Abstract:
An elongate electrical lead assembly that reduces localized heating due to MR scanner-induced currents includes a first elongate electrical lead having a series of alternating single layer coil sections and multi-layer coil sections, a second elongate electrical lead having a series of alternating single layer coil sections and multi-layer coil sections, and a third elongate electrical lead having a coiled section that coaxially surrounds the first and second electrical leads. Each multi-layer coil section of the second electrical lead is coiled around a respective single layer coil section of the first electrical lead, and each single layer coil section of the second electrical lead is coiled around a respective multi-layer coil section of the first electrical lead.

Description:
FIELD OF THE INVENTION 
     The present invention relates to MRI-guided systems and may be particularly suitable for MRI-guided cardiac systems such as EP systems for treating Atrial Fibrillation (AFIB). 
     BACKGROUND 
     Heart rhythm disorders (arrhythmias) occur when there is a malfunction in the electrical impulses to the heart that coordinate how the heart beats. During arrhythmia, a heart may beat too fast, too slowly or irregularly. Catheter ablation is a widely used therapy for treating arrhythmias and involves threading a catheter through blood vessels of a patient and into the heart. In some embodiments, radio frequency (RF) energy may be applied through the catheter tip to destroy abnormal heart tissue causing the arrhythmia. In other embodiments a catheter tip may be configured to cryogenically ablate heart tissue. 
     Guiding the placement of a catheter during ablation therapy within the heart is important. Conventional catheter ablation procedures are conducted using X-ray and/or ultrasound imaging technology to facilitate catheter guidance and ablation of heart tissue. Conventional Cardiac EP (ElectroPhysiology) Systems are X-ray based systems which use electroanatomical maps. Electroanatomical maps are virtual representations of the heart showing sensed electrical activity. Examples of such systems include the Carto® electroanatomic mapping system from Biosense Webster, Inc., Diamond Bar, Cali., and the EnSite NavX® system from Endocardial Solutions Inc., St. Paul, Minn. 
     Magnetic resonance imaging (MRI) has several distinct advantages over X-ray imaging technology, such as excellent soft-tissue contrast, the ability to define any tomographic plane, and the absence of ionizing radiation exposure. In addition, MRI offers several specific advantages that make it especially well suited for guiding various devices used in diagnostic and therapeutic procedures including: 1) real-time interactive imaging, 2) direct visualization of critical anatomic landmarks, 3) direct high resolution imaging, 4) visualization of a device-tissue interface, 5) the ability to actively track device position in three-dimensional space, and 6) elimination of radiation exposure. 
     Induced RF currents (referred to as RF coupling) on coaxial cables, electrical leads, guide wires, and other elongated devices utilized in MRI environments can be problematic. Such RF coupling may cause significant image artifacts, and may induce undesired RF energy deposition in the tissue in contact/adjacent with the device, resulting in local tissue heating and permanent tissue damage. 
     SUMMARY 
     It should be appreciated that this Summary is provided to introduce a selection of concepts in a simplified form, the concepts being further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of this disclosure, nor is it intended to limit the scope of the invention. 
     According to some embodiments of the present invention, an elongate electrical lead subassembly for use in MRI-compatible medical devices and that reduces localized tissue heating due to MR scanner-induced RF currents in these devices includes at least one first conductor (which may include a plurality of conductors, individually insulated) comprising a series of alternating single layer coil sections and multi-layer coil sections and attached at one end portion to an ablation electrode, and at least one second conductor (which may include a plurality of conductors, individually insulated) comprising a series of alternating single layer coil sections and multi-layer coil sections and attached at one end portion to a sensing electrode upstream of the ablation electrode. Each multi-layer coil section of the at least one second conductor is coiled around a respective single layer coil section of the at least one first conductor, and each single layer coil section of the at least one second conductor is coiled around a respective multi-layer coil section of the at least one first conductor such that the electrical lead subassembly has a substantially constant diameter along at least a segment of its length. The at least one first conductor and the at least one second conductor are insulated conductors. In some embodiments, the at least one first and second conductors are coaxial cables. 
     In some embodiments, the multi-layer coil sections of the at least one first conductor and the at least one second conductor have an impedance greater than about 50 ohms per centimeter at a nuclear magnetic resonance (NMR) operating frequency of an MRI scanner. 
     In some embodiments, the multi-layer coil sections of the at least one first conductor and at least one second conductor include a first coiled layer that extends in a first lengthwise direction for a first physical length, a second coiled layer coiled around the first coiled layer in a substantially opposing lengthwise direction for a second physical length, and a third coiled layer coiled around the second coiled layer in the first lengthwise direction for a third physical length. In some embodiments, coils in at least two of the first, second and third coil layers of the at least one first conductor have a different pitch. In some embodiments, coils in at least two of the first, second and third coil layers of the at least one first conductor have the same pitch. 
     According to some embodiments of the present invention, an elongate electrical lead subassembly for use in MRI-compatible medical devices that reduces localized tissue heating due to MR scanner-induced currents includes a plurality of conductors, each conductor having a series of alternating straight sections and coiled sections. The conductors are arranged such each coiled section of a conductor is in adjacent, axial relationship with a respective coiled section of another conductor, and each conductor is attached at one end portion to an RF tracking coil. 
     According to some embodiments of the present invention, an elongate electrical lead assembly for use in MRI-compatible medical devices includes a first elongate electrical lead subassembly comprising at least one conductor (which may include a plurality of conductors, individually insulated) having a series of alternating single layer coil sections and multi-layer coil sections and connected at one end portion to an ablation electrode, a second elongate electrical lead subassembly comprising at least one conductor (which may include a plurality of conductors, individually insulated) having a series of alternating single layer coil sections and multi-layer coil sections and connected at one end portion to a sensing electrode upstream of the ablation electrode, and a third elongate electrical lead comprising at least one conductor (which may include a plurality of conductors, individually insulated) having a coiled section that coaxially surrounds the first and second electrical leads and connected at one end portion to an RF tracking coil. Each multi-layer coil section of the second electrical lead subassembly is coiled around a respective single layer coil section of the first electrical lead subassembly, and each single layer coil section of the second electrical lead subassembly is coiled around a respective multi-layer coil section of the first electrical lead subassembly. 
     In some embodiments, the third electrical lead includes a plurality of conductors, and the coiled sections of the conductors are in adjacent, axial relationship with each other. 
     In some embodiments, the multi-layer coil sections of the first and second electrical lead subassemblies each include a first coiled layer that extends in a first lengthwise direction for a first physical length, a second coiled layer coiled around the first coiled layer in a substantially opposing lengthwise direction for a second physical length, and a third coiled layer coiled around the second coiled layer in the first lengthwise direction for a third physical length. 
     In some embodiments, the coiled section of the third electrical lead subassembly includes coils wound right to left. In some embodiments, the coiled section of the third electrical lead includes coils wound left to right. 
     In some embodiments, the multi-layer coil sections of the first and second electrical lead subassemblies have an impedance greater than about 50 ohms per centimeter at a nuclear magnetic resonance (NMR) frequency. 
     In some embodiments, the electrical lead assembly includes a fourth electrical lead subassembly having a series of alternating single layer coil sections and multi-layer coil sections and connected at one end portion to a thermistor. Each multi-layer coil section of the fourth electrical lead subassembly is coiled around a respective single layer coil section of the first electrical lead subassembly, and each single layer coil section of the fourth electrical lead subassembly is coiled around a respective multi-layer coil section of the first electrical lead subassembly. 
     According to other embodiments of the present invention, an MRI-compatible medical device that reduces localized tissue heating due to MR scanner-induced currents includes an elongated flexible shaft having a distal end portion, and an opposite proximal end portion, an ablation electrode at the flexible shaft distal end portion, at least one sensing electrode at the shaft distal end portion, and an electrical connector interface, for example, proximate the flexible shaft proximal end portion. A first elongate electrical lead extends longitudinally within the flexible shaft and has opposing proximal and distal end portions. The first electrical lead distal end portion is connected to the ablation electrode and the first electrical lead proximal end is connected to the electrical connector interface. The first electrical lead includes a series of alternating single layer coil sections and multi-layer coil sections. A second elongate electrical lead extends longitudinally within the flexible shaft and has opposing proximal and distal end portions. The second electrical lead distal end portion is connected to the at least one sensing electrode, and the second electrical lead proximal end is connected to the electrical connector interface. The second electrical lead includes a series of alternating single layer coil sections and multi-layer coil sections. Each multi-layer coil section of the second electrical lead is coiled around a respective single layer coil section of the first electrical lead, and each single layer coil section of the second electrical lead is coiled around a respective multi-layer coil section of the first electrical lead. The at least one conductors of the first and second electrical leads are individually insulated and, in some embodiments, may be coaxial cables. 
     In some embodiments, the multi-layer coil sections of the first and second electrical leads include a first coiled layer that extends in a first lengthwise direction for a first physical length, a second coiled layer coiled around the first coiled layer in a substantially opposing lengthwise direction for a second physical length, and a third coiled layer coiled around the second coiled layer in the first lengthwise direction for a third physical length. In some embodiments, coils in at least two of the first, second and third coil layers of the first electrical lead have a different pitch. In some embodiments, coils in at least two of the first, second and third coil layers of the first electrical lead have the same pitch. 
     In some embodiments, the multi-layer coil sections of the first and second electrical leads have an impedance greater than about 50 ohms per centimeter at a nuclear magnetic resonance (NMR) frequency. 
     In some embodiments, the medical device includes at least one RF tracking coil positioned adjacent the distal end portion of the flexible shaft. A third elongate electrical lead extends longitudinally within the flexible shaft and has opposing proximal and distal end portions. The third electrical lead distal end portion is connected to the at least one RF tracking coil, and the third electrical lead proximal end is connected to the electrical connector interface. The third electrical lead includes a first coiled section that coaxially surrounds the first and second electrical leads. In some embodiments, the at least one RF tracking coil includes a plurality of RF tracking coils, and the third electrical lead at least one conductor comprises a respective plurality of conductors having coiled sections in adjacent, axial relationship with each other. 
     In some embodiments, the medical device includes a thermistor positioned adjacent the distal end portion of the flexible shaft. A fourth electrical lead extends longitudinally within the flexible shaft and has opposing proximal and distal end portions. The fourth electrical lead distal end portion is connected to the thermistor and the fourth electrical lead proximal end is connected to the electrical connector interface. The fourth electrical lead includes a series of alternating single layer coil sections and multi-layer coil sections. Each multi-layer coil section of the fourth electrical lead is coiled around a respective single layer coil section of the first electrical lead, and each single layer coil section of the fourth electrical lead is coiled around a respective multi-layer coil section of the first electrical lead. 
     According to other embodiments of the present invention, an elongate electrical lead assembly for use in MRI-compatible medical devices includes a first elongate electrical lead having at least one conductor with first and second multi-layer coil sections with a single layer coil section therebetween, and a second elongate electrical lead having at least one conductor with at least one multi-layer coil section. The first multi-layer coil section has a length greater than a length of the second multi-layer coil section and greater than a length of the single layer coil section. The at least one multi-layer coil section of the second electrical lead is coiled around the single layer coil section of the first electrical lead. A third elongate electrical lead having at least one conductor with a coiled section coaxially surrounds the first and second electrical leads. In some embodiments, the third electrical lead includes a plurality of conductors, and the coiled sections of the conductors are in adjacent, axial relationship with each other. 
     In some embodiments, the electrical lead assembly includes a fourth electrical lead having at least one multi-layer coil section. The at least one multi-layer coil section of the fourth electrical lead is coiled around the single layer coil section of the first electrical lead. 
     In some embodiments, the at least one multi-layer coil section of the first and second electrical leads includes a plurality of adjacent multi-layer coil sections. Each multilayer coil section has a first coiled layer that extends in a first lengthwise direction for a first physical length, a second coiled layer coiled around the first coiled layer in a substantially opposing lengthwise direction for a second physical length, and a third coiled layer coiled around the second coiled layer in the first lengthwise direction for a third physical length. 
     It is noted that aspects of the invention described with respect to one embodiment may be incorporated in a different embodiment although not specifically described relative thereto. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination. Applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to be able to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner. These and other objects and/or aspects of the present invention are explained in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an MRI-guided system configured to show a device tissue interface using near RT MRI data. 
         FIG. 2  is a schematic illustration of an intrabody device with a tracking coil electrically connected to a Scanner channel. 
         FIG. 3  is a schematic illustration of an MRI system with a workstation and display. 
         FIG. 4  is a circuit diagram of an exemplary tracking coil tuning circuit. 
         FIG. 5  is a perspective view of an exemplary ablation catheter in having an ablation electrode and RF tracking coils that can be electrically connected to an interface circuit of an MRI scanner by electrical lead assemblies of the present invention. 
         FIG. 6  is an enlarged partial perspective view of the tip portion of the ablation catheter of  FIG. 5 . 
         FIG. 7  is a cross-sectional view of the tip portion of the ablation catheter of  FIG. 6  taken along lines  7 - 7 . 
         FIG. 8  illustrates the ablation catheter of  FIG. 7  having a thermistor/thermocouple included therein with an electrical lead that extends longitudinally within the shaft lumen from the ablation tip to an electrical connector interface. 
         FIG. 9  is a perspective view of the handle at the proximal end of the ablation catheter of  FIG. 5  with a cover removed and illustrating an exemplary MRI scanner interface circuit that can be connected by electrical lead assemblies of the present invention. 
         FIG. 10A  is a partial side view of a distal end of an exemplary ablation catheter having an ablation electrode, RF tracking coils, and sensing electrodes that can be electrically connected to an interface circuit of an MRI scanner by electrical lead assemblies of the present invention. 
         FIG. 10B  and an enlarged partial view of the distal end of the ablation catheter of  FIG. 10A . 
         FIG. 11  is a schematic illustration of an exemplary ablation catheter having an ablation electrode, RF tracking coils, and sensing electrodes that can be electrically connected to an interface circuit of an MRI scanner by electrical lead assemblies of the present invention. 
         FIG. 12A  is a schematic color illustration of an electrical lead subassembly that includes conductors for an ablation electrode, sensing electrodes, and a thermistor/thermocouple of an MRI-compatible medical device, according to some embodiments of the present invention. 
         FIG. 12B  is a schematic color illustration of an ablation electrode conductor in the electrical lead subassembly of  FIG. 12A . 
         FIGS. 13A-13D  are schematic color illustrations of alternate RF tracking coil electrical lead subassemblies for an MRI-compatible medical device, according to some embodiments of the present invention.  FIG. 13A  illustrates a single conductor for a single RF tracking coil;  FIG. 13B  illustrates two conductors for two RF tracking coils;  FIG. 13C  illustrates three conductors for three RF tracking coils; and  FIG. 13D  illustrates four conductors for four RF tracking coils. 
         FIGS. 14A-14D  are schematic color illustrations of further alternate RF tracking coil electrical lead subassemblies, according to some embodiments of the present invention.  FIG. 14A  illustrates a single conductor for a single RF tracking coil;  FIG. 14B  illustrates two conductors for two RF tracking coils;  FIG. 14C  illustrates three conductors for three RF tracking coils; and  FIG. 14D  illustrates four conductors for four RF tracking coils. 
         FIG. 15A  is a schematic color illustration of an electrical lead assembly according to some embodiments of the present invention that includes the electrical lead subassembly of  FIG. 12A  inserted within the electrical lead subassembly of  FIG. 13D . 
         FIG. 15B  is a schematic color illustration of an electrical lead assembly according to some embodiments of the present invention that includes the electrical lead subassembly of  FIG. 12A  inserted within the electrical lead subassembly of  FIG. 14D . 
         FIG. 16A  is a schematic color illustration of an electrical lead subassembly that includes conductors for an ablation electrode, sensing electrodes, and a thermistor/thermocouple of an MRI-compatible medical device, according to some embodiments of the present invention. 
         FIG. 16B  is a schematic color illustration of an ablation electrode conductor in the electrical lead subassembly of  FIG. 16A . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. It will be appreciated that although discussed with respect to a certain embodiment, features or operation of one embodiment can apply to others. 
     In the drawings, the thickness of lines, layers, features, components and/or regions may be exaggerated for clarity and broken lines (such as those shown in circuit or flow diagrams) illustrate optional features or operations, unless specified otherwise. In addition, the sequence of operations (or steps) is not limited to the order presented in the claims unless specifically indicated otherwise. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items and may be abbreviated as “/”. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and/or clarity. 
     It will be understood that when a feature, such as a layer, region or substrate, is referred to as being “on” another feature or element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another feature or element, there are no intervening elements present. It will also be understood that, when a feature or element is referred to as being “connected” or “coupled” to another feature or element, it can be directly connected to the other element or intervening elements may be present. In contrast, when a feature or element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Although described or shown with respect to one embodiment, the features so described or shown can apply to other embodiments. 
     Spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is inverted, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. Thus, the exemplary term “under” can encompass both an orientation of “over” and “under”. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. Similarly, the terms “upwardly”, “downwardly”, “vertical”, “horizontal” and the like are used herein for the purpose of explanation only unless specifically indicated otherwise. 
     The term “about”, as used herein with respect to a value or number, means that the value or number can vary by +/−twenty percent (20%). 
     The terms “MRI or MR Scanner” are used interchangeably to refer to a Magnetic Resonance Imaging system and includes the magnet, the operating components, e.g., RF amplifier, gradient amplifiers and operational circuitry including, for example, processors (the latter of which may be held in a control cabinet) that direct the pulse sequences, select the scan planes and obtain MR data. Embodiments of the present invention can be utilized with any MRI Scanner including, but not limited to, GE Healthcare: Signa 1.5T/3.0T; Philips Medical Systems: Achieva 1.5T/3.0T; Integra 1.5T; Siemens: MAGNETOM Avanto; MAGNETOM Espree; MAGNETOM Symphony; MAGNETOM Trio; and MAGNETOM Verio. 
     The term “near real time” refers to both low latency and high frame rate. Latency is generally measured as the time from when an event occurs to display of the event (total processing time). For tracking, the frame rate can range from between about 100 fps to the imaging frame rate. In some embodiments, the tracking is updated at the imaging frame rate. For near ‘real-time’ imaging, the frame rate is typically between about 1 fps to about 20 fps, and in some embodiments, between about 3 fps to about 7 fps. The low latency required to be considered “near real time” is generally less than or equal to about 1 second. In some embodiments, the latency for tracking information is about 0.01 s, and typically between about 0.25-0.5 s when interleaved with imaging data. Thus, with respect to tracking, visualizations with the location, orientation and/or configuration of a known intrabody device can be updated with low latency between about 1 fps to about 100 fps. With respect to imaging, visualizations using near real time MR image data can be presented with a low latency, typically within between about 0.01 ms to less than about 1 second, and with a frame rate that is typically between about 1-20 fps. Together, the system can use the tracking signal and image signal data to dynamically present anatomy and one or more intrabody devices in the visualization in near real-time. In some embodiments, the tracking signal data is obtained and the associated spatial coordinates are determined while the MR image data is obtained and the resultant visualization(s) with the intrabody device (e.g., stylet) and the near RT MR image(s) are generated. 
     The term “RF safe” means that the catheter and any (conductive) lead is configured to operate safely when exposed to RF signals, particularly RF signals associated with MRI systems, without inducing unplanned current that inadvertently unduly heats local tissue or interferes with the planned therapy. The term “MRI visible” means that the device is visible, directly or indirectly, in an MRI image. The visibility may be indicated by the increased SNR of the MRI signal proximate the device. The device can act as an MRI transmit/receive or receive antenna to collect signal from local tissue and/or the device actually generates MRI signal itself, such as via suitable medical grade hydro-based coatings, fluid (e.g., aqueous fluid) filled channels or lumens. The term “MRI compatible” means that the so-called component(s) is safe for use in an MRI environment and as such is typically made of a non-ferromagnetic MRI compatible material(s) suitable to reside and/or operate in a high magnetic field environment. The term “high-magnetic field” refers to field strengths above about 0.5T (Tesla), typically above 1.0T, and more typically between about 1.5T and 10T. Embodiments of the invention may be particularly suitable for 1.5T and/or 3.0T systems. 
     The term “intrabody device” is used broadly to refer to any diagnostic or therapeutic medical device including, for example, catheters, needles (e.g., injection, suture, and biopsy), forceps (miniature), knives or other cutting members, ablation or stimulation probes, injection or other fluid delivery cannulas, mapping or optical probes or catheters, sheaths, guidewires, fiberscopes, dilators, scissors, implant material delivery cannulas or barrels, and the like, typically having a size that is between about 5 French to about 12 French, but other sizes may be appropriate. 
     The term “tracking member”, as used herein, includes all types of components that are visible in an MRI image including miniature RF tracking coils, passive markers, and receive antennas. In some embodiments of the present invention a miniature RF tracking coil can be connected to a channel of an MRI Scanner. The MR Scanner can be configured to operate to interleave the data acquisition of the tracking coils with the image data acquisition. The tracking data is acquired in a ‘tracking sequence block’ which takes about 10 msec (or less). In some embodiments, the tracking sequence block can be executed between each acquisition of image data (the ‘imaging sequence block’). So the tracking coil coordinates can be updated immediately before each image acquisition and at the same rate. The tracking sequence can give the coordinates of all tracking coils simultaneously. So, typically, the number of coils used to track a device has substantially no impact on the time required to track them. 
     MRI has several distinct advantages over X-ray imaging technology, such as: excellent soft-tissue contrast, the ability to define any tomographic plane, and the absence of ionizing radiation exposure. In addition, MRI offers several specific advantages that make it especially well suited for guiding transseptal puncture procedures including: 1) near real-time interactive imaging, 2) direct visualization of critical endocardial anatomic landmarks, 3) direct high resolution imaging of the septum, including the fossa ovalis, 4) visualization of the needle tip-tissue interface, 5) the ability to actively track needle position in three-dimensional space, and 6) elimination of radiation exposure. 
     Embodiments of the present invention can be configured to guide and/or place diagnostic or interventional devices in an MRI environment (e.g., interventional medical suite) to any desired internal region of a subject of interest, including, in some embodiments, to a cardiac location. The subject can be animal and/or human subjects. 
     Some embodiments of the invention provide systems that can be used to ablate tissue for treating cardiac arrhythmias, and/or to deliver stem cells or other cardio-rebuilding cells or products into cardiac tissue, such as a heart wall, via a minimally invasive MRI guided procedure while the heart is beating (i.e., not requiring a non-beating heart with the patient on a heart-lung machine). 
       FIG. 1  illustrates an MRI interventional system  10  with a scanner  10 S and a flexible intrabody medical device  80  (e.g., an ablation catheter, mapping catheter, etc.) proximate target tissue  100  at a device-tissue interface  100   i . The system  10  can be configured to electronically track the 3-D location of the device  80  in the body and identify and/or “know” the location of the tip portion  80   t  of the device  80  (e.g., the ablation tip) in a coordinate system associated with the 3-D imaging space. As shown in  FIG. 1 , the device  80  can include a plurality of spaced apart tracking members  82  on a distal end portion thereof. In a particular embodiment, the device  80  can be an ablation catheter and the tip  80   t  can include an ablation electrode  80   e  (typically at least one at a distal end portion of the device). Where used, the electrode  80   e  can be both a sensing and ablation electrode. 
     The tracking members  82  can comprise miniature tracking coils, passive markers and/or a receive antenna. In a preferred embodiment, the tracking members  82  include at least one miniature tracking coil  82   c  that is connected to a channel  10   ch  of an MRI Scanner  10 S ( FIG. 2 ). The MR Scanner  10 S can be configured to operate to interleave the data acquisition of the tracking coils  82   c  with the image data acquisition. 
     Some embodiments of the invention can be utilized with systems that can be used to facilitate ablation of tissue for treating cardiac arrhythmias, or to repair or replace cardiac valves, repair, flush or clean vasculature and/or place stents, and/or to deliver stem cells or other cardio-rebuilding cells or products into cardiac tissue, such as a heart wall, via a minimally invasive MRI guided procedure while the heart is beating (i.e., not requiring a non-beating heart with the patient on a heart-lung machine). The cardiac procedures can be carried out from an inside of the heart or from an outside of the heart. The system may also be suitable for delivering a therapeutic agent or carrying out another treatment or diagnostic evaluation for any intrabody location, including, for example, the brain, gastrointestinal system, genourinary system, spine (central canal, the subarachnoid space or other region), vasculature or other intrabody locations. Additional discussion of exemplary target regions can be found at the end of this document. 
     The system  10  and/or circuit  60   c  ( FIGS. 2-3 ) can calculate the position of the tip of the device  80   t  as well as the shape and orientation of the flexible device based on a priori information on the dimensions and behavior of the device  80  (e.g., for a steerable device, the amount of curvature expected when a certain pull wire extension or retraction exists, distance to tip from different coils  82  and the like). Using the known information of the device  80  and because the tracking signals are spatially associated with the same X, Y, Z coordinate system as the MR image data, the circuit  60   c  can rapidly generate visualizations showing a physical representation of the location of a distal end portion of the device  80  with near RT MR images of the anatomy. 
     In some embodiments, the tracking signal data is obtained and the associated spatial coordinates are determined while a circuit  60   c  in the MRI Scanner  10 S ( FIG. 2 ) and/or in communication with the Scanner  10 S ( FIG. 3 ) obtains MR image data. The reverse operation can also be used. The circuit  60   c  can then rapidly render the resultant visualization(s)  100   v  (see, e.g.,  FIGS. 5A-5D ) with the flexible device(s)  80  shown with a physical representation based on spatial coordinates of the devices in the 3-D imaging space identified using the associated tracking coil data and the near RT MR image(s). 
     The circuit  60   c  can be totally integrated into the MR Scanner  10 S (e.g., control cabinet), partially integrated into the MR Scanner  10 S or be separate from the MR Scanner  10 S but communicate therewith. If not totally integrated into the MR Scanner  10 S, the circuit  60   c  may reside partially or totally in a workstation  60  and/or in remote or other local processor(s) and/or ASIC.  FIG. 3  illustrates that a clinician workstation  60  can communicate with the MR Scanner  10 S via an interface  44 . Similarly, the device  80  in the magnet room can connect to the MR Scanner  10 S via an interface box  86  which may optionally be integrated into the patch panel  250 . 
     As shown in  FIGS. 2 and 3 , for example, the system  10  can include at least one (interactive) display  20  in communication with the circuit  60   c  and/or the Scanner  10 S. The display  20  can be configured to display the interactive visualizations  100   v . The visualizations  100   v  can be dynamic showing the movement of the device  80  relative to the intrabody anatomical structure shown by the displayed near-real time MRI image. 
       FIG. 2  illustrates that the device  80  can include at least one conductor  81 , such as a coaxial cable that connects a respective tracking coil  82   c  to a channel  10   ch  of the MR Scanner  10 S. The MR Scanner  10 S can include at least 16 separate channels, and typically more channels but may operate with less as well. Each device  80  can include between about 1-10 tracking coils, typically between about 1-4. The coils  82   c  on a particular device  80  can be arranged with different numbers of turns, different dimensional spacing between adjacent coils  82   c  (where more than one coil is used) and/or other configurations. The circuit  60   c  can be configured to generate the device renderings based on tracking coil locations/positions relative to one another on a known device with a known shape and/or geometry or predictable or known changeable (deflectable) shape or form (e.g., deflectable end portion). The circuit can identify or calculate the actual shape and orientation of the device for the renderings based on data from a CAD (computer aided design) model of the physical device. The circuit can include data regarding known or predictable shape behavior based on forces applied to the device by the body or by internal or external components and/or based on the positions of the different tracking coils in 3-D image space and known relative (dimensional) spacings. 
     As shown in  FIG. 3 , the display  20  can be provided in or associated with a clinician workstation  60  in communication with an MRI Scanner  10 S. Other displays may be provided. The MRI Scanner  10 S typically includes a magnet  15  in a shielded room and a control cabinet  11  (and other components) in a control room in communication with electronics in the magnet room. The MRI Scanner  10 S can be any MRI Scanner as is well known to those of skill in the art. 
     The tracking coils  82   c  can each include a tuning circuit that can help stabilize the tracking signal for faster system identification of spatial coordinates.  FIG. 4  illustrates an example of a tuning circuit  83  that may be particularly suitable for a tracking coil  82   c . As shown, CON 1  connects the coaxial cable  81  to the tracking coil  82   c  on a distal end portion of the device  80  while J 1  connects to the MR Scanner channel  10   ch . The Scanner  10 S sends a DC bias to the circuit  83  and turns U 1  diode “ON” to create an electrical short which creates a high impedance (open circuit) on the tracking coil to prevent current flow on the tracking coil and/or better tracking signal (stability). The tuning circuit can be configured to have a 50 Ohm matching circuit (narrow band to Scanner frequency) to electrically connect the cable to the respective MR Scanner channel. When the diode U 1  is open, the tracking coil data can be transmitted to the MR Scanner receiver channel  10   ch . The C 1  and C 2  capacitors are large DC blocking capacitors. C 4  is optional but can allow for fine tuning (typically between about 2-12 picofarads) to account for variability (tolerance) in components. It is contemplated that other tuning circuits and/or tracking signal stabilizer configurations can be used. The tuning circuit  83  can reside in the intrabody device  80  (such as in a handle (e.g.,  440 ,  FIG. 31 ) or other external portion), in a connector that connects the coil  82   c  to the respective MRI scanner channel  10   ch , in the Scanner  10 S, in an interface box  86  ( FIG. 2 ), a patch panel  250  and/or the circuit  83  can be distributed among two or more of these or other components. 
     In some embodiments, each tracking coil  82   c  can be connected to a coaxial cable  81  having a length to the diode via a proximal circuit board (which can hold the tuning circuit and/or a decoupling/matching circuit) sufficient to define a defined odd harmonic/multiple of a quarter wavelength at the operational frequency of the MRI Scanner  10 S, e.g., λ/4, 3λ/4, 5λ/4, 7λ/4 at about 123.3 MHz for a 3.0T MRI Scanner. This length may also help stabilize the tracking signal for more precise and speedy localization. The tuned RF coils can provide stable tracking signals for precise localization, typically within about 1 mm or less. Where a plurality (e.g., two closely spaced) of adjacent tracking coils are fixed on a substantially rigid material, the tuned RF tracking coils can provide a substantially constant spatial difference with respect to the corresponding tracking position signals. 
     Additional discussion of tracking means and ablation catheters can be found in U.S. Pat. No. 6,701,176, and U.S. Provisional Application Ser. No. 61/261,103, the contents of which are hereby incorporated by reference as if recited in full herein. Exemplary catheters will be discussed further below. 
       FIGS. 5-8  illustrate a flexible (steerable) ablation catheter  80  having an ablation electrode, RF tracking coils, and a thermistor that can be electrically connected to an interface circuit of an MRI scanner by electrical lead assemblies of the present invention. The illustrated ablation catheter  80  includes an elongated flexible housing or shaft  402  having at least one lumen  404  ( FIG. 7 ) therethrough and includes opposite distal and proximal end portions  406 ,  408 , respectively. The distal end portion  406  includes an ablation tip  410  having an ablation electrode  410   e  ( FIG. 6 ) for ablating target tissue. A pair of RF tracking coils individually identified as  412 ,  414 , and which are equivalent to coils  82   c  of  FIGS. 2-3 , are positioned upstream from the ablation tip  410 , as illustrated. The proximal end portion  408  of the catheter  80  is operably secured to a handle  440 . 
       FIG. 6  is an enlarged partial perspective view of the distal end portion  406  of the ablation catheter  80  of  FIG. 5 . The distal end portion  406  has an ablation tip  410  and two RF tracking coils  412 ,  414 . The RF tracking coils  412 ,  414  are positioned upstream and adjacent the ablation tip  410  in spaced-apart relationship. The RF tracking coils  412 ,  414  are each electrically connected to a respective channel of an MRI scanner for tracking the location of the catheter  80  in 3-D space, via respective cables (e.g., coaxial cables)  416 ,  418  ( FIG. 7 ) extending longitudinally through the catheter shaft lumen  404  and terminating at an electrical connector interface ( 450 ,  FIG. 9 ) that is located, for example, in the handle  440 . 
     In the illustrated embodiment, the ablation tip  410  includes an electrode  410   e  that is connected to an RF wire  420  ( FIG. 8 ) that extends longitudinally within the lumen  404  to an electrical connector interface ( 450 ,  FIG. 9 ), for example, within the handle  440  and that connects the ablation electrode  410   e  to an RF generator. The RF ablation electrode  410   e  is formed from an MRI-compatible conductive material capable of receiving RF energy and ablating tissue. 
     Referring to  FIG. 8 , the catheter  80  includes a thermistor  430  that has a lead  430 L that extends longitudinally within the shaft lumen  404  from the ablation tip  410  to an electrical connector interface, typically at the proximal end of the ablation catheter, for example, in the handle  440  ( FIG. 5 ). The thermistor  430  is configured to measure temperature at and/or adjacent to the ablation tip  410 . The thermistor  430  can be configured to allow temperature to be monitored during ablation and/or at other times. 
       FIG. 9  is a perspective view of the handle  440  of the device  80  illustrated in  FIG. 5 . The handle  440  has a main body portion  441  with opposite distal and proximal end portions  442 ,  444 . A cover (not shown) is removed from the handle main body portion  441  to illustrate the termination of the various conductors (i.e., from the RF tracking coils, ablation electrode, sensing electrodes, thermistor) extending into the handle  440  from the shaft lumen  404  at an electrical connector interface  450  (shown as PCB). Electrical connector interface  450  is electrically connected to an adapter  452  at the proximal end  444  of the handle  440 . Adapter  452  is configured to receive one or more cables that connect the ablation catheter  80  to an MRI scanner  10 S and that facilitate operation of the RF tracking coils  412 ,  414 ,  422 ,  424 . Adapter  452  also is configured to connect the ablation tip  410  to an ablation source. 
       FIGS. 10A-10B  illustrate a flexible (steerable) ablation catheter  80  having an ablation electrode  710   e , RF tracking coils  712 ,  714 ,  716 ,  718 , and sensing electrodes  708   a - 708   d  that can be electrically connected to an interface circuit of an MRI scanner by electrical lead assemblies of the present invention. The illustrated ablation catheter  80  includes an elongated flexible housing or shaft  702  with opposite distal and proximal end portions, only the distal end portion  706  is illustrated. The proximal end portion of the catheter  80  is operably secured to a handle, as is well known. The distal end portion  706  includes a plurality of electrodes  708   a - 708   d  for sensing local electrical signals or properties arranged in spaced-apart relationship, as illustrated. The RF tracking coils  712 ,  714 ,  716 ,  718  are equivalent to coils  80   c  in  FIGS. 2-3  and coils  412 ,  414 ,  422 ,  424  in  FIG. 5 . Tracking coil  712  is positioned between the first and second electrodes  708   a ,  708   b , and tracking coil  714  is positioned between the third and fourth electrodes  708   c ,  708   d , as illustrated. 
       FIG. 11  is a schematic illustration of the distal end portion  1106  of an ablation catheter  80  that includes an ablation tip  1110  having an ablation electrode  1110   e  (equivalent to  410   e  of  FIG. 6 and 710   e  of  FIGS. 10A-10B ) for ablating target tissue, RF tracking coils  1112 ,  1114 ,  1122 ,  1124  (equivalent to coils  80   c  in  FIGS. 2-3 , coils  412 ,  414 ,  422 ,  424  in  FIG. 5 , and coils  712 ,  714 ,  716 ,  718  in  FIGS. 10A-10B ), EGM (electrogram) sensing electrodes  1082  (equivalent to electrodes  708   a - 708   d  in  FIGS. 10A-10B ) positioned between the first and second tracking coils  1112 ,  1114 , a sensing electrode  1082  positioned between the tracking coil  1114  and the tracking coil  1122 , and a thermistor  1512 . A conductor C 1  connects the ablation electrode  1110   e  to an RF generator. Electrical conductors (e.g., coaxial cables) C 2  connect the tracking coils  1112 ,  1114 ,  1122 ,  1124  to the electrical interface (e.g.,  450 ,  FIG. 9 ) of an MRI scanner, electrical conductors C 3  connect the sensing electrodes  1082  to the electrical interface, and electrical connector C 4  connects the thermistor  1512  to the electrical interface, as described above. 
     As described above, the ablation electrode  1110   e  delivers RF energy to tissue to cause thermal ablation of tissue. The sensing electrodes  1082  are utilized to measure cardiac potentials. The thermistor  1512  is utilized to measure the temperature of the ablation electrode  1110   e  and/or temperature of local tissue. The RF tracking coils  1112 ,  1114 ,  1122 ,  1124  generate NMR signals so that the MRI scanner can obtain location information of the one or more coils in a 3D MRI space. These electrodes, thermistors and tracking coils are connected by various conductors C 1 -C 4 . 
     Referring to  FIGS. 12A-12B, 13A-13D, 14A-14D, 15A-15B, and 16A-16B , various electrical lead assemblies that can be formed from the conductors C 1 -C 4  of  FIG. 11  and that can attenuate RF coupling and local temperature rise are illustrated.  FIG. 12A  illustrates an electrical lead subassembly  1500  having conductors connected to an ablation electrode  1110   e , one or more sensing electrodes  1082 , and a thermistor  1512  of an MRI-compatible ablation catheter (e.g.,  80 ,  FIG. 5 ), according to some embodiments of the present invention. The electrical lead subassembly  1500  includes a first insulated conductor C 1 , multiple second insulated conductors C 3 , and a third insulated conductor C 4 . As shown in  FIG. 12B , conductor C 1  has a series of alternating single layer coil sections C 1a  and multi-layer coil sections C 1b . Conductor C 1  is connected at one end to the ablation electrode  1110   e  and to an electrical interface (e.g.,  450 ,  FIG. 9 ) at the opposite end, as described above. In some embodiments, conductor C 1  may include a plurality of individually insulated conductors, and may be co-wound insulated conductors. Conductor C 1  can have low resistivity to carry high current for ablation. The multi-layer sections C 1b  of conductor C 1  can be adjusted such that they have an impedance of higher than 50 ohms/cm at NMR frequency. The impedance of each multilayer section C 1b  is a function of pitch (number of co-wound conductors), length of the multi-layer coil section and diameter of the coil and conductors. 
     As illustrated in  FIG. 12A , each conductor C 3  is connected at one end to a respective sensing electrode  1082  and at an opposite end to an electrical interface (e.g.,  450 ,  FIG. 9 ), as described above. The conductor C 4  is connected at one end to a thermistor  1512  and at an opposite end to the electrical interface (e.g.,  450 ,  FIG. 9 ). In some embodiments, each conductor C 3  may include a plurality of individually insulated conductors, and may be co-wound insulated conductors. Similarly, conductor C 4  may include a plurality of individually insulated conductors, and may be co-wound insulated conductors. As shown, each conductor C 3  has a respective series of alternating single layer coil sections C 3a  and multi-layer coil sections C 3b  (e.g., typically tri-layer configurations). Similarly, conductor C 4  has a respective series of alternating single layer coil sections C 4a  and multi-layer coil sections C 4b . The multi-layer sections C 3b  of each conductor C 3  can be adjusted such that they have a selected impedance (e.g., an impedance greater than 50 ohms/cm at an NMR frequency). Similarly, the multi-layer sections C 4b  of conductor C 4  can be adjusted such that they have a selected impedance (e.g., an impedance greater than 50 ohms/cm at an NMR frequency). 
     As illustrated in  FIG. 12A , each multi-layer coil section C 3b  of each conductor C 3  is coiled around a respective single layer coil section C 1a  of conductor C 1  and each single layer coil section C 3a  of each conductor C 3  is coiled around a respective multi-layer coil section C 1b  of conductor C 1 . Similarly, each multi-layer coil section C 4b  of conductor C 4  is coiled around a respective single layer coil section C 1a  of conductor C 1  and each single layer coil section C 4a  of conductor C 4  is coiled around a respective multi-layer coil section C 1b  of conductor C 1 . This configuration allows the electrical lead subassembly  1500  to have a substantially constant diameter D 1  along this segment (typically the entire length), as illustrated. 
     Each of the multi-layer coil sections C 1b , C 3b , C 4b  serves as a respective current suppression module (CSM) and can have an impedance greater than about 50 ohms per centimeter at a nuclear magnetic resonance (NMR) operating frequency of an MRI scanner. In some embodiments, each of the multi-layer coil sections C 1b , C 3b , C 4b  have three layers of windings. For example, each multi-layer coil section C 1b , C 3b , C 4b  includes a first coiled layer that extends in a first lengthwise direction for a first physical length, a second coiled layer coiled around the first coiled layer in a substantially opposing lengthwise direction for a second physical length, and a third coiled layer coiled around the second coiled layer in the first lengthwise direction for a third physical length. In some embodiments, the first layer may be coiled left to right, the second layer coiled right to left on top of the first layer, and the third layer may be coiled left to right on top of the first and second layers. The coils in the first, second and third layers may have the same pitch or may have a different pitch. See, for example, PCT Publication No. WO 2008/115383 entitled “Methods and Apparatus for Fabricating Leads with Conductors and Related Flexible Lead Configurations”, which is incorporated herein by reference in its entirety. 
     Referring now to  FIGS. 13A-13D , a second electrical lead subassembly  1502  configured to be attached to one or more catheter RF tracking coils  1112 ,  1114 ,  1122 ,  1124  is illustrated. The second electrical lead subassembly  1502  includes a separate conductor (or separate plurality of conductors) C 2  for each respective RF tracking coil. For example,  FIG. 13A  illustrates the second electrical lead subassembly  1502  for a single RF tracking coil  1112 ,  FIG. 13B  illustrates the second electrical lead subassembly  1502  for two RF tracking coils  1112 ,  1114 ,  FIG. 13C  illustrates the second electrical lead subassembly  1502  for three RF tracking coils  1112 ,  1114 ,  1122 , and  FIG. 13D  illustrates the second electrical lead subassembly  1502  for four RF tracking coils  1112 ,  1114 ,  1122 ,  1124 . Each conductor C 2  includes at least one coiled section C 2a  typically configured to have a complex impedance of greater than, for example, 100 ohms at the NMR frequency, although other impedance values can be obtained. Conductor C 2  may be one or more coaxial cables or one or more twisted wire pairs. 
     Depending on the overall length of the second electrical lead subassembly  1502 , each conductor C 2  may have one or more coiled sections C 2a . Typically the length of each coiled section C 2a  is about a quarter (¼) wavelength at the NMR frequency. In the illustrated embodiments of  FIGS. 13A-13D , each conductor C 2  includes a plurality of spaced-apart coiled sections C 2a . Also as illustrated in  FIGS. 13B-13D , if two or more RF tracking coils are utilized, the respective conductors C 2  of the different RF tracking coils are arranged such that the coiled sections C 2a  are in adjacent, axial relationship with each other. As illustrated in  FIGS. 13A-13D , the straight sections C 2b  of the conductors C 2  are positioned to the outside of each coiled section C 2a . 
     In the illustrated embodiment of  FIGS. 13A-13D , the coils in each coiled section C 2a  are wound left to right. However, embodiments of the present invention are not limited to the illustrated configuration of  FIGS. 13A-13D . For example, as illustrated in  FIGS. 14A-14D , the coils in each coiled section C 2a  can be wound right to left. In the embodiment of  FIGS. 14A-14D , each conductor C 2  has a straight forward section C 2b  followed by a coiled back section (i.e., coiled section C 2a  that is wound right to left) followed by another forward straight section C 2b . The impedance of this configuration (i.e., the first straight forward section, the coiled back section, and the second straight forward section) may be, for example, higher than 100 ohms at the NMR frequency. However, the impedance of this configuration may have other values as well. For example, the impedance of this configuration may be, for example, higher than 50 ohms at the NMR frequency, higher than 200 ohms at the NMR frequency, etc. 
     The inner diameter D i  of the coiled sections C 2a  in  FIGS. 13A-13D  and  FIGS. 14A-14D  is larger than the outer diameter D 1  of the first electrical lead subassembly  1500  of  FIG. 12A . This is such that the electrical lead subassembly  1500  of  FIG. 12A  can be inserted within the coiled sections of the second electrical lead subassembly  1502  to form electrical lead assembly  1504 , as illustrated in  FIGS. 15A and 15B . In  FIG. 15A , the second electrical lead subassembly  1502  has the configuration of  FIG. 13D  (i.e., with the coils in each coiled section C 2a  wound left to right). In  FIG. 15B , the second electrical lead subassembly  1502  has the configuration of  FIG. 13D  (i.e., with the coils in each coiled section C 2a  wound right to left). 
     Referring to  FIG. 16A , an elongate electrical lead subassembly  1500 ′ for an MRI-compatible medical device, such as an ablation catheter, according to other embodiments of the present invention is illustrated. The illustrated electrical lead subassembly  1500 ′ is an alternative to the subassembly  1500  of  FIG. 12A . The illustrated subassembly  1500 ′ includes a conductor C 1  that is connected to an ablation electrode  1110   e , multiple conductors C 3  that are connected to respective sensing electrodes  1082 , and a conductor C 4  that is connected to a thermistor  1512 . As illustrated in  FIG. 16B , the conductor C 1  has first and second multi-layer coil sections C 1b  with a single layer coil section C 1a  therebetween. The conductors C 3  and C 4  each have a multi-layer coil section C 3b , C 4b  that is coiled around the single layer coil section C 1a  of the conductor C 1 . This configuration allows the electrical leas subassembly  1500 ′ to have a substantially constant diameter D 1  along this segment length (typically substantially the entire length), as illustrated. 
     In the drawings and specification, there have been disclosed embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims. Thus, the foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.