MRI-compatible interventional medical devices and related methods

Abstract

The MRI compatible wire guide 100 includes a continuous core member 110 formed of a metallic material and having a first length, and a continuous jacket 130 disposed over and completely encapsulating the entire continuous core member, the continuous jacket 130 being formed of a dielectric material and having a second length longer than the first length. The jacket may include a first shaft portion formed of a non-polymeric dielectric material and a second shaft portion formed of a polymeric dielectric material.

Description

[Technical Field]

[0001] The present disclosure relates generally to the field of medical devices. More particularly, the present disclosure relates to interventional medical devices, such as wire guides, useful in interventional procedures performed under magnetic resonance imaging (MRI), methods of imaging a body part using MRI, methods of performing interventional medical procedures under MRI, and methods of manufacturing interventional medical devices. [Background technology]

[0002] Interventional procedures performed under MRI have several advantages over x-ray-guided interventions. For example, patients are not exposed to ionizing radiation. MRI also provides the ability to characterize tissue and fluid flow during interventional procedures. For at least these reasons, the use of interventional MRI has gained widespread acceptance, and the number of procedures that can be performed under MRI has generally increased.

[0003] However, the art remains devoid of a limited number of interventional medical devices suitable for use under MRI, which continues to limit the increased use of interventional MRI procedures. As a result, patients have yet to fully benefit from interventional MRI techniques and, in practice, are often still limited to inconvenient and potentially ineffective options for certain treatments.

[0004] Wire guides are essential for performing interventional procedures, and therefore, the development of MRI-compatible wire guides represents an important step in the widespread adoption of interventional MRI procedures. To date, the development of MRI-compatible wire guides has primarily focused on the use of relatively complex segmented structures and non-metallic materials to avoid the anticipated RF heating, deflection, and image artifacts believed to be associated with the use of devices with metallic components under MRI. While purpose-built designs of segmented, non-metallic wire guides can indeed avoid RF heating, deflection, and artifacts, wire guides made according to these designs have also been found to have drawbacks. For example, segmented, non-metallic wire guides may have poor mechanical properties, trackability, and torqueability, limiting their clinical adoption despite the anticipated benefits offered by MRI compatibility of such devices. Summary of the Invention [Problem to be solved by the invention]

[0005] Thus, there remains a need for new and improved MRI-compatible wire guides and related methods, including methods for imaging portions of body vessels using MRI, methods for performing interventional medical procedures under MRI, and methods for manufacturing interventional medical devices. [Means for solving the problem]

[0006] Various exemplary interventional medical devices useful in interventional procedures performed under MRI are described.

[0007] An exemplary wire guide includes a continuous core member formed of a metallic material and having an outer surface, and a jacket disposed over the core member such that the outer surface of the core member is completely encapsulated by the jacket.

[0008] Another exemplary wire guide includes a continuous core member formed of a metallic material and having an outer surface, the core member having a first susceptibility; a marker disposed on the outer surface of the core member and formed of a second metallic material having a second susceptibility different from the first susceptibility; and a jacket disposed over the core member and the marker such that no portion of the outer surface of the core member is exposed to the external environment surrounding the wire guide.

[0009] Another exemplary wire guide includes a continuous core member formed of a metallic material and having an outer surface, the core member having a first susceptibility; a jacket disposed on the core member such that no portion of the outer surface of the core member is exposed to the external environment surrounding the wire guide; and a marker disposed within the thickness of the jacket and formed of a second metallic material having a second susceptibility different from the first susceptibility.

[0010] Various exemplary methods for imaging a portion of a patient's body vasculature using MRI are described.

[0011] An exemplary method for imaging a portion of a patient's body vessel using MRI includes: positioning a portion of the patient in or adjacent to an MRI system having a scanner such that, when the MRI system scanner is activated, the portion of the body vessel is located within an area where a magnetic field of the system scanner is present; grasping a wire guide having a continuous core member and a continuous jacket disposed over the entire core member, the core member being formed of a metallic material and having a first length, and the jacket having a second length longer than the first length; inserting a distal end of the wire guide into the body vessel; inserting the distal end of the wire guide through the body vessel until the distal end of the wire guide is located at a first position within a first portion of the body vessel located within the MRI system scanner; operating the MRI system scanner to scan the portion of the patient located within the scanner and including the first portion of the body vessel; obtaining a magnetic resonance image of the first portion of the body vessel; and withdrawing the wire guide from the body vessel.

[0012] Another exemplary method for imaging a portion of a patient's body vessel using MRI includes: positioning a portion of the patient in or adjacent to an MRI system having a scanner such that, when the scanner of the MRI system is activated, the portion of the body vessel is located within an area where a magnetic field of the system scanner is present; grasping a wire guide including a continuous core member and a continuous jacket disposed over the entire core member, the core member being formed of a metallic material and having a first length, and the jacket having a second length longer than the first length; inserting a distal end of the wire guide into the body vessel; inserting the distal end of the wire guide through the body vessel until the distal end of the wire guide is located at a first position within a first portion of the body vessel located within the scanner of the MRI system; operating the scanner of the MRI system to scan a portion of the patient located within the scanner and including the first portion of the body vessel as the distal end of the wire guide is inserted through the patient's body vessel, thereby obtaining a magnetic resonance image of the first portion of the body vessel; and withdrawing the wire guide from the body vessel.

[0013] Another exemplary method for imaging a portion of a patient's body vessel using MRI includes: positioning a portion of the patient in or adjacent to an MRI system having a scanner such that, when the MRI system scanner is activated, the portion of the body vessel is located within an area where the system scanner's magnetic field is present; grasping a wire guide including a continuous core member and a continuous jacket disposed over the entire core member, the core member being formed of a metallic material and having a first length, and the jacket having a second length longer than the first length; inserting a distal end of the wire guide into the body vessel; inserting the distal end of the wire guide through the body vessel until the distal end of the wire guide is located at a first position within a first portion of the body vessel located within the MRI system scanner; repeatedly operating the MRI system scanner to scan a portion of the patient located within the scanner and including the first portion of the body vessel as the distal end of the wire guide is inserted through the patient's body vessel, to repeatedly obtain magnetic resonance images of the first portion of the body vessel; and withdrawing the wire guide from the body vessel.

[0014] Various exemplary methods of performing an interventional medical procedure under MRI are also described.

[0015] An exemplary method of performing an interventional medical procedure under MRI includes: positioning a portion of a patient in or adjacent to an MRI system having a scanner such that, when the MRI system scanner is activated, a portion of a body vessel is positioned within an area where the system scanner's magnetic field is present; grasping a wire guide having a wire guide proximal end and a wire guide distal end, the wire guide comprising a continuous core member and a continuous jacket disposed over the entire core member, the core member being formed of a metallic material and having a first length, and the jacket having a second length longer than the first length; inserting the wire guide distal end into the body vessel; and inserting the wire guide distal end through the body vessel until the wire guide distal end is positioned at a first position within a first portion of the body vessel positioned within the MRI system scanner. the medical device distal end over the wire guide proximal end to position the wire guide proximal end within the lumen of the elongate member of the medical device; inserting the medical device distal end over the wire guide into the body vessel until the medical device distal end reaches the point of treatment within the body vessel; manipulating the medical device proximal end to cause manipulation of the medical device distal end at the point of treatment; operating a scanner of an MRI system to scan a portion of a patient disposed within the scanner and including a first portion of the body vessel; obtaining a magnetic resonance image of the first portion of the body vessel; withdrawing the medical device from the body vessel; and withdrawing the wire guide from the body vessel.

[0016] Another exemplary method of performing an interventional medical procedure under MRI includes: positioning a portion of a patient in or adjacent to an MRI system having a scanner such that a portion of a body vessel is located within an area where the MRI system scanner is present when the scanner is activated; grasping a wire guide having a wire guide proximal end and a wire guide distal end, the wire guide comprising a continuous core member and a continuous jacket disposed over the entire core member, the core member being formed of a metallic material and having a first length, and the jacket having a second length longer than the first length; inserting the wire guide distal end into the body vessel; inserting the wire guide distal end through the body vessel until the distal end of the wire guide is located at a first position within a first portion of the body vessel located within the MRI system scanner; and inserting a medical device proximal end and a wire guide distal end into the body vessel. the medical device distal end is positioned within the lumen of the elongate member of the medical device; passing the medical device distal end over the wire guide proximal end to position the wire guide proximal end within the lumen of the elongate member of the medical device; inserting the medical device distal end over the wire guide into the body vessel until the medical device distal end reaches the point of treatment within the body vessel; manipulating the medical device proximal end to cause manipulation of the medical device distal end at the point of treatment; repeatedly operating a scanner of an MRI system disposed within the scanner to scan a portion of the patient including a first portion of the body vessel as the distal end of the wire guide is inserted through the patient's body vessel, to repeatedly obtain magnetic resonance images of the first portion of the body vessel; withdrawing the medical device from the body vessel; and withdrawing the wire guide from the body vessel.

[0017] Another exemplary method of performing an interventional medical procedure under MRI includes: positioning a portion of a patient in or adjacent to an MRI system having a scanner such that, when the MRI system scanner is activated, a portion of a body vessel is positioned within an area where a magnetic field of the system scanner is present; grasping a wire guide having a wire guide proximal end and a wire guide distal end, the wire guide comprising a continuous core member and a continuous jacket disposed over the entire core member, the core member being formed of a metallic material and having a first length, and the jacket having a second length longer than the first length; inserting the wire guide distal end into the body vessel; and inserting the wire guide distal end through the body vessel until the distal end of the wire guide is positioned at a first position within a first portion of the body vessel positioned within the MRI system scanner; and and a medical device distal end, grasping the medical device comprising an elongate member defining a lumen; passing the medical device distal end over the wire guide proximal end to position the wire guide proximal end within the lumen of the elongate member of the medical device; inserting the medical device distal end over the wire guide into the body vessel until the medical device distal end reaches the point of treatment within the body vessel; manipulating the medical device proximal end to cause manipulation of the medical device distal end at the point of treatment; repeatedly operating a scanner of an MRI system disposed within the scanner to scan a portion of the patient including a first portion of the body vessel as the medical device distal end over the wire guide enters the body vessel, repeatedly obtaining magnetic resonance images of the first portion of the body vessel; withdrawing the medical device from the body vessel; and withdrawing the wire guide from the body vessel.

[0018] Another exemplary method of performing an interventional medical procedure under MRI includes: positioning a portion of a patient in or adjacent to an MRI system having a scanner such that, when the MRI system scanner is activated, a portion of a body vessel is positioned within an area where a magnetic field of the system scanner is present; grasping a wire guide having a wire guide proximal end and a wire guide distal end, the wire guide including a continuous core member and a continuous jacket disposed over the entire core member, the core member being formed of a metallic material and having a first length, and the jacket having a second length longer than the first length; inserting the wire guide distal end into the body vessel; and inserting the wire guide distal end through the body vessel until the distal end of the wire guide is positioned at a first position within a first portion of the body vessel positioned within the MRI system scanner; and the distal end of the medical device is positioned over the proximal end of the wire guide to position the proximal end of the wire guide within the lumen of the elongate member of the medical device; inserting the distal end of the medical device over the wire guide into the body vessel until the distal end of the medical device reaches the point of treatment within the body vessel; manipulating the proximal end of the medical device to cause manipulation of the distal end of the medical device at the point of treatment; repeatedly operating a scanner of an MRI system disposed within the scanner to scan a portion of the patient including a first portion of the body vessel while manipulating the proximal end of the medical device to cause manipulation of the distal end of the medical device at the point of treatment to repeatedly obtain magnetic resonance images of the first portion of the body vessel; withdrawing the medical device from the body vessel; and withdrawing the wire guide from the body vessel.

[0019] Another exemplary method of performing an interventional medical procedure under MRI includes: positioning a portion of a patient in or adjacent to an MRI system having a scanner such that, when the MRI system scanner is activated, a portion of a body vessel is positioned within an area where the system scanner's magnetic field is present; grasping a wire guide having a wire guide proximal end and a wire guide distal end, the wire guide including a continuous core member and a continuous jacket disposed over the entire core member, the core member being formed of a metallic material and having a first length, and the jacket having a second length longer than the first length; inserting the wire guide distal end into the body vessel; and inserting the wire guide distal end through the body vessel until the distal end of the wire guide is positioned at a first position within a first portion of the body vessel positioned within the MRI system scanner; and inserting a medical device having a medical device proximal end and a medical device distal end, the medical device defining a lumen. the proximal end of the wire guide into the body vessel; manipulating the proximal end of the medical device to cause manipulation of the medical device distal end at the point of treatment; inserting the distal end of the medical device over the wire guide into the body vessel until the distal end of the medical device reaches the point of treatment within the body vessel; manipulating the proximal end of the medical device to cause manipulation of the medical device distal end at the point of treatment; inserting the distal end of the wire guide through the body vessel, inserting the distal end of the medical device over the wire guide into the body vessel, and manipulating the proximal end of the medical device, repeatedly operating a scanner of an MRI system disposed within the scanner to scan a portion of the patient including a first portion of the body vessel, repeatedly acquiring magnetic resonance images of the first portion of the body vessel; withdrawing the medical device from the body vessel; and withdrawing the wire guide from the body vessel.

[0020] Various exemplary methods of manufacturing the wire guide are also described.

[0021] An exemplary method of manufacturing a wire guide includes forming a continuous core member of a metallic material, the continuous core member having an outer surface, and disposing a jacket over the continuous core member such that the outer surface of the core member is in continuous contact with the jacket and such that no portion of the outer surface of the core member is exposed to the external environment surrounding the wire guide.

[0022] Another exemplary method of manufacturing a wire guide includes forming a continuous core member formed of a metallic material and having an outer surface; disposing a jacket over the continuous core member such that the outer surface of the core member is in continuous contact with the jacket and such that no portion of the outer surface of the core member is exposed to the external environment surrounding the wire guide; evaluating the jacket to determine whether the outer surface of the core member is in continuous contact with the jacket; and transporting the wire guide to an intended user of the wire guide only if the evaluating step determines that the outer surface of the core member is in continuous contact with the jacket.

[0023] An exemplary method for manufacturing a plurality of wire guides includes forming a plurality of continuous core members, each continuous core member of the plurality of continuous core members formed of a metallic material and having an outer surface, disposing a jacket on the outer surface of each continuous core member such that the outer surface of each continuous core member is in continuous contact with the jacket and such that no portion of the outer surface of each continuous core member is exposed to an external environment surrounding the wire guides of the plurality of wire guides, and evaluating each jacket to determine whether the outer surface of each continuous core member is in continuous contact with the jacket disposed on the outer surface of the continuous core member. An optional step includes destroying any wire guide from the plurality of wire guides for which the evaluating step determines that the outer surface of the continuous core member is not in continuous contact with the jacket disposed on the continuous core member.

[0024] These and other exemplary methods of imaging portions of a body vessel using MRI, methods of performing interventional medical procedures under MRI, interventional medical devices such as wire guides useful for performing treatment under MRI, and methods of manufacturing interventional medical devices can be further understood by reviewing the detailed description and reference drawings of selected examples below. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a perspective view of an exemplary interventional medical device. [Figure 2] FIG. 2 is a side view of the exemplary interventional medical device shown in FIG. 1. [Figure 3] 3 is a longitudinal cross-sectional view of the exemplary interventional medical device shown in FIG. 1 taken along line 3-3 of FIG. 2. [Figure 4] 4 is an enlarged cross-sectional view of the interventional medical device shown in FIG. 1 taken along line 4-4 of FIG. 2. [Figure 5] 5 is an enlarged cross-sectional view of the interventional medical device shown in FIG. 1 taken along line 5-5 in FIG. 2. [Figure 6] FIG. 1 is a longitudinal, intermediate, cross-sectional view of another exemplary interventional medical device. [Figure 7] FIG. 1 is a medial cutaway side view of another exemplary interventional medical device. [Figure 8] FIG. 1 is a medial cutaway side view of another exemplary interventional medical device. [Figure 9] FIG. 1 is a medial cutaway side view of another exemplary interventional medical device. [Figure 10] 1 is a flowchart diagram of an exemplary method for imaging a portion of a body vessel. [Figure 11] FIG. 1 is a flowchart diagram of an exemplary method for performing an interventional medical procedure under MRI. [Figure 12]FIG. 10 is a flowchart diagram of another exemplary method for performing an interventional medical procedure under MRI. [Figure 13] 1 is a flowchart representation of an exemplary method for manufacturing a wire guide. [Figure 14] 1 is a flowchart representation of an exemplary method for manufacturing multiple wire guides. [Figure 15] Graphical representation of raw RF induction heating of various test wire guide structures over 2-7 minute scans on a 1.5T MRI system. The left panel shows the measured temperature during the scan of a wire guide with a continuous Nitinol core, and the right panel shows the temperature rise normalized to the initial temperature in the corresponding panel on the left. [Figure 16] 1 shows in tabular form the data referenced in the examples described herein. [Figure 17] 1 shows in tabular form the data referenced in the examples described herein. [Figure 18] 1 shows in tabular form the data referenced in the examples described herein. [Figure 19] 1 shows in tabular form the data referenced in the examples described herein. [Figure 20] 1 shows mathematical formulas referenced in the examples described herein. [Figure 21] 1 shows mathematical formulas referenced in the examples described herein. [Figure 22] 1 shows mathematical formulas referenced in the examples described herein. DETAILED DESCRIPTION OF THE INVENTION

[0026] The following detailed description and accompanying drawings describe and illustrate various exemplary methods for imaging a portion of a body vessel using MRI, methods for performing an interventional medical procedure under MRI, wire guides useful for performing an interventional procedure under MRI, and methods for manufacturing wire guides. The descriptions and illustrations of these examples are provided to enable one skilled in the art to perform the methods for imaging a portion of a body vessel using MRI, methods for performing an interventional medical procedure under MRI, and methods for manufacturing interventional medical devices, as well as to manufacture and use interventional medical devices such as wire guides. The inclusion of detailed descriptions of these examples is not intended in any way to limit the scope of the invention or its protection. The invention can be practiced or carried out in various ways, and the examples described and illustrated herein are not intended to be exhaustive.

[0027] As used herein, the term "attached" refers to a member being fixed to another member such that the members do not completely separate from one another when used in accordance with the intended use of the item containing the member in attached form.

[0028] As used herein, the term "circumference" refers to a boundary that surrounds the exterior of a body, element, or feature and does not impart any structural organization to the body, element, or feature.

[0029] As used herein, the term "continuous" refers to a structural configuration of an element in which the element extends uninterrupted from a first end of the element to a second end of the element with no additional terminations between the first and second ends. This term includes structural configurations in which two structural members, such as segments of the same or different material, are joined end-to-end with no internal terminations in the combined structure.

[0030] As used herein, the term "magnetic susceptibility" refers to an intrinsic property of a material related to how magnetized the material is in an applied magnetic field.

[0031] As used herein, the term "marker" refers to a first material discretely deposited on a second material such that the first material is visible under MRI and distinguishable from the second material under MRI, a portion of an interventional device in which the first material is incorporated into a second material such that the combination of the first and second materials is visible under MRI and distinguishable from the second material under MRI, and a portion of an interventional device in which the material forming the portion of the interventional device has been manipulated such that the portion is visible under MRI and distinguishable from the remainder of the interventional device under MRI.

[0032] As used herein, the term "MRI system" refers to a magnetic resonance imaging device comprising a magnet and a scanner and suitable for medical imaging purposes. This term includes MRI systems that define a bore in which a patient or a portion of a patient may be positioned, open MRI systems, and portable MRI systems that may be moved relative to a patient to position the patient or a portion of a patient relative to the scanner of the MRI system prior to the start of an imaging procedure.

[0033] As used herein, the term "passive" in relation to a marker refers to a marker that is not powered or is powered only by the electromagnetic field of a magnetic resonance scanner.

[0034] As used herein, the term "susceptibility" without the word "magnetic" refers to the ability of an element to affect an external magnetic field. Susceptibility depends on various properties of the element, including its size, density, geometric configuration, volume, and other physical properties, as well as the magnetic susceptibility of the material from which the element is formed.

[0035] As used herein, the term "treatment" refers to a medical procedure performed on or at a portion of a patient's body. Examples of treatments include delivery of a drug to a site within a body vessel, altering the local environment within a body vessel, such as by heating or cooling, and removal of tissue or a portion of tissue from a site within a patient's body (i.e., a biopsy).

[0036] As used herein, the term "wire" refers to a strand or rod of material. The term does not require any particular cross-sectional shape, composition, physical properties, or manufacturing method by which the referenced element is made.

[0037] 1, 2, 3, 4, and 5 illustrate an exemplary wire guide 100. The wire guide is an interventional medical device useful for interventional procedures performed under MRI. Wire guide 100 includes a core member 110 formed of a first material having a first susceptibility and a jacket 130 disposed over core member 110. An optional marker 150 is attached to core member 110 and, if included, is formed of a second material having a second susceptibility different from the first susceptibility. In embodiments in which marker 150 is included, the first and second materials can be the same or different. Thus, the first and second materials can have the same or different magnetic susceptibilities. If included, marker 150 can be attached to core member 110 in any suitable manner, such as by adhesive, swaging, or other suitable form of attaching one member to another. Also, if included, jacket 130 is advantageously disposed over the exterior surface of marker 150 to provide the desired fully enclosed structure, as described above.

[0038] The core member 110 is a continuous elongate member having a proximal end 112, a distal end 114, a longitudinal axis 102 extending between the proximal and distal ends 112, 114, and an axial length extending from the proximal end 112 to the distal end 114. In this example, the core member 110 has an outer surface 116 that is in continuous contact with the jacket 130. Importantly, the entire outer surface 116 is completely encapsulated by the jacket 130. That is, no portion of the outer surface 116 of the core member 110 is exposed to the external environment surrounding the wire guide 110.

[0039] The core member 110 is formed of a metallic material, such as a metal or alloy. The core member 110 can be formed of any suitable metallic material, and the selection of an appropriate metallic material for the core member in a wire guide according to an embodiment can be based on various considerations, including any desired handling characteristics and any material selected for markers, if included. Examples of metallic materials that may be suitable for the core member include, but are not limited to, nickel-titanium alloys (such as nitinol, black oxide superelastic nitinol SE508 straight stock, matte finish nitinol, polished nitinol, etc.), nickel chromium, nickel cobalt, titanium, nickel oxide, cobalt chromium nickel molybdenum alloys (such as alloys available under the Elgiloy trade name from Elgiloy Specialty Metals, Elgin, Illinois), combinations of those described herein, and shape memory alloys, including any other metallic material deemed suitable for a particular embodiment.

[0040] As will be described in more detail below, the jacket 130 is a continuous jacket disposed over the entire length 104 of the core member 110. The continuity of the jacket 130 over the entire length 104 of the core member 110 is important to the performance of the example wire guide 100 described herein. The core member 110 can include features that aid in detecting any disruption in the continuity of the jacket 130, which can help ensure the use of a wire guide having a truly continuous jacket 130. For example, the core member 110 can include a high-contrast colored jacket on its surface and disposed underneath the jacket 130. The high-contrast color of this underlying jacket is relative to any color of the jacket 130. For example, if the jacket 130 is a dark color, such as black or gray, a lighter underlying jacket, such as a yellow jacket, can provide a high-contrast color that, if visible during pre-use inspection of the wire guide, can alert the user to any disruption in the continuity of the jacket 130 and enable the user to evaluate whether or not to use the wire guide in the planned procedure. Additionally, the core member 110 may include a coating that responds to exposure to an external substance other than the jacket 130, such as water. For example, the core member 110 may include a coating that changes color upon contact with an external substance, such as water. The color change may also be visible under ambient light or another wavelength, such as an ultraviolet wavelength or another wavelength. If the core member includes such a coating, inspecting the wire guide or wire guides for an appropriate color change under an appropriate wavelength of light may be incorporated into the method of manufacturing the wire guide or wire guides.

[0041] The core member 110 can have any suitable configuration, and one of ordinary skill in the art would be able to select an appropriate configuration for a particular embodiment of the wire guide based on various considerations, including the intended use of the wire guide and the nature of any body vessels in which the wire guide is to be placed. In the illustrated example, the core member 110 is a wire having a substantially continuous outer diameter along its length 104. Core members having a taper along their length at their distal end are also believed to be suitable.

[0042] The core member 110 can have any suitable axial length, and one of ordinary skill in the art would be able to select an appropriate length for the core member in a particular embodiment of a wire guide based on various considerations, including the intended use of the wire guide and the nature of any body vessels in which the wire guide is to be placed. Examples of lengths that may be suitable for a core member in a wire guide according to the present invention include, but are not limited to, lengths equal to, greater than, less than, or about 100 centimeters, 110 centimeters, 120 centimeters, 130 centimeters, 140 centimeters, 150 centimeters, 240 centimeters, 250 centimeters, 260 centimeters, 270 centimeters, 280 centimeters, lengths between about 50 centimeters and about 350 centimeters, lengths between about 100 centimeters and about 280 centimeters, lengths between about 120 centimeters and about 260 centimeters, and any other lengths that may be suitable for a particular embodiment of a wire guide.

[0043] The jacket 130 is a continuous jacket disposed over the entire length 104 of the core member 110, such that the jacket completely encloses the core member 110. The jacket 130 has a proximal end 132, a distal end 134, and an axial length extending from the proximal end 132 to the distal end 134. The length of the jacket 130 is greater than the length of the core member 110, ensuring that the terminal surfaces 122, 124 at the proximal and distal ends 112, 114 of the core member 110 are each completely covered by the jacket 130.

[0044] The jacket is formed of one or more dielectric materials. In the illustrated embodiment, the jacket 130 is formed of a polymeric material. Any polymeric material that is a dielectric material can be used, and one skilled in the art would be able to select an appropriate polymeric material for the jacket in a particular embodiment of the wire guide based on various considerations, including any desired handling and performance characteristics of the wire guide, such as torque transmission and pushability. Examples of suitable polymeric materials include, but are not limited to, thermoformable polymeric materials, such as polyamide materials. These polymeric materials are considered desirable at least for their ability to melt and flow between and around elements during a thermoforming or heat-shrinking process. Nylon is considered particularly advantageous, at least because it is readily available and has well-characterized properties. Fluoropolymers, such as polytetrafluoroethylene, are also considered particularly advantageous, as they have some of the best-characterized dielectric properties. Polyurethane and other polymeric materials are also considered advantageous. If desired, additional jackets or other materials can be applied to the jacket 130. For example, a lubricious jacket can be applied as a topcoat over the jacket 130. The jacket 130 can have a varying composition along the axial length of the wire guide 100. For example, a different polymer concentration can be used at one or both ends relative to the polymer concentration present in the jacket disposed over the axial midpoint of the wire guide. A polymer concentration that provides a jacket that is stiffer, more durable, or both, can also be used at one or both ends to provide resistance to tearing or other disruption of the continuity of the jacket 130, which is important to the desired performance of the wire guide 100.

[0045] In other embodiments, two or more dielectric materials can form the jacket. For example, a jacket can be used having a first shaft portion formed of a first polymer that is a dielectric material and a second shaft portion formed of a second, different polymer that is a dielectric material. Indeed, two different polymers can provide different properties, such as flexibility, hardness, and other characteristics, while both providing desired dielectric properties. Furthermore, as described in more detail below, a jacket on a wire guide according to embodiments can include a first shaft portion formed of a polymer that is a dielectric material and a second shaft portion formed of a non-polymer that is a dielectric material, such as a ceramic or other non-polymer dielectric material.

[0046] The continuity of the jacket 130 over the entire length 104 of the core member 110 is important to the performance of the example wire guide 100 described herein. As such, the jacket 130 may comprise elements, such as fibers and other additives, that resist the formation of disruptions in the continuity of the jacket 130. Additionally, the jacket 130 may be treated during the manufacture of the wire guide in a manner that makes the jacket 130 more resistant to such disruptions than would be the case if such treatment were not performed. For example, the jacket 130 may be subjected to electron beam irradiation, gamma irradiation, or other suitable treatment to crosslink the polymers of the jacket 130 and make the jacket 130 more resistant to disruptions in the continuity of the jacket 130.

[0047] The wire guide 100 may include one or more markers 150. If included, the markers 150 may be disposed directly on the core member 110 such that the jacket 130 is disposed over the markers 150 and the core member 110. Alternatively, the included markers may be structurally disposed on the wire guide 100 such that the markers 150 are not in direct structural contact with the core member 110. In the exemplary wire guide 100 shown in FIGS. 4-8, the markers 150 are disposed directly on the core member such that no portion of the jacket 130 is disposed between the markers 150 and the core member 110. Alternatively, the markers may be disposed within the thickness of the jacket such that a portion of the jacket is disposed between the inner surface of the marker and the outer surface of the core member. In these embodiments, the markers do not directly contact the core member. If included, the markers 150 are passive markers, formed of a metal or alloy and having a susceptibility that differs from the susceptibility of the core member 110. Alternatively, the outer surface of the jacket and the one or more markers included in the wire guide according to some embodiments can be contiguous with each other, such that the core member is fully encapsulated by the combination of the jacket and the one or more markers. In these embodiments, the outer surface of the jacket and the one or more markers are advantageously flush with each other. Alternatively, the markers can be placed on a previously placed jacket.

[0048] The markers 150 can have any structural configuration, and one skilled in the art would be able to select an appropriate structural configuration for a particular embodiment of a medical device based on various considerations, including any desired visualization characteristics when the medical device is used with an imaging modality such as MRI. Examples of suitable configurations include, but are not limited to, rings, strips, plugs, twisted bands, twisted rings, multiple bands attached to each other, multiple rings attached to each other, and other configurations. A circumferential band of material, as best shown in FIGS. 4, 5, and 6, is believed to be particularly advantageous. A wire guide according to an embodiment can also include any number of markers, and one skilled in the art would be able to select an appropriate number of markers for a particular embodiment of a medical device based on various considerations, including any desired visualization pattern when the wire guide is used with an imaging modality such as MRI. Examples of suitable numbers include, but are not limited to, one, two or more, two, multiple, three, four or more, four, five, six, seven, eight, nine, ten, and eleven or more.

[0049] The markers 150 may be located at any suitable axial location relative to the longitudinal axis 102 of the core member 110, and one of ordinary skill in the art would be able to select an appropriate location for the markers relative to the longitudinal axis of the core member in a particular embodiment of the wire guide based on various considerations, including any desired visualization pattern when the medical device is used with an imaging modality such as MRI. As best shown in Figures 4, 5, and 6, the markers 150 in the exemplary wire guide 100 are located near the distal end 114 of the core member 110, but are axially positioned within the distal end 120 of the wire guide 100, which extends from a point beyond the longitudinal midpoint on the longitudinal axis 102 of the core member 110 to the distal end 114 of the core member 110. Other examples of suitable locations include, but are not limited to, the axial portion of the wire guide 100 near the longitudinal midpoint of the core member 110, the distal end 114 of the core member 110, the proximal end 112 of the core member 110, the distal end 134 of the jacket 130, and within the proximal end 132 of the jacket 130, as well as combinations of these locations with multiple markers.

[0050] The marker 150 has a susceptibility that differs from the magnetic susceptibility of the core member 110. Thus, the marker may be formed of any metal, alloy, or other material that provides a desired relative susceptibility compared to the susceptibility of the core member 110. One skilled in the art would be able to select an appropriate material for the marker in a particular embodiment of a medical device based on various considerations, including the composition of the reinforcing member in the medical device. Suitable combinations of materials for the core member and marker in a wire guide according to the present invention are discussed in more detail below. Examples of suitable materials for the marker include, but are not limited to, metals such as titanium, nickel, and other metals; stainless steel alloys (including 304V stainless steel and 316LVM stainless steel); nickel-iron alloys such as Mumetal (including Mumetal conforming to ASTM A753 Alloy 4, MUMETAL® magnetic shielding alloys available from Magnetic Shield Corporation, Bensenville, Illinois; MUMETALL® alloys available from VACUUMSCHMELZE GmbH & Co. KG, Hanau, Germany; and MUSHIELD™ magnetic shielding alloys conforming to ASTM A753 Alloy 3 available from The MuShield Company, Londonderry, New Hampshire); ferromagnetic materials; paramagnetic materials; alloys containing at least 50% iron by weight; 316 stainless steel; and any other material deemed suitable for a particular embodiment. An alternative embodiment includes a marker disposed on the outer surface of the jacket of the wire guide. For example, the marker can be printed or glued onto the outer surface of the wire guide. For example, an ink containing a material having a magnetic susceptibility greater than that of the core member of the wire guide, such as an ink containing magnetic particles, an ink containing iron oxide nanoparticles, or an ink containing iron oxide nanoparticles bound to a phospholipid, can be printed on the outer surface of the jacket to form the markers in the wire guide according to one embodiment. Markers can also be disposed on a surface by other suitable processes, such as chemical vapor deposition and plating.Alternatively, a tape including a material with a magnetic susceptibility greater than that of the core member of the wire guide, such as magnetic tape, can be adhered to the outer surface of the sheath of the wire guide to form the markers in the wire guide according to one embodiment. The selection of one or more markers to include in a wire guide according to a particular embodiment can also be based on one or more magnetic field strengths in which the wire guide is intended to be used. For example, a wire guide including markers may be used to complete one or more interventional procedures under MRI using one or more magnetic field strengths (e.g., 0.55 T, 1.5 T, or 3.0 T). One or more materials can be selected for one or more markers in a wire guide according to one embodiment based on these expected magnetic field strengths and the expected visual artifacts produced by one or more markers formed from a particular material and having a particular structural configuration.

[0051] The core member in a wire guide according to the present invention has a susceptibility that differs from the susceptibility of the marker in the wire guide. Thus, the marker in a wire guide according to the present invention has a susceptibility that differs from the susceptibility of the core member in the wire guide. Any combination of materials for these elements that provides the relative susceptibility relationships for these elements that are believed to be important to the performance of the wire guide according to the present invention can be used in a wire guide according to a particular embodiment. Indeed, the core member and the marker can be formed of the same material or different materials, so long as the relative susceptibility relationships for these elements are provided. In some embodiments, different materials having different magnetic susceptibilities are used for the core member and the marker. In these embodiments, the core member and the marker have different susceptibilities and are formed of materials having different magnetic susceptibilities. In these embodiments, one skilled in the art would be able to select a material for one of these elements in a wire guide according to a particular embodiment based on various considerations, including the composition of the other of these elements and any desired performance or imaging characteristics of the wire guide. Examples of suitable combinations of different materials for the core member and the marker include, but are not limited to, a first material for the core member and a second material for the marker, such as a paramagnetic material for the core member and a ferromagnetic material for the marker; an alloy containing 1% or less by weight of iron for the core member and an alloy containing at least 50% by weight of iron for the marker; a cobalt-chromium alloy for the core member and a stainless steel for the marker; a nickel-cobalt alloy such as MP35N for the core member and a stainless steel such as 304V stainless steel or 316LVM stainless steel for the marker. In other embodiments, the core member and the marker are formed from the same material. In these embodiments, the core member and the marker have different susceptibilities from the reinforcing member and the marker, but the core member and the marker have the same magnetic susceptibility. For example, in the illustrated embodiment, the core member 110 and the marker 150 can be formed from the same material, giving the core member 110 and the marker 150 the same magnetic susceptibility.To provide different susceptibilities for these elements 110, 150, one element, such as marker 150, can be work hardened or manipulated in some way to provide a different susceptibility than the other element.

[0052] FIG. 6 illustrates another exemplary wire guide 200. The wire guide 200 is similar to the wire guide 100 described above and illustrated in FIGS. 1, 2, 3, 4, and 5, except as detailed below. In this embodiment, the wire guide 200 includes a core member 210 formed of multiple core segments 210a, 210b, and 210c, each of which has an axial length that is different from the axial lengths of the other core segments 210a, 210b, and 210c. A jacket 230 formed of a dielectric material is disposed over all of the core segments 210a, 210b, and 210c. Thus, each of the core segments 210a, 210b, and 210c is completely encapsulated by the jacket 230.

[0053] Core segment 210a has a first end 260 and a second end 262. Core segment 210b has a first end 264 and a second end 266. Core segment 210c has a first end 268 and a second end 270. Thus, in this embodiment, core member 210 is not a continuous core member, but rather an interrupted core member with internal ends. This structural arrangement may be desirable, for example, in certain embodiments of the wire guide. Each of core segments 210a, 210b, and 210c is formed from a first material having a first susceptibility. However, it should be noted that core segments 210a, 210b, and 210c may have different susceptibilities and may be formed from different materials. Also, while wire guide 200 comprises multiple core segments 210 a, 210 b, 210 c arranged end-to-end, it should be noted that in other exemplary embodiments, the wire guide may comprise multiple core members coextensive along the length or a portion of the length of the wire guide. For example, the wire guide may comprise multiple core members arranged side-by-side, helically wound about a central longitudinal axis, or arranged in another suitable structural configuration.

[0054] Figure 7 illustrates another exemplary wire guide 300. Wire guide 300 is similar to wire guide 100 described above and shown in Figures 1, 2, 3, 4, and 5, except as further described below. Accordingly, wire guide 300 includes a continuous core member 310 formed of a material having a first susceptibility. A jacket 330 formed of a first dielectric material is disposed over continuous core member 310 and includes first and second jacket portions 330a and 330b. A circumferential band 380 formed of a second dielectric material different from the first dielectric material is axially disposed around continuous core member 310 and between first and second jacket portions 330a and 330b. The circumferential band 380 is attached to the first jacket portion 330a and the second jacket portion 330b, such as by adhesive or other suitable attachment, and forms a substantially continuous outer surface with the first jacket portion 330a and the second jacket portion 330b. Any suitable dielectric materials can be used for the first and second dielectric materials, as long as they are different materials. For example, the first dielectric material can be a first polymer and the second dielectric material can be a second polymer. Advantageously, the first dielectric material is a polymer and the second dielectric material is a non-polymer. Particularly advantageously, the first dielectric material is a polymer and the second dielectric material is a ceramic.

[0055] FIG. 8 illustrates another exemplary wire guide 400. The wire guide 400 is similar to the wire guide 300 described above and illustrated in FIG. 7, except as further described below. Thus, the wire guide 400 includes a continuous core member 410 formed of a material having a first susceptibility. A jacket 430 formed of a first dielectric material is disposed over the continuous core member 410. A circumferential band 480 formed of a second dielectric material, different from the first dielectric material, is disposed around the continuous core member 410. Any suitable dielectric materials can be used for the first and second dielectric materials, as long as they are different materials. For example, the first dielectric material can be a first polymer, and the second dielectric material can be a second polymer. Advantageously, the first dielectric material is a polymer and the second dielectric material is a non-polymer. Particularly advantageously, the first dielectric material is a polymer and the second dielectric material is a ceramic, as described below.

[0056] In this embodiment, the circumferential band 480 extends from one end 482 of the wire guide 400 to the other end 484 of the wire guide 400 along an axial length 486 that is less than the entire axial length of the wire guide 400. Also, in this embodiment, the circumferential band 480 is a cap that defines a termination surface 488 at the end 482 of the wire guide 400. The axial length 486 may be any axial length relative to the entire axial length of the wire guide, and one of ordinary skill in the art would be able to select an appropriate axial length for the circumferential band 480 in a particular embodiment of the wire guide based on various considerations, including the properties of the material from which the circumferential band 480 is formed. Examples of appropriate axial lengths relative to the entire axial length of the wire guide include, but are not limited to, about 5%, about 10%, about 15%, about 20%, about 25%, about 40%, and about 50%. Advantageously, the axial length of the circumferential band is less than about 20% of the entire axial length of the wire guide. Also advantageously, the axial length of the circumferential band is less than about 10% of the overall axial length of the wire guide. The inclusion of a circumferential band 480 according to this embodiment, and in particular a ceramic circumferential band, is believed to be particularly advantageous because at least the ceramic material disposed at one end of the wire guide provides a desirable dielectric material while providing a material whose integrity is less likely to be disrupted than a polymer during manual handling of the wire guide at that end during use of the wire guide.

[0057] FIG. 9 illustrates another exemplary wire guide 500. The wire guide 500 is similar to the wire guide 400 described above and illustrated in FIG. 8, except as further described below. Thus, the wire guide 500 includes a continuous core member 510 formed of a material having a first susceptibility. A jacket 530 formed of a first dielectric material is disposed over the continuous core member 510. A circumferential band 580 formed of a second dielectric material different from the first dielectric material is disposed around the continuous core member 510. Any suitable dielectric materials can be used for the first and second dielectric materials, as long as they are different materials. For example, the first dielectric material can be a first polymer, and the second dielectric material can be a second polymer. Advantageously, the first dielectric material is a polymer and the second dielectric material is a non-polymer. Particularly advantageously, the first dielectric material is a polymer and the second dielectric material is a ceramic, as described below.

[0058] In this embodiment, the circumferential band 580 extends from one end 584 of the wire guide 500 to the other end 582 of the wire guide 500 along an axial length 586 that is less than the entire axial length of the wire guide 500. Also, in this embodiment, the circumferential band 580 is a cap that defines a termination surface 588 at the end 584 of the wire guide 500. The axial length 586 can be any axial length relative to the entire axial length of the wire guide, and one of ordinary skill in the art would be able to select an appropriate axial length for the circumferential band 580 in a particular embodiment of the wire guide based on various considerations, including the properties of the material from which the circumferential band 580 is formed. Examples of appropriate axial lengths relative to the entire axial length of the wire guide include, but are not limited to, about 5%, about 10%, about 15%, about 20%, about 25%, about 40%, and about 50%. Advantageously, the axial length of the circumferential band is less than about 20% of the entire axial length of the wire guide. Also, advantageously, the axial length of the circumferential band is less than about 10% of the overall axial length of the wire guide. The inclusion of a circumferential band 580 according to this embodiment, and particularly a ceramic circumferential band, is believed to be particularly advantageous because at least the ceramic material disposed at one end of the wire guide provides a desired dielectric material while also providing a material suitable for inserting end 584 of wire guide 500 through biological material, such as an occlusion, tissue, or other biological material within a body vessel. Also, in this embodiment, circumferential band 580 defines a taper 590, reducing the diameter at end 584 of the wire guide.

[0059] Wire guides according to embodiments are useful in performing interventional procedures under MRI.

[0060] FIG. 10 illustrates an exemplary method 600 for imaging a portion of a body vessel.

[0061] A first step 610 includes positioning a portion of a patient within or adjacent to an MRI system having a scanner such that a portion of a body vessel is positioned within an area where the MRI system scanner's magnetic field is present when the MRI system scanner is activated. Another step 612 includes grasping a wire guide having a continuous metallic core member and a continuous jacket disposed over the core member. Another step 614 includes inserting a distal end of the wire guide into the patient's body vessel. Another step 616 includes inserting the distal end of the wire guide through the patient's body vessel until the distal end of the wire guide is positioned at a first position within the first portion of the body vessel positioned within the MRI system scanner. Another step 618 includes operating the MRI system scanner to scan a portion of the patient positioned within the scanner and including the first portion of the body vessel. Another step 620 includes acquiring a magnetic resonance image of the first portion of the body vessel. Another step 622 includes removing the wire guide from the body vessel.

[0062] Step 610 can be performed by any suitable technique, and the technique used in a method according to a particular embodiment depends on various considerations, including the nature and configuration of the MRI system and scanner used, and the nature and location of the body vessels where imaging is performed. Conventional MRI systems typically include a patient support surface, such as a table or bed, that can be moved relative to a bore defined by the MRI system to position the desired portion of the patient within the scanner's magnetic field. For these MRI systems, step 610 can be performed by moving the patient support system relative to the MRI system's scanner until the desired portion of the patient is located within the MRI system's bore. For open, portable, and other MRI systems that do not define a bore within which the patient or portion of the patient can be placed, step 610 can be performed by positioning the desired portion of the patient within an area where the MRI system's scanner's magnetic field will be present when the MRI system's scanner is activated. For example, in the case of a portable MRI system, the system can be moved to the patient by transporting the portable MRI system to the patient's bedside and then moving the portable MRI system relative to a patient support surface on which the patient is positioned, such as a hospital bed, so that a portion of the body's blood vessels is positioned within the magnetic field of the scanner or within an area where the magnetic field of the MRI system's scanner is present when the scanner of the MRI system is activated.

[0063] Any suitable portion of the patient may be used in step 610, and the selection of an appropriate portion of the patient when performing a method according to certain embodiments may be based on various considerations, including the desired images, any treatments to be performed, and other considerations. Examples of potentially suitable portions of the patient include, but are not limited to, the extremities (e.g., arms, legs), chest, breasts, spine, neck, head, abdomen, pelvis, prostate, peripronate structures, tissue surrounding portions of the patient described herein, and / or any other portion of the patient that may be suitable for a method according to certain embodiments. Also, in this step, the patient may be any animal for which imaging is desired, including humans and other mammals.

[0064] Step 612 can be performed by manually grasping a suitable wire guide or by using a suitable tool or device, such as a robotic arm. Selection of a suitable wire guide for performing step 612 is believed to be important to the performance of method 600. The selected wire guide should have a continuous metal core member with a jacket that completely encapsulates the core member, such as a jacket disposed over the entire length of the core member and having a length greater than the length of the core member. Examples of wire guides suitable for use in performing step 612 include the exemplary wire guides described in detail below and illustrated in the drawings.

[0065] Step 614 can be performed using conventional interventional techniques, such as the Seldinger technique, to introduce the distal end of the wire guide into any suitable body vessel at the point of insertion. For example, a needle can be used to pierce the skin and enter the body vessel. Once access to the body vessel is established in this manner, the distal end of the wire guide can be passed through the needle lumen and enter the body vessel. The needle can then be withdrawn beyond the proximal end of the wire guide, leaving the distal end of the wire guide extending into the body vessel. Furthermore, the distal end of the wire guide can be inserted into any suitable body vessel. The body vessel into which the distal end of the wire guide is inserted during performance of a method according to certain embodiments can be selected based on a desired location for scanning, imaging, treatment, or other considerations. Examples of suitable body vessels include, but are not limited to, vessels of the peripheral vasculature. Step 614 can be performed before or after step 610 is performed, or while step 610 is being performed. Those skilled in the art will be able to select an appropriate relative order for steps 610 and 614 based on various considerations, including the nature of the MRI system and scanner, as well as other considerations.

[0066] Step 616 may be performed by applying a distal force to a portion of the wire guide that remains outside the patient's body, such as the proximal end of the wire guide or an intermediate portion of the wire guide, so as to move the distal end of the wire guide axially within the lumen of the body vessel and away from the point of insertion into the body vessel. Step 616 is performed until the distal end of the wire guide is positioned at a first location within a first portion of the body vessel, the first portion being of interest for subsequent step 618 of operating the scanner of the MRI system and step 620 of acquiring images.

[0067] Step 618 may be performed by operating the MRI system to scan the portion of the patient placed in the scanner of the MRI system by performing step 610. Step 618 may be performed using any suitable MRI parameters applicable to the scanner of the MRI system (e.g., gradient refocusing echo imaging, spin echo imaging, true high speed imaging with steady state precession, high speed low flip angle shot spoiled gradient echo imaging, magnetic field strengths such as 0.55T, 1.5T, 3T, about 0.055T to 1.5T, and less than 1T, slice thickness, flip angle, field of view, resolution, gradient fields, and any other one or more MRI parameters deemed suitable for a method according to a particular embodiment).

[0068] Step 620 may be performed by acquiring an image from the scanner of the MRI system used in step 618. Step 620 of acquiring a magnetic resonance image of the first portion of the body vessel may involve acquiring a single still image. Optionally, step 620 may be repeated any desired number of times to acquire multiple magnetic resonance images that may be grouped as a cine showing motion. Further, as an alternative to, or in addition to, acquiring an image, method 600 may include a step of visualizing the wire guide, visualizing one or more markers associated with the wire guide, or both.

[0069] Step 622 may be performed by applying a proximal force to a portion of the wire guide that remains outside the patient's body, such as the proximal end of the wire guide or an intermediate portion of the wire guide, so that the distal end of the wire guide moves axially within the lumen of the body vessel toward the point of insertion into the body vessel. This step 622 is performed until the distal end of the wire guide passes the point of insertion and the wire guide completely exits the body lumen. Ultimately, this step 622 results in the wire guide exiting the patient's body. At this point, execution of method 600 is complete.

[0070] Steps 616, 618, and 620 may be performed separately and sequentially. For example, performance of step 618 may begin after step 616 is completed. Also, performance of step 620 may begin after step 618 is completed. However, other orderings of these steps are possible and may be advantageous for methods according to certain embodiments. For example, if multiple images are desired to aid in navigation of the wire guide through a body vessel, steps 618 and 620 may each be performed multiple times while step 616 is being performed. That is, step 618 of operating the scanner of the MRI system to scan a portion of a patient positioned within the scanner and including a first portion of the body vessel, and step 620 of acquiring magnetic resonance images of the first portion of the body vessel may be performed multiple times while step 616 of inserting the distal end of the wire guide through the patient's body vessel is being performed. In these examples, steps 618 and 620 may be performed any suitable number of times during the performance of step 616, and one of ordinary skill in the art would be able to select an appropriate number of times for each step to include in a method according to a particular embodiment based on various considerations, including the capabilities of the MRI system, the nature of the body's vessels and any navigation challenges they present, as well as other considerations. Examples of appropriate numbers for the performance of steps 618 and 620 during the performance of step 616 include, but are not limited to, 1 time, 2 times, 3 or more times, 3 times, multiple times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 or more times, 11 times, 12 times, 13 or more times, 20 times, 50 times, 100 times, and 1000 times.

[0071] Performance of the method provides one or more images of a portion of a body vessel that can be used for a variety of purposes, including educational, research, diagnostic, therapeutic, and informational purposes.

[0072] FIG. 11 illustrates an exemplary method 700 for performing an interventional medical procedure under MRI.

[0073] A first step 710 includes positioning a portion of a patient in or adjacent to an MRI system having a scanner such that a portion of a body vessel is positioned within an area where the MRI system's scanner's magnetic field is present when the MRI system's scanner is activated. Another step 712 includes grasping a wire guide having a continuous metallic core member and a continuous jacket disposed over the core member. Another step 714 includes inserting a distal end of the wire guide into the patient's body vessel. Another step 716 includes inserting the distal end of the wire guide through the patient's body vessel until the distal end of the wire guide is positioned within a first portion of the body vessel having the first portion. Another step 718 includes operating the scanner of the MRI system to scan a portion of the patient positioned within the scanner and including the first portion of the body vessel. Another step 720 includes acquiring a magnetic resonance image of the first portion of the body vessel. Another step 722 includes grasping a medical device having a medical device proximal end and a medical device distal end, the medical device including an elongate member defining a lumen. Another step 724 includes inserting the distal end of the medical device over the wire guide into the patient's body vessel until the distal end of the medical device reaches the point of treatment within the body vessel. Another step 726 includes manipulating the proximal end of the medical device to cause manipulation of the distal end of the medical device at the point of treatment. Another step 728 includes withdrawing the medical device from the body vessel. Another step 730 includes withdrawing the wire guide from the body vessel.

[0074] Step 710 can be performed by any suitable technique, and the technique used in a particular embodiment of the method depends on various considerations, including the nature and configuration of the MRI system used and the nature and location of the body vessels where imaging is performed. Conventional MRI systems typically include a patient support surface, such as a table or bed, that can be moved relative to the MRI system's scanner to position the desired portion of the patient within the scanner's magnetic field. For these MRI systems, step 710 can be performed by moving the patient support system relative to the MRI system's scanner until the desired portion of the patient is located within the MRI system's scanner. As described above for method 700, this step 710 can also be performed in other MRI systems that do not define a bore, such as open MRI systems and portable MRI systems. For example, in the case of a portable MRI system, step 710 can be performed by moving the portable MRI system relative to the patient to position the desired portion of the patient within an area where the MRI system's scanner's magnetic field will be present when the MRI system's scanner is activated.

[0075] Any suitable portion of the patient may be used in step 710, and the selection of the appropriate portion of the patient when performing a method according to certain embodiments may be based on various considerations, including the location of the desired treatment point, the nature of the treatment to be performed, and other considerations. Examples of potentially suitable patient portions include, but are not limited to, the extremities (e.g., arms, legs), chest, breasts, spine, neck, head, abdomen, pelvis, prostate, peripronate structures, tissue surrounding the patient portions described herein, and / or any other portion of the patient that may be suitable for a method according to certain embodiments. Also, in this step, the patient may be any animal for which imaging is desired, including humans and other mammals.

[0076] Step 712 can be performed by manually grasping a suitable wire guide or by using a suitable tool or device, such as a robotic arm. Selection of a suitable wire guide for performing step 712 is believed to be important to the performance of method 700. The selected wire guide should have a continuous metal core member with a jacket that completely encapsulates the core member, such as a jacket disposed over the entire length of the core member and having a length greater than the length of the core member. Examples of wire guides suitable for use in performing step 712 include the exemplary wire guides described in detail below and illustrated in the drawings.

[0077] Step 714 can be performed using conventional interventional techniques, such as the Seldinger technique, to introduce the distal end of the wire guide into any suitable body vessel at the point of insertion. For example, a needle can be used to pierce the skin and enter the body vessel. Once access to the body vessel is established in this manner, the distal end of the wire guide can be passed through the needle lumen and enter the body vessel. The needle can then be withdrawn beyond the proximal end of the wire guide, leaving the distal end of the wire guide extending into the body vessel. Furthermore, the distal end of the wire guide can be inserted into any suitable body vessel. The body vessel into which the distal end of the wire guide is inserted during performance of a method according to certain embodiments can be selected based on a desired location for scanning, imaging, treatment, or other considerations. Examples of suitable body vessels include, but are not limited to, vessels of the peripheral vasculature. Step 714 can be performed before or after step 710 is performed, or while step 710 is being performed. Those skilled in the art will be able to select the appropriate relative order of steps 710 and 714 based on various considerations, including the nature of the MRI system and scanner, as well as other considerations.

[0078] Step 716 may be performed by applying a distal force to a portion of the wire guide that remains outside the patient's body, such as the proximal end of the wire guide or an intermediate portion of the wire guide, so that the distal end of the wire guide moves axially within the lumen of the body vessel, away from the point of insertion into the body vessel. Step 716 is performed until the distal end of the wire guide is positioned at a first location within a first portion of the body vessel, the first portion being of interest for subsequent step 718 of operating the scanner of the MRI system and step 720 of acquiring images.

[0079] Step 718 may be performed by operating the MRI system to scan the portion of the patient placed in the scanner of the MRI system by performing step 710. Step 718 may be performed using any suitable MRI parameters applicable to the scanner of the MRI system (e.g., gradient refocusing echo imaging, spin echo imaging, true high speed imaging with steady state precession, high speed low flip angle shot spoiled gradient echo imaging, magnetic field strengths such as 0.55T, 1.5T, 3T, about 0.055T to 1.5T, and less than 1T, slice thickness, flip angle, field of view, resolution, gradient fields, and any other one or more MRI parameters deemed suitable for a method according to a particular embodiment).

[0080] Step 720 may be performed by acquiring an image from the scanner of the MRI system used in step 718. Step 720 of acquiring a magnetic resonance image of the first portion of the body vessel may involve acquiring a single still image. Optionally, step 720 may be repeated any desired number of times to acquire multiple magnetic resonance images that may be grouped as a cine showing motion. Further, as an alternative to, or in addition to, acquiring an image, method 700 may include a step of visualizing the wire guide, a step of visualizing one or more markers associated with the wire guide, or both.

[0081] Step 722 can be performed by manually grasping a suitable medical device or by using a suitable tool. Any suitable medical device can be used in step 722, so long as the medical device comprises an elongate member defining a lumen configured to receive the wire guide. The medical device selected for use in a method according to a particular embodiment depends on various considerations, including the nature of the body vessel, the point of treatment, and the desired effect of performing the method. Examples of suitable medical devices include, but are not limited to, catheters, balloon catheters, cannulas, biopsy devices, extraction devices, and other medical devices. Additionally, medical devices can include deployable medical devices that can be deployed from the medical device in step 726, described below, and left in the body vessel after performing method 700. For example, medical devices used in this step 722 can include stents, such as a self-expanding stent, a balloon-expandable stent, or other stents; graft devices, such as a stent-graft; valves, such as prosthetic heart valves or other valve devices; filters; or any other type of deployable medical device.

[0082] Step 724 can be performed by applying a distal force to a portion of the medical device that remains outside the patient's body, such as the proximal end of the medical device or an intermediate portion of the medical device, so that the distal end of the medical device moves axially within the lumen of the body vessel away from the point of insertion into the body vessel. Step 724 is performed until the distal end of the medical device reaches the point of desired treatment within the body vessel.

[0083] Step 726 may be performed in any suitable manner appropriate for the medical device inserted through the body vessel in step 724. For example, if the medical device is a balloon catheter, step 726 may be performed by passing inflation fluid through the inflation lumen of the medical device to a connector on the proximal end of the device to inflate a balloon on the distal end at the point of treatment. Additional operations may also be included in the performance of step 726, as required by the medical device.

[0084] Step 728 can be performed by applying a proximal force to a portion of the medical device that remains outside the patient's body, such as the proximal end of the medical device or an intermediate portion of the medical device, so that the distal end of the medical device moves axially within the lumen of the body vessel along the wire guide toward the point of insertion into the body vessel. This step 728 is performed until the distal end of the medical device passes the point of insertion and the medical device completely exits the body vessel. Ultimately, this step 728 results in the medical device exiting the patient's body.

[0085] Step 730 may be performed by applying a proximal force to a portion of the wire guide that remains outside the patient's body, such as the proximal end of the wire guide or an intermediate portion of the wire guide, so that the distal end of the wire guide moves axially within the lumen of the body vessel toward the point of insertion into the body vessel. This step 730 is performed until the distal end of the wire guide passes the point of insertion and the wire guide completely exits the body lumen. Ultimately, this step 730 results in the wire guide exiting the patient's body. At this point, execution of method 700 is complete.

[0086] The various steps of method 700 may be performed separately and sequentially. For example, performance of step 718 may begin after step 716 is completed, and performance of step 720 may begin after step 718 is completed. Performance of step 724 may begin after step 720 is completed. However, other orderings of these steps are possible and may be advantageous for methods according to certain embodiments. For example, if multiple images are desired to aid in navigation of the wire guide through a body vessel, steps 718 and 720 may each be performed multiple times while step 716 is being performed. That is, step 718 of operating the scanner of the MRI system to scan a portion of a patient positioned within the scanner and including a first portion of the body vessel, and step 720 of acquiring magnetic resonance images of the first portion of the body vessel may be performed multiple times while step 716 of inserting the distal end of the wire guide through the patient's body vessel is being performed. In these examples, steps 718 and 720 may be performed any suitable number of times during the performance of step 716, and one of ordinary skill in the art would be able to select the appropriate number of times for each step to include in a method according to a particular embodiment based on various considerations, including the capabilities of the MRI system, the nature of the body's vessels and any navigation challenges they present, as well as other considerations.

[0087] Additionally, if multiple images are desired to aid in navigation of the medical device over the wire guide and through the body vessel, each of steps 718 and 720 can be performed multiple times while step 724 is being performed. That is, step 718 of operating the scanner of the MRI system to scan a portion of a patient positioned within the scanner and including a first portion of the body vessel, and step 720 of acquiring magnetic resonance images of the first portion of the body vessel, can be performed multiple times while step 724 of inserting the distal end of the medical device over the wire guide into the patient's body vessel is being performed. In these examples, steps 718 and 720 can be performed any appropriate number of times during the performance of step 724, and one of ordinary skill in the art would be able to select an appropriate number of times for each step to include in a method according to a particular embodiment based on various considerations, including the capabilities of the MRI system, the nature of the body vessel and any navigation challenges it presents, as well as other considerations. Examples of suitable numbers of times to perform steps 718 and 720 while step 724 is being performed include, but are not limited to, 1 time, 2 times, 3 or more times, 3 times, multiple times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 or more times, 11 times, 12 times, 13 or more times, 20 times, 50 times, 100 times, and 1000 times.

[0088] Also, if multiple images are desired to monitor manipulation of the distal end of the medical device at the point of treatment, steps 718 and 720 can each be performed multiple times while step 726 is being performed. That is, step 718 of operating the scanner of the MRI system to scan a portion of a patient positioned within the scanner and including a first portion of a body vessel, and step 720 of acquiring magnetic resonance images of the first portion of the body vessel, can be performed multiple times while step 726 of manipulating the proximal end of the medical device to cause manipulation of the distal end of the medical device at the point of treatment is being performed. In these examples, steps 718 and 720 can be performed any appropriate number of times during the performance of step 726, and one of ordinary skill in the art would be able to select an appropriate number of times for each step to include in a method according to a particular embodiment based on various considerations, including the capabilities of the MRI system, the nature of the body vessel and any navigation challenges it presents, as well as other considerations. Examples of suitable numbers of times to perform steps 718 and 720 while step 726 is being performed include, but are not limited to, 1 time, 2 times, 3 or more times, 3 times, multiple times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 or more times, 11 times, 12 times, 13 or more times, 20 times, 50 times, 100 times, and 1000 times.

[0089] Performance of the method provides one or more images of a portion of a body vessel that can be used for a variety of purposes, including educational, research, diagnostic, therapeutic, and informational purposes.

[0090] 12 illustrates an exemplary method 800 for performing an interventional medical procedure under MRI. Method 800 is similar to method 700 described above, except as detailed below.

[0091] A first step 810 includes positioning a portion of a patient in or adjacent to an MRI system having a scanner such that a portion of a body vessel is positioned within an area where the MRI system's scanner's magnetic field is present when the MRI system's scanner is activated. Another step 812 includes grasping a wire guide having a continuous metallic core member and a continuous jacket disposed over the core member. Another step 814 includes inserting a distal end of the wire guide into the patient's body vessel. Another step 816 includes inserting the distal end of the wire guide through the patient's body vessel until the distal end of the wire guide is positioned within a first portion of the body vessel having the first portion. Another step 818 includes operating the scanner of the MRI system to scan a portion of the patient positioned within the scanner and including the first portion of the body vessel. Another step 820 includes acquiring a magnetic resonance image of the first portion of the body vessel. Another step 822 includes grasping a medical device having a medical device proximal end and a medical device distal end, the medical device including an elongate member defining a lumen. Another step 824 includes inserting the distal end of the medical device over the wire guide into the patient's body vessel until the distal end of the wire guide reaches a point of treatment within the body vessel. Another step 826 includes manipulating the proximal end of the medical device to cause manipulation of the distal end of the medical device at the point of treatment. Another step 828 includes withdrawing the medical device from the body vessel. Another step 830 includes grasping a second medical device having a second medical device proximal end and a second medical device distal end, the second medical device comprising an elongate member defining a lumen. Another step 832 includes inserting the distal end of the second medical device over the wire guide into the patient's body vessel until the distal end of the second medical device reaches a point of treatment within the body vessel. Another step 834 includes manipulating the proximal end of the second medical device to cause manipulation of the distal end of the second medical device at the point of treatment. Another step 836 includes withdrawing the second medical device from the body vessel. Another step 838 includes removing the wire guide from the body vessel.

[0092] As described above for methods 600 and 700, step 810 may be performed by moving the patient relative to the MRI system, such as with the MRI system defining a bore in which the patient is positioned for the imaging procedure. Step 810 may also be performed by moving a portable MRI system relative to the patient to position the patient or a portion of the patient within an area where the magnetic field of the MRI system scanner will be present when the MRI system scanner is activated.

[0093] Step 814 may be performed before or after step 810 is performed, or while step 814 is being performed. Those skilled in the art will be able to select the appropriate relative order of steps 810 and 814 based on various considerations, including the nature of the MRI system and scanner, as well as other considerations.

[0094] In some methods, it may be desirable to preload the wire guide onto a medical device having an elongate member defining a lumen. In these methods, the distal end of the medical device can be inserted substantially over the wire guide before inserting the distal end of the wire guide into a body vessel. In these methods, the distal end of the medical device is inserted over the wire guide until only a relatively small portion of the wire guide extends beyond the distal end of the medical device. The wire guide and medical device are then inserted into the body vessel and navigated together within the body vessel.

[0095] Methods of manufacturing a wire guide and methods of manufacturing a plurality of wire guides are also provided.

[0096] FIG. 13 illustrates an exemplary method of manufacturing a wire guide 900. A first step 910 includes forming a continuous core member of a metallic material, the continuous core member having an outer surface. Another step 912 includes placing a jacket over the continuous core member such that the outer surface of the core member is in continuous contact with the jacket and such that no portion of the outer surface of the core member is exposed to the external environment surrounding the wire guide. An optional step 914 includes evaluating the jacket to determine whether the outer surface of the core member is completely encapsulated by the jacket, in continuous contact with the jacket, or both. Another optional step 916 includes transporting the wire guide to its intended user only if the evaluating step 916 determines that the outer surface of the core member is in continuous contact with the jacket.

[0097] Step 910 can be performed using any suitable process or technique, including cutting a length of core member from an off-the-shelf supply of core member material. Additionally, any suitable material can be used in performing step 910, as described above with respect to the core members of the exemplary wire guides described herein. To form a wire guide according to one embodiment, the material should be a metallic material. Examples of metallic materials that may be suitable for forming the core member during step 910 include, but are not limited to, shape memory alloys, including nitinol, nickel-titanium alloys such as black oxide superelastic nitinol SE508 straight stock, matte finish nitinol, polished nitinol, combinations of those described herein, and any other metallic materials that may be suitable. Step 910 can include various processes and techniques commonly used in forming metallic wire guides, including grinding the end to form the desired tip shape.

[0098] Step 912 may be performed using any suitable process or technique, including extruding a polymer material onto a continuous core member to form a jacket, reflowing a polymer material onto a continuous core member to form a jacket, and other suitable processes and techniques.

[0099] If included, step 914 may be performed by performing a visual inspection of the jacket to identify any disruptions in the continuity of the jacket, performing a visual inspection of the jacket to determine if there are any visible portions of the continuous core member, moistening the continuous core member to determine if fluid leaks from the jacket, evaluating the conductive, conductive, or both properties of the core member, and other suitable visual inspection, leak testing, or other suitable quality control techniques. If desired, multiple steps may be included to evaluate the jacket, such as a leak testing step, which is described in more detail below.

[0100] If included, step 916 may be performed by shipping the wire guide to the purchasing user, end user, or end user's agent after it has been determined that the outer surface of the core member is in continuous contact with the jacket.

[0101] In an alternative method of manufacturing a wire guide, two or more segments, each comprising a continuous core member and a jacket surrounding the continuous core member, may be joined from the previous individual segments into a continuous wire guide having a continuous jacket that completely encapsulates the row of continuous core members by arranging the segments end-to-end in a row and reflowing the jacket via a heat treatment. The positioning of the segments and reflowing of the jacket may be performed so that the individual continuous core members abut each other in the final wire guide with no insulating material between them, or so that after the jacket is reflowed, a portion of the jacket is disposed between the individual continuous core members. This alternative method may be advantageous, for example, to include a distal end having a jacket that includes a different dielectric material than the jacket of another segment used in the body of the wire guide.

[0102] FIG. 14 illustrates an exemplary method for manufacturing a plurality of wire guides 1000. A first step 1010 includes forming a continuous core member, each of the plurality of continuous core members being formed from a metallic material and having an outer surface. Another step 1012 includes disposing a jacket including one or more dielectric materials on the outer surface of the continuous core member such that the continuous core member is completely enclosed by the jacket. This step 1012 may be performed such that the outer surface of the core member is in continuous contact with the jacket. This step 1012 is repeated for each continuous core member formed in step 1010. Another step 1014 includes evaluating each jacket to determine whether the continuous core member associated with the jacket in step 1012 is completely enclosed by the jacket. Optional step 1016 includes destroying any wire guide from the plurality of wire guides for which the evaluating step determines that the continuous core member is not completely enclosed by the jacket. Another optional step 1018 includes transferring the first wire guide to a first intended user only if the evaluating step 1014 results in the continuous core member being completely encapsulated by the jacket. Another optional step 1020 includes transferring the second wire guide to a second intended user only if the evaluating step 1014 results in the continuous core member being completely encapsulated by the jacket.

[0103] Methods for manufacturing wire guides and methods for manufacturing a plurality of wire guides can utilize the dielectric properties of the metal and jacket of the continuous core member in one or more steps for evaluating the encapsulation of the continuous core member by the jacket in each wire guide manufactured by the associated method. For example, the method may include applying a current to one end of the continuous core member and measuring the current at the opposite end of the continuous core member to determine whether leakage of the applied current is occurring. If leakage is detected, the wire guide may be discarded because it likely has a jacket that does not completely encapsulate the continuous core member. One particular method includes immersing the wire guide in a conductive fluid, such as saline, electrically coupling the continuous core member of the wire guide to a current source to induce a current in the continuous core member, and measuring the current in the conductive fluid to determine whether leakage of the applied current is occurring into the conductive fluid. Discarding the wire guide if leakage of current is detected may also be included. Detecting leakage of current is believed to be particularly advantageous as a quality control measure in methods for manufacturing wire guides and methods for manufacturing a plurality of wire guides, at least because leakage of current is believed to correlate with increased temperature of the wire guide under MRI. Identification of a wire guide exhibiting current leakage is believed to be a reliable indicator of a wire guide exhibiting excessive heating under MRI due to incomplete encapsulation of the continuous core member by the jacket.

[0104] Specific examples Figure 15 includes graphical representations of raw RF induction heating of various test wire guide configurations during 2- to 7-minute scans in a 1.5T MRI system. The left panel shows the measured temperatures for four scans of a wire guide with a continuous nitinol core completely covered by a jacket (HiWire® nitinol core wire guide available from Cook Medical, Bloomington, Indiana), and the right panel shows the temperature rise normalized to the initial temperature. The top three sets of panels reflect data for a wire guide with an intact jacket, while the bottom two panels reflect data for a wire guide whose proximal end was cut to expose the proximal termination face of the wire guide prior to scanning in the MRI system. Data from four separate temperature probes is included.

[0105] 16 shows a table of experimental data showing the maximum temperature rise for a) a wire guide having a continuous nitinol core completely covered by a jacket (HiWire® nitinol core wire guide available from Cook Medical, Bloomington, Indiana), and b) a wire guide having a segmented structure. Given the teachings of the art suggesting that a segmented structure is necessary to avoid undesirable RF heating under MRI, this data surprisingly reveals that a wire guide having an intact jacket over a continuous nitinol core does not exhibit the significant RF heating expected in an MRI scanner. Data from four separate temperature probes is included.

[0106] Also surprisingly, the data reflected in the bottom two panels of FIG. 15 indicate that partial insulation of the wire guide by a jacket (i.e., test wire guides in which the proximal end was cut to expose the proximal termination face of the wire guide prior to scanning in an MRI system) results in excessive heating, which is believed to be due to the concentration of all propagating electromagnetic waves on a small area of ​​the exposed termination face of the core member and the inability of these waves to escape the insulation provided by the jacket along the length of the continuous core member. Based on this, the inventors believe that a wire guide having a continuous core completely covered by a jacket will exhibit less heating than a bare continuous core in the same environment, and that a continuous core covered by a jacket but with the bare end of the core member exposed will exhibit a greater temperature rise in the same environment. For at least this reason, it is believed that inspection of the jacket in wire guides according to the present invention and possible exposure of the core member to the external environment surrounding the wire guide is important.

[0107] Computational modeling and simulation (CM&S) was used to evaluate normalized tissue heating due to radiofrequency (RF) heating. MRI scanners create images using a large static magnetic field (typically 1.5 T, but also 3 T, 1.2 T, and low-field scanners 0.7 T and 0.55 T), three gradient magnetic fields, and a set of coils that transmit and receive radiofrequency (RF) waves. Clinical MRI systems typically use an RF body coil to transmit RF energy, which heats the surrounding tissue. Finite element analysis (FEA) of a typical coated wire guide in an ASTM F2182 gel phantom was performed using COMSOL Multiphysics® v6.0 to quantify normalized tissue heating as a function of insulation coating thickness and conductivity, as shown in the tables in Figures 17 and 18. The table in Figure 19 shows the conductivity for several typical wire guide insulation materials.

[0108] The RF module in COMSOL solves Maxwell's equations subject to initial and boundary conditions, as well as the constituent material properties. The frequency domain wave equation is solved for the electric field (E) shown in Equation 1 in Figure 20. The eigenvalue problem is solved for the permeability of a vacuum (μ), the relative permeability (μ r =μ / μ0), dielectric constant of vacuum (ε0), relative permittivity (ε r = ε / ε0), and is solved for frequency (ω) taking into account the conductivity (σ) of the material.

[0109] The COMSOL heat transfer module solves the heat equation (Equation 2 presented in Figure 21) for heat conduction in solids, subject to initial and boundary conditions. The transient heat equation is determined by the time (t), the heat source (q) being solved for in the electromagnetic simulation, the density (ρ) of the material, and the specific heat (c p ), and the thermal conductivity (k) are taken into account to solve for temperature (T). For in vivo simulations only, a perfusion term was included in the bioheat transfer equation.

[0110] Maxwell's equations and the heat conduction equation are coupled in COMSOL using Joule heating, also known as resistive heating, as the heat source in the heat conduction equation. Joule heating is the process of releasing heat (q) by passing an electric current (J) through a conductor, as shown in Equation 3 in Figure 22, taking into account the electric field (E) in Equation 1.

[0111] Those skilled in the art will recognize that, in light of the overall teachings of the present disclosure, various modifications and alternatives to the described and illustrated examples can be developed, and that various elements and features of one example described and illustrated herein can be combined with various elements and features of another example without departing from the scope of the present invention. Therefore, the specific configurations of elements and steps disclosed herein have been selected by the inventors merely to explain and illustrate examples of the present invention, and are not intended to limit the scope of the present invention or its protection, which is given the full scope of the appended claims and any equivalents thereof.

Claims

1. a continuous core member formed of a metallic material and having a first length; a continuous jacket disposed over and completely encapsulating the entire continuous core member, the continuous jacket being formed of a dielectric material and having a second length greater than the first length; 1. An MRI compatible wire guide comprising:

2. The MRI compatible wire guide of claim 1 , wherein the wire guide further comprises a marker formed of a metallic material.

3. The MRI compatible wire guide of claim 2 , wherein the core member has a first susceptibility and the marker has a second susceptibility different from the first susceptibility.

4. The MRI compatible wire guide of claim 3 , wherein the core member and the markers are formed from the same material.

5. The MRI compatible wire guide of claim 3 , wherein the core member and the markers are formed of different materials.

6. The MRI compatible wire guide of claim 5, wherein the core member comprises a nickel-titanium alloy and the marker comprises a stainless steel alloy.

7. The MRI compatible wire guide of claim 3 , wherein the core member has an outer surface and the markers are disposed on the outer surface.

8. The MRI compatible wire guide of claim 3 , wherein the jacket has a thickness, and the markers are positioned within the thickness of the jacket.

9. The MRI compatible wire guide of claim 3 , wherein the marker comprises a circumferential band disposed about the core member.

10. 10. The MRI compatible wire guide of claim 1, wherein the jacket has a first shaft portion formed from a first dielectric material and a second shaft portion formed from a second, different dielectric material.

11. The MRI compatible wire guide of claim 10 , wherein the first dielectric material comprises a first polymer and the second dielectric material comprises a second polymer.

12. The MRI compatible wire guide of claim 10 , wherein the first dielectric material comprises a polymer and the second dielectric material comprises a non-polymer.

13. The MRI compatible wire guide of claim 12 , wherein the second dielectric material comprises a ceramic.

14. the jacket having a third shaft portion formed of a third dielectric material; The MRI compatible wire guide of claim 10 , wherein the second shaft portion is axially disposed between the first shaft portion and the third shaft portion.

15. 15. The MRI compatible wire guide of claim 14, wherein the first dielectric material and the third dielectric material are the same dielectric material.

16. The MRI compatible wire guide of claim 15 , wherein the first dielectric material and the third dielectric material comprise a polymer.

17. The MRI compatible wire guide of claim 16 , wherein the second dielectric material comprises a non-polymer.

18. 18. The MRI compatible wire guide of claim 17, wherein the second dielectric material comprises a ceramic.

19. a continuous core member formed of a metallic material and having a first length; a continuous jacket disposed over the continuous core member and completely enclosing the entire continuous core member, the continuous jacket having a first axial portion formed of a first dielectric material, a second axial portion formed of a second, different dielectric material, and a second length greater than the first length; 1. An MRI compatible wire guide comprising:

20. a continuous core member formed of a metallic material and having a first length; a continuous jacket having a proximal jacket end, a distal jacket end, a first shaft portion extending from the proximal jacket end toward the distal jacket end and formed of a non-polymeric dielectric material, and a second shaft portion extending from the distal jacket end toward the proximal jacket end and formed of a polymeric dielectric material, the continuous jacket being disposed over and completely encapsulating the continuous core member and having a second length greater than the first length; 1. An MRI compatible wire guide comprising: An MRI compatible wire guide, wherein the first shaft portion extends along a shaft length that is less than about 20% of the second length.

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