Abstract:
There is provided a system for opening and temporarily supporting a section of a generally tubular organ. The system includes a dilation catheter which has an integrally connected shape memory catheter tip. The shape memory catheter tip is made of a shape memory alloy. The shape memory catheter tip assumes a first shape at a first temperature and a second shape at a second temperature. Accordingly, the shape memory catheter tip is inserted into the body of the patient, while being in a narrow shape and expands within the body of the patient.

Description:
This application is a parent case of patent application Ser. No. 09/274,851. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method and a device for widening tubular organs in general and to a method and a device for widening arteries in particular. 
     BACKGROUND OF THE INVENTION 
     Devices and methods for widening tube shaped organs, in general and in the human body, in particular, are known in the art. 
     U.S. Pat. No. 5,716,410, to Wang et al, is directed to a catheter for vascular use. The catheter includes a directing mechanism and an inflatable balloon at the tip. The tip also includes a temporary stent, made of thermoplastic material. The catheter is inserted into the body of the patient, via a wide surface artery and the operator directs the catheter toward the destination location. When the tip is positioned at the destination location, then the operator pumps fluid to the balloon, via a tube, running along the catheter and starts inflating the balloon. 
     Reference is now made to FIG. 2, provided by Wang et al as FIG. 1, which is an illustration of a catheter, known in the art. 
     At the same time, the thermoplastic stent is heated, thereby unlocking its shape. The balloon, as it inflates, applies circumferencial pressure on the stent and the tubular organ, thereby forcing them to extend. Accordingly, the circumference of the tubular organ becomes larger. When the balloon brings the thermoplastic stent to the destination diameter, then the thermoplastic stent is cooled, thereby fixing its shape at a larger diameter, where it supports the tubular organ at an enlarged position. 
     Then, the operator, reduces the pressure within the balloon, which in turn deflates and becomes smaller than the enlarged circumference of the tubular organ. The thermoplastic stent is then kept within the tubular organ for a time period which may range from a few minutes to as long as a week. Finally, the thermoplastic stent is reheated, thereby unlocking its shape, and enabling its removal from the body of the patient. 
     It will be appreciated by those skilled in the art, that a balloon is often longer than the segment to be treated. Hence, the inflatable portion of the balloon extends beyond the desired segments to healthy segments, and can cause damage thereto. 
     Furthermore, when a balloon is inflated inside a blood vessel, it occludes the blood flow distally and becomes a full barrier for any blood flow therein. It will be appreciated by those skilled in the art that many blood vessel related balloon treatments are performed in coronary arteries. Accordingly, such a procedure, while blocking blood flow through the treated blood vessel, may cause ischemia or even cardiac arrest. 
     The balloon blocks the blood flow both in the axial (through the blood vessel) and radial directions blocking branches. 
     The complete obstruction, a balloon related treatment is usually limited to one or two minutes of inflation, since the patient can not tolerate long time inflations, because of severe pain and chest discomfort, due to ischemia. 
     It will be appreciated by those skilled in the art that a blood vessel is generally a flexible organ. This fact, combined with the short time period in which a balloon expands the circumference of the blood vessel, (as much as 40% of the cases) causes the balloon treated blood vessel to assume its original size (recoil) immediately, or within few months shortly after the treatment. 
     A stent is generally an element which is inserted into the tubular organ with the aid of a catheter. The initial shape of a stent is of an elongated cylinder, having a diameter which is smaller than the narrowed section of the tubular organ, through which it has to pass. At the beginning of the treatment, the stent is positioned in the stenosed segment. 
     Then, the circumference of the stent is widened, by various methods, known in the art. One of these methods includes inserting a balloon into the stent and applying pressure by inflating it therewith. Accordingly, the stent widens, thereby applying pressure on the narrowed blood vessel. As a result, the stent widens the cross section of the diseased segment. 
     Finally, the balloon is deflated and is removed from the stent, which remains in its widened position, forcing the widened blood vessel to remain at its new state. Afterwards, the stent is covered by local tissue and is anchored thereto. This poses a disadvantage in the usage of a stent since such a stent can not be removed. A stent is an alien element within a living organism, which might produce thrombus in it. 
     In many cases (15%-40%) instant stenosis occurs. The mechanism of this narrowing is intimal proliferation thereby causing a new blockage at the same location. It is known by those skilled in the art that sometimes, such a reoccurring blockage is difficult to treat and in some cases, surgery is needed, to remove and replace the clogged section. 
     In some instances the stent may be lost and migrate distally in the coronary artery, or sometimes in the aorta and its branches. The stent also can be stucked. 
     Shape memory effect (SME) is a phenomena, in shape memory alloys (SMA) of a reversible transition from one solid phase into the other (i.e., from Martensite into Austenite or from Austenite to Martensite). Heating the alloy causes the transition from Martensite into Austenite. Cooling the alloy causes the reverse transition, from Austenite into Martensite. NiTi alloys are examples for such shape memory alloys. 
     Martensite and Austenite are two solid state phases, which are typical for alloys. Each of these phases is characterized in a certain crystaline structure. 
     Basically there are two types of shape memory effects. The first type is called the one way shape memory effect (OWSM), where the material transits from one of the above phase states to the other, only once. The second type is called the two way shape memory effect (TWSM), where the material transits from one of the phase states to the other and back in a reversible process. 
     Shape memory alloys, such as Ni—Ti, Ni—Ti—X, Cu—Ni—Al, Cu—Zn—Al, Fe—Mn—Si, Ni—Ti—Co, Ni—Cu—X, Ni—Al and the like, are known in the art. These alloys exhibit a shape memory effect. In the martensite condition, the shape alloy material is relatively flexible and soft, and can be easily deformed. When the material undergoes the transition into an austenite state, it becomes more rigid, and is able to apply force and generate work, deform and enlarge the cross section of the blood vessel. 
     U.S. Pat. No. 5,540,713 to Shnepp-Pesch et al, is directed to an apparatus for widening a stenosis in a body cavity, also known as a shape memory stent. Shnepp-Pesch describes a stent made from a shape memory alloy, assuming a first predetermined shape at a first predetermined temperature and second predetermined shape at a second predetermined temperature. When heated from the first temperature to the second one, the shape memory stent changes its shape from a narrow generally cylindrical shape to a wider generally cylindrical shape. 
     Shnepp-Pesch describe a plurality of shapes which are applicable as shape memory stents. Reference is now made to FIGS.  1 A- 1 H, provided by Shnepp-Pesch et al, as FIGS. 1A,  1 B,  2 A,  2 B,  3 A,  3 B,  4 A and  4 B, respectively. These figures describe four shape memory stent structures, each at two states, one narrowed and the other enlarged. 
     It will be appreciated by those skilled in the art that this stent basically suffers the same disadvantages as any other stent, known in the art, as listed above. 
     SUMMARY OF THE PRESENT INVENTION 
     It is an object of the present invention to provide a system for opening and temporarily supporting generally tubular organs, in general and arteries in particular. 
     It is a further object of the present invention to provide a novel method for temporarily supporting a tubular organ, in general and vascular organs in particular. 
     In accordance with the present invention, there is thus provided a system for opening and temporarily supporting a section of a generally tubular organ. The system includes a dilation catheter which has an integrally connected shape memory catheter tip. The shape memory catheter tip is made of a shape memory alloy. The shape memory catheter tip assumes a first shape at a first temperature and a second shape at a second temperature. Accordingly, the shape memory catheter tip is inserted into the body of the patient, while being in a narrow shape and expands within the body of the patient. 
     According to one aspect of the invention, the shape memory catheter tip is generally hollow, thereby enabling flow of bodily fluid therethrough. It is noted that the flow of fluid can be performed both in a radial direction as well as in an axial direction. 
     The system can further include an energy control unit, connected to the dilation catheter, for controlling the temperature of the shape memory catheter tip and an energy transfer unit. The energy transfer unit is connected between the shape memory catheter tip and the energy control unit. It is generally located within the dilating catheter and transfers energy between the energy control unit and the catheter tip. According to one aspect of the invention, the energy transfer unit is connected to the shape memory catheter tip, thereby transferring energy to and from. According to another aspect of the invention, the energy transfer unit is not integrally connected to the shape memory catheter tip, thereby transferring energy to and from the vicinity of the catheter tip. 
     The shape memory catheter tip can include a generally cylindrical coil. 
     According to a further aspect of the invention, the first shape is generally the shape of a cylindrical coil having a first diameter and the second shape is generally the shape of a cylindrical coil having a second diameter. Hence, when the shape memory catheter tip transforms from the first shape to the second shape, it widens the organ, which is attached thereto, for example, an artery. 
     According to one aspect of the invention, the generally cylindrical coil has a solid cross section. According to one aspect of the invention, the generally cylindrical coil has a hollow cross section and hence, enables the flow of fluid therethrough. 
     It is noted that the generally cylindrical coil can have a cross section, which is selected from the list consisting of radial cross section, elliptical cross section, semi radial cross section, semi elliptical cross section, a near rectangular cross section and the like. 
     The energy transfer means can include a conduit or a plurality of conduits and the temperature control unit can accordingly include means for providing temperature controlled fluid towards the shape memory unit via the energy transfer means. 
     According to one aspect of the invention, the one of the conduits, is opened in the vicinity of the shape memory catheter tip, thereby releasing temperature controlled fluid in the vicinity of the shape memory catheter tip. 
     According to a further aspect of the invention, the shape memory catheter tip includes a generally cylindrical coil, having a hollow cross section, through which temperature controlled fluid can flow. 
     According to one aspect of the invention, the cylindrical coil is connected to one of the conduits at a first end, and is open at a second end. Hence the conduit transfers temperature controlled fluid to the shape memory catheter tip, via the first end, and the shape memory catheter tip releases the temperature controlled fluid via the second end. 
     According to another aspect of the invention, the cylindrical coil is connected to a first one of the conduits at a first end thereof, and to a second one of the conduits, at the second end thereof. Hence the first conduit transfers temperature controlled fluid to the shape memory catheter tip, via the first end, and the second conduit receives temperature controlled fluid from the shape memory catheter tip, via the second end. 
     It is noted that the temperature control unit can include a power supply unit, which is electrically connected to the shape memory unit, thereby electrically heating the shape memory unit from the first temperature to the second temperature. Accordingly, the energy transfer means can include an electricity conducting unit, such as electrical wires, which are electrically connected to the shape memory unit. 
     The shape memory alloy, used to manufacture the shape memory catheter tip can be selected from the list consisting of: Ni—Ti, Ni—Ti—X, Cu—Ni—Al, Cu—Zn—Al, Fe—Mn—Si, Ni—Ti—Co, Ni—Cu—X, Ni—Al and the like. 
     It is noted that the shape memory catheter tip can be characterized to operate at a plurality of temperatures. Accordingly, the first temperature is equal or below the temperature of the environment, in which the shape memory catheter tip is placed. 
     Alternatively the first temperature can be in the range of 38 degrees Celsius and 65 degrees Celsius or in the range of 42 degrees Celsius and 50 degrees Celsius. Similarly, the second temperature can be in the range of 5 degrees Celsius and 35 degrees Celsius or in the range of 20 degrees Celsius and 32 degrees Celsius. It is noted in the manufacturing process, the first and second temperatures can be swapped (i.e., the first temperature is lower than the second temperature). 
     In accordance with a further aspect of the present invention, the system further includes elastic means, such as a spring, which are attached to the shape memory catheter tip having an initial shape. The initial shape is generally similar to the first shape of the shape memory catheter tip. The elastic means apply force on the shape memory catheter tip so as to deform the shape memory catheter tip to the initial shape of the elastic means. 
     According to one aspect, where the shape memory catheter tip is made of a hollow cross section tube, the elastic means can be inserted within the shape memory unit. According to another aspect of the invention, the elastic means are attached to the shape memory unit, on the outside. 
     It is noted that the front section of the shape memory catheter tip can be shaped as a guiding front end. 
     Alternatively, the system according to the invention can further include a guiding unit having a guiding tip, wherein the guiding unit is located within the dilation catheter and the guiding tip extends beyond the shape memory catheter tip. Accordingly, the guiding tip is operable to move relative to the shape memory catheter tip. 
     It is noted that the first diameter can be smaller than the second diameter. Alternatively, the first diameter can be larger than the second diameter. 
     The shape of the shape memory catheter tip in the martensite state can be narrow with respect to the shape of the shape memory catheter tip in the austenite state. Alternatively, the shape of the shape memory catheter tip in the martensite state can be wider with respect to the shape of the shape memory catheter tip in the austenite state. With reference to the above elastic means, the initial shape assumes a shape which is similar to the shape of the shape memory catheter tip in the martensite state, and hence can be narrow or wide, respectively. 
     It is noted that the conduits which are connected to the catheter tip can be concentric or side by side. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: 
     FIGS. 1A-1H, are schematic illustrations of a tubular restraining devices, which are known in the art; 
     FIG. 2 is a schematic illustration of a catheter having a balloon as its tip, which is known in the art; 
     FIG. 3 is a schematic illustration of a device for treating a tubular organ, constructed and operative in accordance with a preferred embodiment of the invention; 
     FIGS. 4A and 4B are illustrations of the tip end of the device of FIG. 3, constructed and operative in accordance with another preferred embodiment of the present invention; 
     FIGS. 5A,  5 B,  5 C,  5 D and  5 E are illustrations of typical cross sectional variations for helical SMA element of FIGS. 4A and 4B; 
     FIG. 6 is a schematic illustration of a method for operating the device of FIG. 3, operative in accordance with another preferred embodiment of the present invention; 
     FIG. 7 is a schematic illustration of a system, constructed and operative in accordance with a further embodiment of the present invention; 
     FIG. 8 is a schematic illustration in detail of the connection section of a helical SMA element and the inner side of the guiding catheter; 
     FIG. 9 is a schematic illustration in detail of a catheter tip, constructed and operative in accordance with another preferred embodiment of the present invention; 
     FIGS. 10A,  10 B,  10 C,  10 D,  10 E,  10 F and  10 G are illustrations of typical cross sectional variations for the catheter tip of FIG. 9; 
     FIG. 11 is a schematic illustration of a catheter tip, constructed and operative in accordance with a further preferred embodiment of the present invention; 
     FIG. 12 is a schematic illustration of a catheter tip, constructed and operative in accordance with another preferred embodiment of the present invention; and 
     FIG. 13 is a schematic illustration of a catheter tip, and energy transfer means, constructed and operative in accordance with a further preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention overcomes the disadvantages of the prior art by providing a novel device which is a catheter, having a hollow SMA element as its tip. 
     Furthermore, the present invention provides a novel method for operating the device of the invention, which overcomes the disadvantages of the prior art. 
     Reference is now made to FIG. 3 which is a schematic illustration of a device, generally referenced  100 , for treating a tubular organ, constructed and operative in accordance with a preferred embodiment of the invention. 
     The device  100  includes a guiding catheter  102 , a “Y” connector  110 , a hollow SMA tip  104 , a guidance unit  108  and a fluid supply and temperature control unit  106 . 
     The guide wire  108  is inserted through guiding catheter  102  via the “Y” connector  110 . The temperature control unit is connected to the Hollow SMA tip which is inserted via the “Y” connector  110  and over the guide wire  108 . 
     The guiding catheter  102  is an elongated tubular element which guides and locates the tip  104  within the patients tubular organ, which for example, can be a blood vessel, a urether, urethra, bile duct, colon eosophagus, stenosed valve, etc. and the like. The user of the device  100 , which is a medically trained person, uses the guidance Wire  108  to insert over it SMA tip into the diseased segment. 
     Reference is also made now to FIGS. 4A and 4B, which are illustrations of the tip end of the device  100 , of FIG.  3 . FIG. 4A shows the tip  104  inserted into a blood vessel  152 , having a section  158 , which is relatively narrower than the rest of the blood vessel. 
     The tip  104  includes a hollow shaped SMA element which is adapted to perform a transition from one shape at a first predetermined temperature range to another shape, at a second predetermined temperature range. 
     In the present example, the tip includes a helical SMA element  156 . The helical SMA element  156  has a narrow circumference shape at a temperature, which is equal or lower to a first temperature value T 1 , as shown in FIG.  4 A. The helical SMA element  156  has a wide cross section shape at a temperature, which is equal or higher to a second temperature value T 2 , as shown in FIG.  4 B. 
     The helical SMA element  156  is inserted over the guide wire  108  through guiding catheter  102  (FIG.  3 ). It is shaped so that its front end  164  (FIG. 4) has a round shape which is designed so that no damage is inflicted onto the blood vessel through which the tip is inserted. At its other end  162 , the helical SMA element  156  is connected to hollow tubes, which are able to supply various fluid temperatures thereon (shown in detail in conjunction with FIG.  8 ). 
     The device  100  is used to expand the circumference of the blood vessel  152 , at its narrowed cross section  158 , using the SMA tip  104 . 
     Accordingly, the user inserts the SMA element  156  into the blood vessel  152  and positions it in the diseased segment  158 . It is noted that all through the insertion phase, the helical SMA element  156  is maintained at a temperature, which is not higher than T 1 , thereby assuming its narrowed form. 
     When the helical SMA element  156  is located within the diseased section  158 , then, the user operates the temperature control unit  106 , which heats the helical SMA element  156  to a temperature which is not lower than T 2 . As the helical SMA element  156  heats, it undergoes a transition from its narrow shape into its wider shape. Accordingly, the helical SMA element  156  applies circumferencial pressure on the diseased segment  158 , thereby forcing it to become wider (FIG.  4 B). 
     According to the present invention, the user can maintain the helical SMA element  156  at its position, for a considerable period of time, which is in the order of minutes, hours and days, as needed. 
     As the shape of the helical SMA element  156  does not block flow. No ischemia is produced and hence, no harm or suffer is inflicted onto the patient, during this time period. 
     After reducing the SMA element  156  to its&#39; original size, the physician can direct it to another location, within the artery and use it again. Accordingly, the device of the present invention can be used for a plurality of narrowed artery locations, one after the other, without the need to remove the catheter out of the patients body. 
     According to the present invention, the heating up and cooling down of the helical SMA element  156  can be performed in a plurality of ways such as inducing a temperature bearing fluid there through, electric current, radiation, induction heating, and the like. 
     According to one aspect of the present invention, the helical SMA element  156  is made of a hollow wire, through which temperature bearing fluid is induced or others. 
     As the diseased segment  158  is forced to be in a widened state (FIG. 4B) for a considerable time, by the helical SMA element  156 , then the probability of it shrinking back to its narrow state (FIG. 4A) decreases significantly. 
     At the end of the treatment, the user, operates the temperature control unit  106 , to lower the temperature of the helical SMA element  156 , which in turn returns to its initial state as shown in FIG.  4 A. Finally, the user takes out the SMA catheter  100  than the guide wire  108  and finally the guiding catheter  102  out of the patients body, or to another vessel which needs to be dilated. 
     It will be noted that according to this aspect of the present invention, no element such as a stent, remains in the artery, to maintain its widened state, at the end of the treatment. Hence, at any time after the treatment, any type of catheter can be inserted into the artery, passing distally through section  158 , for example, for repeating the treatment of section  158 . 
     According to the present invention, the helical SMA element  156  is made of a hollow conduit. A fluid flowing there through having a predetermined temperature, applies that temperature thereon. Accordingly, a temperature change can be applied on the element  156 . 
     The side walls of the catheter are substantially round shaped having a smooth surface, for reducing the probability of inflicting any damage to the inside walls of the treated artery (the intima). 
     Reference is now made to FIGS. 5A,  5 B,  5 C,  5 D and  5 E, which are illustrations of cross sectional variations for helical SMA element  156 , constructed and operative in accordance with the present invention. 
     FIG. 5A shows a circular cross section, FIG. 5B shows an elliptical cross section, FIG. 5C shows a half elliptical cross section, FIG. 5D shows a near rectangle cross section and FIG. 5E shows a solid (full) radial cross section. 
     Reference is now made to FIG. 6, which is a schematic illustration of a method for operating the device  100  of FIG. 3, operative in accordance with another preferred embodiment of the present invention. 
     In step  200 , a guiding wire is inserted into the tubular organ within the body of the patient, and is guided into the section to be treated. This tubular organ can be, for example, a blood vessel, a urether, a urethra, bile duct, colon, eosophagus, stenosed valve, and the like. In the case of a blood vessel, the guiding tip can be inserted from a peripheral artery. 
     In step  201 , the device  100 , which is an SMA catheter is inserted into the tubular organ, guided via the guiding wire towards the section to be treated. 
     In step  202 , the device  100  is guided through the tubular organ towards a selected location, which is a portion of the tubular organ which is narrower than as it should be and need to be widened. In the present example, there is a blockage in this location caused by atherosclerosis. 
     In step  204 , the user, which is part of the medical stuff treating the patient, positions the tip of the SMA catheter in the selected location. The SMA element can be heated by fluid, electric current, radiation, induction heating, and the like. 
     In step  206 , the SMA tip of the device  100  changes from an initial shape to a transition shape. This can be done by means of a phase transition which can be caused by a temperature change (increase). Being in the transition shape, the SMA tip applies circumferencial pressure on the walls of the selected section, thereby forcing it to increase its circumference ( 208 ). The tip is maintained in this position and shape, so as to reduce the probability of the selected section returning to its original circumference shortly after the treatment is ended. 
     In step  210 , the tip element is changed from the transition shape back into the initial shape. This is done by means of a phase transition which is caused by a temperature change (decrease). 
     In step  212 , the device  100  is removed from the tubular organ. It will be noted that the device  100 , can remain in the body of the patient for a subsequent treatment of another such section. 
     It is noted that according to the present invention blood flow is maintained throughout the treatment and the device, according to the invention, does not block blood flow neither in the axial direction, nor in the radial direction. Accordingly, the method of the present invention is applicable for patients which may not endure a blood blocking balloon treatment. 
     Since the device of the present invention is completely removed from the body of the patient and leaves no object therein, then, the probability of intimal proliferation in the treated segment, is significantly reduced. 
     It is noted that the method of the present invention enables the physician to treat conical shaped segment by using conical SMA tip. 
     Reference is now made to FIG. 7, which is a schematic illustration of a system, generally referenced  300 , constructed and operative in accordance with a further embodiment of the present invention. 
     System  300  includes a catheter assembly  302 , a guidance unit  308 , a fluid connector  306  and a temperature control system  320 . 
     The catheter assembly  302  includes a tip  304 , a temperature sensor  336  for sensing the temperature of the treated area as well as the temperature of the tip  304  and a quick release interface  310 . It is noted that the addition of temperature sensors is an option, provided by the invention. This addition enhances the control and accuracy of the temperature of the fluid and hence, the temperature of the SMA tip  304 . 
     The guidance unit  308  enables the physician to guide the tip of the catheter  302 , towards the target area to be treated. 
     The fluid connector  306  enables the physician to supply variable fluid temperature and flow into the catheter  302 , and the like. 
     The temperature control system  320  provides a continuous supply of fluid according to the specification, received from the user via connector  306 . 
     The temperature control system  320  includes a pump  338 , a hot fluid container  322 , a cold fluid container  324 , a cooling unit  326 , a heating unit  328 , control valves  332  and  334  and a sensor  330 . 
     The cooling unit  326  is connected to the cold fluid container  324 . The hot fluid container  322 , is connected to the heating unit  328  and to the control valves  332  and  334 . The control valve  332  is connected between the pump  338  and both containers  324  and  322 . 
     The pump  338  is further connected to the fluid connector  306 , which is further connected to the control valve  334 . 
     The cooling unit  326  cools the fluid which is contained in the cold fluid container  324 . The heating unit  328  heats the fluid which is contained in the hot fluid container  322 . The control valve  332  directs fluids received from the cold fluid container  324  and the hot fluid container  322  and provides the fluid to the pump  338 . 
     The pump  338  provides a fluid at a controlled pressure to the fluid interface  306 . This fluid flows towards the tip  304  thereby applying its temperature, thereon (i.e., when the temperature of the fluid is greater than the temperature of the tip, then the tip will be heated up and when the temperature of the fluid is lower than the temperature of the tip, then the tip will cool down). 
     After modifying the temperature of the tip  304 , the fluid flows back to the temperature control system  320 , via the fluid connector  306 , to be stored in the containers. The control valve  334  provides fluid to the containers  322  and  324 . 
     The fluid sensor  330  monitors the fluid at the output of the pump  338 , thereby providing data relating to the temperature and pressure of the fluid. This data is used to control the pump  338  and the heating element  328  and the cooling element  326 . 
     It is noted that the catheter assembly  302 , can also conduct fluid, directly therethrough, and release it in the vicinity of the tip. Accordingly, the tip can be made of a wire which has a solid cross-section. 
     Reference is further made to FIG. 8, which is a schematic illustration in detail of the connection section of a helical SMA element  356  and the inner side of the guiding catheter  302  (FIG.  8 ). The helical SMA element  356  includes an inlet  362 A and an outlet  362 B, which are connected to a fluid inlet conduit  380 A and a fluid outlet conduit  380 B. The fluid inlet conduit  380 A is connected to the inlet  362 A, while the fluid outlet conduit  380 B is connected to the outlet  362 B. Temperature controlled fluid, provided by system  320 , is provided to the helical SMA element  356  via the inlet fluid conduit  380 A. After modifying the temperature of the helical SMA element  356 , the fluid exits via the outlet fluid conduit  380 B. It is noted that a guiding wire  360  is inserted through the guiding catheter  302  to the end of the tip  304 . 
     According to the present example, the helical SMA element  356  is alternatively connected to two electrically conducting wires  384 A and  384 B, via electrical contacts  364 A and  364 B, respectively. These wires provide a flow of electrical current via the metal body of the helical SMA element  356 , thereby heating it. According to this example, the heating is performed electrically, while the cooling can be performed either by setting the reduced diameter temperature to the body temperature of the patient or by introducing cooled fluid via conduits  380 A and  380 B. 
     Reference is now made to FIGS. 9,  10 A,  10 B,  10 C,  10 D,  10 E,  10 F and  10 G. FIG. 9 is a schematic illustration in detail of a catheter tip, generally referenced  400 , constructed and operative in accordance with another preferred embodiment of the present invention. FIGS. 10A,  10 B,  10 C,  10 D,  10 E,  10 F and  10 G are illustrations of cross sectional variations for catheter tip  400 , which include auxiliary elastic means. 
     Catheter tip  400  includes a helical SMA element  402 , and a helical elastic element  404 , attached thereto. SMA element  402  is generally similar to elements  104  and  304 . 
     According to one aspect of the invention, the helical elastic element  404  is inserted within helical SMA element  402 , as illustrated in FIGS. 10A,  10 B,  10 C,  10 D and  10 E. According to a further aspect of the invention (FIGS.  10 F and  10 G), the helical elastic element  404  is attached to the outer surface of helical SMA element  402 . 
     FIG. 10A is a cross sectional illustration of a variation of SMA element  402 , which includes a hollow helical SMA element  402 A having an elliptic cross section and a helical elastic element  404 B having an “I” cross section. 
     FIG. 10B is a cross sectional illustration of a variation of SMA element  402 , which includes a hollow helical SMA element  402 B having a semi-elliptic cross section and a helical elastic element  404 B having a radial cross section. 
     FIG. 10C is a cross sectional illustration of a variation of SMA element  402 , which includes a hollow helical SMA element  402 C having a near rectangle cross section and a helical elastic element  404 C having a radial cross section. 
     FIG. 10D is a cross sectional illustration of a variation of SMA element  402 , which includes a hollow helical SMA element  402 D having an elliptic cross section and a helical elastic element  404 D having a radial cross section. 
     FIG. 10E is a cross sectional illustration of a variation of SMA element  402 , which includes a hollow helical SMA element  402 E having a radial cross section and a helical elastic element  404 E having an “I” shaped cross section. 
     FIG. 10F is a cross sectional illustration of a variation of SMA element  402 , which includes a hollow helical SMA element  402 F having a radial cross section and an external elastic element  404 F. 
     FIG. 10G is a cross sectional illustration of a variation of SMA element  402 , which includes a solid (full) helical SMA element  402 G having a radial cross section and an external elastic element  404 G. 
     The helical SMA element  402  has a narrow circumference shape at a temperature which is equal to or lower than a first temperature value T 1 . The helical SMA element  402  has a wide circumference shape at a temperature which is equal to or higher than a second temperature value T 2 . 
     The helical elastic element  404  has a narrow diameter shape, which is in the order of the narrow diameter shape of the helical SMA element  402 . 
     It is noted that the helical elastic element  404  can be deformed to a different shape, by an external force and return back by itself, to its original narrow circumference shape. 
     According to the present invention, the catheter tip  400  performs a transition from the narrow circumference shape to a wide circumference shape, by heating the helical SMA element  402  beyond predetermined temperature T 2 . At this stage, the helical SMA element  402  is in an austenite state, where it applies force on helical elastic element  404 , thereby deforming it into a shape which is generally the same shape of the helical SMA element  402  (i.e., a wide circumference). 
     At a later time, the catheter tip  400  performs a transition from the wide circumference shape, back to the narrow circumference shape, by cooling the helical SMA element  402  below predetermined temperature T 1 . 
     Accordingly, the helical SMA element  402  transforms into a martensite state, where it becomes less rigid. Being in the martensite state, the helical SMA element  402  is no longer able to apply sufficient force onto helical elastic element  404 . Hence, the helical elastic element  404 , retracting to its initial shape, deforms the helical SMA element  402 , into a shape which is generally the same initial shape of the helical elastic element  404  (i.e., a narrow circumference). 
     According to a further aspect of the invention, which is illustrated in FIG. 9, the temperature controlled fluid is provided through the guiding catheter  410  and released in the vicinity of the shape memory catheter tip. It is noted that the shape memory catheter tip can be cooled or heated, by this temperature controlled fluid, to temperatures other than the temperature of the environment in which the tip is placed. When the supply of temperature controlled fluid stops, then the shape memory catheter tip is either cooled or heated to this environment temperature. 
     Reference is now made to FIG. 11, which is a schematic illustration of a catheter tip, generally referenced  450 , constructed and operative in accordance with a further preferred embodiment of the present invention. Tip  450  is made of a hollow SMA tube which enables the flow of temperature controlled fluid therethrough. The tip  450  is inserted in the body of the patient over a guiding wire  460 . 
     According to this aspect of the invention, one end tip  450  is opened. The temperature controlled fluid which is provided to the tip, travels through the tip  450  and is released through the tip end  452 , in the vicinity of the shape memory catheter tip  450 . 
     Reference is now made to FIG. 12, which is a schematic illustration of a catheter tip, generally referenced  470 , constructed and operative in accordance with another preferred embodiment of the present invention. shape memory catheter tip  470  includes a guiding tip  472 , which extends at the front of the tip  470 . The shape memory catheter tip  470  is guided in the tubular organ to its destination, using this guiding tip, without the requirement of a guiding wire. It is noted that a guiding wire can also be used as further guiding assistance. 
     It is noted that each part of a catheter, according to the invention, and especially the catheter tip, can be coated with an anti-coagulation material such as Heparin. 
     Reference is now made to FIG. 13, which is a schematic illustration of a catheter tip, generally referenced  500 , and energy transfer means, generally referenced  502 , constructed and operative in accordance with a further preferred embodiment of the present invention. 
     Energy transfer means include two concentric conduits  504  and  506 , where conduit  504  is the outer conduit and conduit  506  is the inner conduit. The outer conduit  504  transfers the temperature controlled fluid to the tip  500  and the inner conduit  506  receives temperature controlled fluid from the tip and transfers it outside. It is noted that the directions of flow within the two conduits  504  and  506  can be swapped so that the inner conduit  506  transfers the temperature controlled fluid to the tip  500 , while the outer conduit  504  transfers the temperature controlled fluid from the tip  500 . 
     The entire assembly is generally inserted via a guiding catheter  510 . It is noted that the concentric structure of the conduits provides reduced surface area and volume, so that a narrower guiding catheter can be used. Furthermore, the concentric structure provides a smoother shape, so that the movement of the conduits within the guiding catheter is easier. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims which follow.