The present invention relates to the technical area of high-intensity focused ultrasound (HIFU) and more precisely focuses on therapeutic treatment by such focused ultrasound.
It is known that therapy by focused ultrasound creates biological lesions in tissue resulting from a combination of thermal effects and acoustic cavitation activity. The form of these tissue lesions comes directly from the profile of the applied ultrasound field. Therefore, for example in the case of a transducer of spherical form, tissue lesions are substantially elliptical while being centred on the focal point.
For some applications, there is the need to form tissue lesions in crown form. For example, a tissue lesion in crown form can surround a tumor in order to isolate it, on a vascular plane, and cause its necrosis. Similarly, a lesion in crown form can be made on the periphery of a vein or an artery at the junction site with an organ.
The prior art has proposed various treatment probes by focused ultrasound with a view to obtaining biological lesions in crown form.
The document US 2006/009 753 describes therapy apparatus whereof the treatment probe comprises a cylindrical transducer of ultrasound waves emission focused by means of a reflector of conical shape. Such therapy apparatus is not easy to manufacture. In addition, the focusing obtained with a reflector is less effective than focusing coming directly from the geometry of the transducer.
Similarly, the document “Local hyperthermia with MR-guided focused ultrasound: Spiral trajectory of the focal point-optimized temperature uniformity in the target region” Journal of Magnetic Resonance Imaging 12: 571-583 (published in 2000) describes therapy apparatus comprising a multi-element transducer of spherical geometry. This document describes the creating of a set of biological lesions following a trajectory in the form of a spiral (in this sense approaching a crown) enclosing the volume to be destroyed, such as a tumor for example. This trajectory is adopted with a view to obtaining a more homogeneous thermal dose in the volume to be destroyed. However, such apparatus enables formation of biological lesions in crown form only by repetition and spatial juxtaposition of elementary lesions.
Patent application EP 0 421 290 describes a transducer of spherical shape at the centre of which a plane inactive zone is arranged. The effect of such construction is to modify the focusing profile of the ultrasound waves to obtain, when the diameter of the plane inactive surface is sufficiently large, a focal patch of conical form in which the maximum pressure is always centred on the axis of symmetry of the transducer and not on a peripheral crown.
In an attempt to resolve this problem, patent application EP 0 421 290 proposes cutting a transducer of geometry spherical into several sectors which are spread apart from one another or turned with a certain angulation to separate the focusing points and place them at a distance from the axis of symmetry of the transducers. It is clear that this mechanical construction is relatively complicated to do and difficult to control. In addition, per construction, the number and position of the focal points are fixed, considerably limiting treatment possibilities.
In general, it should be noted that it is always possible to synthesise an annular focal patch from a multi-element transducer of spherical shape since each ultrasound element has a size of less than a demi-wavelength. Since the wavelength is very small relative to the size of the transducer, this solution cannot be employed in practice without attracting a very large number of ultrasound elements and the technical problems and costs associated with this large number of ultrasound elements.
By way of complement, it must be considered that the treated volume depends on different parameters, in particular including the exposure duration and temporal and spatial spacing between the ultrasound shots. When these parameters are correctly defined, the treated volume remains restrained to the focal zone of the emitting surface, allowing this technique to be used as a barely invasive surgery instrument.
For treating larger volumes it is known to shift the focal zone. The first technique consists of mechanically moving the ultrasound emitter between each ultrasound exposure. A second known technique consists of electronically moving the focal zone by exciting the emitters with a delay law.
Currently, it must be considered that treatments by focused ultrasound are to date mainly conducted using pause times between the ultrasound exposures to allow cooling of the tissue and ultrasound emitters. This results in a relatively large increase in the length of treatment. In addition, the cavitation and thermal reheating activity are not maintained in the treatment zone during the pause time, which attenuates the efficacy of the treatment.
In the prior art, it has been proposed to execute continuous ultrasound shots during which the ultrasound emitters and the intermediary tissue are permanently stressed, creating a risk of destruction of the ultrasound emitters and burning of the tissue, such as interface lesions or superficial burns, outside the target zone.
The aim of the invention is thus to rectify the disadvantages of the prior art by proposing novel therapy apparatus conceived to focus ultrasound waves according to a crown and/or in focal volumes distributed according to a crown, the number and position of the focal volumes being able to be regulated simply and non-limiting as a function of the tissue lesion to be produced, the operation of this apparatus maintaining continuous heating of the tissue in the treatment zone, while protecting the tissue located on the acoustic path outside the treatment zone.
To attain such an aim, the object of the invention is to propose therapy apparatus for the treatment of tissue by emission of focused ultrasound waves.
According to the invention, the apparatus comprises:
According to a preferred embodiment, the ultrasound elements are distributed over an emission face of focused ultrasound waves having a revolution surface engendered by rotation about an axis of symmetry, of a segment of a concave or convex curve of given length having a centre of curve located at a distance from the axis of symmetry, with R≠0.
According to a preferred variant embodiment, the revolution surface is engendered by a segment of an arc of a circle of given length, of given radius and with a centre located at a distance of the axis of symmetry with this distance≠0.
According to another variant embodiment, the distance of the centre of the segment of an arc of a circle from the axis of symmetry is less than the radius of the arc of a circle.
Advantageously, the revolution surface delimits in its central region an opening centred on the axis of symmetry and adapted to receive an imaging transducer.
According to an advantageous characteristic of the subject matter of the invention, the categories of ultrasound emitters correspond either to concentric rings, or to radial sectors, or to radial groups of ultrasound emitters.
According to a first variant embodiment, the ultrasound emitters are distributed according to concentric rings and in that the control circuit comprises a signal generator controlled to deliver signals to activate the ultrasound emitters of each of said concentric rings, with a delay or phase law for ensuring shifting of the focusing crown according to the focusing axis.
According to another embodiment, the ultrasound emitters are distributed into radial sectors and in that the control circuit comprises a signal generator controlled to deliver signals to activate the ultrasound emitters of each of said radial sectors, with a delay or phase law for ensuring shifting of the focusing crown.
According to a preferred variant embodiment, the ultrasound emitters are distributed into concentric rings, divided into radial sectors and the control circuit comprises a signal generator controlled to deliver signals to activate the ultrasound emitters of each of said radial sectors, with a delay or phase law for ensuring shifting of the focusing crown.
Advantageously, the radial sectors of ultrasound emitters are combined to form radial groups and in that the control circuit comprises a signal generator controlled to deliver signals to activate the ultrasound emitters of each of said radial groups.
The control circuit preferably comprises a signal generator controlled to deliver for each radial group, signals to activate the ultrasound emitters of each of the radial groups, with a delay or phase law.
Advantageously, the control circuit comprises a signal generator controlled to deliver signals to activate according to a sequence which varies or which repeats cyclically, a category of ultrasound emitters corresponding either to a ring, a sector or a radial group of ultrasound emitters.
The control circuit preferably comprises a signal generator controlled to deliver signals to activate assemblies of categories of ultrasound emitters composed either of distinct categories of ultrasound emitters or categories whereof at least some are common to the assemblies.
Other subject matter of the invention focuses on decreasing the number of connection cables of the ultrasound emitters. To this effect, the radial groups form identical assemblies of ultrasound emitters and the control circuit is connected to the ultrasound emitters by means of coaxial cables, whereof on the one hand, the cores of all the ultrasound emitters of the same row in the different radial groups are connected together and, on the other hand, the grounds of all the ultrasound emitters of the same radial group are connected to one another, the signal to activate the ultrasound emitters being converted into ultrasound energy solely by the ultrasound emitters of the radial groups whereof the grounds are physically connected to the ground of the activation signal.
Various other characteristics will emerge from the following description in reference to the attached drawings which show, by way of non-limiting examples, embodiments of the subject matter of the invention.
As will emerge more clearly from
The transducer 2 has an emission face 8 of focused ultrasound waves. According to a preferred exemplary embodiment illustrated more particularly in
According to a first preferred variant embodiment illustrated in
According to a preferred variant embodiment illustrated in
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According to the exemplary embodiments illustrated in
As will become clear from the above description, the emission face 8 of the transducer is of toric geometry. In general, the emission face 8 of the transducer has a form which is a function of the geometry of the segment of a curve engendering the emitting surface of ultrasounds by rotation about an axis of symmetry, the segment of a curve being able to have various shapes.
According to another characteristic of the invention, the ultrasound emitters 3 are organised on the emission face 8 so as to be distributed into several categories N1 to NM each defining a point, a patch, a zone or generally a focal volume or a focusing volume. As will become clear from the remainder of the description, the focal volumes are independent and substantially contiguous.
According to a variant embodiment, the control circuit 7 delivers signals to activate the ultrasound emitters 3 of the concentric rings a1 to ai; with a delay or phase law for ensuring shifting of the focusing crown according to the focusing axis A. The control circuit 7 thus executes dynamic electronic focusing so as to shift the crown focal from its natural position C0 to a distal position C1 and a proximal position C2. Each focusing crown C1, C2 is positioned in the space by the focal distance respectively F1, F2 and its radius respectively R1, R2. Such configuration adapts to treatment of tumors of different sizes and situated at different depths in the tissue.
It should also be noted that
The control circuit 7 is adapted to deliver signals to the ultrasound emitters of the radial groups as described hereinabove. The ultrasound emitters of each radial group are activated so as to concentrate the energy into a single focal volume. This focusing corresponds in the example illustrated to that obtained with a group of spherical shape even though the group has come from toric geometry. It is thus possible to concentrate the energy distributed on a focal crown in as many distinct focal volumes E as groups of ultrasound emitters G1 to Gk. This concentration for example concentrates and reinforces tissue necrosis at one or more particular points of the tumor to be treated. It can also be envisaged to simultaneously form several local focal patches distributed on one focal crown.
According to another characteristic of the subject matter of the invention, the signal generator of the control circuit 7 is controlled to activate independently, alternatively and substantially consecutively the rings a1 to ai the radial sectors s1 to sj or the radial groups of ultrasound emitters G1 to Gk such as described hereinabove in
As emerges more clearly from
Contrary to dynamic focusing methods, it is to be considered that the ultrasound emitters of a category are activated independently and substantially consecutively from the ultrasound emitters of the other category. As is evident from the preceding description, the categories of ultrasound emitters N1 to Nm are activated alternatively, that is, successively or one after the other. As will be described in greater detail following the description, the categories of ultrasound emitters N1 to Nm are activated according to an order or a determined sequence, variable or not.
Advantageously and ideally, the ultrasound shot T2 of the category N2 is realised immediately following the ultrasound shot T1 of the category N1 without delay or advance. In practice, it must be considered that the control circuit 7 substantially consecutively activates the categories of the ultrasound emitters so as to ensure continuous insonification in the focusing zone. In fact, it proves that the instrumentation employed can in practice cause discontinuity or recovery between the shots. It is considered that a shot T2 of a category N2 is substantially consecutive to a shot T1 of a category N1 if the delay time taken between the end of the shot T1 and the start of the shot T2 is not sufficient to lose the benefit of the cavitation and thermal heating activities of the preceding shots. Similarly, two shots T1 and T2 are considered substantially consecutive if the recovery time between these shots is sufficiently short not to produce burning of the tissue.
As is evident from
Distribution of the ultrasound emitters into different categories continuously applies on the same focal volume the thermal dose necessary for destruction of this volume from several distinct categories excited sequentially and each acting in an independent and substantially contiguous focal volume.
It is thus possible to continuously treat lesions having a large volume, without stressing the same elements at each ultrasound shot. To the extent where each category contains several ultrasound emitters, it is possible to combine this treatment principle with electronic focusing, as described hereinabove. The ultrasound emitters of each category are then activated with a delay or phase law for ensuring electronic shifting of the treatment zone. It must be understood that this delay or phase law is applied solely for the ultrasound emitters belonging to the same category. In other terms, there is no electronic focusing between the different categories. Of course, it can be feasible to ensure mechanical shifting of the ultrasound emitters.
Although the target zone is heated continuously, the tissue located between the ultrasound emitters and the treatment zone receives ultrasounds only sequentially, which produces their cooling. In fact, the tissue located on the acoustic path is exposed to the ultrasound emitted by each category solely when the latter is activated. Also, reheating the ultrasound emitters of each category is controlled by their sequential activation. The ultrasound emitters of a category are cooled during activation of a following category.
The ultrasound emitters can be activated in different ways. Therefore, the control circuit 7 can deliver signals to activate the categories of ultrasound emitters according to a sequence which repeats cyclically. For example, the categories N1, N2, N3, N4 are activated one after the other, and this activation sequence N1, N2, N3, N4 is repeated over time.
Naturally, it can be provided that the activation sequence varies over time. For example, during the first sequence, the categories N1 to N4 are sequentially activated in the order N1 to N4, whereas during the following sequence, the categories are activated sequentially in the following order: N1, N3, N2, N4.
According to another possible variant, the control circuit 7 delivers signals to activate assemblies of categories of ultrasound emitters composed of distinct categories of ultrasound emitters. Therefore, sequential group activation can be envisaged for the categories for example N1-N2, N3-N4. In other words, the ultrasound emitters of the categories N1 and N2 are activated simultaneously, then those of the categories N3-N4. This sequential group activation can be done cyclically (N1-N2, N3-N4, N1-N2, N3-N4 . . . ) or be modified in the following form, for example (N1-N2, N3-N4, N1-N4, N2-N3 . . . ).
According to another variant embodiment, the control circuit 7 delivers signals to activate assemblies of categories of ultrasound emitters composed of categories, at least some of which are common to all assemblies. Such a variant is advantageously employed by a transducer comprising a large number of categories Ni. Group activation of the categories N1-N2-N3-N4 can thus be envisaged, then of categories N4-N5-N6-N7, then of groups N7-N8-N9-N10, etc. According to this example, there is recovery of the categories equal to 25%. The recovery surface must be sufficiently small so as not to produce, during consecutive shots, burning of the tissue located between the ultrasound emitters of the recovery zones and the focusing zone.
The subject matter of the invention is applied particularly advantageously in all treatments by focused ultrasound, in particular treatment of cancer of the prostate and treatment of liver tumors.
According to another advantageous characteristic, the subject matter of the invention aims at decreasing the number of coaxial connection cables between the ultrasound emitters 3 and the control circuit 7. To reduce the number of cables it is proposed to execute switching of the electrical grounds of the ultrasound emitters 3 in order to substantially decrease the number of coaxial cables necessary, as well as the need for control electronics (signal generator and power amplifier).
As is more evident from
The invention is not limited to the examples described and illustrated, as various modifications can be made without departing from its scope.
Number | Date | Country | Kind |
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0652813 | Jul 2006 | FR | national |
0652816 | Jul 2006 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR07/51601 | 7/5/2007 | WO | 00 | 4/10/2009 |