Abstract:
An endoscopic device for generating acoustic waves with a sheath defining a center axis contains a first transducer for generating a first beam of acoustic energy radiating outwards of the endoscope sheath and a second transducer for generating a second beam of acoustic energy radiating outwards of the endoscope sheath. Both beams have different directions and intersect outside of the endoscope forming a focus spot. The second transducer is linearly movable parallel to the center axis with respect to the first transducer to displace the second beam and therefore to displace the intersection of the beams and therefore of the focus spot.

Description:
PRIORITY CLAIM 
     This application claims priority to pending European Application No. 12191867.6 filed on 8, Nov. 2012. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the ablation of pathological tissues, such as tumors, or nodules, through a precise local heating. This is done by applying physical energy radiation e.g. by acoustic waves into the targeted tissue, which is converted into heat therein. As soon as the temperature reaches a certain level of about 80° C., tissue is coagulated and a necrosis develops. 
     2. Description of Related Art 
     For a non-invasive treatment, in the U.S. Pat. No. 6,379,320 B1 a focused ultrasound source is provided in the tip of an endoscope for radiating radially. The focus spot cannot be adjusted; therefore, the endoscope must be brought close to the region to be treated, which is often not possible. 
     An endoscope with integrated ultrasound source is disclosed in DE 44 43 947 A1. For generating an ultrasound wave, which is focused at a variable distance, a large number of phased-array transducer elements are provided which are driven by individual oscillators. This requires complex electronics, and the power output of the transducer is limited due to acoustic crosstalk between the individual transducer elements 
     The US patent application publication US 2003/0004439 A1 discloses and intrabody HIFU (High Intensity Focused Ultrasound) applicator, which uses a plurality of ultrasound transducers mounted on a flexible holder. These transducers are transported by an endoscope into the body, but operated outside of the endoscope. Therefore, a significant amount of space is required within the body, which severely limits the application range of this instrument 
     SUMMARY OF THE INVENTION 
     The embodiments are based on the object of providing an endoscopic HIFU ultrasound applicator, which delivers a high acoustic energy level, has an adjustable focus spot and can be kept within an endoscope 
     In an embodiment, acoustic energy is delivered by at least two radiation emitters within an endoscope, whereby at least one radiation emitter is linearly movable relative to another radiation emitter. Both emitters are radiating under different angles into the same direction having an intersection under an intersecting angle outside the endoscope. This intersection defines the focus spot of the ultrasound applicator. By moving at least one radiation emitter, the position of the intersection and therefore the focus spot moves. To achieve a good absorption of the acoustic energy in tissue, preferably a frequency in the range between one and 10 MHz is selected. Due to the invention, the focus spot can be moved and adapted to actual requirements. It may be anywhere between the surface of the endoscope and deep within the surrounding tissue. The maximum depth that may be up to 40 mm. By means of an actuating element like a wire or even a motor or any other actuator, the focus point may be adjusted during treatment. By using a moving focus spot, a certain area of the tissue may be scanned to treat a larger volume. Such a scanning may also be done automatically or at least controlled by a control unit like a computer. Generally, the position of the focus spot may be dynamically controlled by such a control unit and adapted to a predefined and/or required area. For this purpose, the control unit may be connected to an ultrasound and/or x-ray imaging system. 
     Herein, generally reference is made to an endoscope. It is understood that the invention may also be applied to any kind of similar instruments like a laparoscope, a catheter, or any intraluminal or interstitial probe, which are referred herein also under the term of ‘endoscope’. 
     Furthermore, reference is made to emitters, which may be any kind of acoustic energy sources like any kind of ultrasonic transducers, e.g. Piezo transducers, capacitive or piezoelectric micromachined ultrasound transducers (cMUTS and pMUTS), piezocomposite transducers, shockwave transducers. An emitter is an active device and is no reflector like a mirror for reflecting acoustic energy generated by a transducer, nor a deflecting element like a prism. 
     In a first embodiment of the invention, two emitters are provided. A first emitter preferably radiates radially outwards of the endoscope. A second emitter is linearly movable with respect to the first emitter, preferably along the center axis of the endoscope. The beams of radiation of the first emitter and the second emitter are intersecting outside of the endoscope and forming the focus spot. Preferably, the first and the second emitters are transducers. 
     In a second embodiment, at least one of the emitters is a reflector, while the other emitter is a transducer. Acoustic energy is generated by a transducer directed to the at least one reflector, which diverts the radiation energy outside the endoscope. 
     It is further preferred, if there is a cover, which most preferably is of elastic material, for closing an opening within the endoscope sheath over the emitters to allow unattenuated radiation of acoustic energy to the outside of the endoscope. It is further preferred, if an inner volume under the cover is filled with a preferably non or low-absorbing acoustic fluid. 
     In a further embodiment of the invention an imaging device, like ultrasound transducer, optical system or elastographic system may be provided within the endoscope. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment and with reference to the drawings. 
         FIG. 1  shows a first embodiment of an endoscopic device for generating acoustic waves. 
         FIG. 2  shows the basic function. 
         FIG. 3  shows another embodiment with modified emitters. 
         FIG. 4  shows a further embodiment with a reflector. 
         FIG. 5  shows an embodiment with two movable and one stationary emitters. 
         FIG. 6  shows an embodiment with two movable emitters. 
         FIG. 7  shows an endoscope. 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , a first embodiment of an endoscopic device for generating acoustic waves is shown. A first transducer  40  and a second transducer  30  are contained within an endoscope sheath  10 , having an opening to allow the exit of acoustic energy to an outside of the endoscope. The first transducer  40  generates a first beam  51  of acoustic energy, which preferably exits the endoscope under a predetermined angle, preferably under a right angle to the center axis  16  of the endoscope. The second transducer  30  generates a second beam  50  of acoustic energy, which preferably exits the endoscope under an angle different to the exit angle of the first transducer. The first beam  51  and the second beam  50  intersect under an intersecting angle  53  outside of the endoscope at an intersecting point  60 , also referred as focus spot. Preferably, the second transducer  30  is mounted to a first slider  20 , which may be moved in the direction  17  of the center axis  16  of the endoscope. The slider may contain at least one conduit  21  for liquids and/or electrical lines. There may be a cover  11  covering the opening of the endoscope sheath  10  and further enclosing an inner volume  14 , which preferably is filled with an acoustic coupling fluid. Preferably there is at least one sealing  12  for sealing the inner volume at a gap of movement of the first slider  20  against the endoscope sheath  10 . When moving the first slider  20 , the inner volume  14  changes. Accordingly acoustic fluid must be filled in or removed, which may be done through the at least one conduit  21 . The cover  11  may also be an elastic cover, which may extend or shrink, when the first slider  20  is moved. 
     In  FIG. 2 , the basic function of the endoscope device is shown. The first slider  20  as shown in the previous figure may be moved to second position  22 , which is more distant from the first transducer  40  than the first position. From the second position, it radiates a second beam  55  of acoustic energy, basically under the same angle as from the first position. The second beam  55  is intersecting with the first beam  51  of the first transducer under a second intersecting angle  56  resulting in the second focus spot  61 . As there was only a linear displacement of the second transducer, the second beam  55  from the second position is parallel to the second beam  50  from the first position. Consequently the second intersecting angle  56  is the same or approximately the same as the first intersecting angle  53 . The second focus spot  61  has moved outward from the first focus spot  60 . Accordingly, a linear movement of the second transducer  30  by moving the slider  20  results in a preferably radial displacement of the focus spot. The focus spot may also be moved by moving the first transducer and keeping the second transducer fixed or even by moving both transducers. When moving the first transducer, the focus spot not only moves radially, but it also moves laterally in the direction of the center axis  16 . 
     In  FIG. 3 , another embodiment with modified radiation sources is shown. Here the radiation sources  40  and  30  are focused transducers emitting narrower beams  51  and  50  resulting in a smaller focus spot  60 . Here the energy density at the surface of the endoscope defined by the cover  11  is comparatively low and prevents unwanted effects like coagulation of the tissue at the surface of the endoscope. 
     In  FIG. 4 , a further embodiment with a mirror is shown. Herein the second emitter is a reflector  32 . The acoustic energy is generated by a transducer  31 , which may be located in the end section  13  of the endoscope. This transducer  31  radiates acoustic energy towards the reflector  32  which itself deflects the acoustic energy into a second beam  50  to form a focus spot  60  together with a first beam  51 . The basic function is the same, as if there would be a transducer  30  instead of the reflector  32 . 
     In  FIG. 5 , an embodiment with two movable radiation sources is shown. This embodiment is based on the previous embodiments. Furthermore, a third transducer  70  has been added. This first transducer  70  generates a third beam  52  intersecting first beam  51  under a third intersecting angle  54 . The focus spot accumulates the energy of all three beams  50 ,  51 ,  52 . The first transducer  70  may be supported by a second slider  25 , which may also be moved parallel to the center axis  16  of the endoscope. This second slider may be moved for the same amount, but in the opposite direction of the first slider to keep a small focus spot. It may also be used independently of the first slider to form a variable and/or increased focus spot. 
     In  FIG. 6 , a similar embodiment, but without the stationary emitter  40  is shown. This embodiment permits to adjust the position of the focus spot not only radially but also in the whole z-x plane. Here, the first slider  20  may be moved into first directions  17 , preferably by a first drive means  80  and preferably parallel to the center axis  16  as shown by the arrow  17 . Furthermore, the second slider  25  may be moved into second directions  18 , preferably by a second drive means  81  and preferably parallel to the center axis  16  as shown by the arrow  18 . Such a drive means may be a linear motor preferably having at least one coil and/or at least one permanent magnet. It may also be a drive wire, driven by an external motor or hand operated. If the first and second sliders  20  and  25  are moved in opposite directions and of the same quantity, the focus spot moves in the radial direction  63 . If the first and second sliders  20  and  25  are moved in the same direction and of the same quantity, the focus spot moves laterally in the direction  62 . When moving only one slider, the focus spot not only moves radially, but it also moves laterally. 
     In  FIG. 7 , an endoscope is shown. The endoscope has a sheath  10  defining a center axis  16 . There is a proximal end having a handle  15  and a distal end bearing the transducers, which are covered by a cover  11 . 
     It will be appreciated to those skilled in the art having the benefit of this disclosure that this invention is believed to provide endoscopic devices for generating acoustic waves. Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims. 
     LIST OF REFERENCE NUMERALS 
     
         
           10  endoscope sheath 
           11  cover 
           12  ceiling 
           13  end section 
           15  handle 
           14  inner volume 
           16  center axis 
           17  direction of movement 
           18  second direction of movement 
           20  first slider 
           21  conduits 
           22  second position of first slider 
           25  second slider 
           30  second emitter 
           31  transducer 
           32  reflector 
           40  first emitter 
           50  second beam 
           51  first beam 
           52  third beam 
           53  first intersecting angle 
           54  first intersecting angle 
           55  second beam from second position 
           56  second intersecting angle 
           60  focus spot 
           61  second focus spot 
           62  movement of focus spot parallel to x-axis 
           63  movement of focus spot parallel to y-axis 
           70  third emitter 
           80  first drive means 
           81  second drive means