasound to an object, the apparatus comprising a base and multiple transducers of a predetermined shape, wherein the transducers of a

predetermined shape are arranged on a base, a driver system arranged to drive the multiple transducers and a controller to generate signals to the driver system to generate the high energy focused ultrasound wherein the geometrical arrangement is obtained by a seed curve of which consecutive generating points correspond to locations of the respective transducers on the base surface.

High energy focused ultrasound apparatus according to claim 1, wherein the seed-curve is determined by a Fermat spiral, and respective locations of the respective transducers correspond to consecutive generating points of the Fermat spiral.

High energy focused ultrasound apparatus according to claim 1, wherein a start point of the seed-curve is at a center of the base surface.

High energy focused ultrasound apparatus according to claim 1 or 2, wherein the areas of the multiple transducers on the base surface are substantially uniform.

High energy focused ultrasound apparatus according to any of the claims 1 to 4, wherein the base surface is a spherical surface.

High energy focused ultrasound apparatus according to any of the claims 1 to 5, wherein the areas of the multiple transducers are circular.

High energy focused ultrasound apparatus according to any of the claims 1 to 5, wherein the respective shape of the respective areas of the transducers are conforming convex polygons comprising the respective generating points, determined such that a point in one of the convex polygons is closer to the generating point of the one polygon than to any other generating points of the other convex polygons.

8. High energy focused ultrasound apparatus according to any of the claims 1 to 7, wherein the transducers comprises a first and second electrode and a piezoelectric material provided between the first and second electrode.

9. High energy focused ultrasound apparatus according to claim 8, wherein the first electrode of the transducers is integrated in a common electrode provided in the base surface.

10. High energy focused ultrasound apparatus according to claim 8 or 9, wherein the second electrodes of the respective transducers are arranged to define the areas of respective transducers.

11. High energy focused ultrasound apparatus according to any of the preceding claims wherein the controller of the HIFU apparatus is further arranged to generate signals for the driver system 6 to generate amplitudes and phase of driving signals to the ultra-sound transducers 5 to generate ultra-sound waves for imaging the part of the body to be subjected to the HIFU ultrasound waves and to receive reflected ultrasound waves and to convert the received acoustic waves in to image signals and display the obtained ultrasound signals on the LCD monitor for guidance of the HIFU beams and the ablation procedure.

12. High energy focused ultrasound apparatus according to any of the claims 1 to 10, wherein the high energy ultrasound apparatus comprises an ultrasound imaging transducer arranged at the base.