the following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views . the detailed description and drawings illustrate examples of various embodiments of the claimed invention , and are not intended to be limiting . refer now to fig1 - 5 which illustrate cross sectional views of a portion of a guidewire 10 including a connection 20 joining a proximal guidewire section 14 and a distal guidewire section 16 . fig1 illustrates the guidewire 10 and the connection 20 before a final grinding step , and fig2 illustrates the guidewire 10 and the connection 20 after the final grinding step , which provides a smooth outer profile . the embodiment of fig1 and 2 utilizes an overlapping tapered joint 12 and a tubular connector 18 . the embodiment of fig3 is similar to the embodiment of fig1 and 2 , except that the connection 20 between the proximal guidewire section 14 and the distal guidewire section 16 does not utilize a connector tube 18 , but rather utilizes a connector material 19 . the embodiment of fig4 is similar to the embodiment of fig1 and 2 , except that the connection 20 between the proximal guidewire section 14 and the distal guidewire section 16 does not utilize an overlapping joint 12 , but rather uses a butt joint 13 . the embodiment of fig5 is also similar to the embodiment of fig1 and 2 , except that the connection 20 between the proximal guidewire section 14 and the distal guidewire section 16 utilizes an overlapping joint 12 that is not tapered . the proximal and distal guidewire sections 14 / 16 may have a solid cross - section as shown , or a hollow cross - section , and may be formed of metals or metal alloys suitable for metal joining techniques such as welding , soldering , brazing , crimping , friction fitting , adhesive bonding , etc . as used herein , the proximal section 14 and the distal section 16 may generically refer to any two adjacent guidewire sections along any portion of the guidewire . furthermore , although discussed with specific reference to guidewires , the present invention may be applicable to almost any intravascular device having two adjacent metallic shaft sections . for example , the present invention may be applicable to metallic hypotube shafts for intravascular catheters ( e . g ., rapid exchange balloon catheters , stent delivery catheters , etc .) or metallic drive shafts for intravascular rotational devices ( atherectomy catheters , ivus catheters , etc .). the proximal guidewire section 14 may be formed of relatively stiff material such as straightened 304v stainless steel wire . alternatively , proximal portion 14 may be comprised of a metal or metal alloy such as a nickel - titanium alloy , nickel - chromium alloy , nickel - chromium - iron alloy , cobalt alloy , or other suitable material . in general , the material used to construct proximal portion 14 may be selected to be relatively stiff for pushability and torqueability . the distal guidewire section 16 may be formed of a relatively flexible material such as a straightened super elastic or linear elastic alloy ( e . g ., nickel - titanium ) wire . alternatively , distal portion 16 may be comprised of a metal or metal alloy such as stainless steel , nickel - chromium alloy , nickel - chromium - iron alloy , cobalt alloy , or other suitable material . in general , the material used to construct distal portion 16 may be selected to be relatively flexible for trackability . the distal end 24 of the proximal portion 14 and the proximal end 26 of distal portion 16 ( i . e ., the joined ends ) may form an overlapping tapered joint 12 as shown in fig1 - 3 . alternatively , the joined ends 24 / 26 may form a butt joint 13 as shown in fig4 . as a further alternative , the joined ends 24 / 26 may form an overlapping joint 12 that is not tapered as shown in fig5 . the non - tapered end portions 24 / 26 may have a uniform profile ( diameter ) 23 as shown in fig6 a , a bulbous portion 25 for purposes of mechanical interlocking as shown in fig6 b , or a helical form 27 for purposes of mechanical interlocking as shown in fig6 c . in each of the embodiments illustrated in fig1 - 3 and 5 , the end portions 24 / 26 overlap to form an overlapping joint 12 . the overlapping joint 12 blends the stiffness of proximal portion 14 and distal portion 16 by combining the properties of each end section 24 / 26 making up the cross section of the overlapping joint 12 . thus , the joint 12 forms a flexibility transition region that has a relative flexibility that is between the flexibility of the proximal portion 14 and the flexibility of the distal portion 16 . in the tapered embodiments illustrated in fig1 - 3 , the ends 24 / 26 may be tapered or otherwise formed to have a mating geometry , wherein the cross - sectional area of each end section 24 / 26 gradually decreases toward the middle of the connection 20 . the tapered overlapping portion 12 may define a uniform or a non - uniform transition of the sections 24 / 26 , depending on the transition characteristics desired . for example , the end sections 24 / 26 may be linearly tapered as shown , tapered in a curvilinear fashion , or tapered in a step - wise fashion . if tapered linearly as shown , the angle of the taper may vary . using the longitudinal center axis of the guidewire 10 as a reference , as measured from the extreme ends of the end sections 24 / 26 , the angle of the taper is acute ( i . e ., less than 90 degrees ), and may be in the range of 5 degrees to 45 degrees , for example . varying the angle of the tapered ends 24 / 26 also varies the length of the overlapping joint 12 in accordance with geometric principles . the length of the overlapping joint 12 may be selected to obtain a more ( longer length ) or less ( shorter length ) gradual transition in stiffness . as mentioned previously , the proximal guidewire section 14 and the distal guidewire section 16 may be formed of different materials ( i . e ., materials having different moduli of elasticity ) resulting in a difference in flexibility . for example , the proximal guidewire section 14 may be formed of stainless steel wire and the distal guidewire section 16 may be formed of nickel - titanium alloy wire , both having the same dimensions , resulting in a 3 : 1 difference in elastic modulus . such a difference in elastic modulus ( i . e ., flexibility ) may result in a stress concentration point during flexure and / or torsion that may have a tendency to kink . by virtue of the gradual transition in stiffness provided by the overlapping portion 12 , stress is distributed along the entire length of the connection 20 thereby decreasing the probability that guidewire 10 may kink at the junction . a gradual transition in stiffness may also allow the connection 20 to be located further distally . according to this embodiment , the distal portion 16 may be manufactured to be shorter than proximal portion 14 . including a relatively long proximal section 14 may advantageously increase the torquability and pushability of the guidewire 10 . although only one connection 20 is shown , additional connections 20 may be used to connect other guidewire sections of varying stiffness . the connector 18 may comprise a tubular structure such as a hypotube as shown or a coiled wire . the connector 18 may have an inside diameter sized appropriately to receive the ends 24 / 26 of the proximal portion 14 and the distal portion 16 , and an outside diameter sufficient to accommodate a final grinding procedure . the final diameter of the guidewire 10 and the connector 18 may be in the range of 0 . 010 to 0 . 018 inches , for example . by way of example , not limitation , the connector 18 may have a length of about 1 . 0 to 3 . 0 inches for an overlapping portion 12 of about 0 . 75 to 2 . 5 inches . the connector 18 may be comprised of a metal or metal alloy , and may include radiopaque materials . suitable metals and metal alloys include stainless steels , nickel - titanium alloys ( e . g ., nitinol ), nickel - chromium alloys , nickel - chromium - iron alloys , cobalt alloys , nickel , or other suitable materials . alternatively , connector 18 may be comprised of a polymer or a metal - polymer composite , including a radiopaque filler . the word nitinol was coined by a group of researchers at the united states naval ordinance laboratory ( nol ) who were the first to observe the shape memory behavior of this material . the word nitinol is an acronym including the chemical symbol for nickel ( ni ), the chemical symbol for titanium ( ti ), and an acronym identifying the naval ordinance laboratory ( nol ). some types of alloys are particularly suitable for connector 18 for purposes of connecting a stainless steel proximal section 14 and a nickel titanium alloy distal section 16 , or visa - versa . an example is a nickel - chromium - iron alloy available under the trade name inconel 625 , which advantageously welds to both stainless steels and nickel - titanium alloys . inconel 625 may be obtained from california fine wire company of grover beach , calif ., and has the following composition : another example of a suitable alloy which welds to both stainless steels and nickel - titanium alloys is available under the trade name alloy c276 from fort wayne metals research products corporation of fort wayne , ind ., which has the following composition : another example of a suitable alloy which welds to both stainless steels and nickel - titanium alloys is available under the trade name alloy b2 from fort wayne metals research products corporation of fort wayne , ind ., which has the following composition : to manufacture the connection 20 of the guidewire 10 , the ends 24 / 26 of the proximal and distal guidewire sections 14 / 16 may be ground to form the desired shape ( e . g ., uniform diameter 23 , bulbous portion 25 , helix 27 , or taper ) to accommodate the overlapping joint 12 . if a butt joint 13 is to be used , such a shape need not be ground . a recess step may be ground into the proximal and distal guidewire sections 14 / 16 to accommodate the connector tube 18 . if a connector tube 18 is not to be used , such a recess step need not be ground . for the embodiments utilizing a connector tube 18 , the connector tube 18 is positioned over one of the ends 24 / 26 of the proximal and distal guidewire sections 14 / 16 . the distal end 24 of the proximal portion 14 and proximal end 26 of the distal portion 16 are then positioned adjacent one another in an overlapping 12 or an end - to - end 13 arrangement . the proximal and distal guidewire sections 14 / 16 and the connector tube 18 may be bonded , welded ( e . g ., resistance or laser welded ), soldered , brazed , or otherwise connected by a suitable technique depending on the material selected for each component . alternatively , the ends 24 / 26 and the connector tube 18 may be crimped together or may be sized to establish a friction fit therebetween . if a connector tube 18 is not used , the ends 24 / 26 may be bonded , welded ( e . g ., resistance or laser welded ), soldered , brazed , or otherwise connected , using a connector material 19 . connector material 19 may be the same as or similar to the material of the connector 18 . in all cases , because the connection 20 may reside within a catheter lumen during use , it is preferred that a permanent connection ( as opposed to a releasable connection ) be used . it is to be appreciated that various welding processes may be utilized without deviating from the spirit and scope of the present invention . examples of welding processes which may be suitable in some applications include laser welding , resistance welding , tig welding , microplasma welding , electron beam , and friction or inertia welding . laser welding equipment which may be suitable in some applications is commercially available from unitek miyachi of monrovia , calif . and rofin - sinar incorporated of plymouth , mich . resistance welding equipment which may be suitable in some applications is commercially available from palomar products incorporated of carlsbad , calif . and polaris electronics of olathe , kans . tig welding equipment which may be suitable in some applications is commercially available from weldlogic incorporated of newbury park , calif . microplasma welding equipment which may be suitable in some applications is commercially available from process welding systems incorporated of smyrna , tenn . once connected , the connector tube 18 and the proximal and distal guidewire sections 14 / 16 are centerless ground to provide a smooth and uniform profile across the connection 20 , and to straighten out small misalignments between the proximal and distal guidewire sections 14 / 16 . other portions of the guidewire 10 may be ground as well to provide the desired tapers and changes in diameter . once finally ground , a flexible coil tip and / or a polymer jacket ( optionally covering connection 20 ) may be placed on the guidewire 10 , and a lubricious coating ( e . g ., hydrophylic ) may be applied . the centerless grinding technique may utilize an indexing system employing sensors ( e . g ., optical / reflective , magnetic ) to avoid excessive grinding of the connection 20 . in addition , the centerless grinding technique may utilize a cbn or diamond abrasive grinding wheel that is well shaped and dressed to avoid grabbing the connector 20 during the grinding process . it should be understood that this disclosure is , in many respects , only illustrative . changes may be made in details , particularly in matters of shape , size , and arrangement of steps without exceeding the scope of the invention . the invention &# 39 ; s scope is , of course , defined in the language in which the appended claims are expressed .
alternative designs and materials suitable for connecting different guidewire sections together . more particularly , connecting two portions of a guidewire having different material compositions with a connector having a third composition which is readily weldable to each of the dissimilar portions of the guidewire . a transition area may be designed to provide a region of desired flexibility characteristics .