Device for non-invasive treatment of biological tissue

Abstract: The present invention relates to a device for non-invasive treatment of biological tissue, whereby the treatment aim at changing or degenerating said tissue. This device has a treatment transducer (2) comprising at least one ultrasonic transducer (3 and/or 4) which is provided to treat intervertebral discs (1), preferably nucleus pulposus (1a), by means of ultrasound, whereby the ultrasonic field of the ultrasonic transducer (3 and/or 4) is focused in said intervertebral disc (1), preferably in nucleus pulposus (1a), for heating the tissue therein, to such temperatures that the tissue in the focal area (5) degenerates, whereby the pressure in the intervertebral disc (1) and thus, the pressure against the spinal cord (6) is reduced.

Description: The present invention relates to a device for non-invasive treatment of biological tissue, whereby the treatment aim at changing or degenerating said tissue. The lifetime prevalence of sciatica is 40 percent and 1-2 percent of the population will develop nerve compression by a lumbar disc herniation requiring invasive (surgical) treatment, usually during the fourth and fifth decades of life. Surgical removal of discal hernia, discectomy, has been performed for almost seven decades. The diagnostic procedures going from myelography using oil to nonionic contrastmedia over to computerized tomography (CT) and magnetic resonance imaging (MRI) has led to a rapid increase of the number of spinal operations based on diversity of surgical procedures. There are four necessary prerequisites for intervention of disc herniation: a/ functionally incapacitating pain in the leg extending below the knee with a nerve root distribution, b/ nerve root tension signs with or without neurological abnormalities, c/ failure of clinical improvement after four to eight weeks, d/ diagnostic confirmation (e.g. through imaging study). The introduction of non-surgical or minimal invasive surgical procedures started 1964 with chymopapain and chemonucleolysis which brought about the era of percutaneous treatment for herniated discs. The clinical success of chymopapain with good results in 60-75 percent led to an extensive use. Unfortunately, it had an anaplylaxis rate estimated to be about 1 percent. The enzyme polymerizes the long chains of proteoglycans in the nucleus pulposus with subsequent loss or water binding capacity. This causes reduction in the volume and pressure of the nucleus and the herniated fragment, eventually explaining the immediate relief of sciatica in patients following chemanucleolysis. Most authors agree that relief of leg pain after chymopapain is less frequent than after surgery. Several new methods using percutaneous techniques have evolved since 1975, using endoscopic equipment and recently also non-endoscopic technique with an automated percutaneous suction of tissue by means of a probe. Recently, laser (electromagnetic) radiation created by external stimulation of a laser medium, has been used. For directing the laser radiation to the treatment area however, a probe is required, i.e. the method is invasive. All these methods are to a certain extent invasive (require surgical operations) and problems such as disc infection and nerve root injury are encountered although less frequently than after open surgery. The intervertebral disc is comparable to other non-vascularized biological tissue. It has a central nucleus pulposus with a gelatinous character and a surrounding stiffer anulus. The matrix in the disc includes several proteins with different rates of turn over and energy demand. There is today no non-invasive treatment that will affect the disc in such a manner that it will reduce its volume and pressure in the nucleus and thereby possibly diminish a discal hernia. Attempts to achieve tissue degeneration with high intensity focused ultrasound (HIFU) have been going on for several years in cancer research projects (Bush 1993, Billard 1990, Lele 1980, Linke 1973, Sibille 1993). The advantage of ultrasound as a generator of energy, compared to e.g. electromagnetic fields, is that ultrasound is a non-invasive method to generate tissue heating at depths. Focusing of the ultrasound and placing the focus inside the tissue to be treated, makes the heating effect to develop at the desired location instead of at the skin and the tissue in between (Lele 1980). If the transducer surface is spherical, the transducer has a fixed focus (Lele 1980). It is also possible to achieve a flexible focus by means of phased array (Diederich 1991, Ebbini 1988, Ebbini 1991 and Holmer 198?). Prior art also includes a number of patent specifications relating to methods and devices wherein ultrasound is utilized for various therapeutic purposes without any type of surgical operations on the patient. One such patent specification is US-A-5 435 311 relating to an "ultrasound therapeutic system" for treatment of e.g. malignant tumours or various types of calculi such as gallstone, kidney stone, etc.. The device of US-A-4 787 394 relating to an "ultrasound therapy apparatus", has a similar purpose. Other devices and methods utilizing ultrasound for a corresponding therapeutic purpose, are described in e.g. US-A-5 327 884 and US-A-5 501 655. Similar tissue degeneration as with ultrasound can also be made with other methods, such as percutaneous laser discectomy and percutaneous radio-frequency coagulation by means of cauterizing instruments (Buchalt 1992, Troussier 1995), but these methods are invasive. The object of the present invention has been to provide a device for non-invasive treatment of back problems. This is arrived at according to the invention by providing a device with the features of claim 1. By providing the device with said features, it is possible to treat intervertebral discs, preferably nucleus pulposus, in a lenient manner, i.e. without degenerating tissue outside the intervertebral disc and this treatment can be carried through non-invasively, which means that one does not have to insert foreign objects into the body and obviates thereby the risks and additional costs this might incur. The invention will be further described below with reference to the accompanying drawings, in which fig. 1 schematically illustrates a device according to the invention during treatment of an intervertebral disc, whereby a treatment table is shown in cross-section; fig. 2 illustrates an enlarged part of the device of fig. 1; fig. 3 schematically illustrates a treatment transducer forming part of the device of fig. 1 and its ultrasonic field during treatment of the intervertebral disc; fig. 4 is a flow chart according to which the treatment of the intervertebral disc is carried through by means of the device according to the invention; and fig. 5 is a picture of an intervertebral disc treated with the device according to the invention. The device illustrated in the drawings is intended for treatment of biological tissues in the form of intervertebral discs 1, preferably nucleus pulposus 1a. For this purpose, the device comprises a treatment transducer 2 which includes two ultrasonic transducers 3 and 4 (so called therapeutic transducers). These are arranged to each transmit an ultrasonic field 3a and 4a respectively, such that these meet to define a focal area 5. During treatment, said focal area 5 is located in the intervertebral disc 1, preferably nucleus pulposus 1a, to be treated for heating the tissue therein to such temperature that the tissue in the focal area 5 degenerates, whereby the pressure in the intervertebral disc 1 and thus, the pressure against the spinal cord 6, is reduced. The ultrasonic transducers 3, 4 are provided to transmit ultrasonic fields 3a, 4a which to not heat biological tissue outside the focal area such that it degenerates. By using at least two ultrasonic transducers 3, 4, the ultrasound effect is distributed over larger areas and therefore, a lower power per transducer can be used. This results in that eventual heat increases in the skin are minimized for the power to be put in the intervertebral disc 1. The power and frequency of the ultrasonic fields 3a, 4a, the temperature of the tissue in the focal area 5 and the transmitting time of the ultrasonic fields 3a, 4a may vary depending on various factors, but the frequency should lie within the range of 0,5 - 2,5 MHz, the temperature of the tissue in the focal area within the range of 45-80°C and the total transmitting time of the ultrasonic fields 3a, 4a within the interval of 5-60 minutes. The ultrasonic transducers 3, 4 can be arranged to transmit ultrasonic fields 3a, 4a, the focal area 5 of which is adaptable relative to the space M between the end plates 7, 8 surrounded by the vertebrae 9, 10 and which surround the intervertebral disc 1, such that said focal area 5 can lie between the end plates 7, 8 without heating thereof to tissue-degenerating temperatures. A focal area 5 with such adapted extension can be obtained by providing the ultrasonic transducers 3 and 4 respectively, with means 11, preferably in the form of transducer elements with concave spherical transducer surface. Hereby, a larger or better focussing is achieved and the focal area 5 is given a substantially planar extension, as is shown in fig. 3. The ultrasonic transducers 3, 4 may also include means 12 for, if required, displacing the focal area 5, adapted preferably as mentioned to the space M between the end plates 7, 8, to the intervertebral disc 1, preferably nucleus pulposus 1a. These means 12 can be transducer elements of the phased array type. For being able to locate to focal area 5 in the intervertebral disc 1, preferably nucleus pulposus 1a, it may some-times - depending on the relative positions of the ultrasonic transducers 3, 4 and the intervertebral disc 1 - be advantageous or necessary to shrink or reduce the extention of one or both the ultrasonic fields 3a, 4a for avoiding heating of tissue outside the intervertebral disc 1 which may not be heated to tissue-degenerating temperatures. This can be achieved while the ultrasonic transducers 3, 4 have a plurality of means 12, preferably said transducers of phased array type, which momentarily can be deactivated or put out of operation for reducing the extension of the ultrasonic field 3a and/or 4a. The ultrasonic transducers 3, 4 can preferably be located relative to the intervertebral disc 1 so that they transmit ultrasonic fields 3a and 4a which together define a focal area 5 with a substantially planar extension and which are situated substantially in parallel with and in a plane P wherein the intervertebral disc 1 is located. The ultrasonic transducers 3, 4 can be arranged to transmit ultrasonic fields 3a, 4a with a focal area 5 the extension of which can be varied for adaptation to the size of the intervertebral disc 1 and/or nucleus pulposus 1a. A diagnostic device 13 may include at least one ultrasonic transducer 14 which is provided, prior to the ultrasound treatment, to transmit an ultrasonic field 14a for registrering the location of the intervertebral disc 1. The position of the ultrasonic transducers 3, 4 relative to the ultrasonic transducer 14 are also known and in this way, their positions relative to the intervertebral disc 1 can be determined. The ultrasonic transducers 3, 4 can be arranged to be controlled depending on information registered in the diagnostic device 13 regarding the current position of the intervertebral disc 1, preferably nucleus pulposus 1a, so that the focal area 5 is moved to coincide with the intervertebral disc 1, preferably nucleus pulposus 1a. The positions of the ultrasonic transducers 3, 4 can e.g. be controlled by changing their positions relative to their attachments. The control can be determined by a computer. Said control of the ultrasonic transducers 3, 4 can be carried through by means of a control device 15 either automatically or by a surgeon marking on a screen (not shown) a point/an area in nucleus pulposus 1a in which the focal area 5 is desired. A computer (not shown) can determine the necessary parameters in the ultrasonic transducers 3, 4 such that the focal area 5 becomes correct. A reading device 16 can be provided for registering displacements of the intervertebral disc 1 relative to the ultrasonic transducers 3 and 4 which occur when the patient moves during treatment. A setting device 17 can be provided to automatically control the ultrasonic transducers 3, 4 to set so that the focal area 5 again will lie in the intervertebral disc 1, preferably nucleus pulposus 1a, after said displacement. There might also be a non-invasive temperature-supervising device 18 for supervising the temperature in the intervertebral disc 1 during treatment. This temperature -supervising device 18 may cooperate with a control unit 19 which is provided to control the ultrasonic transducers 3, 4 such that undesired temperature changes in the intervertebral disc 1 are prevented during treatment. The temperature-supervising device 18 may cooperate with the ultrasonic transducer 14 of the diagnostic device 13 for supervising or monitoring the temperature in the intervertebral disc 1 by means of ultrasound. The ultrasonic transducers 3, 4 are preferably arranged obliquely behind the spine on opposite sides of the spinal cord 6, so that they can transmit their ultrasonic fields 3a, 4a in a direction beside said spinal cord 6 on opposite sides thereof and so that they meet in front thereof in order to together define the focal area 5 in the intervertebral disc 1, preferably nucleus pulposus 1a. During treatment, a treatment table 20 can be used, which has a support surface 21 for the patient 22. This support surface 21 can be curved or settable into a curved shape such that the space M between the vertebrae 9, 10 at the intervertebral disc 1 to be treated, increases when the patient 22 rests with his or her back against said support surface 21. The ultrasonic transducers 3, 4 and 14 can be mounted on a frame 23, whereby the mutual positions of said transducers 3, 4 and 14 can be known. Said frame 23 with the transducers 3, 4 and 14 is preferably displaceable relative to the treatment table 20 and the patient 22 for setting the transducers 3, 4 and 14 relative to an intervertebral disc 1, preferably nucleus pulposus 1a, to be treated, in a patient 22 on the treatment table 20. To avoid disturbances of the ultrasonic fields 3a, 4a transmitted by said transducers 3, 4 and 14, a gasvoid liquid in a liquid container 24 can be located between the transducers and the adjacent skin of the patient 22. Air between the transducers 3, 4 and 14, the liquid container 24 and adjacent skin can for the same purpose be removed by locating a gel 25 schematically illustrated with broken lines. Treatment by means of the device described above is shown in the flow chart of fig. 4, whereby the diagnosis is already made, i.e. it is already determined which intervertebral disc 1 should be treated. By means of the "ultrasound picture" obtained from the diagnostic device 13, the frame 23 and the patient 22 and eventually the ultrasonic transducers 3, 4 are oriented separately so that the angle of incidence of the therapeutic transducers 3, 4 is correct. Hereby, it is achieved that the ultrasonic fields 3a, 4a of the ultrasonic transducers 3, 4 lie in the same plane P as the intervertebral disc 1 to be treated, and so that the therapeutic transducers 3, 4 are directed towards the patient 22 from behind. On the abovementioned screen, a point in the nucleus pulposus 1a is marked in which the focal area 5 (a so called movable focus which is displaced by means of the abovementioned means 12) for the therapeutic transducers 3, 4 shall be located. A computer then establish the requirements for the various transducer elements in the therapeutic transducers 3, 4. Eventually, adjacent bones can be marked as zones which the ultrasonic fields 3a, 4a are not allowed to reach. Said computer may e.g. deactivate the transducer elements which are closest and reduces thereby the size of the ultrasonic field 3a or 4a in question. This reduction of the ultrasonic field 3a and/or 4a can be compensated with a longer treatment time and/or treatment effect. The "fixed focus" mentioned in the flow chart is the focal area obtained by means of the abovementioned means 11. It should also be mentioned that instead of ultrasonic transducers, other therapeutic and/or diagnostic transducers, transmitters or applicators, e.g. transducers or transmitters of electromagnetic radiation, can be used in the device described above. Drugs can be used in connection with and/or after treatment with the abovementioned device, namely pressure reducing/volume decreasing drugs, e.g. steroids or corticon™, and/or dehydrating drugs, e.g. impugan™, and/or antiinflammatory drugs, e.g. voltaren™. By means of the pressure reducing/volume decreasing drugs, it is possible, in connection with and/or after treatment with ultrasound, to improve the pressure reduction/volume decrease in nucleus pulposus obtained thereby. By means of the dehydrating drugs, it is possible to improve the removal of fluid from the treatment area in connection with and/or after treatment with ultrasound. By means of said antiinflammatory drugs, it is possible to oppose inflammations in the treatment area in connection with and/or after treatment with ultrasound. The invention is not limited to the device described above and illustrated in the drawings, but may vary within the scope of the following claims. Thus, the diagnostic device 13 can operate with something else than ultrasound. Instead of the patient 22 lying on his back on a treatment table 20, whereby the treatment equipment is situated beneath his or her back, the patient 22 and treatment equipment can be positioned otherwise. Thus, the patient 22 can e.g. be lying on his or her face and the treatment equipment be mounted on an arm permitting location thereof in a treatment position. REFERENCES Billard BE, Hynynen K and Roemer R B, 1990, Effects of physical parameters on high temperature ultrasound hyperhtermia . Ultrasound in Med. & Biol., 16 (4), 409-420 Buchelt M, Kutschera H-P, Katterschafka T, Kiss H, Schneider B and Ullrich R, 1992, Erb.YAG and Hol.YAG Laser Ablation of Meniscus and Intervertebral discs . Lasers in Surgery and Medicine, 12, 375-381 Bush N L, Rivens I, ter Haar G R and Bamber J C, 1993, Acoustic properties of lesions generated with an ultrasound therapy system . Ultrasound in Med & Biol, 19 (9), 789-801 Diederich C J and Hynynen K, 1991, The feasibility of using electrically focused ultrasound arrays to induce deep hyperthermia via body cavities . IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 38 (3), 207-219 Ebbini E S and Cain C A, 1991, A Spherical-Section Ultrasound Phased Array Applicator for Deep Localized Hyperthermia . IEEE Transactions on Biomedical Engineering, 38 (7), 634-643 Ebbini E S, Umemura S-I, Ibbini M and Cain C A, 1988, A cylindrical-section ultrasound phased-array applicator for hyperthermia cancer therapy . IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 35 (5), 561-572 Holmer N-G and Lindström K, 198?, Från A-mode till Phased array i Diagnostiskt ultraljud-Grunderna , editerad av Holmer, s 65-67 Lele P P, 1980, Induction of deep, local hyperthermia by ultrasound and electromagnetic fields . - Problems & choices . Radiation and Environmental Biophysics, 17, 205-217 Linke C A, Carstensen E L, Frizzell L A, Elbadawi A and Fridd C W, 1973, Localized tissue destruction by high-intensity focused ultrasound . Arch Surg, 107 (6), 887-891 Sibille A, Prat F, Chapelon J-Y, El Fadil F A, Henry L, Theillère Y, Ponchon T and Cathignol D, 1993, Extracorporeal ablation of liver tissues by high intensity focused ultrasound . Oncology, 50, 375-379 Troussier B, Lebas J F, Chirossel J P, Peoc'h M, Grand S, Leviel J L and Phelip X, 1995, Percutaneous Intradiscal Radio-Frequency Thermocoagulation - A Cadaveric Study . Spine, 20 (15), 1713-1718

Claims: Device for non-invasive treatment of the tissue of an intervertebral disc (1), whereby the treatment aims at changing or degenerating said tissue, said device comprising a treatment transducer (2) comprising at least two ultrasonic transducers (3, 4) having means (11), preferably in the form of transducer elements with a concave spherical transducer surface, for transmitting ultrasonic fields (3a, 4a) with a focal area (5) which has a substantially planar extension which is adaptable relative to a space (M) between end plates (7, 8) of a vertebrae (9, 10) surrounding the intervertebral disc (1) such that said focal area (5) lies between said end plates (7, 8), the ultrasonic transducers (3, 4) of the treatment transducer (2) further including means (12), preferably transducer elements of the phased array type, for displacing said focal area (5) and for varying the extension of said focal area (5), the ultrasonic transducers (3, 4) being located such that said focal area (5) is placeable substantially parallel to a plane (P) in which the intervertebral disc (1) is located. Device according to claim 1, wherein the ultrasonic transducers (3, 4) of the treatment transducer (2) are capable of transmitting ultrasonic waves having a frequency of 0,5 - 2,5 MHz. Device according to any preceding claim, wherein the ultrasonic transducers (3, 4) of the treatment transducer (2) are capable of transmitting ultrasonic fields (3a, 4a) which in the focal area (5) heat the tissue to a temperature of 45-80°C. Device according to any preceding claim, further comprising means for deactivating one or more of said transducers or put out of operation for reducing the extension of the ultrasonic fields (3a, 4a) for preventing said ultrasonic fields from heating biological tissues outside the intervertebral disc (1) to tissue-degenerating temperatures. Device according to any preceding claim, further comprising a non-invasive temperature-supervising device (18), preferably by means of ultrasound, to supervise the temperature in the intervertebral disc (1) during treatment, and a control unit for controlling the ultrasonic transducers (3, 4) of the treatment transducer (2) such that undesired temperature changes in the intervertebral disc (1) are prevented. Device according to any preceding claim, further comprising a diagnostic device (13) for registering the location of the intervertebral disc (1) relative to the ultrasonic transducers (3, 4) of the treatment transducer (2), and the ultrasonic transducers (3, 4) of the treatment transducer (2) are arranged to be controlled depending on information registered by the diagnostic device (13) so that the focal area (5) of their ultrasonic fields (3a, 4a) is moved to coincide with the intervertebral disc (1). Device according to claim 6, wherein the diagnostic device (13) includes an ultrasonic transducer (14) which transmits an ultrasonic field for registering the location of the intervertebral disc (1) relative to the treatment transducer (2). Device according to any preceding claim, further comprising a reading device (16) for registering displacements of the intervertebral disc (1) relative to the ultrasonic transducers (3, 4) of the treatment transducer (2) due to patient movements during treatment, and a setting device (17) for controlling the ultrasonic transducers (3, 4) of the treatment transducer (2) so that the focal area (5) of the ultrasonic fields (3a, 4a) is capable of lying in the intervertebral disc (1) after displacement thereof. Device according to claim 7, the ultrasonic transducers (3, 4) of the treatment transducer (2) and the diagnostic device (13) having an ultrasonic transducer (14) are mounted on a frame (23) relative to a treatment table (20), whereby the mutual positions between said transducers (3, 4, 14) are known, wherein the frame (23) is displaceable relative to a patient (22) for setting said transducers (3, 4, 14) relative to an intervertebral disc (1) of the patient (22).

Inventors: LIDGREN LARS, SEVERSON JOHAN, STROEMQVIST BJOERN, LIDGREN, LARS, SEVERSON, JOHAN, STROEMQVIST, BJOERN, Strömqvist, Björn
Applicants: ULTRAZONIX DNT AB
Application year: 1998
Main classification: A61N7
IPC codes: A61B18, A61N7, A61B17, A61F7