Patent Publication Number: US-2011077676-A1

Title: Prostate Treatment Stent

Description:
PRIORITY APPLICATIONS The present application claims priority from Israel patent application 164563, filed on Oct. 13, 2004, the disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of prostate treatment. 
     BACKGROUND OF THE INVENTION 
     Benign prostate enlargement is a common affliction among older men. Prostate enlargement involves swelling of the prostate, which blocks the urinary path. A common treatment for prostate enlargement is resection, which includes cutting away a portion of the prostate gland. The resection may be performed by a scalpel inserted through the penis to the prostate using a resectoscope. In such a procedure, however, the view of a physician performing the resection is limited and a mistaken move of the physician may cause serious damage to the patient. Other methods of treatment of benign prostate enlargement include heat treatment and/or low temperature ablation. 
     U.S. Pat. No. 5,928,217 to Mikus et al., the disclosure of which is incorporated herein by reference, describes a stent for placement in the urethra, for heating the prostate. 
     U.S. Pat. No. 5,588,965 to Burton et al., the disclosure of which is incorporated herein by reference, describes a device which gradually applies radial pressure against the prostate enlargement in order to slowly dilate the obstructed portion of the urethra. The device expands 5-20 French within 24 hours. 
     In other cases, a stent is implanted in the prostate to keep it open. U.S. Pat. No. 5,601,591 to Edwards et al., the disclosure of which is incorporated herein by reference, describes a stent for introduction into the urethra. The stent is formed of coils spaced from each other, by between 1-2 millimeters, in order to allow urethra tissue to enter into spaces between the coils, for anchoring. 
     The long term implantation of a stent in the prostate, however, is problematic in itself. U.S. Pat. No. 6,416,545 to Mikus et al., the disclosure of which is incorporated herein by reference, describes a removable stent. The stent is used to heat the prostate in addition to supporting the prostate. After the prostate is substantially healed the stent is cooled and removed from the patient&#39;s body. 
     U.S. Pat. No. 6,238,368 to Devonec, the disclosure of which is incorporated herein by reference, describes a stent which both supports the prostate and provides a therapeutic agent which is cytoreductive to the prostate. 
     PCT publication WO 03/101311, the disclosure of which is incorporated herein by reference, describes a shape memory clip used to connect portions of an intestine. The clip presses portions of the intestine together. When the intestine sufficiently heals, a portion of the intestine held by the clip dies, such that the clip falls into the intestine and is evacuated from the patient&#39;s body. 
     U.S. Pat. No. 6,460,542 to James, the disclosure of which is incorporated herein by reference, mentions prosthetic devices for female bladder support. The James patent warns from the prosthetic devices exerting too much pressure, which may cause necrosis. 
     SUMMARY OF THE INVENTION 
     An aspect of some embodiments of the invention relates to an implant device for removal of blocking tissue from the urethra. The device traps blocking tissue and applies force to the trapped tissue in order to cause the blocking tissue to fall out of the way and exit the urethra, widening the urethra. In some embodiments of the invention, the device reshapes the urethra to a desired open configuration. The force is optionally applied gradually over a long period, so as to avoid traumatic effects on the tissue. 
     The applied force is expected to starve or otherwise kill the cells of the tissue trapped by the device. In some embodiments of the invention, the force is applied for between about 7-30 days, although the device may be configured for shorter or longer time periods and/or the device may be used, in some cases for longer or shorter than the configured period. In an exemplary embodiment of the invention, a force of between about 100-300 grams is applied by the device. Optionally, the device applies a force of less than 250 grams, less than 150 grams or even less than 100 grams. In some embodiments of the invention, portions of the device move at a low rate of less than 1 mm in 24 hours, or even less than half a millimeter in 24 hours. 
     In some embodiments of the invention, the device is coated with a drug, for example, in order to aid the dissection process, counteract inflammation and/or counteract infection. In some embodiments of the invention, the device includes a coil having a plurality of turns and the tissue is held between adjacent turns of the coil. In other embodiments, the device comprises a cylindrical tube with slits cut therein. In some embodiments of the invention, the device includes small protrusions (e.g., teeth) which penetrate the dissected tissue and enhance the dissection. Alternatively or additionally, at least some of the surfaces of the device which are intended to contact tissue are roughened, to an extent at which the device cannot be moved against tissue unless a substantial force is applied. Optionally, the roughened surfaces have a plurality of peaks having heights of at least 50 micrometers, 100 micrometers or even 300 micrometers. 
     In some embodiments of the invention, the rough surfaces are achieved by mechanical etching, for example rubbing sand paper or glass paper against the surfaces to be roughened and/or by laser etching. Alternatively or additionally, the rough surfaces are achieved by dipping the implant in an etching solution which roughens the surfaces of the implant, for example by random eating away of material of the implant. Further alternatively or additionally, the rough surfaces are achieved by a dipping the implant in a solution which causes irregular growth of a coating on the implant. 
     In some embodiments of the invention, the implant device is elastic, using any bio-compatible device structure and/or materials, such as super elastic materials, a bimetal structure and/or shape memory materials. Alternatively, a non-elastic device is used to apply the force, for example a device with a ratchet mechanism. Optionally, an external energy source is used to apply the force, for example a heat source and/or a magnet. Alternatively, an internal power source (e.g., battery) is located on the device within the patient. Alternatively or additionally, an external force may be applied mechanically by a handle of the device located outside the patient. 
     The device is constructed, in some embodiments of the invention, to contract radially in parallel to its axial contraction, to allow easier removal or even automatic expulsion from the urethra when its dissection task is completed. 
     In other embodiments of the invention, the implant expands radially with the axial contraction, so as to provide support against expanding tissue blocking the urethra. In still other embodiments of the invention, the implant is designed to have a complex radial behavior. For example, at first the implant optionally expands in order to increase pressure on the tissue and towards completion of the removal of the blocking tissue, the implant contracts radially, in order to allow easy removal thereof. 
     An aspect of some embodiments of the invention relates to a medical kit provided with an elastic tissue dissection device mounted in a stretched configuration on an insertion apparatus of the device. The dissection device and insertion apparatus are optionally provided in a sterile package. 
     An aspect of some embodiments of the invention relates to a method of inserting an elastic implant into the urethra. The method includes mounting the implant in a stretched state onto a delivery apparatus and inserting the implant into the urethra. Optionally, the stretched state comprises an axially stretched state. Alternatively or additionally, in the stretched state, the implant is wound around its axis a number of times, so as to decrease the radius of the elastic implant relative to a passive state of the implant. 
     Optionally, the elastic implant is held in the stretched state by the delivery apparatus. After the elastic implant is in position where it is to be released, the implant is released from the delivery apparatus. 
     When the implant is stretched axially, urethra obstructing tissue optionally enters gaps in the stretched elastic implant. The delivery apparatus is then caused to release the implant. Optionally, the elastic implant contracts axially, so as to trap the tissue that entered the gaps and apply elastic force at the trapped tissue. 
     Alternatively or additionally, the elastic implant is held open by sugar or any other dissolvable material. Inside the urethra, the sugar dissolves, obstructing tissue enters gaps in the elastic implant and the implant contracts so as to apply force on tissue trapped in the gaps. 
     In some embodiments of the invention, in which the implant is wound around itself, before the implant is released within the patient, the implant is rewound state in which the winding is cancelled. 
     An aspect of some embodiments of the invention relates to a two step method of safely treating prostate tissue without damaging the sphincter. The method includes inserting to the urethra, in a first stage, an overtube, which is adapted to allow determination of an extent of insertion of the overtube into the urethra, together with viewing apparatus for determining the location of the sphincter. Optionally, the viewing apparatus comprises an optical fibre, located within the overtube. The sphincter is located using the viewing apparatus and the extent of penetration of the overtube is recorded. Alternatively or additionally, the overtube is anchored in the patient, such that the distal end of the overtube protects the sphincter from damage. Thereafter, in a second stage, the viewing apparatus is removed from the outer tube, and a tissue treatment apparatus is passed through the outer tube to treat the tissue. 
     There is therefore provided in accordance with an exemplary embodiment of the invention, a method of dissecting urethra obstructing tissue, comprising capturing urethra obstructing tissue between portions of an implant and applying pressure on the tissue caught between the portions of the implant, for longer than 1 hour, 6 hours, or even 12 hours, optionally until the tissue dies or falls off. 
     Optionally, the implant applies different pressure levels along a length corresponding to an axis of the urethra. Alternatively, the implant applies substantially equal pressure along its length. Optionally, the implant comprises an elastic device. Optionally, applying the pressure comprises applying pressure for at least a day or even for at least a week. 
     Optionally, the implant comprises sharp tips pointed outward from the implant. 
     Optionally, the implant comprises tips pointed in directions in which the implant is adapted to capture tissue. Optionally, applying the pressure comprises applying pressure parallel to the axis of the urethra. Optionally, capturing tissue comprises inserting the implant into the urethra in a stretched state and releasing the implant such that it contracts and grasps tissue while contracting. Optionally, applying the pressure comprises applying by a non-elastic implant. Optionally, capturing tissue by an implant comprises inserting to the urethra an implant coated by a bio-active material. Optionally, the bio-active material comprises a tissue dissection drug. Optionally, the drug comprises a counter inflammation drug. Optionally, the implant comprises a coil. Optionally, capturing tissue comprises inserting the coil into the urethra in a winded state and rewinding the coil within the urethra. Optionally, the coil is formed of a wire having different thickness or cross-section shape along its length. Optionally, the coil has different length gaps between different pairs of turns of the coil. Optionally, the coil is pulled inside out in its production process. Optionally, the implant radially contracts when stretched axially. 
     There is further provided in accordance with an exemplary embodiment of the invention, a tissue dissecting implant kit, comprising an implant comprising a plurality of rings coupled to each other elastically, such that an elastic pressure is applied on tissue caught between adjacent rings and a sterile package encompassing the implant, wherein when the implant is in a stretched state resulting from pulling the implant from opposite ends, substantially the same pressure is applied between each pair of adjacent rings. 
     Optionally, the implant comprises a coil formed of a wire having different thickness or cross-section shape along its length. 
     There is further provided in accordance with an exemplary embodiment of the invention, a tissue dissecting implant kit, comprising an implant comprising a plurality of rings coupled to each other elastically, such that an elastic pressure is applied on tissue caught between adjacent rings and a sterile package encompassing the implant, wherein the implant contracts radially when it contracts axially, at a first axial stretching extent and expands radially when it contracts axially, at a second axial stretching extent. 
     Optionally, the implant comprises a coil. 
     There is further provided in accordance with an exemplary embodiment of the invention, a tissue dissecting implant kit, comprising an implant comprising a plurality of rings coupled to each other elastically, such that an elastic pressure is applied on tissue caught between adjacent rings and a sterile package encompassing the implant, wherein the implant has different distances between adjacent rings along its length or has different material thickness or cross-section shape along its length. 
     Optionally, the implant comprises a coil. Optionally, the implant has different distances between adjacent rings along its length. 
     There is further provided in accordance with an exemplary embodiment of the invention, a tissue dissecting implant kit, comprising an implant comprising a plurality of rings coupled to each other elastically, such that an elastic pressure is applied on tissue caught between adjacent rings and a sterile package encompassing the implant, wherein at least some of the ring surfaces facing each other have non-smooth surfaces. 
     Optionally, the non-smooth surfaces comprise rough surfaces having a feel similar to sand paper. Optionally, the non-smooth surfaces comprise small protrusions. Optionally, the rings are substantially circular or polygonal. Optionally, the implant comprises a coil. Alternatively, the implant comprises a cylinder with slits. 
     There is further provided in accordance with an exemplary embodiment of the invention, a tissue dissecting implant kit, comprising an elongate tube, sized and shaped to fit into a urethra, having a plurality of slits in a circumference of the tube, such that when the tube is stretched along its length it applies a contraction force on tissue within the slits and a sterile package in which the tube is packaged. 
     Optionally, the tube has a substantially cylinder shape in its rest state. 
     There is further provided in accordance with an exemplary embodiment of the invention, a tissue dissecting implant kit, comprising a sterile package and an axially elastic implant having a cylindrical shape, sized and shaped to fit in the urethra, the elastic implant adapted to apply a force of between about 100-1000 grams on tissue caught within the implant. 
     Optionally, the implant comprises pointed tips directed axially. 
     Optionally, at least a portion of the implant is coated with a material that counteracts inflammation. Optionally, at least a portion of the implant is coated with a material that counteracts tissue growth on the implant. Optionally, at least a portion of the implant is coated with a material that enhances tissue death. Optionally, the implant comprises a coil. Optionally, the implant comprises a cylindrical tube with slits cut therein. Optionally, the implant is adapted to contract radially when it contracts axially. Optionally, the implant is adapted to expand radially when it contracts axially. 
     There is further provided in accordance with an exemplary embodiment of the invention, a tissue dissecting implant, comprising an axially elastic implant adapted for insertion into the urethra and a bioactive material coupled to at least a portion of the implant. 
     Optionally, the bioactive material comprises a tissue dissection drug, a counter inflammation drug and/or a counter infection drug. Optionally, the bioactive material coats at least a portion of an outer surface of the implant. Optionally, the bioactive material coats at least some of the member surfaces facing another member. Optionally, the bioactive material coats at least a portion of the implant. Optionally, the bioactive material is embedded in at least a portion of the implant. Optionally, the implant comprises a plurality of members adapted to apply a dissecting force to tissue caught between the members. 
     There is further provided in accordance with an exemplary embodiment of the invention, a tissue dissecting implant, comprising an axially elastic implant adapted for insertion into the urethra, wherein the implant radially contracts when stretched axially. 
     There is further provided in accordance with an exemplary embodiment of the invention, a method of generating a medical implant for the urethra, comprising providing a coil suitable for implanting in the urethra and turning the coil inside out. 
     Optionally, providing the coil comprises providing a coil having at least ten turns. 
     Optionally, providing the coil comprises providing a coil having different distances between adjacent turns. 
     There is further provided in accordance with an exemplary embodiment of the invention, an implant delivery system for inserting an implant to the urethra, comprising a probe adapted to be inserted to a urethra, an implant holding unit adapted to hold an axially elastic implant in a stretched state on the probe and a release unit adapted to release the implant from the holding unit. 
     Optionally, the implant holding unit is adapted to hold the implant in an axially stretched state. Optionally, the implant holding unit is adapted to hold the implant in a winded state. Optionally, the release unit is adapted to rewind the implant. Optionally, the implant delivery system comprises a cover which separates the implant from the urethra until the implant is to be released. Optionally, the implant holding unit comprises strings that are torn by the release unit. 
     There is further provided in accordance with an exemplary embodiment of the invention, a method of implanting an implant into the urethra, comprising mounting the implant in a stretched state onto a probe suitable for insertion into the urethra, inserting the probe into the urethra, with the implant in the axially stretched state; and releasing the implant from the probe within the urethra, such that the implant axially condenses. 
     Optionally, mounting the implant in a stretched state comprises mounting in an axially stretched state. Optionally, the implant expands radially when it condenses axially. Optionally, the implant is released from the minimally invasive tool after tissue enters the implant in a manner which dampens the axial contraction of the implant. Optionally, mounting the implant in a stretched state comprises mounting in a wound state. 
     There is further provided in accordance with an exemplary embodiment of the invention, a method of treating the urethra, comprising inserting to the urethra an outer tube, inserting within the outer tube a viewing apparatus, setting a position of the outer tube in the urethra, which position protects the sphincter, using the viewing apparatus and applying a treatment to the urethra while the sphincter is protected by the outer tube. 
     Optionally, applying the treatment comprises removing the viewing apparatus from the outer tube and inserting a treatment probe through the outer tube. Optionally, applying the treatment comprises applying RF ablation, cutting tissue with a knife and/or implanting a tissue dissection implant. Optionally, the viewing apparatus comprises an optic fiber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Particular exemplary embodiments of the invention will be described with reference to the following description of embodiments in conjunction with the figures, wherein identical structures, elements or parts which appear in more than one figure are generally labeled with a same or similar number in all the figures in which they appear, in which: 
         FIG. 1  is a schematic illustration of an elastic dissection implant, in accordance with an exemplary embodiment of the invention; 
         FIGS. 2A and 2B  are schematic illustrations of stages in inserting an implant into a narrowed urethra path, in accordance with an exemplary embodiment of the invention; 
         FIGS. 3A and 3B  are top and cross-sectional views of an implant insertion system, in accordance with an exemplary embodiment of the invention; 
         FIGS. 3C and 3D  are schematic illustrations of an implant delivery system, in accordance with an exemplary embodiment of the invention; 
         FIG. 4  is a flowchart of acts performed in inserting an implant into a patient, in accordance with an exemplary embodiment of the invention; 
         FIG. 5  is an enlarged view of a distal end of the insertion system of  FIG. 3 , in accordance with an exemplary embodiment of the invention; 
         FIGS. 6A and 6B  schematically illustrate a process of removing an implant from a prostate, in accordance with an exemplary embodiment of the invention; 
         FIG. 6C  schematically illustrates a process of removing an implant from a urethra, in accordance with another exemplary embodiment of the invention; 
         FIG. 7A  is a schematic illustration of an elastic prostate implant, in accordance with an exemplary embodiment of the invention; 
         FIG. 7B  is a schematic illustration of an elastic prostate implant, in accordance with another exemplary embodiment of the invention; 
         FIGS. 8A-8F  are schematic illustrations of implant configurations, in accordance with an exemplary embodiment of the invention; 
         FIG. 9  is a schematic cross-sectional view of a tissue dissection tool, in accordance with an exemplary embodiment of the invention; 
         FIG. 10  is a schematic illustration of an implant insertion system, in accordance with an exemplary embodiment of the invention; and 
         FIGS. 11A-11E  illustrate a method for inserting a reshaping implant, in accordance with an exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1  is a schematic illustration of an elastic prostate implant  100 , in accordance with an exemplary embodiment of the invention. Implant  100  includes an axially compressing device, such as a coil-shaped wire including a plurality of turns  106 . Implant  100  has an elastic structure which axially compresses absent an external force. In  FIG. 1 , implant  100  is stretched such that gaps  104  are formed between turns  106 . As described below, gaps  104  receive urethra-obstructing tissue which is to be removed and slowly press on the obstructing tissue until it is cut away and/or falls off due to tissue necrosis. In some embodiments of the invention, implant  100  includes anchoring structures, such as holes  102 , at both ends, for use in stretching implant  100  to the state shown in  FIG. 1 . Holes  102  are optionally used during insertion of implant  100  to the urethra and/or for removal of the implant from the urethra. 
     Optionally, implant  100  is radially durable such that implant  100  does not collapse radially under pressure of the obstructing tissue. In some embodiments of the invention, while employed, implant  100  prevents blockage of urine passage, by allowing urine to pass through implant  100 . Optionally, implant  100  also serves to expand urethra path  206  while the implant  100  is in the patient, by radially pushing the obstructing tissue. 
       FIGS. 2A and 2B  are schematic illustrations of stages in inserting implant  100  into a narrowed urethra path  206 , in accordance with an exemplary embodiment of the invention. Urethra path  206  is narrowed by obstructing tissue  209  which is generally believed to block the urethra path due to a swelling of the prostate  210 . Implant  100 , optionally covered by a protective cover  322 , is pushed into the urethra path  206 , in an axially stretched orientation. 
     Protective cover  322  is then removed, so as to allow portions  208  of obstructing tissue  209  to enter gaps  104  of implant  100 , as shown in  FIG. 2B . 
     Size 
     In an exemplary embodiment of the invention, the radius of implant  100  is large enough such that tissue portions  208  enter into gaps  104  between the turns  106  of the implant. In some embodiments of the invention, implant  100  has a radius of substantially the same size as of a stent known in the art, used to support the prostate and keep the urethra open. Alternatively, implant  100  has a slightly larger radius than a stent suggested to be employed on the patient, in order to allow more tissue to enter into gaps  104 . 
     In some embodiments of the invention, physicians have a plurality of implants  100  of different sizes and a suitable implant is selected according to the patient. The patient&#39;s size may be determined from previous medical data and/or using imaging apparatus (e.g., of the obstruction, of the extent of the prostate growth) or insertion of a measurement device. In an exemplary embodiment of the invention, implant  100  has a radius of between about 3-11 millimeters, optionally between 4-10 millimeters. The gaps  104  between turns  106  are optionally sufficiently axially long to allow entrance of large amounts of tissue into the gaps, for example at least 0.5 millimeters, at least 2 mm or even at least 5 millimeters. Larger gaps (e.g., 7-11 mm, or even larger) are optionally used when the obstructing tissue is relatively hard or dense and/or when it is required to catch substantial amounts of tissue. In some embodiments of the invention, however, in order to allow for a substantial number of turns along implant  100 , each turn has a length of less than 8 mm, less than 5 mm or even less than 2 mm. In an exemplary embodiment of the invention, smaller gaps  104 , for example of 0.3-2 mm, are used. The size of gaps  104  optionally depends on the material forming implant  100 . When a metal such as aluminum or stainless steel is used, gaps of up to about 5 mm are achievable. For Nitinol, gaps of even 15 mm are achievable. 
     In some embodiments of the invention, implant  100  has a length L slightly larger (e.g., 5-10% larger) than an obstruction treated, so as to treat the entire length of the obstruction at once. In some embodiments of the invention, implants  100  are provided in packages including implants of various sizes. Alternatively, the length L of implant  100  is as long as, or even longer than, any expected urethra obstruction to be treated. For smaller urethra obstructions, only part of implant  100  is operative, while the remaining part contracts within the patient&#39;s bladder  214  or within non-obstructed portions of the urethra, immediately after installation. Alternatively, a physician may shorten implant  100  by cutting one end of the implant, before installation in the patient. Alternatively or additionally, an implant  100  shorter than the obstruction is used. In accordance with this alternative, as well as the other alternatives, a plurality of consecutive treatment sessions may be performed. Optionally, in a first treatment session, an implant  100  with a relatively small radius is used. In following treatment sessions, implants with larger radius are used. Alternatively, a plurality of consecutive treatment sessions are performed with implants  100  of the same length. 
     In an exemplary embodiment of the invention, implant  100  has a length, when stretched, of between at least 50 millimeters, 60 millimeters or even at least 70 millimeters, according to the length of the urethra obstruction. The non-stretched length of implant  100  optionally depends on the material from which implant  100  is comprised. For stainless steel, a non-stretched length of about 40 mm corresponds to a stretched length of 60-70 millimeters, while for nitinol a length of 8-10 mm optionally corresponds to 60-70 millimeters. 
     In an exemplary embodiment of the invention, implant  100  includes between 15-35 turns  106  per centimeter in its rest state. Alternatively, a larger number of turns (e.g., 35-60) are included in each centimeter. 
     The tissue portions  208  entering into gaps  104  optionally anchor implant  100  within urethra path  206  so as to prevent implant  100  from being pushed out of the urethra path  206 , for example by urinating. Alternatively or additionally, implant  100  includes radial protrusions which anchor the implant in place. 
     In some embodiments of the invention, the radius of implant  100  is substantially the same in a stretched state as in a contracted state. Alternatively, implant  100  is planned to expand radially when it contracts axially. In some embodiments of the invention, implant  100  is inserted into the patient axially stretched and radially contracted. When implant  100  is properly positioned in the patient, the axial stretching is released, so that implant  100  catches obstructing tissue in gaps  104 . The radial expansion of implant  100  improves the anchoring of the implant in the patient&#39;s tissue and/or increases the amount of enlargement tissue caught by implant  100 . In addition, the radial expansion with axial contraction allows easier insertion and/or removal of implant  100  in its axially stretched state. In other embodiments of the invention, implant  100  contracts radially when it contracts axially, so that it easily exits when the killing of the obstruction tissue is completed. In still other embodiments of the invention, in the maximally stretched state, implant  100  has a medium radius. In axially contracting from the maximally stretched state, the radius expands to a maximal radius. Thereafter, in continuous axial contraction, the radius reduces in order to allow easy removal of the implant. 
     Pressure 
     Implant  100  optionally applies a generally axial compressive pressure against tissue entering into gaps  104 . The pressure applied by implant  100  is optionally relatively weak so as not to cause substantial pain to the patient. Alternatively or additionally, the pressure of implant  100  is set to a level that causes all the tissue entering into gaps  104  to cut off from the prostate within a predetermined time range, optionally between 1-4 weeks. The pressure, however, is not set to too low a level which is not sufficient for killing the tissue. In some embodiments of the invention, the pressure is large enough to cut off callus tissue which may obstruct the urethra. Alternatively, a low pressure implant  100  is used generally on patients, unless it is determined that the patient has (or may have) callus tissue, in which case a higher pressure implant is used. 
     In some embodiments of the invention, the pressure is set to gradually cut off the blood flow to the cells of the tissue enlargement, so that sudden ischemia which could cause gangrene does not occur. Optionally, experimentation is performed in order to determine a best pressure level. In some embodiments of the invention, different implants  100 , which apply different pressure levels, are used on different patients according to one or more attributes of the patients, such as age, tissue hardness and/or existing inflammation. 
     In an exemplary embodiment of the invention, a starting force of at least 100 grams, for example between 150-300 grams is applied by implant  100  on the tissue within gaps  104 . Alternatively, lower starting forces such as less than 100 grams (e.g., 30 grams) or even as low as 1-20 grams are used. Further alternatively, higher starting forces of at least 300 grams, 500 grams or even at least 800 grams are used, for example when the patient has very soft obstructing tissue or when the patient has very tough tissue. 
     The force applied by implant  100  optionally reduces with axial compression of the implant. In some embodiments of the invention, implant  100  includes a slowly degrading coating or other layer that reduces the force applied by implant  100 . The degrading coating includes, for example, a sugar or a polymer that dissolves in water. The coating degrades with time, so that the force increases with time, in parallel to the decreasing of the force due to the axial contraction of implant  100 . In some embodiments of the invention, the degrading coating is applied such that the force of implant  100  remains substantially constant over the entire treatment until implant  100  totally axially contracts. Alternatively, the coating is chosen to achieve a desired predetermined profile. The predetermined profile optionally has an increasing force profile, so as to take advantage of the patient&#39;s getting used to the applied force. Alternatively, a decreasing force profile is used. Further alternatively or additionally, a force profile which includes both increasing and decreasing segments is used. 
     In some embodiments of the invention, implant  100  is coated with a soft spongy coating in order to reduce the pressure applied by the implant when it is toward the end of its compression. These embodiments are optionally used when it is expected that the tissue toward the end of its dissection cannot withhold the force applied by the implant in its close to compressed state. 
     Implant  100  optionally applies different force along its length, for example stronger force being applied toward the axial center of the implant, as is the case in some simple springs. Alternatively, implant  100  is produced such that it applies the same force over its entire axial length. Further alternatively or additionally, implant  100  has any other axial force application profile. For example, an implant  100  to be used for a specific patient may be selected according to the axial distribution of the obstruction tissue and/or its hardness, in the patient. 
     The pressure profile of implant  100  is optionally controlled by changing the thickness and/or axial width of the material of implant  100  over its length. Alternatively or additionally, implant  100  is produced with different distances between adjacent turns along the length of the implant. Turns that are closer to each other in a rest state, optionally apply a stronger force than turns that are farther away in the rest state. If, however, as discussed below, implant  100  is pulled inside out in its production, turns that are farther from each other in their rest state apply a stronger force than closer turns. 
     In some embodiments of the invention, different axial portions of implant  100  are stretched to different lengths in order to control the pressure applied by the different portions. Optionally, implant  100  is designed to be stretched to different extents in different portions along its length. Generally, portions that are stretched to a greater extent apply more force on the tissue. 
     Alternatively or additionally, implant  100  has different thickness and/or axial width along its length, in order to achieve a desired pressure profile, which varies along the length of the implant. 
     The use of different pressure levels along the length of implant  100  optionally causes dissected tissue to fall off at different times. Causing dissected to fall off at different times, optionally reduces the chances of clogging the urethra with dissected tissue. In an exemplary embodiment of the invention, the pressure varies gradually from a high pressure on one end of implant  100  to a lower pressure on an opposite end of the implant. The high pressure end is optionally located on the end of the urethra closer to the body orifice, such that dissected tissue falling off earlier due to the high pressure is not clogged by the obstructing tissue not yet dissected, on its way out of the patient. Alternatively to gradual changes in the pressure, the pressure changes in steps. 
     In some embodiments of the invention, the pressure between each two turns  106  is directed at having the two turns adjacent each other, such that when the turns touch each other the pressure applied is substantially zero. Alternatively, the pressure between adjacent turns  106  is directed at having the turns change places, such that even when the turns  106  touch each other the turns apply pressure. In some embodiments of the invention, a spring which applies pressure even when the turns are adjacent each other is achieved by pulling a spiral implant inside out. Optionally, after producing the spiral, one end of the spiral is held stationary, while the other end of the spiral is pulled through the spiral, so as to turn it inside out. Optional materials to be used with a spiral implant pulled inside out are plastic, nitonol and/or nirosta. In some embodiments of the invention, implant  100  is planned to advance in a certain direction, as it contracts axially. Optionally, implant  100  is formed of shape memory materials which induce the movement along with the axial contraction. Operation 
     The slow operation of implant  100  prevents damage to the control valve (i.e., the sphincter) of the urethra due to a mistake of a physician. For example, if implant  100  is released on the sphincter, due to an inaccurate move on the part of a physician, the improper positioning of the implant can be corrected, even if the mistake is determined hours after the implant is employed. 
     Tissue cut off by the pressure of implant  100  generally falls into the path  204  and is optionally naturally washed out of the patient in the patient&#39;s urine stream. In some embodiments of the invention, the urine stream aids in detaching tissue, which is at least partially dissected. Alternatively, after the tissue is killed, the tissue remains connected to the urethra. A dissecting tool guided by implant  100  is used to remove the dead tissue. Further alternatively or additionally, the dead tissue separates from the urethra but remains in the urethra channel. An invasive tool is used to remove the dead tissue from the urethra path. 
     After all the tissue entering into gaps  104  is cut, implant  100  is optionally automatically freed from its anchoring to the urethra and is automatically expelled from the patient with the urine passing in path  204 . Alternatively, implant  100  is actively removed, for example, using a medical procedure as described below. Further alternatively, after completing its task, implant  100  is dissolved or broken into pieces, which are removed with the urine, as described below. As described above, different implants  100  may be designed with different ending radius, such that a physician may select whether to use a self ejecting implant  100  or an implant which needs to be removed in a medical procedure. 
     Exemplary Materials of Implant 
     Implant  100  optionally comprises an elastic bio-compatible material, suitable for implantation in the urethra for a period of a few weeks. In some embodiments of the invention, implant  100  comprises a material (e.g., gold) which minimizes or totally inhibits tissue growth, bacterial growth and/or crystallization on the implant. Such tissue growth may interfere in the dissection operation of implant  100  and/or may limit the effectiveness of implant  100  in keeping the urine path of the patient open. Alternatively or additionally, implant  100  is coated with a suitable coating (e.g., gold) which prevents tissue growth. 
     Alternatively or additionally, implant  100  comprises a durable but cheap material, such as stainless steel and/or various plastics. In other embodiments of the invention, implant  100  comprises a super elastic material (e.g., nitinol, B-metal), allowing minimization of the material content of implant  100 . The use of minimal material is sometimes desired when apparatus is used within a patient. In some embodiments of the invention, a shape memory material and/or a bi-metal structure is used for implant  100 . The properties of the material may be used to externally control the force applied by implant  100  and/or to aid in insertion or removal of the implant. For example, the implant may be brought to a shrunken state for insertion or removal. In some embodiments of the invention, the external control is performed by heating and/or cooling the implant. Alternatively or additionally, the external control is performed by apply magnetic forces to the implant. 
     In some embodiments of the invention, implant  100  comprises a non-biodegradable material, such as any of the above mentioned materials. Alternatively, implant  100  comprises a bio-degradable material, which slowly dissolves within the urethra. 
     The bio-degradable materials used for implant  100  are optionally ones that degrade slowly, such that the implant falls apart only after the implant contracts substantially entirely. Optionally, materials that degrade near inert tissue and/or in urine, are used. Possible biodegradable materials for forming implant  100  are described, for example, in “Biodegradable, Elastic Shape Memory Polymers for Potential Biomedical Applications”, by Andreas Lendlein, Science Express, April 2002, the disclosure of which is incorporated herein by reference. 
     In some embodiments of the invention, implant  100  is entirely formed of a bio-degradable material (or a plurality of bio-degradable), such that there is no need to remove implant  100  from the patient and/or it is easier to remove the implant from the patient. Alternatively, implant  100  is formed of bio-degradable and non-bio-degradable materials in interleaved sections, such that when the bio-degradable materials degrade, the non-bio-degradable materials are small enough to exit the body naturally and/or it is easier to remove them from the patient. 
     Optionally, implant  100  has a degradable structure such that the degradation of the implant becomes of structural meaning only after a predetermined time in which the urethra obstruction cells are expected to be entirely dissected. In some embodiments of the invention, implant  100  is formed such that once the degradation causes the structure to deteriorate, the total collapse and subsequent evacuation through the urine is fast (e.g., within a few hours or days). For example, implant  100  may be made of a relatively thick material which dissolves in layers. Only when the last layer of the implant begins to dissolve does the implant collapse and stop its dissection operation. 
     In an exemplary embodiment of the invention, implant  100  includes a degradable plastic structure on a nitinol string. After the plastic degrades, only the nitinol string remains, possibly with some plastic remnants thereon, and the nitinol string is removed from the patient. 
     Smoothness or Roughness 
     Implant  100  optionally has a smooth outer radial surface so as to minimize the interaction between the implant and outer prostate tissue not caught in gaps  104 . The smoothness optionally prevents anchoring of implant  100 . In some cases, the smoothness hampers the pressure of the elasticity and/or minimizes inflammation and/or pain. Alternatively, the outer radial surface is sandblasted and/or teethed in order to enhance cell death also radially and/or to prevent too strong a pressure being applied by the elasticity. In some embodiments of the invention, the elasticity of implant  100  is defined according to the expected radial friction with the prostate walls. In some embodiments of the invention in which friction is desired, a friction coating is used to provide the friction, for example a nano-particle coating. When a bioactive coating is used, the use of a nano-particle coating also increases the contact area between the drug an the tissue to interact with the drug. 
     In some embodiments of the invention, implant  100  includes axially directed teeth and/or sandblasting directed at gaps  104 , which optionally enhance the cell killing of the implant, on tissue within gaps  104 . 
     Coating 
     Implant  100  is optionally coated with a suitable drug, solution or other bioactive material which prevents growth of crystals and/or tissue on the implant. In some embodiments of the invention, the coating is passive, i.e., the coating includes a material (or materials) to which growth does not cling and/or which does not induce growth. Alternatively or additionally, the coating is active, i.e., the coating includes chemicals that attack growth and/or prevent its formation. 
     Alternatively or additionally to preventing growth, implant  100  is coated with a bioactive material which hastens decay of surrounding live and/or dead tissue. In some embodiments of the invention, the coating is placed on the entire surface area of the implant. Alternatively, only portions of the surface area of the implant are coated, for example inner surface areas and/or side portions facing gaps  104 . 
     Further alternatively or additionally, implant  100  is coated with a fluorescent or other imaging aiding material, to aid in identifying the implant in medical images. In some embodiments of the invention, coating is used for other reasons, such as enlarging or decreasing the friction between the implant and the prostate. 
     Alternatively to being coated with the bioactive material, the bioactive material is embedded within the implant or is placed in a miniature pocket on or coupled to the implant. In some embodiments of the invention, the bioactive material is slowly released to the surrounding tissue over more than  24  hours or even over more than a week. Optionally, the bioactive material is released according to a predetermined scheme. Alternatively, the release of the bioactive material is induced by tissue inflammation, urinating or any other internal biological effect within the patient. Alternatively, the release of the bioactive material is induced externally from outside the patient, using any method known in the art. Further alternatively, the bioactive material may be coupled to the implant in any other method known in the art. 
     Structure 
     In some embodiments of the invention, implant  100  is formed of a wire which is turned into a spiral shape. Optionally, the wire has a circular or elliptical cross section. Alternatively, the wire has a square, rectangular, triangular, star or diamond cross-sectional shape, which applies more pressure on the tissue captured in gaps  104 . In some embodiments of the invention, the points of the diamond and/or triangle are directed axially at the captured tissue. Alternatively or additionally, the points are directed radially inward toward tissue captured within the implant. Alternatively, implant  100  is smooth inward in order not to interfere passage through the implant. In some embodiments of the invention, the wire forming implant  100  comprises a flat (thin) rectangular shape. 
     The use of simple geometrical shapes allows relatively cheap production. In some embodiments of the invention, however, more complex wire shapes are used, for example, in order to include more points and/or flat areas in desired directions. 
     Alternatively to forming implant  100  from a wire, implant  100  is cut out of a tube or a flat sheet. 
     The width w 1  ( FIG. 1 ) of turns  106 , is optionally substantially equal to the length of gaps  104  in the stretched state. Alternatively, the width wl of turns  106  is smaller than gaps  104 , with a ratio of between about 1:2 and 1:4. Alternatively, width w 1  of turns  106  is smaller than gaps  104  in the stretched state. The ratio between the width of turns  106  and the length of gaps  104  affects the extent of stretching of the tissue walls of the urethra. In some embodiments of the invention, the force applied by implant  100  is adjusted according to the expected stretching, in order not to cause too much stretching and/or undesired slippage of implant  100  within the urethra. In some embodiments of the invention, the width wl of turns  106  is equal over the entire length of implant  100 . Alternatively, the width w 1  of the turns varies over the length of implant  100 , for example in order to vary the pressure applied by implant  100  over its length. 
     In some embodiments of the invention, the shape of implant  100  is adjusted to limit the stretching and/or scarring of tissue. The shape of the implant is optionally adjusted, in some embodiments of the invention, in order to direct tissue scarring in a desired direction or location, which is, for example, better suitable for healing. 
     Insertion Method 
       FIG. 3A  is a top view of a probe system  300  for inserting implant  100  into the urethra of a patient, in accordance with an exemplary embodiment of the invention. 
       FIG. 3B  is a cross-sectional view of system  300 , in accordance with an exemplary embodiment of the invention. System  300  includes an implant carrier  350 , which holds implant  100  in a stretched state. 
     In addition, system  300  optionally includes a balloon catheter  360 , which aids in inserting and/or positioning implant  100  into the prostate. A balloon  362  at the distal end of balloon catheter  360  leads the way of implant  100  on its way along the urethra, opening the path of the urethra (which is blocked by obstructing tissue) and preventing damage to the implant. Alternatively, any other gadget is used to lead the way of implant  100 , such as an umbrella or a protective cap. Implant carrier  350  optionally includes a bar  302  on which implant  100  is placed. An optional protective cover  322  protects implant  100  radially and/or protects the urethra from implant  100 , while the implant is inserted into the patient. Balloon catheter  360  optionally includes, at its proximal end, a balloon control  364  which is used to inflate and/or deflate balloon  362 . An inflation tube  366 , passing through implant carrier  350 , connects balloon  362  to balloon control  364 . 
     Balloon catheter  360  and implant carrier  350  are optionally inserted to the patient on a guide wire  304 . Alternatively or additionally, implant carrier  350  is inserted through a previously inserted tube and/or a catheter used for diagnosis. 
       FIG. 4  is a flowchart of acts performed in inserting implant  100  to a patient, in accordance with an exemplary embodiment of the invention. Implant  100  is mounted ( 402 ) on implant carrier  350 . Balloon  362  is inflated ( 404 ) and cover  322  is slid ( 406 ) over implant  100 . A guide wire  304  is inserted ( 408 ) into the patient and implant carrier  350  and balloon catheter  360  are passed ( 410 ) into the patient together over guide wire  304 . The position of implant  100  is determined ( 412 ) and the position is adjusted ( 414 ), until ( 416 ) the implant is properly positioned. Balloon  362  is then deflated ( 418 ) and implant carrier  350  releases ( 420 ) implant  100 . Implant carrier  350 , balloon catheter  360  and guide wire  304  are removed ( 422 ) from the patient. 
     Referring in more detail to mounting ( 402 ) implant  100  on carrier  350 , in some embodiments of the invention, implant  100  is mounted on carrier  350  by the physician, immediately before insertion to the patient. In some embodiments of the invention, the physician cuts implant  100  into size before it is mounted. Alternatively, implant  100  is supplied pre-mounted on carrier  350 . For example, in accordance with this alternative, carrier  350  may be supplied within a sterile package with implant  100  mounted thereon in a stretched state. In some embodiments of the invention, implant  100  is mounted on carrier  350  already stretched. Alternatively, implant  100  is set to a deformed state (e.g., using a shape memory material) which remains for at least a predetermined time required for implant insertion, but later allows the implant to retain to its usual pressure enforcing state. 
       FIGS. 3C and 3D  are schematic illustrations of an implant delivery system  380  suitable for stretching implant  100  immediately before insertion and/or after insertion, in accordance with an exemplary embodiment of the invention. As shown in  FIG. 3C , delivery system  380  comprises a tubular body  382  and an internal shaft  384 . Implant  100  is mounted on the distal end of tubular body  382 , using any method known in the art, including methods described herein above. It is noted that, for simplicity, not all elements of the deliver system are shown in  FIGS. 3C and 3D , for example a protective cover (corresponding to cover  322 ) may be included. It is noted, however, that if, for example, the stretching of implant  100  is performed within the urethra, a protective cover is not required and in some embodiments of the invention, is not deployed. 
     When implant  100  is to be stretched, a handle  388  of shaft  384  is pushed axially, so as to push a notch  386  coupled to implant  100  distally, and thus stretch implant  100 , to the state shown in  FIG. 3D . 
     Further alternatively or additionally, a stopper (not shown) is inserted into implant  100  holding it in its open state. When implant  100  is inserted into place the stopper is removed to allow the implant  100  to axially collapse and apply pressure on the obstruction tissue. In an exemplary embodiment of the invention, the stopper is in the form of a comb with prongs extending perpendicular to shaft  384 , being placed in the gaps between the turns  106  of implant  100 . Optionally, the stopper is elastic so that it can be removed by pulling handle  388  proximally. Alternatively or additionally, implant  100  has an elliptical cross-section. The stopper extends into implant  100  when it runs along the shorter axis of the implant. When it is to be removed, the stopper is rotated, by rotating handle  388 , and then the stopper is removed. 
     In still other embodiments of the invention, implant  100  is stretched by a balloon placed within implant  100 . When it is required to stretch the implant, the balloon is inflated. The shape of the balloon determines the extent to which tissue enters into gaps  104 . After the tissue enters into the gaps of implant  100 , the balloon is deflated and removed from the patient. 
     In some embodiments of the invention, before mounting implant  100  or before selecting a pre-mounted implant, the patient is diagnosed, in order to select an implant suitable for the patient. The diagnosis optionally includes imaging the obstructing tissue and/or inserting a measurement catheter for determining the patient&#39;s size and/or inflammation state. 
       FIG. 5  is an enlarged view of a distal end of system  300 , in accordance with an exemplary embodiment of the invention. Implant  100  is held by a sleeve  308  which surrounds inflation tube  366  and guide wire  304 . Sleeve  308  carries levers  328  and  338  which are controllable from a handle  354  ( FIG. 3A ) of implant carrier  350 . In a first state, levers  328  and  338  hold implant  100  in an expanded state while the implant is inserted into the patient. When implant  100  is determined to be properly positioned near the enlarged prostate tissue  108 , levers  328  and  338  are moved into a release state, disconnecting implant  100  from implant carrier  350 . 
     In some embodiments of the invention, sleeve  308  carries two distal levers  328  and two proximal levers  338 . The use of two proximal levers  338  and two distal levers  328  provide stable holding of implant  100 . Alternatively, more than four levers  328  and  338  may be used, or fewer than four levers may be used. 
     In some embodiments of the invention, the releasing ( 420 ) of implant  100  is performed simultaneously by all of levers  338  and  328 . Alternatively, a slow release is performed, in order not to exert a large force on the tissue at the time of release. Optionally, distal levers  328  are released first and then proximal levers  338  are released, such that the proximal side of implant  100  remains in its position in the beginning of the obstructing tissue. Alternatively, the proximal levers  338  are released first. Further alternatively, each lever is released separately. 
     Optionally, before releasing implant  100 , implant  100  is held in its stretched state for a sufficient time to allow obstructing tissue to enter gaps  104 . Alternatively, implant  100  is pushed into place, such that obstructing tissue enters into the gaps  104  of the implant immediately upon insertion. 
     In some embodiments of the invention, an internal tube is positioned within implant  100  during the release of the implant, in order to limit the depth of entrance of tissue into the gaps. Optionally, the physician can select which of a plurality of internal tubes to use and/or whether to use a tube at all. Alternatively, the internal tube has portions of different radius. The physician controls the depth of entrance of obstructing tissue into gaps  104  by moving the internal tube axially. 
     Referring in more detail to determining ( 412 ) the position of implant  100 , in some embodiments of the invention, the position is determined using an external imaging apparatus, such as x-ray or ultrasound. Alternatively or additionally, system  300  carries a viewing optical channel, for example within sleeve  308 , which provides images of the urethra from inside. Further alternatively or additionally, system  300  is inserted until the additional resistance of enlargement area  202  against balloon  362  is felt by a physician performing the insertion. System  300  is then inserted an additional precise distance in order to bring implant  100  to enlargement area  202 . 
     Alternatively or additionally, implant  100  or system  300  includes an expandable element (e.g., balloon  362 ) at its distal end. System  300  is pushed all the way into the patient&#39;s bladder  214 , allowing the expandable element to expand and prevent pulling implant  100  away from the bladder  214 . Thus, the physician knows that if balloon  362  was sufficiently expanded, a first end of implant  100  is positioned in the bladder  214  and the other end could not reach the patient&#39;s sphincter. Optionally, after implant  100  is properly positioned, the expandable element is collapsed and removed from the patient with system  300 . 
     In some embodiments of the invention, implant  100  is left in place for a predetermined time, after which implant  100  is removed from the patient. Alternatively or additionally, images (e.g., ultrasound images) of implant  100  are acquired periodically (e.g., once every 3-9 days), to verify that no problems have occurred and/or to determine when the implant is to be removed from the patient. In the acquired images, the distance between neighboring turns  106  is optionally determined and accordingly the time until implant  100  completely contracts axially and needs to be removed, is determined. Optionally, the patient acquires the images on his own, and transmits the images to a physician for analysis. 
     While implant  100  is in place, its presence may be used to aid in surgical treatment procedures. In some embodiments of the invention, a tissue cutting apparatus is used to cut the tissue bulging into the center of the implant  100 . The tissue cutting apparatus is optionally linked to the implant  100 , which is distanced from the sphincter according to previous position verification, so that the tissue cutting apparatus does not inadvertently damage the sphincter. 
     In some embodiments of the invention, as mentioned above, the delivery system may employ an optical fiber used to view the urethra and prevent damage to the sphincter  212  ( FIG. 11C ). Alternatively or additionally, the delivery may be performed without a balloon on the delivery apparatus. An exemplary embodiment for delivery of implant  100  is described hereinbelow with reference to  FIGS. 11A-11E . It is noted that the embodiments of  FIGS. 3 ,  10  and  11 A- 11 E are shown by way of example and additional delivery systems may be used, including combinations of the embodiments of  FIGS. 3 ,  10  and  11 A- 11 E. 
     Removal Apparatus 
       FIGS. 6A and 6B  schematically illustrate a process of removing implant  100  from a urethra  200 , in accordance with an exemplary embodiment of the invention. As mentioned above, in some embodiments of the invention, when implant  100  completes the dissecting of the obstructing tissue, implant  100  exits the patient&#39;s body automatically with the patient&#39;s urine. In other embodiments, however, implant  100  is removed using a removal system  600 . 
     Removal system  600  includes an outer tube  608  which surrounds a hook holding body  602  that defines an internal channel  604 . Hook holding body  602  carries a hook  606  which is free to move laterally within body  602 . During insertion of removal system  600 , a balloon catheter  610  is optionally passed through channel  604 , with an inflated balloon  612  leading the path into the urethra  200 . Once the distal end of body  602  is brought close to implant  100 , balloon  612  is deflated and balloon catheter  610  is removed from channel  604 . 
     Referring now to  FIG. 6B , in some embodiments of the invention, an optical fiber  620  (or any other viewing apparatus) is inserted into channel  604 . Optical fiber  620  may be used, for example, to aid in fitting hook  606  into holes  102  ( FIG. 1 ). Hook  606  is pushed distally toward implant  100 , while hook holding body  602  remains in place. Hook  606  is optionally flexible such that it bends radially when it exits body  602 . If necessary, the distance between body  602  and implant  100  is adjusted, so as to adjust the point at which hook  606  reaches implant  100  and thus fit hook  606  on to implant  100 . The physician then retracts system  600 , pulling implant  100  along with hook  606 . At first, body  602  is optionally retracted relative to outer tube  608 , so as to bring implant  100  into the outer tube. Thereafter, outer tube  608 , body  602  and hook  606  are pulled out together from the urethra. Pulling implant  100  into outer tube  608  before removing the implant from the patient reduces the chances of implant  100  getting stuck again on prostate or urethra tissue. 
       FIG. 6C  schematically illustrates a process of removing implant  100  from a urethra  200 , in accordance with another exemplary embodiment of the invention. In  FIG. 6C , instead of pulling the proximal end of implant  100  as shown in  FIG. 6B , hook  606  is passed through implant  100  to the distal turn  633  of the implant. Hook  606  is then used to pull implant  100  through itself into outer tube  608 . By pulling implant  100  through itself into outer tube  608 , the dragging of implant  100  on the patient&#39;s tissue is optionally avoided. 
     The removal procedure may be performed after the dissecting of the expanding tissue is completed or in emergency cases, before the dissection is completed. Optionally, in such emergency cases, dissection apparatus known in the art (e.g., cryo, ablation, cutting) is used before insertion of removal system  600  to remove the expanded tissue between turns  106 , as this tissue anchors implant  100  within prostate  210 . In an exemplary embodiment of the invention, implant  100  is removed by stretching it axially, in order to release the tissue caught by the implant. 
     Other Implant Structures 
     Alternatively to using implant  100 , other elastic implant structures may be used. In some embodiments of the invention, an implant is formed of a plurality of springs connected axially by struts. Alternatively or additionally, an implant is formed of a plurality of thin strings connected radially. Optionally, the connection allows a degree of freedom, so that the contraction of each of the springs proceeds at its own pace. Thus, the dissection of soft tissue at one side can proceed at a different rate than dissection of hard tissue on another side. Additional implants are now described, with reference to  FIGS. 7A-7B  and  8 A- 8 F. 
       FIG. 7A  is a schematic illustration of an elastic prostate implant  700 , which may be used instead of implant  100 , in accordance with an exemplary embodiment of the invention. Implant  700  comprises an elongate tube having a hollow cylinder shape with a plurality of slits  702 ,  704 ,  706  and  708  along its length. The slits divide implant  700  into a plurality of strips  714 , which are connected to each other. Stretching implant  100 , for example by pulling handles  712  on opposite ends away from each other, opens slits  702 ,  704 ,  706  and  708  into gaps which receive obstruction tissue. 
     Optionally, along the length of implant  100  there are a plurality of slits  702  and opposite side slits  706 , at the same axial position along the length of implant  700 . Thus, only a small strip  710  of implant  700  and another strip on an opposite side (not shown) connects the portions of implant  700  divided by the slits  702  and  706 . Between each two slits  702 , slits  704  and  708  are optionally formed at substantially 90° relative to slits  702  and  706 . Thus, implant  700  opens tissue grasping gaps in all directions. Alternatively, only slits  702  and  706  are defined in implant  700 , so that only obstructing tissue in a portion of the circumference is dissected by implant  700 . An implant in accordance with this alternative is optionally used when the obstructing tissue protrudes only from s specific direction. 
     In some embodiments of the invention, implants  100  and  700  have equal opening area for receiving tissue to be dissected, all around the circumference in 360°. Alternatively, an implant has openings around less than the entire circumference, for example around 270°, 180° or 90°. Such implants may be used, for example, when the obstructing tissue does not cover the entire circumference of the prostate and/or when it is desired to perform the dissection process in a more gradual manner. In an exemplary embodiment of the invention, the dissection is performed in a plurality of stages of insertion of implants. In a first stage, an implant with slots over a limited area of the circumference and/or having a short length is used. If the patient does not react negatively (e.g., with fever), a full scale 360° implant is used in a second stage. 
     Alternatively to configuring the implant to catch tissue in only some directions, at the time of insertion the implant is prevented from capturing tissue in some of the gaps and/or directions. In some embodiments of the invention, cover  322  ( FIG. 3A ) is formed of a plurality of separately controllable portions. Optionally, in each circumference portion, cover  322  includes a separate cover. According to the desired directions in which the dissection is to be performed, portions of the cover are removed. The implant is then released to engage tissue in the directions in which the cover was removed but not contact tissue in directions in which the cover was not removed. After the implant ( 100  or  700 ) is released, the remaining cover portions are removed together with carrier  350 . In some embodiments of the invention, cover  322  includes between 4-6 separate covers. Alternatively or additionally, the implant is inserted into the patient along with one or more barriers which separate the implant from tissue which is not to be dissected. Implant  100  is optionally allowed to move freely relative to the barrier, so that it does not distort. 
     Due to its structure, implant  700  provides substantially even pressure along its length, without complex production adaptations for changing the applied pressure of different portions of implant  700 . It is noted, however, that if it is desired axial portions of implant  700  may be reinforced in order to increase the pressure along portions of the length of implant  700 . The reinforcement may be performed by using a larger width or thickness in some axial portions and/or by selective annealing of axial portions of implant  700 . It is noted that similar methods may be used to control the pressure of implant  100 . 
     Using implant  700 , the dissected tissue is cut off in non-contiguous pieces, each slit  702 ,  704 ,  706  and  708  being responsible for a separate fragment of obstructing tissue. Implant  100 , in contrast, optionally cuts a contiguous obstructing tissue fragment. In some embodiments of the invention, due to the pressure on the obstructing tissue, the tissue cells die and separate into small tissue fragments. 
       FIG. 7B  is a flattened plan view of an implant  800 , in accordance with another exemplary embodiment of the invention. Implant  800  is similar to implant  700 , but includes sharp tips  802 , which add to the pressure applied to the obstruction tissue and/or help engagement of the tissue by the implant. Sharp tips  802  are optionally pointed in the directions in which the pressure is applied. In some embodiments of the invention, all the sharp tips  802  are in the same direction, so as to allow easier removal of the implant, when necessary. Alternatively, an implant may include sharp tips in both directions in which pressure is applied, so as to increase the pressure on the tissue. Further alternatively or additionally, an implant includes tips in directions orthogonal to the applied pressure and/or diagonal to the direction of the pressure, for example, in order to anchor the implant in the tissue and/or in order to increase the dissection effect radially outward, by pressing the obstruction tissue against the prostate. In other embodiments of the invention, tips extending outward radially are not used, so as not to interfere with the axial contraction of implant  800 , while the tissue within the gaps is dissected. 
     Alternatively or additionally to using small sharp tips  802 , large sharp tips are used. In  FIG. 7B , slits  820  are formed in implant  800 . Tips  822  within the slits  820  are optionally bent outward radially, in order to engage urethra tissue. Tips  822  are optionally bent outward to a small extent, for example of 5-10°. Alternatively or additionally, at least some of tips  822  are bent out of implant  800  by a large extent, of 20-30° or even more, e.g., between 40-70°. 
     In some embodiments of the invention, tips  822  are extended outwardly at the time of production of the implant or, at the latest, at the time of loading the implant on implant carrier  350 . Alternatively or additionally, tips  822  are pushed out after the implant is installed in the patient. Optionally, an internal tube inserted with implant carrier  350  is used to push out tips  822 . 
     Tips  822  are optionally all pointed in a same axial direction. Thus, implant  800  can move axially in one direction, so that implant  800  is allowed to contract axially as the tissue is dissected. Alternatively, tips  822  are directed in both axial directions. Further alternatively or additionally, implant  800  includes tips directed perpendicular to the axial axis of implant  800 . Further alternatively or additionally, implant  800  includes tips directed in substantially any other direction. 
       FIGS. 8A and 8B  are schematic illustrations of an implant  850  in open and closed configurations, in accordance with an exemplary embodiment of the invention. Implant  850  includes an elastic mouth  852 , which opens when ends  854  are moved closer to each other. In some embodiments of the invention, implant  850  is placed in the patient axially between ends  854 . Alternatively, implant  850  is placed horizontally or diagonally. 
     Before employment, ends  854  are pressed closer to each other in order to open mouth  852 . Once obstructing tissue enters into mouth  852 , ends  854  are released so mouth  852  closes on the tissue as shown in  FIG. 8B . 
       FIGS. 8C and 8D  are schematic illustrations of an implant  860  in open and closed configurations, in accordance with another exemplary embodiment of the invention. 
       FIGS. 8E and 8F  are schematic illustrations of an implant  870  in open and closed configurations, in accordance with another exemplary embodiment of the invention. 
     Implant  860  includes small teeth which enhance the pressure on the obstructing tissue, by separating the captured tissue into different cavities. This is in contrast to the flat configuration of implant  870  and the configuration of implant  850 , in which there is a single large dent  858  ( FIG. 8A ). It is noted that other configurations may be used according to the texture of the obstructing tissue, the desired dissection time and other dissection related attributes. 
     Non Elastic Dissection Device 
     Instead of using an elastic implant which automatically compresses with the progression in the dissection of the obstruction tissue, a tool with a manually adjustable pressure level is used, as is now described. Periodically, a physician or the patient change the mechanical state of the tool, until the dissection is completed. 
       FIG. 9  is a schematic cross-sectional view of a tissue dissection tool  950 , in accordance with an exemplary embodiment of the invention. Tool  950  includes a plurality of pressure inducing units  952 , formed of opposite members  954 . Pressure inducing units  952  catch portions  222  of prostate enlargement  208 , so as to dissect these portions. In some embodiments of the invention, a channel  958  passes all along dissection tool  950 , allowing urine to pass out through the tool. 
     A proximal handle  956  is used to control the distance between the members  954  of pressure inducing units  952 , and hence the amount of pressure on the prostate portions caught by pressure units  952 . In some embodiments of the invention, the patient and/or a physician periodically turn a control on handle  956 , so as to increase (or reduce, if necessary) the pressure applied on the dissected tissue. The increase in the applied pressure is optionally performed at predetermined time (e.g., once every 2-3 days). Alternatively or additionally, the increase in the pressure is performed based on feedback on the progression of the dissection, for example from medical acquired images (e.g., ultrasound images). The feedback may also include patient indications on pain or relief. Alternatively or additionally, the feedback is based on the resistance met in turning handle  956 . 
     Alternatively to using a rotating handle  956 , a handle which is pulled axially in order to increase the applied force, is used. Alternatively to using channel  958 , a thin thread may be used to pull pressure units  952  to a closed position. In some embodiments of the invention, the each pair of members  954  is controlled by a lever (not shown) which closes the gap between the members when the thread is pulled. Alternatively or additionally, the thread is connected to distal members  954  in each unit  952 , while a proximal member  954  remains stationary. The thread may include, for example, Kevlar, stainless steel, prolan and/or any other strong material. Alternatively to a single thread, a dissection tool may be controlled by a plurality of threads, which are optionally marked to indicate which units  952  are controlled by each thread. For example, different threads may control units  952  of different cross sectional sectors and/or of different axial areas. The use of threads instead of a massive handle may be more convenient for some patients. 
     In some embodiments of the invention, a torque limiter, for example using a clutch mechanism, is employed between handle  956  and pressure units  952 . The torque limiter limits the force that can be applied to pressure units  952  and prevents inadvertent sudden and/or painful cutting of the tissue. 
     Optionally, after pressure units  952  are closed entirely, dissection tool  950  is removed from the patient. Alternatively, pressure units  952  are re-opened, and another dissection period is commenced. After pressure units  952  are re-opened, enlargement tissue is allowed to reenter the units for a predetermined period. Thereafter, the pressure units are slowly closed to cause the dissection. 
     In some embodiments of the invention, all of pressure units  952  are controlled together by handle  956 . Alternatively, at least two pressure units  952  are controlled separately. This alternative is more complex, but allows the patient and/or physician more freedom in controlling the dissection. In some embodiments of the invention, the separate control allows controlling different axial portions separately. Alternatively or additionally, the separate control allows control of different radial portions separately. 
     Handle  956  optionally extends proximally from the patient, to allow simple control by the patient or a physician. Alternatively, the proximal end of handle  956  is within the patient, and a compatible wrench is used to turn the control portion of handle  956 . Alternatively or additionally, a pre-programmed automatic controller with a miniature motor or pre-wound spring is embedded within dissection tool  950 . The miniature motor is optionally positioned in the bladder and/or in the inner side of the implant. The automatic controller increases the pressure applied by units  952 , without need of user intervention. 
     In some embodiments of the invention, the elasticity of the implant is enhanced and/or replaced by magnets on opposite ends of the implant, which are oriented to attract each other. Alternatively or additionally, one of the ends of the implant is formed of a magnetic material. An external magnet is used to apply force which compresses the implant and applies force on the captured tissue. The size of the magnet may be adjusted in order to control the pressure applied to the tissue caught by the implant. 
     Alternatively or additionally, implant  100  is configured to contract when a low electrical current is applied to the implant. Implant  100  may include a current source implanted in the patient or an external current source may be used. 
     In some embodiments of the invention, the urine flow of the patient and/or the chemical form of the urine is used to provide energy used in applying pressure to the tissue by the implant. In an exemplary embodiment of the invention, the implant comprises a material which slowly deforms as it absorbs fluids. 
     Implant  100  is formed, in some embodiments of the invention, from one or more materials which change with heat and/or under other external conditions, such as electrical current. Applied heat optionally causes the implant to contract and apply pressure to the tissue. 
     In some embodiments of the invention, implant  100  is formed alternately from two different materials one of which contracts in heat and the other expands in heat. Applying a required heat pattern can cause the implant to exit the patient without requiring an invasive procedure. 
     Optionally in embodiments which use external force (e.g., magnet, heat), the external force is applied over long periods of time in order to affect the dissection of tissue. Alternatively, the implant includes a ratchet mechanism which prevents the implant from releasing the pressure level it reached. Each time it is required to further compress the implant, the external pressure is applied with a sufficient time and/or power in order to reach the next ratchet level. Further alternatively or additionally, the external force is used in addition to the elasticity of the implant, for example in order to overcome tough tissue and/or in order to enhance the dissection in a beginning and/or ending stage. 
     Other Insertion Methods 
     The method of insertion of an implant, shown in  FIGS. 3A and 3B  was brought as an example and other methods may also be used. 
       FIG. 10  is a schematic illustration of a system  980  for inserting an implant  100 , in accordance with an exemplary embodiment of the invention. System  980  includes a base  982  from which a proximal bar  984  and a distal bar  986  protrude. At their distal ends, bars  984  and  986  are connected to ends of implant  100 , optionally with a fast release mechanism. In some embodiments of the invention, the fast release mechanism of proximal bar  984  includes a fast release knot  988 . A string  990  to be pulled in order to release knot  988  optionally passes through bar  984 . In some embodiments of the invention, distal bar  986  includes a snap mechanism  992 . Optionally, releasing snap mechanism  992  requires applying at least a minimal pull force to distal bar  986  relative to implant  100 , which is achievable only when implant  100  properly grasps the prostate tissue. Thus, implant  100  cannot be released prematurely. 
     Alternatively to using different release mechanisms on distal bar  986  and on proximal bar  984 , the same mechanism may be used for both bars  984  and  986 . 
     As mentioned above, in some embodiments of the invention, implant  100  is in an axially stretched state when inserted into the patient. Alternatively or additionally to being stretched axially, one end of implant  100  is wound while the other end is held stationary, in a manner which decreases the cross-section radius of implant  100 . Referring back to  FIGS. 3C and 3D , before an insertion procedure, implant  100  is mounted on implant delivery system  380 . In addition to, or instead of, being axially stretched, handle  388  is rotated, while notch  386  grasps a distal end of implant  100 , and a proximal end of implant  100  remains stationary or is wound in an opposite direction. After implant  100  is wound sufficiently, its internal radius decreases, such that its insertion into the patient is easier. After implant  100  is inserted into place, handle  388  is rotated in an opposite direction, until the winding of implant  100  is reversed. The reversal of the winding causes he radius of the implant to increase until tissue is caught between the turns of implant  100 . Then, the axial stretching of implant  100  by delivery system  380  is released and system  380  is removed from the patient. 
     Alternatively to releasing the winding of implant  100  by turning handle  380  in an opposite direction, implant  100  may be released abruptly, to expand in an uncontrolled manner. 
     Referring in detail to the winding of implant, in some embodiments of the invention, the winding reduces the radius of the implant by at least  20 %,  40 % or even  60 %. In an exemplary embodiment of the invention, the winding reduces the radius of the implant from  8  French to less than  5  French or even less than  3  French. 
     Alternatively to winding implant  100  from its distal end, the winding may be performed from its proximal end, while, for example, notch  386  holds the distal end of the implant. 
     Safe Insertion 
       FIGS. 11A-11E  illustrate a system and method for accurately accessing prostate tissue, for example for inserting an implant for reshaping prostate tissue, in accordance with an exemplary embodiment of the invention. 
       FIG. 11A  is a schematic illustration of an insertion unit  1000 , in accordance with an exemplary embodiment of the invention. Insertion unit  1000  comprises an endoscopic inner tube  104  which is movable within an outer tube  1002 . Inner tube  1004  includes a viewing fiber  1006  or any other viewing apparatus, such as an endoscopic camera. At its distal end, inner tube  1004  optionally has a conic shape, to aid in insertion of insertion unit  1000  into the urethra. Outer tube  1002  optionally has a diameter slightly larger (e.g., less than 10% larger) than the diameter of inner tube  1004 , allowing relative motion of the tubes relative to each other. In an exemplary embodiment of the invention, inner tube  1004  has a diameter of about 6.8 mm and outer tube  1002  has a diameter of about 7.2 mm. Other diameters may be used according to the size of the patient&#39;s urethra. 
     In some embodiments of the invention, outer tube  1002  includes length markings which allow easy determination of the extent to which insertion unit  1000  is in the urethra. Alternatively, any other method may be used to determine the extent of insertion of insertion unit  1000  into the urethra. For example, tube  1002  may have a position sensor (e.g., a magnet or coil) on its distal end. According to readings of the position sensor, the extent of insertion of tube  1002  is determined. 
       FIG. 11B  is a schematic illustration of insertion unit  1000  within the urethra, in accordance with an exemplary embodiment of the invention. In a first stage, shown in  FIG. 11B , optical fiber  1006  is brought to the proximity of sphincter  212 . The extent of penetration of insertion unit  1000  is registered when sphincter  212  is viewed in the proximity of the distal end of fiber  1006 . In a second stage, outer tube  1002  is pushed to the end of the prostate where prostate meets the bladder  214 . Optionally, viewing fiber  1006  is used to verify that outer tube  1002  reached the meeting point of the prostate and bladder  214 . The extent of penetration to the distal end of the prostate is then registered. The difference between the extents of penetration at the entrance to the bladder  214  and at sphincter  212  is the length of the prostate. In some embodiments of the invention, according to the determined length, a suitable implant is selected. 
     Inner tube  1004  is then removed from within outer tube  1002 , while outer tube  1002  remains within the urethra. 
     As shown in  FIG. 11C , an implant carrier  1020  is inserted into outer tube  1002  and outer tube  1002  is retracted such that the distal end of outer tube  1002  is at or slightly beyond sphincter  212 . The retraction is optionally performed based on the distance registration when viewing fiber  1006  identifies sphincter  212 , for example using the markings on outer tube  1002 . 
     In some embodiments of the invention, implant carrier  1020  is first inserted into outer tube  1002  and thereafter outer tube  1002  is retracted. Alternatively, implant carrier  1020  is inserted into outer tube  1002  only after the tube is retracted back to sphincter  212 . Further alternatively, outer tube  1002  is not pushed ahead to the entrance to bladder  214 , at all. Implant carrier  1020  optionally includes a protective cover  1024 , which isolates the implant from the urethra before it is deployed. Protective cover  1024  optionally has a handle  1026 , which may be pulled back in order to expose implant  100 , as shown in  FIG. 11D . An inner implant holder  1030  ( FIG. 11E ) of which only a handle  1032  is shown in  FIG. 11C , actually carries the implant  100 . A handle  1045  allows a physician to hold implant carrier  1020 . A locking unit  1038  keeps handle  1026  of protective cover  1024  in place. Removal of locking unit  1038  allows retraction of handle  1026  and exposure of implant  100 , as shown in  FIG. 11D . In some embodiments of the invention, handle  1026  is spring mounted, such that upon removal of locking unit  1038 , implant  100  is automatically exposed. 
     As shown in  FIG. 11D , implant  100  is optionally longer than the prostate enlargement area of most patients, such that a portion of implant  100  is within bladder  214 . Once implant  100  is in place and exposed, handle  1032  is retracted, as shown in  FIG. 11E , so as to disconnect ties between implant carrier  1020  and implant  100 . Optionally, implant  100  is connected to implant holder  1030  through strings  1042  and  1044 . Strings  1042  and  1044  optionally have weak points which tear when handle  1032  is retracted. The release of implant  100  optionally causes the implant to anchor in prostate tissue. A portion  1048  ( FIG. 11D ) of implant  100 , located within bladder  214 , is not anchored in tissue and therefore contracts axially (as shown schematically in  FIG. 11E ) upon release of implant  100  from implant holder  1030 . The remaining portion of implant  100  anchors in the prostate tissue, so that it does not contract abruptly but rather slowly performs the reshaping. 
     In some embodiments of the invention, handle  1032  cannot be retracted in order to release implant  100 , before handle  1026  was retracted to expose implant  100 , so that prostate tissue enters gaps of the implant, anchoring the implant. 
     After implant  100  is properly positioned, outer tube  1002  and implant carrier  1020  are removed from the urethra. 
     Alternatively or additionally to recording the extent of penetration of outer tube  1002  into the patient, once the sphincter  212  is identified, outer tube  1002  is slightly advanced and is then anchored in place so that it does not move until after implant  100  is in place. 
     The method described above with reference to  FIGS. 11A-11E  may be used also for other prostate treatment methods, such as mechanical cutting of enlargement tissue, cryo-treatment, RF ablation and/or other ablation methods. After positioning outer tube  1002 , the cutting and/or treatment tool to be used is passed through outer tube  1002  to the treatment location. Thus, the distal end of outer tube  1002  protects sphincter  112  from the tissue treatment apparatus used. 
     Although the above description relates to use in the urethra, similar devices can be used in other body channels which may be obstructed, such as in a channel between the kidney and the bladder or between the cholecyst and the liver. Similar devices may optionally be used in the esophagus and/or in the intestine. Furthermore, similar devices to those described above may be used to remove polyps in many body organs. The implant used is adapted to the body portion in which it is employed in the materials used, the size, shape and/or other attributes. 
     In some embodiments of the invention, system  300  and/or other insertion and/or removal tools are flexible tools which conform to the shape of the body channel into which it is inserted. Alternatively, system  300  and/or other insertion and/or removal tools are rigid, allowing easier insertion of the tools. 
     It will be appreciated that the above described methods may be varied in many ways. It should also be appreciated that the above described description of methods and apparatus are to be interpreted as including apparatus for carrying out the methods and methods of using the apparatus. 
     The present invention has been described using non-limiting detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. For example, the removal of the stent may be performed by an endoscopic tweezers, rather than by the apparatus of  FIGS. 6A and 6B . It should be understood that features and/or steps described with respect to one embodiment may be used with other embodiments and that not all embodiments of the invention have all of the features and/or steps shown in a particular figure or described with respect to one of the embodiments. Variations of embodiments described will occur to persons of the art. 
     It is noted that some of the above described embodiments may describe the best mode contemplated by the inventors and therefore may include structure, acts or details of structures and acts that may not be essential to the invention and which are described as examples. Structure and acts described herein are replaceable by equivalents which perform the same function, even if the structure or acts are different, as known in the art. Therefore, the scope of the invention is limited only by the elements and limitations as used in the claims. When used in the following claims, the terms “comprise”, “include”, “have” and their conjugates mean “including but not limited to”.