Patent Publication Number: US-2021178127-A1

Title: Guidewires for medical devices

Description:
FIELD 
     The field of the application relates to medical devices, and more specifically, to guidewires for medical devices, and medical devices having such guidewires. 
     BACKGROUND 
     Guidewires have been used in the medical field to access passages inside patients. In some cases, it may be desirable for a guidewire to have good torqueability, which allows a torque motion applied about a longitudinal axis of the guidewire at a proximal end of the guidewire to cause a corresponding twisting motion at a distal end of the guidewire. 
     Also, it may be desirable for a distal segment of a guidewire to retain a certain bent shape during use. This allows the distal segment of the guidewire to access certain passage with specific geometry inside the patient. If the distal segment of the guidewire cannot retain its bent shape during use, then it may not be able to access a target passage. 
     In addition, it may be desirable for a guidewire to have a soft distal segment. This prevents the guidewire from causing injury to the patient, and also allows the guidewire to elastically flex or bend as it is advanced inside the patient through passages of different shapes. 
     However, it is difficult for a guidewire to achieve all of the above desirable features. A guidewire may have a soft distal segment, but such guidewire may have poor shape retention ability at the distal segment and poor torqueability. On the other hand, a guidewire may have great shape retention ability at the distal segment and good torqueability. However, such guidewire may have a stiff distal segment. The above desirable features are difficult to accomplish together because a soft distal segment of a guidewire usually cannot achieve good torqueability due to the softness of the material that is used to make the distal segment. Also, the material that is used to make the soft distal guidewire segment may not allow the distal guidewire segment to maintain its shape during use. 
     New guidewires for medical devices would be desirable. 
     SUMMARY 
     A guidewire includes: a shaft having a proximal end, a distal end, and a body extending from the proximal end to the distal end; a blunt tip; and a sleeve; wherein the body of the shaft comprises at least a segment that is surrounded by the sleeve, the segment coupled to the blunt tip; and wherein the segment of the body of the shaft comprises a flat portion having one or more openings extending through a thickness of the flat portion. 
     Optionally, the one or more openings comprise only one elongated slot extending through the thickness of the flat portion. 
     Optionally, the flat portion has a long side that is parallel to a longitudinal axis of the guidewire, and wherein the slot has a long side that is parallel to the long side of the flat portion. 
     Optionally, the one or more openings comprise a series of openings arrange along a longitudinal axis of the flat portion. 
     Optionally, each of the openings in the series is a rectangular slot extending through the thickness of the flat portion. 
     Optionally, each of the openings in the series is a circular slot extending through the thickness of the flat portion. 
     Optionally, the one or more openings comprise rows of openings arranged in a staggered configuration. 
     Optionally, the guidewire further includes a radiopaque marker extending through one of the one or more openings. 
     Optionally, the radiopaque marker has a first portion abutting a first side of the flat portion, a second portion within the one of the one or more openings, and a third portion abutting a second side of the flat portion, the second side being opposite from the first side of the flat portion. 
     Optionally, the first portion of the radiopaque marker has a first cross sectional dimension, the second portion of the radiopaque marker has a second cross sectional dimension, and the third portion of the radiopaque marker has a third cross sectional dimension; wherein the first cross sectional dimension is larger than the second cross sectional dimension; and wherein the third cross sectional dimension is larger than the second cross sectional dimension. 
     Optionally, the flat portion comprises a stamped core wire. 
     Optionally, the guidewire further includes a coil disposed between the flat portion and the sleeve. 
     Optionally, the coil is made from a radiopaque material. 
     Optionally, the coil is made from Platinum Tungsten. 
     Optionally, the sleeve is made from Nitinol. 
     Optionally, the sleeve comprises a plurality of slots. 
     Optionally, the body of the shaft comprises a tapering portion that is proximal the flat portion. 
     Optionally, the body of the shaft comprises a cylinder portion that is proximal the tapering portion. 
     Optionally, the flat portion is bendable to form a bent shape and is configured to retain the bent shape after the flat portion is bent. 
     Optionally, the segment also comprises an additional flat portion distal to the flat portion. 
     Optionally, the segment also comprises a connecting portion connecting the flat portion and the additional flat portion, wherein the connecting portion, the flat portion, and the additional flat portion have an unity configuration. 
     A medical device includes a catheter, and the guidewire, wherein the catheter includes a lumen for accommodating the guidewire. 
     A guidewire includes: a shaft having a proximal end, a distal end, and a body extending from the proximal end to the distal end; a blunt tip; and a sleeve; wherein the body of the shaft comprises at least a segment that is surrounded by the sleeve, the segment coupled to the blunt tip; and wherein the segment of the body of the shaft comprises a flat portion with a first major surface and a second major surface opposite from the first major surface, and wherein the flat portion comprises one or more radiopaque markers secured on the first major surface. 
     Optionally, the one or more radiopaque markers comprise a first planar marker having a width that is the same as a width of the flat portion. 
     Optionally, the guidewire further includes a second planar marker secured on the second major surface of the flat portion. 
     Optionally, the one or more radiopaque markers comprise first multiple radiopaque markers spaced apart from each other. 
     Optionally, the first multiple radiopaque markers are aligned in a row along a longitudinal axis of the flat portion. 
     Optionally, the guidewire further includes second multiple radiopaque markers spaced apart from each other and secured on the second major surface of the flat portion. 
     Optionally, the flat portion also comprises one or more radiopaque markers secured on the second major surface. 
     A guidewire includes: a shaft having a proximal end, a distal end, and a body extending from the proximal end to the distal end; a blunt tip; and a sleeve; wherein the body of the shaft comprises at least a segment that is surrounded by the sleeve, the segment coupled to the blunt tip; and wherein the segment of the body of the shaft comprises a flat portion with an exterior surface, and wherein the flat portion comprises a plurality of grooves at the exterior surface. 
     A guidewire includes: a shaft having a proximal end, a distal end, and a body extending from the proximal end to the distal end; a blunt tip; and a sleeve; wherein the body of the shaft comprises at least a segment that is surrounded by the sleeve, the segment coupled to the blunt tip; and wherein the guidewire further comprises a radiopaque coil surrounding at least a part of the segment, the part of the segment having opposite sides with indentations along each of the opposite sides for allowing the radiopaque coil to be screwed over the part of the segment. 
     Optionally, the part of the segment comprises a flat portion. 
     Optionally, the segment comprises a flat portion, and the part of the segment is proximal to the flat portion. 
     Other and further aspects and features will be evident from reading the following detailed description. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate the design and utility of embodiments, in which similar elements are referred to by common reference numerals. These drawings are not necessarily drawn to scale. In order to better appreciate how the above-recited and other advantages and objects are obtained, a more particular description of the embodiments will be rendered, which are illustrated in the accompanying drawings. These drawings depict only exemplary embodiments and are not therefore to be considered limiting in the scope of the claims. 
         FIG. 1A  illustrates a guidewire. 
         FIG. 1B  illustrates the guidewire of  FIG. 1A , further having a sleeve and a tip. 
         FIG. 1C  illustrates the guidewire of  FIG. 1B , further having a coil. 
         FIG. 1D  illustrates the guidewire of  FIG. 1B , further having a coil that is spaced away from a wall of a sleeve. 
         FIG. 1E  illustrates the guidewire of  FIG. 1A , further having a sleeve and a tip. 
         FIG. 1F  illustrates a member for making a guidewire. 
         FIG. 2A  illustrates a guidewire. 
         FIG. 2B  illustrates the guidewire of  FIG. 2A , further having a sleeve and a tip. 
         FIG. 2C  illustrates the guidewire of  FIG. 2B , further having a malleable structure. 
         FIG. 2D  illustrates the guidewire of  FIG. 2B , further having a coil. 
         FIG. 2E  illustrates the guidewire of  FIG. 2D , further having a malleable structure and a coil. 
         FIG. 2F  illustrates a member for making a guidewire. 
         FIG. 3A  illustrates a guidewire. 
         FIG. 3B  illustrates the guidewire of  FIG. 3A , further having a coil. 
         FIG. 3C  illustrates the guidewire of  FIG. 3B , further having a malleable structure and coil. 
         FIG. 3D  illustrates the guidewire of  FIG. 3A , further having a malleable structure. 
         FIG. 4  illustrates a guidewire. 
         FIG. 5  illustrates another guidewire. 
         FIG. 6  illustrates another guidewire. 
         FIG. 7  illustrates another guidewire. 
         FIG. 8  illustrates another guidewire. 
         FIG. 9  illustrates another guidewire. 
         FIGS. 10A-10H  illustrates a method of making a guidewire. 
         FIG. 11  illustrates a flat portion of a segment of a guidewire. 
         FIG. 12  illustrates another flat portion of a segment of a guidewire. 
         FIG. 13  illustrates another guidewire. 
         FIG. 14  illustrates another guidewire. 
         FIG. 15  illustrates a technique for securing a radiopaque marker to a part of a guidewire. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments are described hereinafter with reference to the figures. It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are represented by the same reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the invention or as a limitation on the scope of the invention. In addition, an illustrated embodiment needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated, or if not so explicitly described. 
       FIG. 1A  illustrates a guidewire  100  in accordance with some embodiments. The guidewire  100  includes a shaft  110  having a proximal end  112 , a distal end  114 , and a body  116  extending from the proximal end  112  to the distal end  114 . The body  116  of the shaft  110  comprises a distal segment  120  having a plurality of different cross sections along a length of the distal segment  120 . At least an outer part  130  of the body  116  that is proximal to the distal segment  120  is made of a material having a shear modulus of at least 13000 ksi. By means of non-limiting examples, the material of the outer part  130  of the body is Molybdenum Rhenium alloy or Tungsten Rhenium alloy. 
     In the illustrated embodiments, the shaft  110  includes a first layer  140 , a second layer  142 , and a third layer  144 . The third layer  144  is outside the second layer  142 , and the second layer  142  is outside the first layer  140 . As shown in the figure, the third layer  144  comprises the outer part  130  of the body  116  that is proximal to the distal segment  120 . In some embodiments, the third layer  144  of the shaft  110  may be made from Molybdenum Rhenium alloy or Tungsten Rhenium alloy. Also, in some embodiments, the first layer  140  may be made of Molybdenum Rhenium alloy, Tungsten Rhenium alloy, stainless steel, Nitinol, NeoNickel alloy (e.g., MP35N alloy), or Cobalt-Chromium alloy. The second layer  142  may be made from Nitinol, or any of the other materials. 
     In the illustrated embodiments, a part  150  of the first layer  140  is distal to a distal end  152  of the second layer  142 , and a part  154  of the second layer  142  is distal to a distal end  156  of the third layer  144 , thereby allowing the part  150  of the first layer  140  and the part  154  of the second layer  142  to form at least a portion of the distal segment  120  of the body  116  of the shaft  110 . Such configuration is advantageous because it provides the distal segment  120  having a cross sectional dimension that is smaller compared to that of a remaining part of the body  116  (that is proximal to the distal segment  120 ). As a result, the distal segment  120  is softer compared to the remaining part of the body  116 , and may flex or bend more easily. 
     In some embodiments, the part  150  of the first layer  140  may be compressed to form an elongated cross sectional shape for the part  150  of the first layer  140 . For example, in one implementation, the first layer  140  may have a circular cross sectional shape, and the part  150  of the first layer  140  may be compressed into a planar structure having an elongated cross sectional shape, or any of other non-circular cross sections. This feature is advantageous because it provides a bias in the direction of bending for the part  150  of the first layer  140 . The compressing of the part  150  of the first layer  140  may be achieved by stamping the part  150  of the first layer  140  in some embodiments. 
     In one specific implementation, both the first and third layers  140 ,  144  are made from Molybdenum Rhenium alloy, and the second layer  142  is made from Nitinol that is sandwiched between the two Molybdenum Rhenium alloy layers  140 ,  144 . In another specific implementation, the first layer  140  is made from stainless steel or Cobalt-Chromium alloy (e.g., MP35N alloy), the second layer  142  is made from Nitinol, and the third layer is made from Molybdenum Rhenium alloy. In either implementation, the Nitinol layer  142  provides kink resistance and a softer distal segment  120 . The first layer  140  is shapeable during use, and provides desirable shape retention capability. Also, because of its relatively high shear modulus, the outer Molybdenum Rhenium alloy layer  144  provides a desirable torqueability. Furthermore, because of the axial stiffness of the outer Molybdenum Rhenium alloy layer  144 , the guidewire  100  also has a desirable pushability. 
     As shown in  FIG. 1B , in some embodiments, the guidewire  100  may also include a sleeve  180  disposed around at least a part of the distal segment  120  (e.g., the distal end  114 ) of the shaft  110 . As shown in the figure, the sleeve  180  has a blunt tip  182 . The distal end  114  of the shaft  110  is coupled to the blunt tip  182 . The sleeve  180  may be any tubular member, and may be made from any materials, such as metal, polymer, etc. In some embodiments, the sleeve  180  may be made from Nitinol. The sleeve  180  may have a plurality of slots and/or openings to increase a flexibility of the sleeve  180 . By means of non-limiting examples, the sleeve  180  may be implemented using slotted hypotube, coiled sleeve, tungsten-loaded polymer sleeve, or a combination of the foregoing. 
     Referring to  FIG. 1C , in some embodiments, the guidewire  100  may also include a marker coil  190  disposed inside the sleeve  180 . As shown in the figure, one end of the marker coil  190  is secured to the tip  182 , while a body of the marker coil  190  is secured to or is abut against a wall of the sleeve  180 . In other embodiments, the coil  190  may be coupled to only the tip  182 , and not to the wall of the sleeve  180  ( FIG. 1D ). In other embodiments, the proximal end of the marker coil  190  may be secured to the second layer  154  (e.g., to the distal end  152  of the second layer  154 ), such as by an adhesive, welding, mechanical connector, fusion, etc. In further embodiments, at least a part of the sleeve  180  may be formed by the marker coil  190  ( FIG. 1E ). As shown in the figure, the marker coil  190  has a cross sectional dimension that corresponds with (e.g., is the same as) a cross sectional dimension of the sleeve  180 . In some cases, an entirety of the length of the sleeve  180  may be made from a coil, such as a marker coil. 
     In the illustrated embodiments of  FIGS. 1A-1E , the distal part  150  of the segment  120  is malleable. Thus, the distal part  150  of the segment  120  is bendable to form a bent shape. The distal part  150  is made from a material that allows it to retain the bent shape after the distal part  150  of the segment  120  is bent. In other embodiments, the distal part  150  (or the first layer  140  comprising the distal part  150 ) may be made from a material that does not have sufficient shape retention capability. In such cases, the guidewire  100  may further include a malleable structure attached to the blunt tip  182 . The malleable structure may be inside the sleeve  180 . During use, the malleable structure is bendable to form a bent shape and is configured to retain the bent shape after the malleable structure is bent. In some embodiments, the malleable structure may be made from Molybdenum Rhenium alloy or Tungsten Rhenium alloy. 
     The guidewire  100  is advantageous because it provides a desirable torqueability, a desirable pushability, and a desirable shape retention ability, while achieving a desirable softness at the distal segment  120 . In particular, the outermost layer  144  provides a desirable torqueability due to it being made from a material having a sufficiently high (e.g., of at least 13000 ksi) shear modulus. Also, the distal segment  120  has a desirable bending stiffness, and the distal part  150  also has a desirable bending stiffness and shape retention capability. Accordingly, the guidewire  100  has optimal combination of soft distal segment, shapeability, and torqueability. 
       FIG. 1F  illustrates a member  194  for making the guidewire  100 . The member  194  includes the first layer  140 , the second layer  142 , and the third layer  144 . In some embodiments, a part of the third layer  144  may be removed to expose the part  154  of the second layer  142 . Also, a part of the second layer  142  may be removed to expose the part  150  of the first layer  140 . The above actions will result in the shaft  110  having multiple different cross sectional shapes along its length, like that shown in  FIGS. 1A-1E . In some embodiments, the removing of the part of the third layer  144 , and the part of the second layer  142 , may be accomplished by grinding, cutting, sanding, or any combination of the foregoing. 
     In the above embodiments, the shaft  110  of the guidewire  100  has three layers  140 ,  142 ,  144 . In other embodiments, the shaft  110  of the guidewire  100  may have more than three layers, or fewer than three layers (e.g., two layers). 
       FIG. 2A  illustrates a guidewire  100  in accordance with some embodiments. Unlike the guidewire of  FIG. 1A , the guidewire  100  of  FIG. 2A  has only two layers  140 ,  142 . Refer to  FIG. 2A , the guidewire  100  includes a shaft  110  having a proximal end  112 , a distal end  114 , and a body  116  extending from the proximal end  112  to the distal end  114 . The body  116  of the shaft  110  comprises a distal segment  120  having a plurality of different cross sections along a length of the distal segment  120 . At least an outer part  130  of the body  116  that is proximal to the distal segment  120  is made of a material having a shear modulus of at least 13000 ksi. By means of non-limiting examples, the material of the outer part  130  of the body is Molybdenum Rhenium alloy or Tungsten Rhenium alloy. 
     In the illustrated embodiments, the shaft  110  includes a first layer  140 , and a second layer  142 . The second layer  142  is outside the first layer  140 . As shown in the figure, the second layer  142  comprises the outer part  130  of the body  116  that is proximal to the distal segment  120 . In some embodiments, the second layer  142  of the shaft  110  may be made from Molybdenum Rhenium alloy or Tungsten Rhenium alloy. Also, in some embodiments, the first layer  140  may be made of a material having a shear modulus that is less than the shear modulus of the second layer  142 . By means of non-limiting examples, the first layer  140  may be made from stainless steel, Nitinol, Cobalt-Chromium alloy (e.g., MP35N alloy), etc. 
     In the illustrated embodiments, the segment  120  of the shaft  110  is made from the first layer  140 . The segment  120  is distal to a distal end  152  of the second layer  142 . The segment  120  of the first layer  140  has a first part  210 , a second part  214 , and a third part  216 . The third part  216  has a cross sectional dimension that is smaller compared to a cross sectional dimension of the first part  210 , and the smaller cross sectional dimension of the third part  216  transitions into the larger cross section dimension of the first part  210  via the second (intermediate) part  214 . Such configuration is advantageous because it provides progressively softer sections in the proximal-to-distal direction. As a result, the distal segment  120  is softer compared to the remaining part of the body  116 , with the distal part  216  providing the softest section, and may flex or bend more easily. In other embodiments, the segment  120  may comprise more parts or fewer parts than those described above. 
     In some embodiments, the third part  216  of the segment  120  may be compressed to form an elongated cross sectional shape for the part  216  of the segment  120 . For example, in one implementation, the first layer  140  may have a circular cross sectional shape, and the part  216  of the first layer  140  may be compressed into a planar structure having an elongated cross sectional shape, or any of other non-circular shapes. This feature is advantageous because it provides a bias in the direction of bending for the part  216  of the first layer  140 . The compressing of the part  216  of the first layer  140  may be achieved by stamping the part  216  of the first layer  140  in some embodiments. 
     In one specific implementation, the second layer  142  is made from Molybdenum Rhenium alloy, and the first layer  140  is made from Nitinol. The inner Nitinol layer  140  provides kink resistance and a soft distal end for the guidewire  100 , while the outer layer  142  provides a desired pushability and a desired torqueability. In another specific implementation, the second layer  142  is made from Molybdenum Rhenium alloy, and the first layer  140  is made from stainless steel, or Cobalt-Chromium alloy (e.g., MP35N alloy). The first layer  140  provides kink resistance and a softer distal segment  120 . The first layer  140  may be shapeable during use, and provides desirable shape retention capability (e.g., with or without the aid of a malleable structure). Also, because of its relatively high shear modulus, the outer Molybdenum Rhenium alloy layer  142  provides a desirable torqueability. Furthermore, because of the axial stiffness of the outer Molybdenum Rhenium alloy layer  142 , the guidewire  100  also has a desirable pushability. 
     As shown in  FIG. 2B , in some embodiments, the guidewire  100  may also include a sleeve  180  disposed around at least a part of the distal segment  120  (e.g., the distal end  114 ) of the shaft  110 . As shown in the figure, the sleeve  180  has a blunt tip  182 . The distal end  114  of the shaft  110  is coupled to the blunt tip  182 . The sleeve  180  may be any tubular member, and may be made from any materials, such as metal, polymer, etc. In some embodiments, the sleeve  180  may be made from Nitinol. The sleeve  180  may have a plurality of slots and/or openings to increase a flexibility of the sleeve  180 . By means of non-limiting examples, the sleeve  180  may be implemented using slotted hypotube, coiled sleeve, tungsten-loaded polymer sleeve, or a combination of the foregoing. 
     In the illustrated embodiments of  FIGS. 2A-2B , the distal part  216  of the segment  120  is malleable. Thus, the distal part  216  of the segment  120  is bendable to form a bent shape. The distal part  216  is made from a material that allows it to retain the bent shape after the distal part  216  of the segment  120  is bent. In other embodiments, as shown in  FIG. 2C , the distal part  216  (or the first layer  140  comprising the distal part  216 ) may be made from a material that does not have sufficient shape retention capability. In such cases, the guidewire  100  may further include a malleable structure  230  attached to the blunt tip  182 . The malleable structure  230  may be inside the sleeve  180 . During use, the malleable structure  230  is bendable to form a bent shape and is configured to retain the bent shape after the malleable structure  230  is bent. In some embodiments, the malleable structure  230  may be made from Molybdenum Rhenium alloy or Tungsten Rhenium alloy, in order to provide a desirable shape retention ability for the guidewire  100 . 
     Referring to  FIG. 2D , in some embodiments, the guidewire  100  may also include a marker coil  190  disposed inside the sleeve  180 . As shown in the figure, one end of the marker coil  190  is secured to the tip  182 , while a body of the marker coil  190  is secured to or is abut against a wall of the sleeve  180 . In other embodiments, the coil  190  may be coupled to only the tip  182 , and not to the wall of the sleeve  180 . In other embodiments, the proximal end of the marker coil  190  may be secured to the distal segment  120  (e.g., to any location that is proximal to the part  216 , such as to the part  214 , the part  210 , etc.). The securing may be accomplished using an adhesive, welding, mechanical connector, fusion, etc. In further embodiments, at least a part of the sleeve  180  may be formed by the marker coil  190 . In such cases, the marker coil  190  has a cross sectional dimension that corresponds with (e.g., is the same as) a cross sectional dimension of the sleeve  180 . In some cases, an entirety of the length of the sleeve  180  may be made from a coil, such as a marker coil. 
     In some embodiments, the guidewire  100  may include both the malleable structure  230  and the marker coil  190  ( FIG. 2E ). 
       FIG. 2F  illustrates a member  290  for making a guidewire. The member  290  includes the first layer  140 , and the second layer  142 . In some embodiments, a part of the second layer  142  may be removed to expose the first layer  140 . Also, parts of the exposed first layer  140  may be removed, with more material being removed distally than proximally. The above actions will result in the shaft  110  having multiple different cross sectional shapes along its length, like that shown in  FIGS. 2A-2E . In some embodiments, the removing of the part of the second layer  142 , and the part of the exposed first layer  140 , may be accomplished by grinding, cutting, sanding, or any combination of the foregoing. 
     In further embodiments, the shaft  110  of the guidewire  100  may have a single layer.  FIG. 3A  illustrates a guidewire  100  in accordance with some embodiments. Unlike the guidewire of  FIG. 1A  and  FIG. 1B , the guidewire  100  of  FIG. 3A  has only one layer in each of a distal segment and a proximal segment of the shaft  110 . Refer to  FIG. 3A , the guidewire  100  includes a shaft  110  having a proximal end  112 , a distal end  114 , and a body  116  extending from the proximal end  112  to the distal end  114 . The body  116  of the shaft  110  comprises a distal segment  120  having a plurality of different cross sections along a length of the distal segment  120 . At least an outer part  130  of the body  106  that is proximal to the distal segment  120  is made of a material having a shear modulus of at least 13000 ksi. By means of non-limiting examples, the material of the outer part  130  of the body is Molybdenum Rhenium alloy or Tungsten Rhenium alloy. 
     In the illustrated embodiments, the shaft  110  includes a proximal segment  300  made of a first material, and the distal segment  120  is made from a second material that is different from the first material. In some embodiments, the proximal segment  300  may be made from Molybdenum Rhenium alloy or Tungsten Rhenium alloy. Also, in some embodiments, the distal segment  120  may be made from Nitinol, stainless steel, or Cobalt-Chromium alloy (e.g., MP35N alloy). 
     As shown in the figure, the distal segment  120  has a single layer, and includes a first part  301 , a second part  302 , a third part  304 , a fourth part  306 , and a fifth part  308 . The fifth part  308  has a cross sectional dimension that is smaller compared to a cross sectional dimension of the third part  304 , and the smaller cross sectional dimension of the fifth part  308  transitions into the larger cross section dimension of the third part  304  via the fourth (intermediate) part  306 . Similarly, the third part  304  has a cross sectional dimension that is smaller compared to a cross sectional dimension of the first part  301 , and the smaller cross sectional dimension of the third part  304  transitions into the larger cross section dimension of the first part  301  via the second (intermediate) part  302 . Such configuration is advantageous because it provides progressively softer sections in the proximal-to-distal direction. As a result, the distal segment  120  is softer compared to the remaining part of the body  116 , with the distal part  308  providing the softest section, and may flex or bend more easily. In other embodiments, the distal segment  120  may comprise more parts or fewer parts than those described above. 
     The proximal segment  300  also has a single layer. The proximal segment  300  may be attached to the distal segment  120  via an adhesive, weld, mechanical connector, or fusion. 
     As shown in the figure, an inner part  330  of the body  116  that is proximal to the segment  120  and the outer part  300  of the body  116  that is proximal to the segment  120  are made from the same material (as shown by the shaded cross section). In one implementation, the outer part  300  and the inner part  330  of the body  116  are made from a same piece of raw material (e.g., Molybdenum Rhenium alloy, Tungsten Rhenium alloy, etc.), so that they have an unity configuration. 
     In some embodiments, the part  308  of the segment  120  may be compressed to form an elongated cross sectional shape for the part  308 . For example, in one implementation, the part  308  may have a circular cross sectional shape, and the part  308  of the segment  120  may be compressed into a planar structure having an elongated cross sectional shape, or any of other non-circular cross sectional shapes. This feature is advantageous because it provides a bias in the direction of bending for the part  308 . The compressing of the part  308  may be achieved by stamping the part  308  in some embodiments. 
     In the illustrated embodiments, the guidewire  100  also includes a sleeve  180  disposed around the distal end  114  of the shaft  110 . As shown in the figure, the sleeve  180  has a blunt tip  182 . The distal end  114  of the shaft  110  is coupled to the blunt tip  182 . The sleeve  180  may be any tubular member, and may be made from any materials, such as metal, polymer, etc. In some embodiments, the sleeve  180  may be made from Nitinol. The sleeve  180  may have a plurality of slots and/or openings to increase a flexibility of the sleeve  180 . By means of non-limiting examples, the sleeve  180  may be implemented using slotted hypotube, coiled sleeve, tungsten-loaded polymer sleeve, or a combination of the foregoing. 
     In one specific implementation, the proximal segment  300  is made from Molybdenum Rhenium alloy, and the distal segment  120  is made from Nitinol. In another specific implementation, proximal segment  300  is made from Molybdenum Rhenium alloy, and the distal segment  120  is made from stainless steel, or Cobalt-Chromium alloy (e.g., MP35N alloy). In either implementation, the distal segment  120  provides kink resistance and a soft distal end for the guidewire  100 , while the proximal segment  300  provides a desired pushability and a desired torqueability. The distal segment  120  may be shapeable during use, and provides desirable shape retention capability (e.g., with or without the aid of the malleable structure  230 ). Also, because of its relatively high shear modulus, the Molybdenum Rhenium alloy proximal segment  300  provides a desirable torqueability. Furthermore, because of the axial stiffness of the Molybdenum Rhenium alloy segment  300 , the guidewire  100  also has a desirable pushability. 
     Referring to  FIG. 3B , in some embodiments, the guidewire  100  may also include a marker coil  190  disposed inside the sleeve  180 . As shown in the figure, one end of the marker coil  190  is secured to the tip  182 . In other embodiments, the proximal end of the marker coil  190  may be secured to distal segment  120  (e.g., to any location that is proximal to the part  308 , such as to the part  306 , the part  304 , or the part  302 , etc.). In other embodiments, the coil  190  may also be coupled to the wall of the sleeve  180 . In further embodiments, at least a part of the sleeve  180  may be formed by the marker coil  190 . In such cases, the marker coil  190  has a cross sectional dimension that corresponds with (e.g., is the same as) a cross sectional dimension of the sleeve  180 . In some cases, an entirety of the length of the sleeve  180  may be made from a coil, such as a marker coil. 
     In the illustrated embodiments of  FIGS. 3A-3B , the distal part  308  of the segment  120  is malleable. Thus, the distal part  308  of the segment  120  is bendable to form a bent shape. The distal part  308  is made from a material that allows it to retain the bent shape after the distal part  308  of the segment  120  is bent. In other embodiments, the distal part  150  may be made from a material that does not have sufficient shape retention capability. In such cases, the guidewire  100  may further include a malleable structure  230  attached to the blunt tip  182  ( FIG. 3C ). The malleable structure  230  may be inside the sleeve  180 . During use, the malleable structure  230  is bendable to form a bent shape and is configured to retain the bent shape after the malleable structure  230  is bent. In some embodiments, the malleable structure  230  may be made from Molybdenum Rhenium alloy or Tungsten Rhenium alloy, in order to provide a desirable shape retention ability for the guidewire  100 . 
     In further embodiments, the guidewire may include the malleable structure  230  without the marker coil  190  ( FIG. 3D ). 
     It should be noted that the guidewire  100  is not limited to the examples of  FIGS. 3A-3D , and that the guidewire  100  may have other configurations in other embodiments. In other embodiments, the guidewire  100  may include more than two segments. For example, in other embodiments, the guidewire  100  may include three or more segments that are connected in series along a longitudinal axis of the guidewire  100 . Also, in other embodiments, at least one of the segments may have multiple layers instead of a single layer. 
     In further embodiments, the proximal segment  300  and the distal segment  120  of the guidewire  100  may be made from a same piece of raw material.  FIG. 4  illustrates a guidewire  100  in accordance with some embodiments. The guidewire  100  includes a shaft  110  having a proximal end  112 , a distal end  114 , and a body  116  extending from the proximal end  112  to the distal end  114 . The body  116  of the shaft  110  comprises a distal segment  120  having a plurality of different cross sections along a length of the distal segment  120 . At least an outer part  130  of the body  106  that is proximal to the distal segment  120  is made of a material having a shear modulus of at least 13000 ksi. By means of non-limiting examples, the material of the outer part  130  of the body is Molybdenum Rhenium alloy or Tungsten Rhenium alloy. 
     In the illustrated embodiments, the shaft  110  also includes a proximal segment  300 , wherein the proximal segment  300  and the distal segment  120  are made from the same material. In some embodiments, the material of the proximal segment  300  and the distal segment  120  may be Molybdenum Rhenium alloy or Tungsten Rhenium alloy. As shown by the shaded cross section, as a result of using the same piece of raw material to make the segments  300 ,  120  of the shaft  110 , an inner part  330  and the outer part  130  of the segment  300 , and the segment  120 , have an unity configuration. 
     As shown in the figure, the proximal segment  300  and the distal segment  120  comprise a single layer, and includes a first part  301 , a second part  302 , a third part  304 , a fourth part  306 , and a fifth part  308 . The fifth part  308  has a cross sectional dimension that is smaller compared to a cross sectional dimension of the third part  304 , and the smaller cross sectional dimension of the fifth part  308  transitions into the larger cross section dimension of the third part  304  via the fourth (intermediate) part  306 . Similarly, the fifth third  304  has a cross sectional dimension that is smaller compared to a cross sectional dimension of the first part  301 , and the smaller cross sectional dimension of the third part  304  transitions into the larger cross section dimension of the first part  301  via the second (intermediate) part  302 . Such configuration is advantageous because it provides progressively softer sections in the proximal-to-distal direction. As a result, the distal segment  120  is softer compared to the remaining part of the body  116 , with the distal part  308  providing the softest section, and may flex or bend more easily. In other embodiments, the distal segment  120  may comprise more parts or fewer parts than those described above. 
     In some embodiments, the part  308  may be compressed to form an elongated cross sectional shape for the part  308 . For example, in one implementation, the part  308  may have a circular cross sectional shape, and the part  308  may be compressed into a planar structure having an elongated cross sectional shape, or any of other non-circular cross sectional shape. This feature is advantageous because it provides a bias in the direction of bending for the part  308 . The compressing of the part  308  may be achieved by stamping the part  308  in some embodiments. 
     In the illustrated embodiments, the guidewire  100  also includes a sleeve  180  disposed around the distal end  114  of the shaft  110 . As shown in the figure, the sleeve  180  has a blunt tip  182 . The distal end  114  of the shaft  110  is coupled to the blunt tip  182 . The sleeve  180  may be any tubular member, and may be made from any materials, such as metal, polymer, etc. In some embodiments, the sleeve  180  may be made from Nitinol. The sleeve  180  may have a plurality of slots and/or openings to increase a flexibility of the sleeve  180 . By means of non-limiting examples, the sleeve  180  may be implemented using slotted hypotube, coiled sleeve, tungsten-loaded polymer sleeve, or a combination of the foregoing. 
     As shown in the figure, the guidewire  100  also includes a marker coil  190  disposed inside the sleeve  180 . The marker coil  190  is coupled to the tip  182 . In some embodiments, the marker coil  190  may also be coupled to the wall of the sleeve  180 . In other embodiments, the proximal end of the marker coil  190  may be secured to distal segment  120  (e.g., to any location that is proximal to the part  308 , such as to the part  306 , the part  304 , or the part  302 , etc.). The securing may be accomplished using an adhesive, welding, mechanical connector, fusion, etc. In other embodiments, the marker coil  190  may form at least a part of the sleeve  180 , or may form an entirety of the sleeve  180 . In further embodiments, the guidewire  100  may not include the marker coil  190 . 
     The guidewire  100  of  FIG. 4  is advantageous because it provides an optimal combination of shapeability, shape retention capability, and torqueability. Due to the entirety of the shaft  110  of the guidewire  100  being made from the same material (e.g., a single raw member), and the resulting shaft  110  may have a small profile (e.g., smaller than that in the embodiments of  FIGS. 1-3 ). Accordingly, the guidewire  100  may be used to access smaller blood vessels, such as distal blood vessels in a brain, thereby reaching more aneurysms that cannot be accessed before. The distal part  308  provides kink resistance and a soft distal end for the guidewire  100 . The distal part  308  and/or the part  304  may be shapeable during use, and provides desirable shape retention capability (without the aid of a malleable structure). However, in other embodiments, the guidewire  100  may optionally further include a malleable structure to enhance the shape retention capability, as similarly discussed. Also, because of its relatively high shear modulus, the shaft  110  made from Molybdenum Rhenium alloy or Tungsten Rhenium alloy provides a desirable torqueability. Furthermore, because of the axial stiffness of shaft  110  made from Molybdenum Rhenium alloy or Tungsten Rhenium alloy, the guidewire  100  also has a desirable pushability. 
     It should be noted that the materials for making the shaft  110  of the guidewire  100  should not be limited to the examples described, and that the shaft  110  may be made from other materials in other embodiments. For example, in other embodiments, the shaft  110  of the guidewire  100  may be made from other materials, as long as a desired torqueability is achieved. In other embodiments, the shaft  110  may be made from any material having a Young&#39;s Modulus (under annealed condition) of at least 6000 ksi, or more preferably at least 30000 ksi, or even more preferably at least 40000 ksi. Also, in other embodiments, the shaft  110  may be made from any material having an ultimate tensile strength (under annealed condition) of at least 100 ksi, and more preferably at least 200 ksi, and even more preferably at least 300 ksi. By means of non-limiting examples, specific materials that may be used include, but are not limited to, Mo-47.5Re, W-25Re, SS304, etc. 
     In addition, it should be noted that the shaft  110  of the guidewire  100  may have different dimensions in different embodiments. For example, in some embodiments, the shaft  110  of the guidewire  100  may have a total length that is anywhere from 50 inches to 100 inches, such as a length that is anywhere from 70 inches to 90 inches. Also, in some embodiments, the distal segment  120  may have a length that is 5 inches to 30 inches, such as a length that is anywhere from 10 inches to 25 inches, or a length that is anywhere from 12 inches to 20 inches. Furthermore, in some embodiments, the distal part  150 / 216 / 308  may have a length that is anywhere from 0.3 inch to 1 inch, such as a length that is anywhere from 0.5 inch to 0.8 inch. In some embodiments in which the distal part  150 / 216 / 308  is stamped, the stamped distal part may have a portion with a constant width, wherein the portion may have a longitudinal length of at least 0.3 inch, such as at least 0.4 inch. In addition, in some embodiments, the distal segment  120  may have a cross sectional dimension (e.g., diameter) that is anywhere from 0.04 mm to 0.5 mm and the distal part  150 / 216 / 308  may have a cross sectional dimension (e.g., diameter) that is anywhere from 0.004 mm to 0 0.1 mm. In other embodiments, the distal segment  120  and/or the distal part  150 / 216 / 308  may have dimensions that are different from those mentioned above. 
     Furthermore, the number of different cross sections along the length of the distal segment  120  is not limited to the examples described previously. In other embodiments, the number of different cross sections along the length of the distal segment  120  may be more, or fewer, than the ones described herein. 
     In addition, in one or more embodiments described herein, a part of the segment  120  may have a flat portion. For example, the part  150  (in the embodiments of  FIG. 1 ), the part  216  (in the embodiments of  FIG. 2 ), or the part  308  (in the embodiments of  FIG. 3 or 4 ), may be stamped to create a flat portion. Also, in some embodiments, the flat portion of the segment  120  may include one or more openings extending through a thickness of the flat portion. This feature is advantageous because it may assist the guidewire  100  in achieving a soft distal end without compromising other performance, such as shapeability and/or shape retention of the guidewire  100 .  FIG. 5  illustrates a guidewire  100  that includes a flat portion  400  with an opening  402 . In the illustrated embodiments, the flat portion  400  may be created by stamping a distal end of a shaft, such as the shaft  110  described with reference to any of the embodiments of  FIGS. 1-4 . As described, the shaft  110  has a proximal end  112 , a distal end  114 , and a body  116  extending from the proximal end  112  to the distal end  114 . The body  116  of the shaft  110  comprises a distal segment  120  having a plurality of different cross sections along a length of the distal segment  120 . In other embodiments, the shaft that includes the flat portion  400  may be any elongated member, such as a core wire. The elongated member may have a cross-sectional dimension that is the same along the length of the elongated member, or may have different cross-sectional dimensions along the length of the elongated member. 
     As shown in  FIG. 5 , the opening  402  of the flat portion  400  extends through the thickness of the flat portion  400 . The flat portion  400  has a long side  404  that is parallel to a longitudinal axis  410  of the flat portion  400 . The opening  402  is in a form of an elongated slot, and has a long side  406  that is parallel to the long side  404  of the flat portion  400 . The opening  402  of the flat portion  400  is advantageous because it reduces the cross-sectional characteristic (such as moment of inertia) of the flat portion  400 . Because a bending stiffness of the flat portion  400  depends on the moment of inertia of the cross-section of the flat portion  400 , by reducing the moment of inertia of the cross-section of the flat portion  400 , the bending stiffness of the flat portion  400  is also reduced accordingly. Thus, the opening  402  of the flat portion  400  has the benefit of making the flat portion  400  more flexible. The dimension of the opening  402  may be configured to achieve a desired stiffness for the flat portion  400 . 
     In the illustrated embodiments, the guidewire  100  also includes a tapering portion  412  that is proximal the flat portion  400 . Also, the guidewire  100  comprises a cylinder portion  414  that is proximal the tapering portion  412 . In some embodiments, the cylinder portion  414 , the tapering portion  412 , and the flat portion  400  may be parts of a shaft (such as, parts of the segment  120  of the shaft  110 ). 
     In some embodiments, the flat portion  400  is bendable to form a bent shape and is configured to retain the bent shape after the flat portion  400  is bent. In other embodiments, the flat portion  400  may be made from a material that allows the flat portion  400  to be elastically bendable, so that the flat portion  400  can springs back after being bent. 
     In other embodiments, instead of having a single opening  402 , the flat portion  400  may include a series of openings  402  arranged along the longitudinal axis  410  of the flat portion  400  ( FIG. 6 ). As shown in the figure, each of the openings  402  in the series is a rectangular slot extending through the thickness of the flat portion  400 . Alternatively, each of the openings  402  in the series may be a circular slot extending through the thickness of the flat portion  400  ( FIG. 7 ). The openings  402  may have other shapes in other embodiments. Furthermore, in other embodiments, the shapes and/or the dimensions of openings  402  of the flat portion  400  may be different. For example, the flat portion  400  may have a first opening  402  with a first shape, and a second opening  402  with a second shape that is different from the first shape. 
     In the embodiments of  FIGS. 6-7 , the openings  402  are arranged in a row along the longitudinal axis  410  of the flat portion  400 . In other embodiments, as shown in  FIG. 8 , the openings  402  may be in multiple rows arranged along the longitudinal axis  410 , with the openings  402  being in a staggered configuration. 
     It should be noted that the number of openings  402 , the size of the openings  402 , the geometry of the openings  402 , and the arrangement of the openings  402  are not limited to the examples illustrated. In other embodiments, the number of openings  402 , the size of the openings  402 , the geometry of the openings  402 , the arrangement of the openings  402 , or any combination of the foregoing, may be selected or optimized to achieve a desired softness and/or shape retention ability for the distal end of the guidewire  100 , depending on the particular application or requirements. Also, in some embodiments, a desired shape retention characteristic of the distal end of the guidewire  100  may be achieved by configuring a thickness of the flat portion  400  of the guidewire  100 . For example, the flat portion  400  may be made thicker in some embodiments to enhance the shape retention ability of the distal end of the guidewire  100 . 
     In any of the embodiments of  FIGS. 5-8 , the guidewire  100  may include other components, such as those similarly described with references to  FIGS. 1-4 . For example, as shown in  FIG. 9 , in other embodiments, the guidewire  100  in any of the embodiments of  FIGS. 5-8  may also include a sleeve  180  disposed around at least a part of the segment  120 . A side view of the flat portion  400  with openings  402  extending through the thickness of the flat portion  400  is also shown. The sleeve  180  may be made from any materials, including but not limited to Nitinol. In some embodiments, the sleeve  180  may include one or more slots extending partially or completely through a thickness of a wall of the sleeve  180 . In one implementation, the sleeve  180  may be a slotted Nitinol sleeve. The guidewire  100  may also include a blunt tip  182  to which the segment  120  and/or the sleeve  180  is attached. The guidewire  100  may further include a coil  190  disposed around the segment  120 . The coil  190  is located between the segment  120  (e.g., the flat portion  400  of the segment  120 ) and the sleeve  180 . In some embodiments, the coil  190  may be made from a radiopaque material so that that coil  190  can function as a radiopaque coil. In one implementation, the coil  190  may be made from Platinum Tungsten. This is advantageous because the softer radiopaque material of the coil  190  may further increase the softness of the distal tip of the guidewire. In other embodiments, the coil  190  may be made from other materials. 
     In addition, in one or more embodiments described herein, the guidewire  100  may also include a radiopaque marker coupled to the flat portion  400  of the segment  120 . For example, the radiopaque marker may be coupled to the opening  402  at the flat portion  400 .  FIGS. 10A-10H  illustrates a method of making a guidewire that includes a flat portion, and a radiopaque marker coupled to the flat portion. First, a raw wire  500  is provided ( FIG. 10A ). In some embodiments, the raw wire  500  has a circular cross-section. In other embodiments, the raw wire  500  may have other cross-sectional shapes, such as a square shape, an elliptical shape, a hexagon, an octagon, etc. Next, the raw wire  500  is grounded, cut, and/or sanded to create a shaft  510  having different cross-sectional dimensions along the longitudinal axis of the shaft  510  ( FIG. 10B ). In other embodiments, the shaft  510  with different cross-sectional dimensions along the longitudinal axis of the shaft  510  may be created using any of the techniques described with reference to  FIG. 1F, 2F , or  3 A. In further embodiments, the creation of different cross-sectional dimensions along the longitudinal axis of the shaft  510  is optional, and the shaft  510  may have an uniform cross-sectional dimensions along the longitudinal axis of the shaft  510 . Next, a portion of the shaft  510  may be stamped to create the flat portion  400  ( FIG. 10C ). The created flat portion  400  has a first major planar surface, and a second major planar surface that is opposite from the first major planar surface. Then, an opening  402  extending through the thickness of the flat portion  400  may be created. The opening  402  may be created by cutting (e.g., laser cutting, mechanical cutting, etc.) or by puncturing the flat portion  400  in some embodiments ( FIG. 10D ).  FIG. 10E  illustrates a side cross-sectional view of the guidewire  100 , particularly showing the opening  402  extending through the thickness of the flat portion  400 . Next, as shown in  FIG. 10F , a radiopaque marker  530  may be inserted into the opening  402  of the flat portion  400 . In the illustrated embodiments, the radiopaque marker  530  has a first portion  532  abutting a first side of the flat portion  400 , and a second portion  534  configured (e.g., sized and/or shaped) for placement into the opening  402  of the flat portion  400 . After the second portion  534  of the radiopaque marker  530  has been placed into the opening  402 , a third portion  536  of the radiopaque marker  530  extending from the second portion  534  is located on the opposite side of the flat portion  400 . Next, the third portion  536  of the radiopaque marker  530  may be stamped to flatten out the third portion  536 . The flattened third portion  536  abuts the second side of the flat portion  400 , thereby anchoring the radiopaque marker  530  at the second side of the flat portion ( FIG. 10G ). As shown in the figure, the first portion  532  of the radiopaque marker  530  has a first cross sectional dimension, the second portion  534  of the radiopaque marker  530  has a second cross sectional dimension, and the third portion  536  of the radiopaque marker  530  has a third cross sectional dimension; wherein the first cross sectional dimension is larger than the second cross sectional dimension; and wherein the third cross sectional dimension is larger than the second cross sectional dimension.  FIG. 10H  illustrates a top/planar view of the flat portion  400  of the guidewire  100 , particularly showing the radiopaque marker  530  being secured to the flat portion  400 . 
     In other embodiments, multiple openings  402  may be created at the flat portion  400  (like those shown in the examples of  FIGS. 6-8 ). In such cases, multiple radiopaque markers  530  may be secured to the flat portion  400  using the technique described with reference to  FIGS. 10A-10H . 
     In other embodiments, instead of anchoring the radiopaque marker  530  against opposite sides of the flat portion  400 , other techniques may be utilized to secure the radiopaque marker  530  relative to the flat portion  400 .  FIG. 11  illustrates another flat portion  400  of a segment of a guidewire  10 . The flat portion  400  may be a stamped core wire, as similarly described. As shown in the figure, the flat portion  400  has a first major surface  600  and a second major surface  602  opposite from the first major surface  600 . The flat portion  400  comprises a first radiopaque marker  610  secured on the first major surface  600  of the flat portion  400 , and a second radiopaque marker  612  secured on the second major surface  602  of the flat portion  400 . In other embodiments, the second radiopaque marker  612  is optional, and the guidewire  100  may not include the second radiopaque marker  612 . 
     As shown in  FIG. 11 , each of the radiopaque marker  610  and the radiopaque marker  612  is a planar marker having a width that is the same as a width of the flat portion  400 . In other embodiments, the radiopaque marker  610  and/or the radiopaque marker  612  may have a width that is less than the width of the flat portion  400 . In further embodiments, the radiopaque marker  610  and/or the radiopaque marker  612  may have a width that is longer than the width of the flat portion  400 . 
     Various techniques may be employed to secure the marker  610  and/or the marker  612  onto the flat portion  400 . For example, the marker  610  and/or the marker  612  may be plated onto the flat portion  400  in some embodiments. In other embodiments, the marker  610  and/or the marker  612  may be secured onto the flat portion  400  via adhesive. In further embodiments, the marker  610  and/or the marker  612  may be applied onto the flat portion  400  through material-deposition techniques. For example, the marker  610  and/or the marker  612  may be achieved by depositing (e.g., electroplating) radiopaque material onto the surface of the flat portion  400 . The radiopaque material may be Au, Pt, or other materials. In other embodiments, the flat portion  400  may be dipped into a solution of radiopaque material, which then hardens to form a radiopaque marker circumferentially disposed around the flat portion  400 . In such cases, the marker  610  and the marker  612  on opposite sides of the flat portion  400  are parts of the circumferential radiopaque marker surrounding the flat portion  400 . The marker  610  and/or the marker  612  is advantageous because, besides being radiopaque for imaging purpose, they also provide shape retention property for the flat portion  400 . Accordingly, this feature may eliminate the need to provide a separate bendable structure (that has shape retention characteristic) between the shaft of the guidewire and an outer sleeve of the guidewire. 
     In other embodiments, instead of having only one radiopaque marker on one side of the flat portion  400  of the guidewire  100 , the flat portion  400  may have first multiple radiopaque markers  610  secured on the first major surface  600  of the flat portion  400  ( FIG. 12 ). The first multiple radiopaque markers  610  are arranged in a row along a longitudinal axis of the flat portion  400 . Each of the radiopaque markers  610  are spaced apart from each other. As shown in the figure, the guidewire  100  also includes second multiple radiopaque markers  612  secured on the second major surface  602  of the flat portion  400 . The second multiple radiopaque markers  612  are arranged in a row along a longitudinal axis of the flat portion  400 . Each of the radiopaque markers  612  are spaced apart from each other. In other embodiments, the second multiple radiopaque markers  612  on the second major surface  602  of the flat portion  400  is optional, and the guidewire  100  may not include the second multiple radiopaque markers  612 . Various techniques may be employed to secure the markers  610  and/or the markers  612  onto the flat portion  400 . For example, the markers  610  and/or the markers  612  may be plated onto the flat portion  400  in some embodiments. In other embodiments, the markers  610  and/or the markers  612  may be secured onto the flat portion  400  via adhesive. In further embodiments, the markers  610  and/or the markers  612  may be applied onto the flat portion  400  through material-deposition techniques. For example, the markers  610  and/or the markers  612  may be achieved by selectively depositing radiopaque material by photolithography or other process onto the surfaces of the flat portion  400 . As shown in  FIG. 12 , the markers  610  and the markers  612  are in the form of radiopaque strips. The markers  610  and/or the markers  612  are advantageous because, besides being radiopaque for imaging purpose, they also serve as stress concentrators and may help in shape retention for the flat portion  400 . In other embodiments, the markers  610  and/or the markers  612  may not be in the form of strips, and other patterns of the markers  610 / 612  may be used. 
     In the above embodiments, the flat portion  400  is described as having one or more openings for reducing a stiffness of the flat portion  400 . In other embodiments, other techniques may be employed to reduce a stiffness of the flat portion  400 . For example, in other embodiments, the flat portion  400  may include one or more grooves  700  at an exterior surface of the flat portion  400  ( FIG. 13 ). The grooves  700  may be implemented as patterned grooves in some embodiments. The groove(s)  700  reduces the cross-sectional dimension of the flat portion  400 , thereby reducing a stiffness (e.g., bending stiffness) of the flat portion  400 . In other embodiments, the flat portion  400  may include both groove(s)  700  and opening(s), like the opening(s)  402  described with reference to  FIGS. 5-10 , to achieve a desired stiffness for the flat portion  400 . In further embodiments, the guidewire  100  of  FIG. 13  may also include one or more markers secured to the flat portion  400 . 
     In addition, in one or more embodiments described herein, instead of having just one flat portion  400 , the segment  120  of the guidewire  100  may include multiple flat portions  400  ( FIG. 14 ). In some embodiments, the flat portions  400  may be created by stamping multiple parts of a core wire that are spaced apart from each other. As a result, each flat portion  400  may have a flat or planar configuration, and adjacent flat portions  400  are connected to each other via a cylindrical portion of the core wire. In other words, a part of the core wire between adjacent flat portions  400  functions as a connecting portion that connects the adjacent flat portions  400 . Since the connecting portion and the adjacent flat portions are all made from the same core wire, they have an unity configuration. The flat portions  400  may have the same thickness in some embodiments. In other embodiments, the flat portions  400  may have different respective thicknesses. The number of flat portions  400 , the thicknesses of the flat portions  400 , the spacing between the flat portions  400 , or any combination of the foregoing, may be selected or optimized to achieve a desired softness and/or shape retention ability for the distal end of the guidewire  100 . In some embodiments, the guidewire  100  of  FIG. 14  may also include one or more markers secured to one or each of the flat portions  400 . 
     Furthermore, it should be noted that the marker  530  described is not limited to having a planar configuration, and that the manner in which the marker  530  is secured to the shaft is not limited to the examples described. In other embodiments, the marker  530  may have different shapes, and/or the marker  530  may be secured to the shaft in other manners. For example, as shown in  FIG. 15 , in some embodiments, the marker  530  of the guidewire  100  may be a radiopaque coil  530  surrounding at least a part of a segment  120  of a shaft of the guidewire  100 . The part of the segment  120  has opposite sides  800 ,  802  with indentations  810  along each of the opposite sides for allowing the radiopaque coil  530  to be screwed over the part of the segment  120 . In some embodiments, the part of the segment  120  surrounded by the radiopaque coil  530  may be a flat portion (e.g., the flat portion  400  described herein). In such cases, the indentations  810  may be grooves extending through the thickness of the flat portion  400 . The indentations  810  may be implemented as cutouts in some embodiments. In other embodiments, the part of the segment  120  surrounded by the radiopaque coil  530  may be another part of the segment  120  that is proximal to the flat portion  400 . In further embodiments, the segment  120  surrounded by the radiopaque coil  530  may not be any flat portion. Instead, the segment  120  surrounded by the radiopaque coil  530  may be an un-flattened portion of a core wire or shaft. The technique shown in  FIG. 15  for attaching the radiopaque coil  530  to the segment  120  is advantageous because it provides mechanical interaction between the segment  120  and the radiopaque coil  530 , and it also save space inside an outer distal sleeve of the guidewire  100 . 
     In any of the embodiments of  FIGS. 10-15 , the guidewire  100  may include other components, such as those similarly discussed with references to  FIGS. 1-4 . For example, as similarly discussed with reference to  FIG. 9 , in other embodiments, the guidewire  100  in any of the embodiments of  FIGS. 10-15  may also include a sleeve  180  disposed around at least a part of the segment  120 . The sleeve  180  may be made from any materials, including but not limited to Nitinol. In some embodiments, the sleeve  180  may include one or more slots extending partially or completely through a thickness of a wall of the sleeve  180 . In one implementation, the sleeve  180  may be a slotted Nitinol sleeve. The guidewire  100  may also include a blunt tip  182  to which the segment  120  and/or the sleeve  180  is attached. The guidewire  100  may further include a coil  190  disposed around at least a part of the segment  120 . The coil  190  is located between the segment  120  (e.g., the flat portion  400  of the segment  120 ) and the sleeve  180 . In some embodiments, the coil  190  may be made from a radiopaque material so that that coil  190  can function as a radiopaque coil. In one implementation, the coil  190  may be made from Platinum Tungsten. This is advantageous because the softer radiopaque material of the coil  190  may further increase the softness of the distal tip of the guidewire. In other embodiments, the coil  190  may be made from other materials. 
     Also, in any of the embodiments described herein, the guidewire  100  may be provided as a part of a medical device. For example, a medical device may include a catheter, and the guidewire  100 , wherein the catheter includes a lumen for accommodating the guidewire  100 . By means of non-limiting examples, the medical device may be a microcatheter, a balloon catheter, a stent delivery catheter, a catheter for removing blockage in a vessel, a delivery catheter for the guidewire  100 , etc. 
     In one method of use of the guidewire  100 , a doctor first bends the distal segment of the guidewire  100  into a desired shape, depending on the geometry of the anatomy that the guidewire  100  will access. For example, the distal segment of the guidewire  100  may be bent to have a L shape, a C shape, a U shape, a S shape, a shape with two or more curves in different planes, etc. The guidewire  100  is then placed in a delivery catheter. Then, an incision is made at a skin of a patient. The delivery catheter with the guidewire  100  therein is inserted through the incision, and into a blood vessel in the patient. The delivery catheter and the guidewire  100  may be advanced distally until the distal end of the guidewire  100  and/or the delivery catheter reaches a target site. The target site may be anywhere in the patient&#39;s body, such as a blood vessel in a limb, in a torso, in a neck, in a head, etc. The delivery catheter houses the guidewire  100  as the delivery catheter is advanced distally. When the delivery catheter reaches a location in the patient that requires the bent shape of the distal segment of the guidewire  100  to access, at least a part of the distal segment may be deployed out of the delivery catheter to let the distal segment assumes its bent shape. The bent shape of the distal segment of the guidewire  100  steers the guidewire  100  into a desired direction, thereby allowing the guidewire  100  and the delivery catheter to be advanced distally into a desired passage. The guidewire  100  described herein is advantageous because it allows a bent shape of the distal segment of the guidewire  100  to be retained, so that the bent shape will not return back to the pre-bent configuration even after the distal segment has traversed different paths in a vessel with different curvatures (or even after the bent distal segment has been placed in a tube, such as a delivery tube). The guidewire  100  is also advantageous because it allows the doctor to effectively torque the guidewire  100  due to the enhanced torqueability of the guidewire  100 , and allows the doctor to push the guidewire  100  distally inside the patient without kinking. 
     Embodiments of the guidewire  100  described herein have desired torqueability, desired shape retention capability, desired pushability, or any combination of the foregoing. In some embodiments, a desired torqueability is considered to be achieved by the guidewire  100  if a twisting or torqueing motion applied at a proximal end about a longitudinal axis of the guidewire  100  to turn the proximal end of the guidewire  100  (or shaft  110 ) by an angle P will result in a turning of the distal end of the guidewire  100  by an angle D that is at least 80% of P, or more preferably at least 90% of P, or even more preferably at least 95% of P (e.g., 100% of P, which means that the distal end of the guidewire  100  has 1:1 response with respect to a torque applied at the proximal end of the guidewire  100 ). Also, in some embodiments, a desired shape retention capability is considered to be achieved by the guidewire  100  if the bent segment with curvature can retain at least 70% of the curvature, or more preferably at least 80% of the curvature, and even more preferably at least 90% of the curvature, after the bent segment is placed in a tube and is pushed back out from the tube. Also, in some embodiments, a desired pushability may be achieved if the guidewire  100  does not kink while being advanced inside a vessel. 
     The following items are exemplary features of embodiments described herein. Each item may be an embodiment itself or may be a part of an embodiment. One or more items described below may be combined with other item(s) in an embodiment. 
     Item 1: A guidewire includes: a shaft having a proximal end, a distal end, and a body extending from the proximal end to the distal end; a blunt tip; and a sleeve; wherein the body of the shaft comprises at least a segment that is surrounded by the sleeve, the segment coupled to the blunt tip; and wherein the segment of the body of the shaft comprises a flat portion having one or more openings extending through a thickness of the flat portion. 
     Item 2: The one or more openings comprise only one elongated slot extending through the thickness of the flat portion. 
     Item 3: The flat portion has a long side that is parallel to a longitudinal axis of the guidewire, and wherein the slot has a long side that is parallel to the long side of the flat portion. 
     Item 4: The one or more openings comprise a series of openings arrange along a longitudinal axis of the flat portion. 
     Item 5: Each of the openings in the series is a rectangular slot extending through the thickness of the flat portion. 
     Item 6: Each of the openings in the series is a circular slot extending through the thickness of the flat portion. 
     Item 7: The one or more openings comprise rows of openings arranged in a staggered configuration. 
     Item 8: The guidewire further includes a radiopaque marker extending through one of the one or more openings. 
     Item 9: The radiopaque marker has a first portion abutting a first side of the flat portion, a second portion within the one of the one or more openings, and a third portion abutting a second side of the flat portion, the second side being opposite from the first side of the flat portion. 
     Item 10: The first portion of the radiopaque marker has a first cross sectional dimension, the second portion of the radiopaque marker has a second cross sectional dimension, and the third portion of the radiopaque marker has a third cross sectional dimension; wherein the first cross sectional dimension is larger than the second cross sectional dimension; and wherein the third cross sectional dimension is larger than the second cross sectional dimension. 
     Item 11: The flat portion comprises a stamped core wire. 
     Item 12: The guidewire further includes a coil disposed between the flat portion and the sleeve. 
     Item 13: The coil is made from a radiopaque material. 
     Item 14: The coil is made from Platinum Tungsten. 
     Item 15: The sleeve is made from Nitinol. 
     Item 16: The sleeve comprises a plurality of slots. 
     Item 17: The body of the shaft comprises a tapering portion that is proximal the flat portion. 
     Item 18: The body of the shaft comprises a cylinder portion that is proximal the tapering portion. 
     Item 19: The flat portion is bendable to form a bent shape and is configured to retain the bent shape after the flat portion is bent. 
     Item 20: The segment also comprises an additional flat portion distal to the flat portion. 
     Item 21: The segment also comprises a connecting portion connecting the flat portion and the additional flat portion, wherein the connecting portion, the flat portion, and the additional flat portion have an unity configuration. 
     Item 22: A medical device includes a catheter, and the guidewire, wherein the catheter includes a lumen for accommodating the guidewire. 
     Item 23: A guidewire includes: a shaft having a proximal end, a distal end, and a body extending from the proximal end to the distal end; a blunt tip; and a sleeve; wherein the body of the shaft comprises at least a segment that is surrounded by the sleeve, the segment coupled to the blunt tip; and wherein the segment of the body of the shaft comprises a flat portion with a first major surface and a second major surface opposite from the first major surface, and wherein the flat portion comprises one or more radiopaque markers secured on the first major surface. 
     Item 24: The one or more radiopaque markers comprise a first planar marker having a width that is the same as a width of the flat portion. 
     Item 25: The guidewire further includes a second planar marker secured on the second major surface of the flat portion. 
     Item 26: The one or more radiopaque markers comprise first multiple radiopaque markers spaced apart from each other. 
     Item 27: The first multiple radiopaque markers are aligned in a row along a longitudinal axis of the flat portion. 
     Item 28: The guidewire further includes second multiple radiopaque markers spaced apart from each other and secured on the second major surface of the flat portion. 
     Item 29: The flat portion also comprises one or more radiopaque markers secured on the second major surface. 
     Item 30: A guidewire includes: a shaft having a proximal end, a distal end, and a body extending from the proximal end to the distal end; a blunt tip; and a sleeve; wherein the body of the shaft comprises at least a segment that is surrounded by the sleeve, the segment coupled to the blunt tip; and wherein the segment of the body of the shaft comprises a flat portion with an exterior surface, and wherein the flat portion comprises a plurality of grooves at the exterior surface. 
     Item 31: A guidewire includes: a shaft having a proximal end, a distal end, and a body extending from the proximal end to the distal end; a blunt tip; and a sleeve; wherein the body of the shaft comprises at least a segment that is surrounded by the sleeve, the segment coupled to the blunt tip; and wherein the guidewire further comprises a radiopaque coil surrounding at least a part of the segment, the part of the segment having opposite sides with indentations along each of the opposite sides for allowing the radiopaque coil to be screwed over the part of the segment. 
     Item 32: The part of the segment comprises a flat portion. 
     Item 33: The segment comprises a flat portion, and the part of the segment is proximal to the flat portion. 
     Although particular embodiments have been shown and described, it will be understood that it is not intended to limit the claimed inventions to the preferred embodiments, and it will be obvious to those skilled in the art that various changes and modifications may be made without department from the spirit and scope of the claimed inventions. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense. The claimed inventions are intended to cover alternatives, modifications, and equivalents.