Abstract:
Electromagnetic field detector located within a catheter, for determining the position and orientation of the catheter according to an electromagnetic field generated in the vicinity of the catheter, the electromagnetic field detector including a ferromagnetic core having a perforation and at least one winding wound around the ferrous core, the perforation providing communication between a first side of the ferrous core and a second side of the ferrous core, the first side facing a proximal side of the catheter and the second side facing a distal side of the catheter, the winding producing a current according to the electromagnetic field, wherein the ferrous core increases the sensitivity of the electromagnetic field detector to the electromagnetic field, by increasing a proportionality factor between the current and the electromagnetic field.

Description:
FIELD OF THE DISCLOSED TECHNIQUE  
       [0001]     The disclosed technique relates to medical devices in general, and to methods and systems for determining the position and orientation of a catheter, in particular.  
       BACKGROUND OF THE DISCLOSED TECHNIQUE  
       [0002]     While performing an operation on an artery or a vein, such as angioplasty or implanting a stent within an artery, it is necessary for the surgeon to know the position and orientation of the tip of the catheter during the operation. The position and orientation can be determined in different ways, for example, by means of an electromagnetic sensor, ultrasonic sensor, or a marker attached to the catheter.  
         [0003]     U.S. Pat. No. 6,353,379 issued to Busletta et al., and entitled “Magnetic Device Employing a Winding Structure Spanning Multiple Boards and Method of Manufacturing thereof”, is directed to a magnetic device which includes a magnetic core, a main circuit board, an overlay board and a plurality of conductors. The magnetic core includes a first portion and a second portion. The main circuit board and the overlay board include a winding structure. The main circuit board and the overlay include a first plurality of winding layers and a second plurality of winding layers, respectively. The conductors include a conductive via, a conductive post and a connector.  
         [0004]     The overlay board is oriented parallel and proximate to the main circuit board. The first portion of the magnetic core is coupled to the main circuit board and the second portion of the magnetic core is coupled to the overlay board. The magnetic core is surface mounted to the main circuit board and to the overlay board. The conductive via are located on each of the main circuit board and the overlay board. The conductive post is located on the main circuit board and connects to the overlay board. The connector is coupled to an edge of the overlay board from the main circuit board. The conductors couple the first plurality of winding layers and the second plurality of winding layers together.  
         [0005]     U.S. Pat. No. 5,850,682 issued to Ushiro and entitled “Method of Manufacturing Chip Type Common Mode Choke Coil”, is directed to a chip type common mode choke coil which includes a plurality of non-magnetic sheets, a first plurality of magnetic sheets and a second plurality of magnetic sheets. On each of the non-magnetic sheets a conductor line at a predetermined orientation is printed. The non-magnetic sheets are stacked on the top of one another and the ends of the conductor lines are alternately connected by through holes. In this manner, part of the conductor lines form a figure-eight-shaped primary coil and the rest of the conductor lines form a figure-eight-shaped secondary coil.  
         [0006]     A laminate is formed by placing the non-magnetic sheets between the first magnetic sheets and the second magnetic sheets and joining them together under pressure. A first hole (i.e., a core arranging hole) is formed at the center of the figure-eight-shaped primary coil and a second hole is formed at another center of the figure-eight-shaped secondary coil. Each of the first hole and the second hole is filled with a magnetic paste.  
       SUMMARY OF THE DISCLOSED TECHNIQUE  
       [0007]     It is an object of the disclosed technique to provide a novel method and system for increasing the sensitivity of an electromagnetic field detector to an electromagnetic field.  
         [0008]     In accordance with the disclosed technique, there is thus provided an electromagnetic field detector located within a catheter, for determining the position and orientation of the catheter according to an electromagnetic field generated in the vicinity of the catheter. The electromagnetic field detector includes a ferromagnetic core having a perforation and at least one winding wound around the ferrous core. The perforation provides communication between a first side of the ferrous core and a second side of the ferrous core. The first side faces a proximal side of the catheter and the second side faces a distal side of the catheter. The winding produces a current according to the electromagnetic field, wherein the ferrous core increases the sensitivity of the electromagnetic field detector to the electromagnetic field, by increasing a proportionality factor between the current and the electromagnetic field.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The disclosed technique will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:  
         [0010]      FIG. 1  is a schematic illustration of a cross section of an electromagnetic field detector, constructed and operative in accordance with an embodiment of the disclosed technique, and located within a catheter;  
         [0011]      FIG. 2  is a schematic illustration of a cross section of an electromagnetic field detector, constructed and operative in accordance with another embodiment of the disclosed technique, and located within a catheter;  
         [0012]      FIG. 3  is a schematic illustration of a cross section of an electromagnetic field detector and a device, constructed and operative in accordance with a further embodiment of the disclosed technique, both the electromagnetic field detector and the device being located within a catheter;  
         [0013]      FIG. 4  is a schematic illustration in perspective of an electromagnetic field detector constructed and operative in accordance with another embodiment of the disclosed technique;  
         [0014]      FIG. 5  is a schematic illustration of a cross section of an electromagnetic field detector and a device, constructed and operative in accordance with a further embodiment of the disclosed technique, both the electromagnetic field detector and the device being located within a catheter; and  
         [0015]      FIG. 6  is a schematic illustration of a cross section of an electromagnetic field detector constructed and operative in accordance with a further embodiment of the disclosed technique, and located within a catheter.  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0016]     The disclosed technique overcomes the disadvantages of the prior art by providing an electromagnetic field detector, which includes a perforated ferromagnetic core within the coil of the electromagnetic field detector. The perforation in the coil, allows the passage of materials and elements which normally pass through the catheter, also to pass freely through the core. Alternatively, the perforation is employed to attach the electromagnetic field detector to another device which is incorporated within the catheter, such as an image detector. Further alternatively, the core includes a protrusion to fit a cavity in the device, in order to attach the electromagnetic field detector to the device in alignment with the longitudinal axis of the catheter.  
         [0017]     Reference is now made to  FIG. 1 , which is a schematic illustration of a cross section of an electromagnetic field detector, generally referenced  100 , constructed and operative in accordance with an embodiment of the disclosed technique, and located within a catheter generally referenced  102 . Electromagnetic field detector  100  includes an electromagnetic coil  104  and a core  106 . Catheter  102  includes a medical operational element  108  at a distal portion  110  of catheter  102 , a mid-portion (not shown) or a proximal portion (not shown) of the catheter. Electromagnetic field detector  100  is located substantially close to or at distal portion  110 . Catheter  102  includes a longitudinal channel  112  for example for passage of a material or an element  114  there through. Material or element  114  can be for example, a guidewire for catheter  102 , a liquid medication, and other elements or materials related to the operation of medical operational element  108 , as further described herein below. The diameter of longitudinal channel  112  is referenced D CA .  
         [0018]     Core  106  includes a perforation  116  of a diameter designated by reference D CI . Perforation  116  provides communication between a side  118  of core  106  and another side  120  of core  106 . Side  118  points toward distal portion  110  and side  118  points toward a proximal portion  122  of catheter  102 . The outer diameter of core  106  is referenced D CO . Electromagnetic coil  104  is in form of a winding around core  106 . Electromagnetic coil  104  is made of a wire having a substantially round cross section, or any other arrangement, such as rectangle, square, another polygon, and the like.  
         [0019]     Electromagnetic coil  104  is coupled with a position and orientation determining system (not shown) by an electric conductor  124 , for determining the position and orientation of catheter  102  or selected portions thereof, such as distal portion  110 , or medical operational element  108 . Alternatively, electromagnetic coil  104  is coupled with the position and orientation determining system via a wireless link. The position and orientation determining system can be similar to a medical positioning system (MPS) disclosed in U.S. Pat. No. 6,233,476 B1 which is assigned to the same assignee as that of the present patent application. Electromagnetic field detector  100  is embedded within catheter  102 . The diameter D CO  can be either substantially equal to, greater or smaller than diameter D CA . The diameter D CI  can be either substantially equal to, greater or smaller than diameter D CA . The longitudinal axes of perforation  116  and longitudinal channel  112  are either substantially parallel or along the same line.  
         [0020]     Core  106  is made of a material whose magnetic permeability is sufficient to impart a greater reactance to a bobbin or coil  104 . This is particularly effective in case of relatively small coils Alternatively, core  106  can be made of a material whose permeability is negligible, such as polymer, glass, silicon, quartz, and the like. An abundance of materials inherent with high permeability is available. For this purpose, a ferromagnetic material is selected for core  106 , such as iron, magnetite, Mu metal, Supermalloy, 4-79 Permalloy, and the like. Following is an explanation for the fact that the current generated by a magnetic circuit which includes a winding around a ferromagnetic core, in the presence of an electromagnetic field, is greater than a magnetic circuit which includes a winding (i.e., a coil, bobbin), without a ferromagnetic core.  
         [0021]     Magnetic flux density B and magnetic field intensity H of a material in which a magnetic field exists, are related by 
 
B=μH   (1) 
 
 where μ is the permeability of the material. In a magnetic circuit whose inductance is L, having a core whose cross sectional area is A, and having a coil of N turns of winding, the electric current i generated by the electromagnetic field is 
 
 i=NBA/L    (2) 
 
 Since the value of μ for a ferromagnetic material is larger than that of air by a few orders of magnitude, according to Equation 1, the magnetic flux density B in the magnetic circuit which includes electromagnetic coil  104  and core  106 , is much greater than if the core was not present. Thus, according to Equation 2, the value of the electric current i generated in electromagnetic coil  104  in the presence of the electromagnetic field, is much greater than if no core was present, and therefore electromagnetic field detector  100  is substantially more sensitive to a given electromagnetic field, than an electromagnetic field detector without a core. In this sense, permeability μ can be regarded as a proportionality factor, by which the sensitivity of electromagnetic field detector  100  to the electromagnetic field is increased. 
 
         [0022]     Medical operational element  108  can include a lumen intervention element, a lumen diagnostic element, a lumen imaging element, and the like. Medical operational element  108  is an element for performing medical operations in the lumen, such as modifying the characteristics of the lumen, or diagnosing the lumen, such as obtaining an image of the lumen. The characteristics of the lumen can be modified by performing a medical procedure thereon, such as percutaneous transluminal coronary angioplasty (PTCA), percutaneous transluminal angioplasty (PTA), vascularizing the lumen, severing a portion of the lumen or a plaque there within (e.g., atherectomy), providing a suture to the lumen, increasing the inner diameter of the lumen (e.g., by a balloon, a self expanding stent, a stent made of a shape memory alloy (SMA), or a balloon expanding stent) and maintaining the increased diameter by implanting a stent.  
         [0023]     Medical operational element  108  can be further used to deliver substances to the lumen. For example, medical operational element  108  can be used to deliver a pharmaceutical substance to a selected site within the lumen, such as for inhibiting angiogenesis of cancerous cells, inhibiting metastasis, stimulating local hormonal activity of tissue cells and stimulating healing following a trauma. Medical operational element  108  can be further used for killing selected cells (either cancerous or non-cancerous) at the activation site of medical operational element  108  or in the vicinity thereof, by irradiating the cells with a radioactive substance, electric current, laser, or subjecting the cells to a cryogenic fluid, and the like. In this case, perforation  116  allows the radioactive substance, pharmaceutical substance or the cryogenic fluid to flow there through. For this purpose, an inner wall  126  of perforation  116  is coated with a biocompatible substance, such as Parylene, polyimide, Teflon, drug, a combination thereof, and the like, in order to avoid or prevent immune reactions in the body of the patient (not shown). The biocompatible substance can have either hydrophobic or hydrophilic properties. Alternatively, perforation  116  allows the electric conductor or the optical conductor (not shown) of medical operational element  108  to pass through.  
         [0024]     Medical operational element  108  can further include, or be used for deployment of, a device within the lumen. Such a device can be for example, a valve (e.g., mitral valve, sphincter), suturing device, implant, biological marker, radiopaque marker, substance delivery device, imaging device, diagnostic device, miniature camera, infrared camera, optical coherence tomography (OCT), magnetic resonance imaging (MRI), intravascular ultrasound (IVUS), sensor, such as pressure sensor, temperature sensor, pH sensor, and the like. The sensor can be in form of a passive ultrasonic transducer, which transmits signals bearing the value of the detected parameter (pressure, temperature, pH etc.), in response to an ultrasonic wave directed from an external source toward the sensor. In this case, perforation  116  allows the electric or optical conductor (not shown) or medical elements of medical operational element  108 , such as optical lens, and the like, to pass through. Perforation  116  allows the passage of a flexible shaft (not shown) which is employed for moving the imaging device, such as an IVUS.  
         [0025]     Medical operational element  108  can also be used to perform a valvuloplasty operation (i.e., repair of an organic or an artificial valve). The lumen can be a portion of the vascular system, ureter, urethra, brain vessels, coronary vessels, vas deferens, lumens of the liver, kidney, lung (e.g., trachea and bronchus), digestive system, gal bladder, prostate gland, urogenital system, and the like. The lumen can be in the body of a human being as well as an animal.  
         [0026]     Medical operational element  108  can be an expansion unit such as a balloon, stent, balloon expanding stent, an ablation unit such as laser, cryogenic fluid unit, electric impulse unit, cutting balloon, rotational atherectomy unit (i.e., rotablator), directional atherectomy unit, transluminal extraction unit, a substance delivery unit such as coated stent, drug delivery balloon, brachytherapy unit, and the like. In this case, perforation  116  allows medical elements, such as the balloon (not shown) in a deflated form, and the pressurized fluid conveying tube (i.e., a substance delivery lumen) thereof (not shown), to pass through.  
         [0027]     The balloon expanding stent unit includes a stent which is located around a balloon. When the balloon is inflated, the stent expands. The cutting balloon unit includes a balloon having a plurality of blades on the periphery thereof, along the longitudinal axis of the catheter. The cryogenic fluid unit includes a fluid delivery lumen through which a fluid at a substantially low temperature is delivered to a desired site of the lumen. The electric impulse unit includes two electrical conductors. An electrical arc generated at the tip of the electrical conductors ablates the desired site of the lumen.  
         [0028]     The rotablator includes a diamond coated tip which is coupled with an external motor via a flexible shaft. The flexible shaft rotates the diamond coated tip at a substantially high speed, wherein the diamond coated tip grinds calcified plaque which is formed on the inner wall of the lumen. The ground material enters the circulation.  
         [0029]     The directional atherectomy unit includes a cutter and a balloon. The cutter is coupled with an external motor via a flexible shaft. The balloon pushes the cutter toward the sidewall opposite to the balloon, thereby allowing the cutter to cut the calcified plaque. The calcified particles are pumped out through the catheter. The transluminal extraction unit includes a cutter which is coupled with an external motor via a flexible shaft. The motor rotates the cutter, wherein the cutter cuts the calcified plaque and the calcified particles are pumped out through the catheter. In above cases, perforation  116  allows the flexible shaft (not shown) to pass through.  
         [0030]     The coated stent is coated with a pharmaceutical substance, wherein the substance is released into a desired region of the lumen, when the coated stent is installed in the lumen. The drug delivery balloon is a balloon which is coupled to a source of a pharmaceutical substance, via a drug (i.e., substance) delivery lumen. The pharmaceutical substance exits the balloon through a plurality of micropores. In this case, perforation  116  allows the drug delivery balloon (not shown), substance delivery lumen (not shown), or both, to pass through. The brachytherapy unit includes a substance delivery lumen, through which radioactive palettes are delivered to a desired site within the lumen. The radioactive palettes remain at the desired site for a prescribed time and then are scavenged out through the substance delivery lumen. Thus, a prescribed dose of radiation is delivered to the desired site of the lumen. In this case, perforation  116  allows the substance delivery lumen (not shown) to pass through. It is noted that perforation  116  allows the passage of all elements and materials there through, which pass through longitudinal channel  112 .  
         [0031]     Electromagnetic coil  104  can be incorporated with an electric shield (not shown) in order to reduce interference due to an electric field. The electric shield encompasses the electromagnetic coil either entirely or partially. The electric shield can be for example in form of a complete cylinder or a partial cylinder whose cross section is in form of a partial circle. If the electric shield is in form of a partial cylinder, eddy currents are reduced.  
         [0032]     The electric shield can be in form of an electrically conductive foil, an electrically insulating material (e.g., polymer) which is coated with an electric conductor, an electrically conductive paint, and the like. The electric shield is grounded. The electric conductor can be made of gold, copper, and the like.  
         [0033]     Reference is now made to  FIG. 2 , which is a schematic illustration of a cross section of an electromagnetic field detector, generally referenced  150 , constructed and operative in accordance with another embodiment of the disclosed technique, and located within a catheter generally referenced  152 . Electromagnetic field detector  150  includes an electromagnetic coil  154  and a core  156 . Catheter  152  includes a medical operational element  158  located at a distal portion  160  of catheter  152 . Catheter  152  includes a longitudinal channel  162  for the passage of a material or an element  164  there through. Core  156  includes a perforation  166  for the passage of material or element  164  there through. Electromagnetic coil  154  is coupled with a position and orientation determining system (not shown) for determining the position and orientation of catheter  152 , by electric conductors  168  or by a wireless link.  
         [0034]     Electromagnetic field detector  150  is embedded within catheter  152 , such that the longitudinal axes of electromagnetic field detector  150  and longitudinal channel  162 , are substantially perpendicular. However, the longitudinal axes of perforation  166  and longitudinal channel  162  are substantially parallel or along the same line. Medical operational element  158  is similar to medical operational element  108  ( FIG. 1 ), and hence, perforation  166  allows the passage of material or element  164  there through, such as a guidewire (not shown), or a material or an element associated with the operation of medical operational element  158 .  
         [0035]     Reference is now made to  FIG. 3 , which is a schematic illustration of a cross section of an electromagnetic field detector, generally referenced  190 , and a device generally referenced  192 , constructed and operative in accordance with a further embodiment of the disclosed technique, both the electromagnetic field detector and the device being located within a catheter generally referenced  194 . Electromagnetic field detector  190  is similar to electromagnetic field detector  100  ( FIG. 1 ). Device  192  is a device which is normally incorporated with catheter  194 , such as an image detector, imaging device (e.g., IVUS, OCT, MRI), and the like. Electromagnetic field detector  190  includes an electromagnetic coil  196  and a core  198 . Core  198  includes a perforation  200  (i.e., an adaptive feature) for coupling electromagnetic field detector  190  with device  192 . The longitudinal axis of perforation  200  is substantially parallel with the longitudinal axis of catheter  194  or it lies substantially along the same line. Device  192  includes a protrusion  202  (i.e., a mating feature) to fit perforation  200 . A biocompatible adhesive can be employed for securing protrusion  202  within perforation  200 . Electromagnetic coil  196  is coupled with a position and orientation determining system (not shown) for determining the position and orientation of device  192 , by electric conductors  204 .  
         [0036]     Catheter  194  is a rapid-exchange type catheter, i.e., a guidewire  206  enters a longitudinal channel  208  of catheter  194  through a side opening  210  of catheter  194 , substantially close to a distal portion  212  of catheter  194 . Electromagnetic field detector  190  and device  192  are located within catheter  194  proximal to side opening  210 .  
         [0037]     The longitudinal axes of perforation  200  and longitudinal channel  208  are substantially parallel or lie substantially along the same line. The longitudinal axes of perforation  200  and protrusion  202  lie substantially along the same line. Preferably, device  192  can rotate about an axis substantially along or parallel with the longitudinal axis of longitudinal channel  208 . Rotation of device  192  provides for easy installation, and may be required for the effective operation of a device such as an IVUS. The coupling between electromagnetic field detector  190  and device  192  via perforation  200  and protrusion  202 , allows alignment of the longitudinal axes of perforation  200  and protrusion  202 . Hence, the position and orientation determining system can determine the position and orientation of device  192 , as well as of catheter  194  in the vicinity of side opening  210 . Side opening  210  is adjacent the distal tip of catheter  194 , thus the position and orientation of device  192  also indicates the position and orientation of the distal tip of catheter  194 .  
         [0038]     In the example set forth in  FIG. 3 , electromagnetic field detector  190  is located between side opening  210  and device  192 . It is noted that device  192  can be coupled to electromagnetic field detector  190 , such that device  192  is located between side opening  210  and electromagnetic field detector  190 .  
         [0039]     Reference is now made to  FIG. 4 , which is a schematic illustration in perspective of an electromagnetic field detector, generally referenced  240 , constructed and operative in accordance with another embodiment of the disclosed technique. Electromagnetic field detector  240  includes an electromagnetic coil  242  wound around a core  244 . One end of core  244  includes two protrusions  246  and  248  (i.e., an adaptive feature). Protrusions  246  and  248  are spaced apart opposing segments of core  244 . Thus, protrusions  246  and  248  form a notch  250  there between. A mating feature of a device (not shown) equivalent to device  192  of  FIG. 3  (e.g., a protrusion whose cross section is compatible with notch  250 ), makes possible to couple electromagnetic field detector  240  with the device. The core beyond notch  250  can be hollow similar to the perforated cores of FIGS.  1  to  3 , or solid similar to core  278  of  FIG. 5 , as decribed herein below.  
         [0040]     Reference is now made to  FIG. 5 , which is a schematic illustration of a cross section of an electromagnetic field detector, generally referenced  270 , and a device generally referenced  272 , constructed and operative in accordance with a further embodiment of the disclosed technique, both the electromagnetic field detector and the device being located within a catheter generally referenced  274 . Electromagnetic field detector  270  includes an electromagnetic coil  276  and a core  278 . Catheter  274  is a rapid-exchange type catheter similar to catheter  194  ( FIG. 3 ), having a side opening  280  for entering a guidewire  282  into a longitudinal channel  284  of catheter  274 . Device  272  is similar to device  192  ( FIG. 3 ).  
         [0041]     Core  278  includes a protrusion  286  (i.e., an adaptive feature) on one side thereof. The cross section of protrusion  286  can be circular as well as polygonal, such as a rectangle, square, and the like. The longitudinal axis of protrusion  286  lies substantially along the longitudinal axis of core  278 . Device  272  includes a cavity  288  (i.e., a mating feature) of a size and a shape to fit protrusion  286 . The longitudinal axis of cavity  288  lies substantially along the longitudinal axis of device  272 . Device  272  is coupled with electromagnetic field detector  270 , by assembling protrusion  286  on to cavity  288 . A biocompatible adhesive can be employed in assembling protrusion  286  on to cavity  288 .  
         [0042]     In the example set forth in  FIG. 5 , electromagnetic field detector  270  is located between side opening  280  and device  272 . It is noted that device  272  can be coupled to electromagnetic field detector  270 , such that device  272  is located between side opening  280  and electromagnetic field detector  270 .  
         [0043]     Reference is now made to  FIG. 6 , which is a schematic illustration of a cross section of an electromagnetic field detector, generally referenced  310 , constructed and operative in accordance with a further embodiment of the disclosed technique, and located within a catheter generally referenced  312 . Catheter  312  includes a medical operational element  314  either at a distal portion  316  thereof or a mid-portion (not shown) thereof. Catheter  312  includes a longitudinal channel  318  for example for passage of a material or an element  320  there through (e.g., a guidewire).  
         [0044]     Electromagnetic field detector  310  includes a core  322  and one or more electromagnetic coils  324  and  326 . Electromagnetic coils  324  and  326  are wound around core  322  and are connected together by an electric conductor  328 . Core  322  includes a perforation  330  to allow passage of element  320 . Electromagnetic coils  324  and  326  are coupled to a position and orientation determining system (not shown) by electric conductors  332 , for determining the position and orientation of catheter  312  or selected portions thereof, such as distal portion  316 , or medical operational element  314 . Since electromagnetic field detector  310  includes more electromagnetic coils than electromagnetic field detector  100  ( FIG. 1 ), the capacitance of electromagnetic field detector  310  is less than that of electromagnetic field detector  100 .  
         [0045]     It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove. Rather the scope of the disclosed technique is defined only by the claims, which follow.