a first preferred embodiment of a magnetically navigable medical guidewire is indicated generally as 20 in fig1 . the guidewire 20 has a proximal end 22 and a distal end 24 and comprises a flexible core wire 26 extending from the proximal end substantially to the distal end . the core wire 26 can be made of nitinol or other suitable material . as shown in fig1 , the proximal end 22 of the guidewire 20 includes a conventional connector 28 having a proximal landing 30 , to which a core wire 32 is attached . the attachment of the core wire 26 is preferably done by a coil 34 extending over the core wire 32 and the proximal landing 30 . the distal end of the core wire 26 is attached in the same manner to a metallic cylinder or sleeve 36 . the cylinder or sleeve 36 may be made of , or at least plated with a radiopaque material so that the distal end of the guidewire 20 can be seen in x - ray imaging . the sleeve 36 is preferably made of gold , a gold alloy , or other biocompatible material . disposed within a hollow section of the sleeve 36 is a magnetically responsive element 38 , which may alternatively be embedded within the sleeve 36 . the magnetically responsive element 38 , which can be made of a permanent magnetic material or a permeable magnetic material , is disposed inside the sleeve 36 . the magnetically responsive element 38 is of sufficient size and shape to cause the distal end portion of the guidewire 20 to align in a selected direction with a magnetic field applied from an external source magnet . suitable permanent magnetic materials include neodymium - iron - boron ( nd — fe — b ). suitable permeable magnetic materials include magnetic stainless steel , such as a 303 or 304 stainless steel , or other alloys such as hiperco . the size and material of the magnetically responsive element 38 are selected so that the distal end portion of the guide wire can be reoriented by the application of a magnetic field of no more than about 0 . 20 tesla . in the preferred embodiment , the length of the magnetically responsive element 38 is preferably about 2 . 2 millimeter , but may alternatively be any length in the range of 0 . 5 to 5 millimeters . in the first preferred embodiment , the distal end of the sleeve 36 is solid and has an external helical thread 40 formed in the tip of the sleeve . alternatively , a solid section 36 a may be mounted on the distal end of the sleeve 36 and the ends of the sleeve and section 36 a are secured to each other , such as by welding . the helical thread 40 may be formed by thread rolling , chasing , etching or other suitable process . in the preferred embodiment , the helical thread 40 may comprise one to ten complete thread turns over a predetermined length in the range of 0 . 5 to 4 millimeters , and preferably has three to four turns over a length of about 2 . 2 millimeters . by way of example only , and without limiting the invention the guidewire 20 of the preferred embodiment has a total length of about 180 cm . the guidewire 20 is sufficiently stiff that it can be advanced in the selected direction by pushing the proximal end of the guidewire 20 , yet flexible enough that the guidewire can be deflected by an applied magnetic field to gain entry to a vessel branch . guidewire deflection can be measured by holding the wire at a set distance proximal to the tip such as 1 cm , and applying a magnetic field of known magnitude , h , at varying angles to the tip until the maximum tip deflection is observed . for example , in the stereotaxis niobe ™ magnetic navigation system , an external field of 0 . 08 tesla can be applied within the subject in any direction . the maximum deflection angle of the guidewire in a 0 . 08 tesla field is thus one way to characterize the guidewire performance in the niobe ™ magnetic navigation system . the inventors have determined that in most circumstances a minimum tip deflection of about 30 degrees is desired for navigation of the guidewire according to the principles of the present invention . in operation , the distal tip of the guidewire 20 in the presence of an applied magnetic field will tend to align with the field direction to the extent allowed by the flexibility of the guidewire . when the distal end has been deflected to a desired orientation , the proximal end 22 of the guidewire 20 is torqued or rotated about its longitudinal axis , to cause the distal end 24 of the guidewire to rotate or spin on an axis substantially in alignment with the field direction . because of the tendency of the device tip to stay aligned with the field , rotating the proximal end of the wire about its axis will cause the distal tip to execute a similar rotation , while maintaining its alignment with the field . this property of “ twisting in place ” is a direct consequence of magnetic actuation , and is a significant advantage over conventional guidewires in which rotation of the tip is not so constrained . the helical thread 40 on the tip of the guidewire distal end 24 will accordingly spin or rotate about the longitudinal axis of the distal end 24 held in a substantially fixed alignment by the external magnetic field . by gently pushing on the proximal end 22 while rotating the guidewire 20 , the distal tip 24 can screw or drill its way through an occluded vessel . the rotation may be produced either manually or with the use of a motor or suitable mechanism . an alternate construction of a preferred embodiment of a guidewire , in accordance with the principles of this invention , is indicated as 20 ′ in fig2 . guidewire 20 ′ is similar in construction go guidewire 20 , and corresponding reference numerals indicate corresponding parts throughout the several views of the drawings . the guidewire 10 ′ has a proximal end 22 and a distal end 24 . as also described above , the alternate construction guidewire 20 ′ comprises a flexible core wire 26 ′ extending from the proximal end substantially to the distal end . the proximal end 22 of the guidewire 20 includes a conventional connector 28 having a proximal landing 30 , to which a core wire 32 is attached . the core wire 26 can be made of nitinol or other suitable material , and may further comprise a wound coil 34 over the length of the core wire 26 . the distal end of the core wire 26 attaches to a magnetically responsive element 38 that is preferably disposed within a metallic cup or encapsulated by a metallic coating , of a gold alloy or other suitable material . the core wire 26 and the encapsulated magnetically responsive element 38 are surrounded or covered by a flexible tube or jacket 50 , made of a polymer or metal . the flexible tube 50 connects to a proximal landing 30 of a connector 28 on the proximal end 22 of the guidewire , and to a metallic distal tip 40 a at the distal end 24 of the guidewire . the connection of the flexible tube 50 may be obtained by laser welding , adhesive bonding , or other suitable joining process . the metallic distal tip 40 a comprises a helical thread as described above , and is preferably made of gold , a gold alloy , or other biocompatible material . by way of example only , and without limiting the invention the guidewire of the preferred embodiment has a total length of about 180 cm . the above - described embodiments are intended to be illustrative only . for example , the mechanical pushing force applied to the proximal end of the guidewire may also be provided by using a motor that is controlled by a surgeon . likewise , more than one magnetically responsive element could be incorporated in the guidewire , and at least one magnetically responsive element could be mechanically flexible and could be made of a material of high magnetic permeability . some or all of the threaded elements could also be made of a magnetic material . there are also numerous types of magnetic surgery procedures for which the guidewire described and the method of controlling the guidewire are important . the invention can be readily adapted so that a surgeon , under guidance from an imaging system , uses the magnetic system to negotiate otherwise difficult turns and movements of the surgical device and to gain passage through an occulated vessel . it will also be recognized that many of the inventive methods and apparatuses may be used in conjunction with any coil in a non - resonant circuit that applies a magnetic force on a suspended or embedded object that is magnetically moveable . many other modifications falling within the spirit of the invention will be apparent to those skilled in the art . therefore , the scope of the invention should be determined by reference to the claims below and the full range of equivalents in accordance with applicable law .
the invented guidewire relates to improvements in a magnetically navigable medical guidewire to enable passage through an occluded or partially occluded vessel . the guidewire comprises an elongate wire having a proximal end and a distal end , wherein the distal end further comprises a magnetically responsive element and a helical thread formed on the tip . the distal end of the guidewire may be preferably aligned substantially in the direction of an applied magnetic field , after which the proximal end of the guidewire may be torqued to rotate the threaded tip while remaining aligned with the applied magnetic field and cause the tip to screw through the blockage in the occluded vessel .