Patent Publication Number: US-11647935-B2

Title: Masked ring electrodes

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 62/536,369, filed 24 Jul. 2017, the entire disclosure of which is incorporated by reference herein. 
    
    
     BACKGROUND 
     a. Field 
     The present disclosure relates to electrophysiology catheters. In particular, the instant disclosure relates to an electrophysiology catheter having one or more partially insulated or masked electrodes that reduce or eliminate far field effects on electrical signals indicative of tissue in a region of interest. 
     b. Background 
     Electrophysiology (EP) mapping catheters are used to generate electrophysiology maps of tissue in a region of interest. The EP mapping data may be used, for example, in the diagnosis and treatment of tissues within a body. For example, EP maps of heart tissue can be used to guide ablation catheters which are used to convey an electrical stimulus to a region of interest within the heart and create tissue necrosis. Ablation catheters may be used to necrose heart tissue to correct conditions such as atrial and ventricular arrhythmias (including, but not limited to, ectopic atrial tachycardia, atrial fibrillation, atrial flutter and ventricular tachycardias). In addition to guiding ablation catheters, EP maps can also be used to evaluate the effectiveness of ablation therapy, or to locate ectopic sources or a critical isthmus. 
     An EP mapping catheter may include one or more electrodes at a distal end that samples electrical activity in tissue. Many EP mapping catheters have a relatively large number of electrodes to enable sampling over a relatively wide area of interest and reduce procedure time. Referring to  FIG.  1   , one type of EP mapping catheter  10  in use today includes a collapsible and expandable basket electrode assembly  12  disposed at the distal end of the catheter  10 . The basket electrode assembly  12  assumes a compressed state as the catheter is maneuvered through an introducer sheath to a region of interest in the body and an expanded state once the catheter reaches the region of interest and emerges from the sheath. The basket electrode assembly  12  includes a plurality of splines  14  on which un-insulated or un-masked electrodes  16  are disposed. The splines  14  are coupled together at proximal and distal ends and bow outward (i.e. a bowed shape) when the basket assembly  12  is in an expanded state. 
     The foregoing discussion is intended only to illustrate the present field and should not be taken as a disavowal of claim scope. 
     BRIEF SUMMARY 
     The present disclosure relates to an electrophysiology catheter. In particular, the instant disclosure relates to an electrophysiology catheter having a plurality of partially-masked electrodes which, when placed in contact with the surface of a tissue of interest, the conductive material of the partially-masked electrode is not in contact with the blood pool. 
     A partially-masked electrode, in accordance with at least one embodiment of the present disclosure, includes a conductive material and an insulated coating having an outer surface. The insulated coating defines a contoured opening that exposes or reveals an area of the conductive material, wherein the contoured opening has an upper perimeter at the outer surface of the insulated coating. The upper perimeter of the opening defines an imaginary boundary area above the exposed area of the conductive material beyond which no part of the exposed conductive material extends. 
     A catheter in accordance with at least another embodiment of the present disclosure includes an elongate, deformable shaft comprising a proximal end and a distal end. The catheter further includes a distal tip assembly coupled to said distal end of said shaft, said distal tip assembly comprising a plurality of partially-masked electrodes disposed thereon. At least one of the plurality of partially-masked electrodes comprises a conductive material and an insulated coating having an outer surface. The insulated coating defines a contoured opening that exposes an area of the conductive material, wherein the contoured opening has an upper perimeter at the outer surface of the insulated coating. The upper perimeter of the opening defines an imaginary boundary area above the exposed area of the conductive material beyond which no part of the exposed conductive material extends. 
     A catheter in accordance with at least another embodiment of the present disclosure includes an elongate, deformable shaft having a proximal end and a distal end. The catheter further includes a distal tip assembly coupled to said distal end of said shaft, said distal tip assembly comprising a plurality of partially-masked electrodes disposed thereon. At least one of the plurality of partially-masked electrodes comprises a conductive material and an insulated coating having an outer surface, wherein the insulated coating defines a contoured opening that exposes or reveals an area of the conductive material. The contoured opening has an upper perimeter at the outer surface of the insulated coating. When the upper perimeter of the insulated coating is placed in contact with a tissue of interest, wherein the tissue of interest is proximate a blood pool, the insulated coating creates a seal between the blood pool and the contoured opening so that no blood in the blood pool can contact the conductive material. 
     A catheter in accordance with at least another embodiment of the present disclosure includes an elongate, deformable shaft having a proximal end and a distal end. The catheter further includes a basket electrode assembly coupled to the distal end of the shaft. The basket electrode assembly comprises a proximal end and a distal end, and is configured to assume a compressed state and an expanded state. The basket catheter assembly includes a first spline comprising a plurality of partially-masked electrodes disposed thereon. At least one of the plurality of partially-masked electrodes comprises a conductive material and an insulated coating having an outer surface, wherein the insulated coating defines a contoured opening that exposes or reveals an area of the conductive material. The contoured opening has an upper perimeter at the outer surface of the insulated coating. The upper perimeter of the opening defines an imaginary boundary area above the exposed area of the conductive material beyond which no part of the exposed conductive material extends. 
     A catheter in accordance with at least another embodiment of the present disclosure includes an elongate, deformable shaft comprising a proximal end and a distal end and a flexible tip portion located adjacent to the distal end of the shaft. The flexible tip portion comprises a flexible framework and a plurality of partially-masked electrodes disposed on the flexible framework and forms a flexible array of partially-masked electrodes adapted to conform to tissue. At least one of the plurality of partially-masked electrodes comprises a conductive material and an insulated coating having an outer surface, wherein the insulated coating defines a contoured opening that exposes or reveals an area of the conductive material. The contoured opening has an upper perimeter at the outer surface of the insulated coating. The upper perimeter of the opening defines an imaginary boundary area above the exposed area of the conductive material beyond which no part of the exposed conductive material extends. 
     A partially-masked electrode in accordance with at least another embodiment of the present disclosure includes a conductive material and an insulated coating having an outer surface. The insulated coating defines a contoured opening that exposes or reveals an area of the conductive material, wherein the contoured opening has an upper perimeter at the outer surface of the insulated coating. When the upper perimeter of the insulated coating is placed in contact with a tissue of interest, wherein the tissue of interest is proximate a blood pool, the insulated coating creates a seal between the blood pool and the contoured opening so that no blood in the blood pool can contact the conductive material. 
     A catheter in accordance with at least another embodiment of the present disclosure includes an elongate, deformable shaft having a proximal end and a distal end. The catheter further includes a basket electrode assembly coupled to the distal end of the shaft. The basket electrode assembly comprises a proximal end and a distal end and is configured to assume a compressed state and an expanded state and includes a first spline comprising a plurality of partially-masked electrodes disposed thereon. At least one of the plurality of partially-masked electrodes comprises a conductive material and an insulated coating having an outer surface, wherein the insulated coating defines a contoured opening that exposes or reveals an area of the conductive material. The contoured opening has an upper perimeter at the outer surface of the insulated coating. When the upper perimeter of the insulated coating is placed in contact with a tissue of interest, wherein the tissue of interest is proximate a blood pool, the insulated coating creates a seal between the blood pool and the contoured opening so that no blood in the blood pool can contact the conductive material. 
     A catheter in accordance with at least another embodiment of the present disclosure includes an elongate, deformable shaft comprising a proximal end and a distal end and a flexible tip portion located adjacent to the distal end of the shaft. The flexible tip portion comprises a flexible framework and a plurality of partially-masked electrodes disposed on the flexible framework and forming a flexible array of partially-masked electrodes adapted to conform to tissue. At least one of the plurality of partially-masked electrodes comprises a conductive material and an insulated coating having an outer surface, wherein the insulated coating defines a contoured opening that exposes or reveals an area of the conductive material. The contoured opening has an upper perimeter at the outer surface of the insulated coating. When the upper perimeter of the insulated coating is placed in contact with a tissue of interest, wherein the tissue of interest is proximate a blood pool, the insulated coating creates a seal between the blood pool and the contoured opening so that no blood in the blood pool can contact the conductive material. 
     A partially-masked electrode, in accordance with at least another embodiment of the present disclosure, includes an insulated coating that is selected and configured to allow the reception of a localization signal by a conductive material of the partially-masked electrode. The insulated coating is selected and configured to prevent the reception of at least a significant amount of a far field signal by the conductive material. 
     A catheter in accordance with at least another embodiment of the present disclosure includes an insulated coating on at least one partially-masked electrode that is selected and configured to allow the reception of a localization signal by a conductive material of the partially-masked electrode. The insulated coating on the at least one partially-masked electrodes configured to prevent the reception of at least a portion of a far field signal by the conductive material. 
     A partially-masked electrode in accordance with various embodiments of the present disclosure wherein the insulated coating is selected and configured to allow the reception of a localization signal by the conductive material; and wherein the insulated coating is configured to prevent the reception of at least a portion of a far field signal by the conductive material. 
     A catheter in accordance with various embodiments of the present disclosure, wherein the insulated coating of at least one of the partially-masked electrodes configured to receive a localization signal through the conductive material; and wherein the insulated coating of at least one of the partially-masked electrodes is configured to prevent the reception of at least a portion of a far field signal via the conductive material. 
     A method of using a catheter in accordance with various embodiments of the present disclosure, the method comprising tracking the location of at least one of the partially-masked electrodes within a body of a patient, wherein the insulated coating of at least one of the partially-masked electrodes is configured to receive a localization signal by the conductive material; and wherein the insulated coating of at least one of the partially-masked electrodes is configured to prevent the reception of at least a portion of a far field signal by the conductive material; and placing the upper perimeter of the insulated coating of at least one of the partially-masked electrodes in contact with a tissue of interest in the body of the patient, the tissue of interest being proximate a blood pool, such that the insulated coating creates a seal between the blood pool and the contoured opening to inhibit the receipt of the far field signal in the blood pool. 
     A method of using a catheter in accordance with various embodiments of the present disclosure, the method comprising: tracking the location of one of a plurality of partially-masked electrodes within a body of a patient; wherein the insulated coating of the partially-masked electrode is configured to receive a localization signal by the conductive material; and wherein the insulated coating of the partially-masked electrode is configured to prevent the reception of at least a portion of a far field signal by the conductive material; placing the upper perimeter of the insulated coating of the partially-masked electrode in contact with a tissue of interest at a first location in the body of the patient, the tissue of interest being proximate a blood pool, such that the insulated coating creates a seal between the blood pool and the contoured opening to inhibit the receipt of the far field signal in the blood pool; and receiving, via the partially-masked electrode, a first local electrical signal from the first location on the tissue of interest at the contoured opening, the first local electrical signal having a first magnitude, wherein as a result of the seal between the blood pool and the contoured opening the first local electrical signal comprises little or no far field signal. 
     The foregoing and other aspects, features, details, utilities, and advantages of the present disclosure will be apparent from reading the following description and claims, and from reviewing the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an isometric view of a prior art electrophysiology mapping catheter. 
         FIG.  2    is a diagrammatic view of an electrophysiology catheter according to an embodiment of the disclosure. 
         FIG.  3    is an enlarged isometric view of a distal tip assembly of the electrophysiology catheter of  FIG.  2    comprising a basket electrode assembly. 
         FIG.  4    is a cross-sectional view of a spline comprising part of the basket electrode assembly of  FIG.  3   , taken along line  4 - 4  in  FIG.  3   . 
         FIG.  5    is an enlarged side view of the region in the dashed circle labeled “ FIG.  5   ” in  FIG.  3   , depicting a partially masked electrode on a section of a spline of the basket electrode assembly depicted in  FIG.  3   . 
         FIG.  6    is an enlarged isometric view of the region in dashed circle  5  in  FIG.  3   . 
         FIG.  7    is an enlarged, cross-sectional view of the partially-masked electrode depicted in  FIGS.  5  and  6   , taken along line  7 - 7  of  FIG.  5   . 
         FIG.  8    is a cross-sectional side view of a partially-masked electrode positioned against a tissue of interest. 
         FIG.  9    is a cross-sectional view taken along line  9 - 9  of  FIG.  5   , with the partially-masked electrode positioned against a tissue of interest. 
         FIG.  10 A  is a graphical user interface display showing measured electrocardiogram voltages of a prior art un-masked electrode and a partially-masked electrode, according to various embodiment of the disclosure. 
         FIG.  10 B  is a graph showing the measured capacitance frequency response of an acrylated urethane masking material, according to an embodiment of the disclosure. 
         FIG.  10 C  is a graph showing the measured impedance of an acrylated urethane masking material, according to an embodiment of the disclosure. 
         FIG.  11    is a top plan view of a distal tip assembly comprising a planar array of partially-masked electrodes, according to another embodiment of the disclosure. 
         FIG.  12    is a top plan view of a distal tip assembly comprising a planar array of partially-masked electrodes, according to another embodiment of the disclosure. 
         FIG.  13    is an isometric view of a distal tip assembly comprising a basket electrode assembly having partially-masked flex circuit electrodes, according to another embodiment of the disclosure. 
         FIG.  14    is an enlarged view of the region in the dashed circle labeled “ FIG.  14   ” in  FIG.  13   , depicting a partially-masked electrode on a section of a spline of the basket electrode assembly depicted in  FIG.  13   . 
         FIG.  15    is an enlarged, cross-sectional view of the partially-masked flex circuit electrode depicted in  FIGS.  13  and  14    taken along line  15 - 15  of  FIG.  14   . 
         FIG.  16    is a cross-sectional view of a partially-masked flex circuit electrode of  FIGS.  13 - 15    positioned against a tissue of interest. 
         FIG.  17    is a plan view of a partially-masked flex circuit electrode according to another embodiment of the disclosure. 
         FIG.  18    is a cross-sectional view of a partially-masked flex circuit electrode of  FIG.  17    taken along line  18 - 18  of  FIG.  17   . 
         FIG.  19    depicts a plan view of a partially-masked flex circuit electrode according to another embodiment of the disclosure. 
         FIG.  20    is a cross-sectional view of the partially-masked flex circuit electrode of  FIG.  19    taken along line  20 - 20 . 
         FIG.  21    depicts a plan view of a partially-masked flex circuit electrode according to another embodiment of the disclosure. 
         FIG.  22    depicts a cross-sectional view of the partially-masked flex circuit electrode of  FIG.  21    taken along line  22 - 22 . 
         FIG.  23    is a flowchart illustrating a method of using catheters having partially-masked electrodes according to various embodiments of the disclosure. 
         FIGS.  24 A- 24 B  are flowcharts illustrating another method of using catheters having partially-masked electrodes according to various embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Typical catheter-based electrodes have predominantly been cylindrically-shaped (e.g., rings, tips, or spots). These electrodes have been used to take electrical signal measurements in a tissue of interest, for example the heart. As these electrodes are in the blood pool (or conductive pool), the electrodes will pick up various electrical signals in the heart, including signals proximal to the electrodes as well as signals distal the electrodes, the latter generally called far field effects. When an electrode is in contact with healthy tissue, a more distinct and/or stronger electrical signal is measured by the electrode. The electrical signal from the tissue is often referred to as a local source. However, in use, only a portion of a typical electrode, such as electrode  16  shown in  FIG.  1   , is in direct contact with the tissue of interest. Most of the electrode  16  is exposed to the blood pool and therefore the resulting output signal of the electrode  16  is a combination of local and far field effects. That is, the far field effects create noise in the received signal which makes it difficult to identify, locate, and/or diagnose unhealthy tissue. 
     Typically, the method to locate, identify, and/or diagnose unhealthy regions of tissue, such as diseased or damaged tissue (e.g., a lesion) includes sensing one or more electrophysiological characteristics from the tissue. However, the local electrical signals from unhealthy tissue are often much weaker than the local electrical signals from healthy tissue. In some instances, the magnitude of the local electrical signals from unhealthy tissue is about equal to or less than the far field magnitude. Therefore, it becomes difficult to distinguish between the far field and local effects. That is, the signal-to-noise ratio when sensing on or near unhealthy tissue may approach 1. The poor signal fidelity and/or low magnitude at the unhealthy tissue of interest makes it difficult to determine, for example, what is a boundary edge or conduction path/gap between unhealthy tissue and healthy tissue. 
     Additionally, as investigations and research in industry progress down the path of smaller electrode sizes and tighter physical positioning to increase the resolution for locating and identifying unhealthy tissue, aspects of the present disclosure are directed to the use of printed or flex circuit electrodes to increase resolution. 
     Some benefits of printed or flex circuit electrodes are that they can be manufactured via batch fabrication, which reduces costs, and allow for the design of small and/or close electrodes and associated electrical connections into a smaller space. In addition, the printed and/or flex circuit electrodes tend to be one-sided electrodes. That is, they are only conductive on one side, and thereby minimize exposure of the electrode to the blood pool enhancing signal fidelity. However, the focus of the industry so far has been on size and/or spacing optimization and not on tissue contact and/or far field isolation. 
     One disadvantage of printed or flex circuit-based electrodes and traces is the increase impedance to that of a typical ring electrode. Increased impedance is detrimental to impedance based location systems (e.g., higher signal-to-noise ratio), and may degrade the accuracy of sensed biosignals (ECG). These issues may also result in the increased noise from the printed or flex circuit electrodes as compared to typical ring electrodes, and may negate some of the isolation benefits of the one-sided structure of the printed or flex circuit electrode. 
     Additionally, printed or flex circuit electrodes tend to be planar and relatively smooth. Both of these qualities result in poor contact with tissue by the printed or flex circuit electrodes which may allow some blood pool contact and far field influence into a sensed electrophysiology signal. 
     In accordance with various embodiments of the present disclosure, catheters including electrodes which are partially-masked with an insulating material facilitate improved EP diagnostics. The insulating material of the partially-masked electrodes creates a seal between the blood pool and the conductive material of the partially-masked electrode which reduces or eliminates the reception of the far field effects by the partially-masked electrode, making it easier to locate and diagnose unhealthy tissue. 
     Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views,  FIG.  2    illustrates one embodiment of an electrophysiology catheter  18  having a plurality of partially-masked electrodes in accordance with the present disclosure. Catheter  18  is provided for use in generating an electrophysiological map of tissue and, in particular, cardiac tissue. It should be understood, however, that catheter  18  may be used in conjunction with various tissue types. Catheter  18  may include a cable connector or interface  20 , a handle  22 , a shaft  24  having a proximal end  26  and a distal end  28 , and a distal tip assembly such as the basket electrode assembly  30  depicted in  FIG.  2   . Catheter  18  may also include other conventional components not illustrated herein such as deflection mechanisms, additional electrodes and corresponding conductors or leads. 
     Connector  20  provides mechanical and electrical connection(s) for cables extending from an electronic control unit (ECU) (not shown) or similar device that is configured to receive signals generated by basket electrode assembly  30 . Connector  20  may be conventional in the art and be disposed at the proximal end  26  of catheter  18 . 
     Handle  22  provides a location for the physician to hold catheter  18  and may further provides a means for steering or guiding shaft  24  within the body. For example, handle  22  may include means to change the length of a guide wire extending through catheter  18  to distal end  28  of shaft  24  to steer distal end  28  and, thus, shaft  24 . Handle  22  may also be conventional in the art and it will be understood that the construction of handle  22  may vary. 
     Shaft  24  is an elongate, deformable member configured for movement within the body. Shaft  24  supports electrode assembly  30 , associated conductors, and, in some embodiments, additional electronics used for signal processing or conditioning. Shaft  24  may also be configured to permit transport, delivery, and/or removal of fluids (including irrigation fluids and bodily fluids), medicines, and/or surgical tools or instruments. Shaft  24  may be made from conventional materials such as polyurethane and defines one or more lumens configured to house and/or transport electrical conductors, fluids, medicines, guide wires or surgical tools or instruments. Shaft  24  may be introduced into a blood vessel or other structure within the body through an introducer sheath. Shaft  24  may then be steered or guided through the body to a desired location such as tissue in a region of interest using guide wires or pull wires or other means known in the art including remote control guidance systems. 
     Referring now to  FIGS.  3  and  4   , basket electrode assembly  30  provides a means for conducting an electrophysiological study of tissue. Assembly  30  may be coupled to a distal end of shaft  24  and includes a proximal end  32  and a distal end  34 . Assembly  30  may include a plurality of splines  36  on which electrodes are disposed and that form an electrode “basket” that is configured to assume a compressed state and an expanded state. Assembly  30  may assume the expanded state in the absence of an extraneous force acting on the assembly  30  (i.e., assembly  30  may be biased to the expanded state by, for example, nickel titanium memory alloy components) or may be urged to the expanded state through mechanical means (e.g., wires that are pulled or pushed) or by an internal balloon that can be expanded within the basket electrode assembly  30 . Assembly  30  may assume the compressed state, for example, as catheter  18  is maneuvered through an introducer sheath within the body to the region of interest and assume the expanded state upon emerging from a distal end of the sheath. Splines  36  are configured to support electrodes in a predetermined configuration to allow contact and/or non-contact mapping of electrical activity in tissue. Referring to  FIG.  4   , each spline  36  may include a tubular body  38 , means, such as wire  40 , for supporting (and biasing) body  38  to assume a predetermined shape, one or more partially-masked electrodes  42  (as shown in  FIG.  3   ), and associated conductors  44 . Although a particular embodiment for a spline, e.g., spline  36 , is illustrated herein, it should be understood that spline(s) may be constructed in a variety of ways. In one embodiment, for example, one or more splines may include a flexible circuit as described and illustrated in U.S. patent application Ser. No. 12/958,992 (published as United States Patent Application Publication no. 2012/0143298 A1), the entire disclosure of which is incorporated by reference as though fully set forth herein. Additional embodiments of splines and/or basket electrode assemblies may be found described in one or more of U.S. patent application Ser. No. 13/072,357 (published as United States Patent Application Publication No. US 2011/0213231 A1) and U.S. patent application Ser. No. 13/340,760 (published as United States Patent Application Publication No. US 2013/0172715), the entire disclosures of which are incorporated by reference as though fully set forth herein. 
     Body  38  provides structural support for partially-masked electrodes  42  and insulates conductors  44  from bodily fluids and other elements. Referring to  FIG.  4   , body  38  is tubular and may be annular in shape. It should be understood, however, that the shape of body  38  may vary. Body  38  may be made from conventional polymeric materials such as polyurethane, and nylon or thermoplastic elastomers such as the elastomer sold under the registered trademark “PEBAX” by Arkema, Inc. and reinforcements such as metallic braids. Body  38  may define a central lumen  46  extending between proximal and distal ends  48 ,  50  (as shown in  FIG.  3   ) of body  38  and configured to allow passage of wire  40  and conductors  44 . It should be understood, however, that body  38  may alternatively define one or more channels each configured to receive one of wire  40  or a conductor  44 . In the illustrated embodiment, wire  40  is illustrated at the center of lumen  46  with conductors  44  disposed circumferentially around wire  40 . It should be understood, however, that the relative arrangement of wire  40  and conductors  44  within lumen  46  may vary. 
     Wire  40  is provided to support and bias body  38  to assume a predetermined shape. Wire may be made from a shape memory alloy such as nitinol (nickel titanium). Wire extends through lumen  46  of body  38  from proximal end  48  of body  38  to distal end  50  and may extend through the bodies  38  of multiple splines  36  to couple one or more splines together. Alternatively, or in addition, splines  36  may be coupled at distal end  50  by a hinge connector  52  or in any of the ways described and illustrated in U.S. patent application Ser. No. 13/340,760 (published as United States Patent Application Publication No. US 2013/0172715), the entire disclosure of which is incorporated by reference as though fully set forth herein. The distal end  34  of the basket electrode assembly  30  may be specialized to form a small, but blunt mechanical connection point so that the distal portion of the catheter  18  may safely be pressed against tissue. 
     Referring again to  FIG.  3   , partially-masked electrodes  42  may be configured to diagnose, sense, and measure electrical activity in tissue such as cardiac tissue. One or more partially-masked electrodes  42  may also be used to provide tissue ablation therapy. Each partially-masked electrode  42  is coupled to a corresponding conductor  44  or one or more electrodes being coupled to the same conductor with the signal being multi-plexed. 
     Referring again to  FIGS.  3  and  4   , conductors  44  may be configured to transmit electrical signals from partially-masked electrodes  42  through shaft  24  of catheter  18  to an electronic control unit or similar device. Conductors  44  may comprise wires or cables or other means for conducting signals and may be disposed with the lumen  46  of a body  38  of a given spline  36 . Each conductor  44  may be coupled at a distal end to a corresponding partially-masked electrode  42  and extend through lumen  46  to the proximal end  32  of basket electrode assembly  30 . 
     Referring now to  FIGS.  5 - 9   , each of the partially-masked electrodes  42  may be formed of a conductive band  54  attached circumferentially about body  38 . For the purposes of clarity, the internals of body  38  shown in  FIG.  4    are not represented in  FIGS.  7 ,  8 , and  9   . The conductive bands  54  may be composed of platinum, gold, stainless steel, iridium, or alloys of these metals, or other biocompatible, electrically-conductive materials or compositions thereof. The conductive bands  54  of each partially-masked ring electrode  42  may have an electrically-insulating, polymer surface coating  56 . The surface coating  56  may be formed of a material with high dielectric properties that can be applied in a very thin layer. Exemplary surface coatings may include thin coatings of polyester, polyamides, polyimides, and blends of polyurethane and polyimides. In one embodiment, for example only and without limitation, surface coating  56  may be Parylene (e.g., Parylene C, Parylene N). In other embodiments, for example only and without limitation, surface coating  56  may be an acrylated urethane. In various embodiments, for example only and without limitation, the thickness of the surface coating  56  may range from about 0.0001 mm to about 0.05 mm. In other embodiments, for example only and without limitation, the thickness of the surface coating  56  may range from about 0.0003 mm to about 0.0006 mm. In various embodiments, for example only and without limitation, the surface coating  56  may be thicker around the opening  58  in order to create a taller “wall” to aid in creating a seal between the conductive band  54  and the blood pool, and thinner around the rest of the conductive band  54  to aid in reception of the localization signal by the partially-masked electrode  42 . 
     An aperture is formed in the insulated surface coating  56  to create a contoured opening  58  that exposes or reveals a small area of the conductive band  54 . The contoured opening  58  may be formed by laser, chemical, or other material removing or etching process to remove a portion of the insulated surface coating  56  to expose the conductive band  54  underneath. The edges or corners of the contoured opening  58  may be curved, rounded, or otherwise contoured to minimize any edge effects that could arise due to the imposition of a sharp edge, corner, or point. In various embodiments, for example only and without limitation, the openings  58  are oriented on the partially-masked electrodes  42  such that when the splines  36  of basket electrode assembly  30  are expanded, the openings  58  are facing the tissue of interest, such that they can contact the tissue of interest. In other embodiments, for example only and without limitation, the openings  58  are oriented on the partially-masked electrodes  42  such that when the splines  36  of basket electrode assembly  30  are expanded, the openings  58  may be maneuvered or oriented such that they are facing the tissue of interest and can contact the tissue of interest. 
     Although the contoured opening  58  is shown as having an oval shape, it will be understood that opening  58  may have other shapes, with or without rounded edges or corners, without departing from the scope of the disclosure, including, for example only and without limitation, a circle, an ellipse, a diamond, a rectangle, a hexagon, a square, a pentagon, an irregular polygon, a triangle. Opening  58  may be of different sizes without departing from the scope of the disclosure. For example only and without limitation, where opening  58  is a circle, the diameter of the opening  58  may range from about 0.010 mm to about 0.050 mm. In one embodiment, for example only and without limitation, the diameter of the opening  58  may be about 0.014 mm. In another embodiment, for example only and without limitation, the diameter of the opening  58  may be about 0.022 mm. In yet another embodiment, for example only and without limitation, the diameter of the opening  58  may be about 0.031 mm. Moreover, although a single opening  58  is shown per partially-masked electrode  42 , it will be understood that each partially-masked electrode  42  may include more than one opening  58  (e.g., 2, 3, 4, or more) without departing from the scope of the disclosure. 
     In some embodiments, for example only and without limitation, the surface area of the conductive band  54  exposed at the opening  58  is only about 10 percent (10%) of the total surface area of the conductive band  54 . Stated another way, about 90 percent (90%) of the conductive band  54  is insulated. Therefore, the electrically-conductive surface area of electrode  42  is only about 10 percent (10%) of the electrically-conductive surface area of a typical un-masked (un-insulated) ring electrode. In various embodiments, for example only and without limitation, the surface area of an un-insulated ring electrode may be about 2.5 mm 2  whereas the surface area of the opening  58  and thus the exposed area of conductive band  54  is about 0.25 mm 2 . In various embodiments, for example only and without limitation, the exposed area of conductive band  54  may be from about 0.01 mm 2  to about 1.0 mm 2 . In other embodiments, for example only and without limitation, the exposed area of conductive band  54  may be from about 0.044 mm 2  to about 0.486 mm 2 . 
     As shown in  FIGS.  6  and  7   , opening  58  has an upper perimeter  58   p  at the outer surface  56   s  of the surface coating  56 . The upper perimeter  58   p  of opening  58  defines an imaginary boundary area  59  above the exposed area of the conductive band  54  beyond which no part of the exposed conductive band  54  extends. The imaginary boundary area  59  is an imaginary surface having an outer edge(s) which is/are coincident and coextensive with the upper perimeter  58   p  of opening  58 . Depending on the shape of opening  58 , the imaginary boundary area  59  may be a plane or may have a contoured surface such as, for example only and without limitation, a saddle shape, a hyperbolic paraboloid, and a parabolic cylinder. The imaginary boundary area  59  is represented in  FIG.  6    by a series of lines covering opening  58  within upper perimeter  58   p . The imaginary boundary area  59  is represented in  FIG.  7    by a dashed line extending from one side of the opening  58  to the other side of the opening within upper perimeter  58   p . Therefore partially-masked electrode  42  includes a gap or void  59   v  between imaginary boundary area  59  and conductive band  54 . 
     Referring now to  FIGS.  8  and  9   , partially-masked electrode  42  is shown interfacing with the surface  60  of a tissue of interest. As shown in the end view of  FIG.  8    and the side view of  FIG.  9   , the surface coating  56  is between the conductive band  54  and the surface  60  of the tissue of interest. Because no part of conductive band  54  extends beyond the imaginary boundary area  59  shown in  FIGS.  6  and  7   , a void  62  is created between the conductive band  54  and the surface  60  of the tissue of interest at the location of the opening  58  in the surface coating  56 . It is desirable to have the void  62  be as small as possible to increase the signal received by the partially-masked electrode  42 . Thus, if the surface  60  of the tissue is touching the conductive band  54  the received signal may be increased. 
     Even if the surface  60  of the tissue does not come into contact with the conductive band  54 , the raised surface coating  56  which is between the conductive band  54  and the surface  60 , the thickness of the surface coating  56  creates a cupped or cup-like profile at the opening  58  which isolates the conductive band  54  of the partially-masked electrode  42  from the conductive path through the blood pool. That is, when the upper perimeter  58   p  of the raised surface coating  56  is placed in contact with the surface  60  of the tissue of interest, the surface coating  56  creates a seal between the blood pool and the opening  58  so that no blood in the blood pool can contact conductive band  54 . When the opening  58  is oriented toward the tissue of interest and the surface coating  56  around the perimeter of the opening  58  makes contact with the surface  60  of the tissue of interest, the conductive band  54  is completely isolated or sealed from any far field effects present in the blood pool. This will be even more effective in smoother tissue than in rougher tissue. With typical unmasked electrodes, due to the combination of the rough surface and far field interference, the signal received by a typical unmasked electrode may be inaccurate. However, with a partially-masked electrode  42 , even if a complete seal may not be able to be achieved against rough ventricle surface, for example. The isolation provided by the surface coating  56  of the partially-masked electrode  42  (with potentially more sealing at a tissue peak than a tissue valley) will still provide net improvement in EP measurements, as compared to a typical un-masked electrode. Except for opening  58 , partially-masked electrode  42  has no other open conductive ends or portions as with typical ring electrodes. This results in a more focused electrode as compared to un-masked electrodes. Thus it is desirable to minimize the volume of the void  62  while maintaining the seal from the blood pool provided by surface coating  56 . 
     By completely isolating partially-masked electrode  42  from any far field effects present in the blood pool, the noise from the far field effects is significantly reduced or eliminated. This increases the signal to noise ratio of the electrical signal measured by the partially-masked electrode  42 . Because the far field effects are no longer measured by the partially-masked electrode  42 , the signal quality and magnitude of the measured weak local electrical signals from unhealthy tissue is improved as compared to a typical un-insulated ring electrode  16 . This also allows for easier identification, locating, detecting and/or diagnosing unhealthy tissue. For example, as shown in  FIG.  10 A , pre-clinical testing has shown that the electrogram (EGM) peak-to-peak voltage (Vpp) signal from partially-masked electrode  42  (identified by arrows labeled PM) is about three to four times the magnitude of a typical un-insulated ring electrode  16  (identified by arrows labeled UM). In one embodiment, the measured peak-to-peak voltage (Vpp) signal from partially-masked electrode  42  was about 13.5 mV compared to 3.5 mV from a typical un-insulated ring electrode  16 . Additionally, the slopes of the EGM signals from partially-masked electrode  42  were steeper than those measured by a typical un-insulated ring electrode  16 . 
     In various embodiments, the surface coating  56  material and/or the surface coating  56  thickness is selected and configured to inhibit or block the receipt of the far field electrical signals when the surface coating  56  creates a seal between the blood pool and the opening  58 , while still allowing the partially-masked ring electrode  42  to receive a localization signal. That is, the surface coating  56  is of a sufficient thickness and has material properties or characteristics such that the far field electrical signals cannot penetrate the surface coating  56  to the underlying conductive band  54 , but still allows the localization signal to penetrate the surface coating  56  to the underlying conductive band  54 . Thus, partially-masked electrode  42  can function as both an electrode for mapping and/or diagnostic purposes and for localization purposes. In essence, the surface coating  56  substantially or completely filters out the far field signals, with minimal or no filtering out of the localization signals. For example, through the selection and configuration of the material and/or thickness of the surface coating  56 , the partially-masked electrode  42  may be tuned to filter out far field signals from about 1.0 Hz to about 600 Hz while being receptive to localization signals at or above approximately 8 kHz. Thus, the partially masked electrode  42  can filter out frequencies around the normal heart rate frequency (i.e., 1.0 Hz to about 1.67 Hz. The insulating properties of the insulated surface coating  56  therefore, may be frequency dependent. 
       FIGS.  10 B and  10 C  illustrate frequency response and impedance of an acrylated urethane insulated surface coating having a thickness of 0.5 mm. It is believed that the measured properties of the acrylated urethane insulated surface coating will behave similarly when applied to conductive band  54  to create an embodiment of partially-masked electrode  42 . For example, as shown in  FIG.  10 B , the capacitance is much higher at lower frequencies (e.g., from about 1.0 Hz to about 300 Hz), and decreases before substantially leveling off at higher frequencies (e.g., from about 400 Hz and above). It is expected that a partially-masked electrode  42 , that is partially-masked with an acrylated urethane insulated surface coating having a thickness of 0.5 mm, will effectively filter out lower frequency signals (including far field biosignals), but will not filter out higher frequency signals (including localization signals). For example only and without limitation, the localization signal may be a current pulse as described in U.S. Pat. No. 7,263,397, the entire disclosure of which is incorporated by reference as though fully set forth herein. Thus it is expected that the partially-masked electrode  42  will work like a high-pass filter, and will have an equivalent circuit like a parallel RC (resistor-capacitor) circuit. The capacitance change shown in  FIG.  10 B  results in the impedance curves shown in  FIG.  10 C . The increase in capacitance, at low frequency, will effectively act as a far-field biosignal filter by dielectric relaxational screening of the non-contact low frequency noise. 
     As shown in  FIG.  10 C , a resultant real component impedance of a tested acrylated urethane insulated surface coating with a thickness of 0.5 mm is equal to (z*cos(θ)). Thus it is expected that a partially-masked electrode  42  having a 0.5 mm thick acrylated urethane insulated surface coating  56  will result in an impedance of about 90 k ohms between 100 Hz and 10 kHz. Accordingly, an insulated surface coating  56  of 5 μm will have an impedance of about 900 ohms. This impedance is within the range measured between partially-masked and unmasked electrodes. Therefore, the increased impedance of the partially-masked electrodes is still usable with impedance-based localization systems, such that the partially-masked electrodes  42  may be used for localization purposes as well as measuring biosignals from tissues of interest. 
     Pre-clinical testing has also shown that partially-masked electrodes, where the surface area of the opening  58  is only about 10 percent (10%) of the total surface area of the conductive band  54 , had a smaller impedance increase than printed or flex circuit electrodes. Thus the impedance localization performance impact is minimized as compared to printed or flex circuit electrodes. The impedance of the partially-masked electrodes only increases from about 200-350 ohms to a range of about 430-610 ohms, as compared to unmasked electrodes. 
     Although partially-masked electrodes  42  are incorporated into a basket catheter having the structure shown in  FIGS.  2  and  3   , it will be understood that partially-masked electrodes  42  may be used in any type of catheter structure without departing from the scope of the disclosure. For example only and without limitation, partially-masked electrodes  42  may be incorporated into any of the basket catheter structures as described and illustrated in U.S. patent application Ser. No. 15/333,798 (published as U.S. Patent Application Pub. No. 2017/0100075), U.S. patent application Ser. No. 15/155,277 (published as U.S. Patent Application Pub. No. 2016/0331254), U.S. Pat. Nos. 9,339,331, and 8,224,416, the entire disclosures of which are incorporated by reference as though fully set forth herein. 
     In addition to being incorporated into basket catheter structures, partially-masked electrodes  42  may be incorporated into another distal tip assembly comprising a planar array of partially-masked electrodes. The distal tip assembly may be, for example, a high density electrode assembly as shown in  FIGS.  11  and  12   .  FIG.  11    depicts a top view of a high density electrode assembly  101  according to various embodiments of the present disclosure. In some embodiments, the high density electrode assembly  101  may include a flexible tip portion  110  that forms a flexible array of partially-masked electrodes  42  having openings  58  in an insulated coating. This planar array (or ‘paddle’ configuration) of partially-masked electrodes  42  comprises four side-by-side, longitudinally-extending arms  103 ,  104 ,  105 ,  106 , which can form a flexible framework on which the partially-masked electrodes  42  are disposed. The four microelectrode-carrier arms comprise a first outboard arm  103 , a second outboard arm  106 , a first inboard arm  104 , and a second inboard arm  105 . These arms are laterally separated from each other. In some embodiments, as shown in  FIG.  11   , there may be a distal member (or ‘button’)  109  where one or more of the arms come together. This distal member  109  may be constructed from metal or some other radiopaque material to provide fluoro visualization and semi-independent planar movement between the outer and inner arms. In other embodiments, high density electrode assembly  101  does not include distal member  109 . In various embodiments, for example only and without limitation, high density electrode assembly  101  may be used for electrophysiology (EP) mapping. In other embodiments, for example only and without limitation, high density electrode assembly  101  may be used for tissue ablation. 
     Each of the four arms may carry a plurality of partially-masked electrodes  42 . For example, each of the four arms can carry partially-masked electrodes  42  spaced along a length of each of the four arms. Although the high density electrode assembly  101  depicted in  FIG.  11    depicts four arms, the high density electrode assembly  101  could comprise more or fewer arms. As shown in  FIG.  11   , one or more of the arms may include electrode  116 , which may be an un-masked, partially-masked, or fully masked electrode. In some embodiments, for example only and without limitation, electrodes  116  may be fully masked and may be used for localization purposes. For example, as described in greater detail above, electrodes  116  may be masked with an insulated coating that isolates the conductive material of electrode  116  from far field or tissue signals (e.g., cardiac signals), but does not isolate electrode  116  from localization signals. Additionally, while the high density electrode assembly  101  depicted in  FIG.  11    depicts 16 partially-masked electrodes (e.g., 4 partially-masked electrodes  42  on first outboard arm  103  and second outboard arm  106  and 4 partially-masked electrodes  42  on first inboard arm  104  and second inboard arm  105 ), the catheters can include more or fewer than 16 partially-masked electrodes. In addition, the first outboard arm  103  and second outboard arm  106  can include more or fewer than 4 partially-masked electrodes and the first inboard arm  104  and second inboard arm  105  can include more or fewer than 4 partially-masked electrodes. 
     While the partially-masked electrodes are shown as substantially equally distributed on arms  103 ,  104 ,  105  and  106 , it will be understood that the electrodes may be spaced at different intervals on each arm without departing from the scope of the disclosure. That is, for example only and without limitation, in various embodiments, electrodes on first outboard  103  may be spaced closer together or further apart than electrodes on first inboard arm  104 . While the electrodes are shown as substantially evenly distributed on arms  103 ,  104 ,  105  and  106 , it will be understood that the electrodes may be unevenly spaced intervals on each arm without departing from the scope of the disclosure. That is, for example only and without limitation, in various embodiments, the electrodes may be located on the arms such that the electrodes are closer together near the distal end of flexible tip portion  110  and further apart near the proximal end of flexible tip portion  110 . Alternatively, for example only and without limitation, in various embodiments, the electrodes may be located on the arms such that the electrodes are farther apart near the distal end of flexible tip portion  110  and closer together near the proximal end of flexible tip portion  110 . 
     In some embodiments, the partially-masked electrodes  42  can be used in diagnostic, therapeutic, and/or mapping procedures. For example and without limitation, the partially-masked electrodes  42  can be used for electrophysiological studies, pacing, cardiac mapping, and ablation. In some embodiments, the partially-masked electrodes  42  can be used to perform unipolar or bipolar ablation. This unipolar or bipolar ablation can create specific lines or patterns of lesions. In some embodiments, the partially-masked electrodes  42  can receive electrical signals from the heart, which can be used for electrophysiological studies. In some embodiments, the partially-masked electrodes  42  can perform location or position sensing functions related to cardiac mapping. 
     In some embodiments, the high density electrode assembly  101  can include a catheter shaft  107 . The catheter shaft  107  can include a proximal end and a distal end. The proximal end of catheter shaft  107  may be connected to or integrally formed with the distal end  28  of shaft  24  of catheter  18 , as shown in  FIG.  2   , in place of electrode assembly  30 . That is, the distal tip assembly of the basket electrode assembly  30  may be swapped with, interchanged with, or substituted with the distal tip assembly of the high density electrode assembly  101 . The distal end can include a connector  108 , which can couple the distal end of the catheter shaft  107  to a proximal end of the planar array. The catheter shaft  107  can define a catheter shaft longitudinal axis aa, as depicted in  FIG.  11   , along which the first outboard arm  103 , first inboard arm  104 , second inboard arm  105 , and second outboard arm  106  can generally extend parallel in relation therewith. The catheter shaft  107  can be made of a flexible material, such that it can be threaded through a tortuous vasculature of a patient. In some embodiments, the catheter shaft  107  can include one or more ring electrodes  111  disposed along a length of the catheter shaft  107 . The ring electrodes  111  can be used for diagnostic, therapeutic, and/or mapping procedures, in an example. In various embodiments, ring electrodes  111  may be partially-masked in the same manner as partially-masked electrodes  42 . In other embodiments, ring electrodes  111  may be un-masked. In yet other embodiments, the high density electrode assembly  101  may include a combination of partially-masked, unmasked, or fully masked ring electrodes. 
     The flexible tip portion  110  can be adapted to conform to tissue (e.g., cardiac tissue). For example, when the flexible tip portion  110  contacts tissue, the flexible tip portion can deflect, allowing the flexible framework to conform to the tissue. In some embodiments, the arms (or the understructure of the arms) comprising the paddle structure (or multi-arm, electrode-carrying, flexible framework) at the distal end of the catheter depicted in  FIG.  11    is preferably constructed from a flexible or spring-like material such as Nitinol and/or a flexible substrate, as discussed herein. The construction (including, for example, the length and/or diameter of the arms) and material of the arms can be adjusted or tailored to create, for example, desired resiliency, flexibility, foldability, conformability, and stiffness characteristics. These characteristics may vary from a proximal end to a distal end of an arm, or between or among the plurality of arms comprising a single paddle structure. The foldability of materials such as Nitinol and/or flexible substrate provide the additional advantage of facilitating insertion of the paddle structure into a delivery catheter or introducer, whether during delivery of the catheter into the body or removal of the catheter from the body at the end of a procedure. 
     Another embodiment of a distal tip assembly comprises a planar array of partially-masked electrodes, wherein the distal tip assembly is a high density electrode assembly  201  of the disclosure is illustrated in  FIG.  12    and is described below. Some features of high density electrode assemblies  201  and  101  are common to one another and, accordingly, descriptions of such features in one embodiment should be understood to apply to the other embodiment. Furthermore, particular characteristics and aspects of one embodiment may be used in combination with, or instead of, particular characteristics and aspects of another embodiment. 
       FIG.  12    illustrates another embodiment of a high density electrode assembly  201  which includes a variety of partially-masked and un-masked electrodes. Other than the differences in the electrodes, high density electrode assembly  201  is substantially the same or identical to high density electrode assembly  101 . High density electrode mapping catheter  201  includes a population of partially-masked electrodes having different sized openings. For example only and without limitation, first outboard arm  103  includes four partially-masked electrodes  42   a  each having an opening  58   a , first inboard arm  104  includes four partially-masked electrodes  42   b  each having an opening  58   b  smaller than opening  58   a , and second inboard arm  105  includes four partially-masked electrodes  42   c  each having an opening  58   c  smaller than openings  58   a  and  58   b . In an embodiment, for example only and without limitation, opening  58   a  may have a diameter about 0.031 mm, opening  58   b  may have a diameter about 0.022 mm, and opening  58   c  may have a diameter about 0.014 mm. Although the openings  58   a ,  58   b , and  58   c  are shown as having an oval shape, it will be understood that openings  58   a ,  58   b , and  58   c  may have other shapes, with or without rounded edges or corners, without departing from the scope of the disclosure, including, for example only and without limitation, a circle, an ellipse, a diamond, a rectangle, a hexagon, a square, a pentagon, an irregular polygon, a triangle. Openings  58   a ,  58   b , and  58   c  may be of different sizes without departing from the scope of the disclosure. Additionally, in various embodiments, for example only and without limitation, second outboard arm  106  of high density electrode assembly  201  includes four un-masked electrodes  16 . In other embodiments, for example only and without limitation, second outboard arm  106  may include partially-masked electrodes having openings of a different shape and/or size from openings  58   a ,  58   b , and  58   c.    
     High density electrode assembly  201  may be used as a test bed for testing one or more parameters, such as for example only and without limitation: opening  58  shapes, opening  58  sizes, coating  56  thickness, coating material, electrode spacing, distribution, and number of electrodes (masked, unmasked, and partially masked). 
     While the partially-masked electrodes shown and described herein are ring electrodes, it will be understood that printed or flex circuit electrodes may be partially-masked without departing from the scope of the disclosure. Thus, the embodiment of  FIGS.  13 - 15    incorporate partially-masked flex circuit electrodes  342  into a distal tip. Some features of partially-masked flex circuit electrodes  34  and partially-masked electrodes  42  are common to one another and, accordingly, descriptions of such features in one embodiment should be understood to apply to other embodiments. Furthermore, particular characteristics and aspects of one embodiment may be used in combination with, or instead of, various aspects of another embodiment. 
     With reference to  FIG.  13   , a distal tip assembly comprising a basket electrode assembly  325  is shown having a plurality of partially-masked flex circuit electrodes  342  (as shown in  FIG.  14   ) which are oriented to contact tissue of interest. Basket electrode assembly  325  is shown with the basket portion of the catheter in an expanded configuration. 
     Basket electrode assembly  325  is shown as it may include an outer tubing  330  housing, a deployment member  331 , and a terminal end  350 . The outer tubing  330  of basket electrode assembly  325  may be connected to, or integrally formed with, the distal end  28  of shaft  24  of catheter  18 , as shown in  FIG.  2    (in place of electrode assembly  30 ). Basket electrode assembly is shown having splines  336   a - f ; however, the basket catheter  325  is not limited to any particular number of splines  336 , as will be readily understood by those having ordinary skill in the art after becoming familiar with the teachings herein. Additional features and structure of basket electrode assembly are shown and described in U.S. patent application Ser. No. 15/333,798 (published as U.S. Patent Application Pub. No. 2017/0100075) the entire disclosure of which is incorporated by reference as though fully set forth herein. 
     Each spline  336  is connected at the proximal end of the splines  336  to the outer tubing  330 , and each spline  336  is connected at the opposite or distal end of the splines  336  to the deployment member  331 . The deployment member  331  is operable to be moved in a first direction (e.g., in the direction of arrow  338   a ) relative to the outer tubing  330  to expand the splines  336  to a deployed position, as shown in  FIG.  13   . The deployment member  331  is also operable to be moved in a second direction (e.g., in the direction of arrow  338   b ) relative to the outer tubing  330  to collapse the splines  336  to an undeployed position. 
     The deployment member  331  may include a pull wire. The deployment member  331  may be a solid stainless steel or Nitinol wire. Alternatively, the deployment member  331  may be a hollow tube (or configured to house tubing). The deployment member  331  should be manufactured to be sufficiently stiff such that the deployment member  331  can be operated remotely (e.g., outside of the patient&#39;s body), and be moved in the directions illustrated by arrows  338   a  and  338   b  to expand and contract the splines  336 . 
     In any event, the basket electrode assembly  325  may be inserted into a catheter shaft (e.g., sheath (not shown) in its undeployed position for placement in the patient&#39;s body (e.g., within a heart chamber). The basket electrode assembly  325  may then be expanded to its deployed position for a medical procedure within the patient&#39;s body. Following the procedure, the basket electrode assembly  325  may again be collapsed to its undeployed position so that the basket electrode assembly  325  may be withdrawn from the patient. 
     In various embodiments, for example only and without limitation, the splines  336  are formed from sheets. The sheets can be formed of a suitable flexible material such as plastic (e.g., polyimide) or metal (e.g., platinum, gold, stainless steel, iridium, or alloys of these metals). As shown in  FIGS.  13 ,  14  and  15   , a population of spaced apart partially-masked flex circuit electrodes  342  and corresponding electrode traces  344  (as shown in  FIG.  14   ) are provided on the splines  336 . With specific reference to  FIG.  15    the partially-masked flex circuit electrodes  342  may be formed of a conductive material  354  which may be printed, adhered, bonded, etched or otherwise provided on the splines  336 , which may serve as a substrate for the partially-masked flex circuit electrodes  342 . 
     The traces  344  may then be connected to electrical wiring and extend through a catheter (e.g., catheter  18  shown in  FIG.  2   ). The electrical wiring may convey electrical signals between the partially-masked flex circuit electrodes  342  and one or more control system (not shown). For example, the electrical signals may be used to control output of ablation electrodes, or for processing input from mapping electrodes for viewing or storage by the user (e.g., on an electrical monitoring device). 
     The conductive material  354  may be composed of platinum, gold, stainless steel, iridium, or alloys including one or more of these metals, or other biocompatible, electrically-conductive material. As shown in  FIG.  15   , an electrically-insulating, polymer surface coating  356  may be applied to each spline  336  and the conductive material  354 . The surface coating  356  may be formed of a material with high dielectric properties that can be applied in a very thin layer. Exemplary surface coatings may include thin coatings of polyester, polyamides, polyimides, and blends of polyurethane and polyimides. In one embodiment, for example only and without limitation, surface coating  356  may be Parylene. In various embodiments, for example only and without limitation, the thickness of the surface coating  356  may range from about 0.0001 mm to about 0.05 mm. In other embodiments, for example only and without limitation, the thickness of the surface coating  356  may range from about 0.0003 mm to about 0.0006 mm. 
     An aperture is formed in the surface coating  356  to create a contoured opening  358  that exposes or reveals a small area of the conductive band  354 . The contoured opening  358  may be formed by laser, chemical, or other material removing or etching process to remove a portion of the surface coating  356  to expose the conductive band  354  underneath. The edges or corners of the contoured opening  358  may be curved, rounded, or otherwise contoured to minimize any edge effects that could arise due to the imposition of a sharp edge, corner, or point. In various embodiments, for example only and without limitation, the openings  358  are oriented on the partially-masked electrodes  342  such that when the splines  336  of basket electrode assembly  325  are expanded, the openings  358  are facing the tissue of interest, such that they can contact the tissue of interest. In other embodiments, for example only and without limitation, the openings  358  are oriented on the partially-masked electrodes  342  such that when the splines  336  of basket electrode assembly  325  are expanded, the openings  358  may be maneuvered or oriented such that they are facing the tissue of interest and can contact the tissue of interest. 
     Although the contoured opening  358  is shown as having an oval shape, it will be understood that opening  358  may have other shapes, with or without rounded edges or corners, without departing from the scope of the disclosure, including, for example only and without limitation, a circle, an ellipse, a diamond, a rectangle, a hexagon, a square, a pentagon, an irregular polygon, a triangle. Opening  358  may be of different sizes without departing from the scope of the disclosure. For example only and without limitation, where opening  358  is a circle, the diameter of the opening  358  may range from about 0.010 mm to about 0.050 mm. In one embodiment, for example only and without limitation, the diameter of the opening  358  may be about 0.014 mm. In another embodiment, for example only and without limitation, the diameter of the opening  358  may be about 0.022 mm. In yet another embodiment, for example only and without limitation, the diameter of the opening  358  may be about 0.031 mm. Moreover, although a single opening  358  is shown per partially-masked flex circuit electrode  342 , it will be understood that each partially-masked flex circuit electrode  342  may include more than one opening  358  (e.g., 2, 3, 4, or more) without departing from the scope of the disclosure. 
     As shown in  FIG.  15   , opening  358  has an upper perimeter  358   p  at the outer surface  356   s  of the surface coating  356 . The upper perimeter  358   p  of opening  358  defines an imaginary boundary area  359  above the exposed area of the conductive material beyond which no part of the exposed conductive material  354  extends. The imaginary boundary area  359  is a planar surface having an outer edge(s) which is/are coincident and coextensive with the upper perimeter  358   p  of opening  358 . Therefore partially-masked flex circuit electrode  342  includes a gap or void  359   v  between imaginary boundary area  359  and conductive band  354 . 
     Referring now to  FIG.  16   , partially-masked flex circuit electrode  342  is shown interfacing with the surface  60  of a tissue of interest. The surface coating  356  is between the conductive material  354  and the surface  60  of the tissue of interest and because no part of conductive material  354  extends beyond the imaginary boundary area  359  shown in  FIG.  15   , a void  62  is created between the conductive material  354  and the surface  60  of the tissue of interest at the location of the opening  358  in the surface coating  356 . It is desirable to have the void  62  be as small as possible to increase the signal received by the partially-masked flex circuit electrode  342 . Thus, if the surface  60  of the tissue is touching the conductive material  354  the received signal may be increased. In some embodiments, for example only and without limitation, an electrical signal may be emitted by the partially-masked flex circuit electrode  342  to attract the surface  60  of the tissue toward the conductive material  354 . 
     The raised surface coating  356 , which is between the conductive material  354  and the surface  60 , creates a cupped or cup-like profile at the opening  358  which isolates the conductive material  354  of the partially-masked flex circuit electrode  342  from the conductive path through the blood pool. That is, when the upper perimeter  358   p  of the raised surface coating  356  is in contact with the tissue of interest, the surface coating  356  creates a seal between the blood pool and the opening  358  so that no blood in the blood pool can contact conductive material  354 . When the opening  358  is oriented toward the tissue of interest and the surface coating  356  around the perimeter of the opening  358  makes contact with the surface  60  of the tissue of interest, the conductive band  354  is completely isolated or sealed from any far field effects present in the blood pool. This will be even more effective in rougher tissue (e.g., ventricle) than in smother tissue (e.g., atria). Thus, except for opening  358 , partially-masked flex circuit electrode  342  has no other open conductive ends or portions as with typical ring electrodes. This results in a more focused electrode as compared to un-masked electrodes. Aspects of the present disclosure are desirable to minimize the volume of the void  62  while maintaining the seal from the blood pool provided by surface coating  356 . 
     By completely isolating partially-masked flex circuit electrode  342  from any far field effects present in the blood pool, the noise from the far field effects is significantly reduced or eliminated. This increases the signal to noise ratio of the electrical signal measured by the partially-masked flex circuit electrode  342 . Because the far field effects are no longer measured by the partially-masked electrode  342 , the signal quality and magnitude of the measured (weak) local electrical signals from unhealthy tissue is improved as compared to a typical un-insulated ring electrode  16 . This also allows for easier identification, locating, detecting and/or diagnosing unhealthy tissue. 
     Another embodiment of a partially-masked flex circuit electrode  442  of the disclosure is illustrated in  FIGS.  17  and  18    and is described below. Some features of partially-masked flex circuit electrode  442  and  342  are common to one another and, accordingly, descriptions of such features in one embodiment should be understood to apply to other embodiments. Furthermore, particular characteristics and aspects of one embodiment may be used in combination with, or instead of, particular characteristics and aspects of another embodiment. 
     With further reference to  FIGS.  17  and  18   , a spline  336 ′ is shown with a conductive material  354  which may be printed, adhered, bonded, etched, or otherwise provided on the spline  336 ′. Additionally, an electrically-insulating, polymer surface coating  456  may be applied to each spline  336 ′. However, unlike partially-masked flex circuit electrode  342  shown in  FIGS.  14 - 16   , the surface coating  456  is not applied on top of conductive material  354 , or is fully removed from conductive material, such that opening  458  in the surface coating  456  has the same area as conductive material  354 . Thus, as shown in  FIG.  18   , surface coating  456  abuts, but does not overlap, conductive material  354 . 
     Another embodiment of a partially-masked flex circuit electrode  542  of the disclosure is illustrated in  FIGS.  19  and  20    and is described below. Some features of partially-masked flex circuit electrode  542  and  342  are common to one another and, accordingly, descriptions of such features in one embodiment should be understood to apply to other embodiments. Furthermore, particular characteristics and aspects of one embodiment may be used in combination with, or instead of, particular characteristics and aspects of another embodiment. 
     With further reference to  FIGS.  19  and  20   , a spline  336 ″ is shown with a conductive material  354  which may be printed, adhered, bonded, etched or otherwise provided on the spline  336 ″. The conductive material  354  has an outer perimeter or outer edge defined by dashed line  355  in  FIG.  19   . In this embodiment, as in several of the other embodiments described herein, the outer perimeter  355  is an ellipsoid, but may define other shapes, including irregular shapes. Additionally, an electrically-insulating, polymer surface coating  556  may be applied to each spline  336 ″ locally around conductive material  354 . That is, unlike partially-masked flex circuit electrodes  342  and  442  shown in  FIGS.  14 - 16  and  17 - 18   , the surface coating  556  is only applied proximate to the outer perimeter  355  of conductive material  354 . Thus, surface coating  556  surrounds the outer edges or sides of conductive material  354  and projects above conductive material  354  but does not otherwise cover all of spline  336 ″. Surface coating  556  therefore only rings around conductive material  354 . An opening  558  smaller than the area of conductive material  354  is provided in surface coating  556 . 
     Another embodiment of a partially-masked flex circuit electrode  642  of the disclosure is illustrated in  FIGS.  21  and  22    and is described below. Some features of partially-masked flex circuit electrode  642 ,  542 ,  442 , and  342  are common to one another and, accordingly, descriptions of such features in one embodiment should be understood to apply to other embodiments. Furthermore, particular characteristics and aspects of one embodiment may be used in combination with, or instead of, particular characteristics and aspects of another embodiment. 
     With further reference to  FIGS.  21  and  22   , a spline  336 ′″ is shown with a conductive material  354  which may be printed, adhered, bonded, etched, or otherwise provided on the spline  336 ″. Additionally, an electrically-insulating, polymer surface coating  656  may be applied to each spline  336 ′″ locally around conductive material. That is, unlike partially-masked flex circuit electrodes  342  and  442  shown in  FIGS.  14 - 16  and  17 - 18   , the surface coating  656  is only applied proximate conductive material  354 . Thus, surface coating  656  surrounds the sides of conductive material  354  and projects above conductive material  354  but does not otherwise cover all of spline  336 . Surface coating  656  therefore only rings around conductive material  354 . Moreover, like opening  458  (see  FIGS.  17  and  18   ) of partially-masked flex circuit electrode  442 , the surface coating  656  is not applied on top of conductive material  354 , or is fully removed from conductive material, such that opening  658  in the surface coating  656  has the same area as conductive material  354 . Thus, as shown in  FIG.  22   , surface coating  656  abuts, but does not overlap, conductive material  354 . 
     While the partially-masked electrodes described herein are described as being oriented and/or maneuvered such that they contact the tissue of interest, it will be understood that in various embodiments for example, additional un-masked and/or partially-masked electrodes may be provided which are oriented such that they do not contact the tissue of interest. These non-contact electrodes may be electrically connected with conductors or leads separately from the conductors or leads to the partially-masked electrodes which contact the tissue of interest. Thus, these electrically separate non-contact electrodes may be used to sense the blood pool and/or far field effects separately from the tissue local field. This arrangement is described in greater detail in PCT Application No. PCT/US2016/058244 (published as WO/2017/070559), the entire disclosure of which is incorporated by reference as though fully set forth herein. 
     Although the partially-masked electrodes described herein are shown as being used in basket electrode assemblies and high density electrode assemblies, it will be understood that the partially-masked electrodes can be used in any type and shape of distal tip assembly for a catheter, including for example only and without limitation, a catheter having a single distal tip assembly which may be steerable. 
     Additionally, in the various embodiments described herein, the insulated surface coating material, the insulated surface coating thickness, and/or the insulated surface coating location may be selected and configured to allow repeated opening and closing of the splines of the basket electrode assemblies and repeated flexure of the arms of the high density electrode assemblies described herein without cracking, flaking, breaking and/or other failure of the insulated surface coating. This aids durability, longevity and/or reliability of the distal tip assembly having the partially-masked electrodes. Such aspects also reduce the potential for the insulated surface coating to be released from the distal tip assembly and remaining in a patient. Moreover, the surface coating material, the surface coating thickness, and/or the insulated surface coating location may be selected and configured such that the insulated surface coating does not impede or inhibit the opening and closing of the splines of the basket electrode assemblies or the flexure of the arms of the high density electrode assembly described herein. For example, the localized insulated surface coating is only proximate the conductive material as shown in  FIGS.  19 - 22   . Because the insulated surface coating is only proximate the conductive material, the impact of the insulated surface coating on the opening and closing of the splines is reduced or eliminated. Additionally, due to a potential increased stiffness of the spline proximate the conductive material, the localized insulated surface coating is less likely to flex during the opening and closing of the splines. The localized insulated surface coating is thus potentially subject to lower stresses and strains as compared to an insulated surface coating along the entire spline (see e.g.,  FIGS.  14 - 18   ). 
     While clinical benefits of the partially-masked electrodes have been described herein, the use of the insulated surface coatings to partially mask electrodes may also provide manufacturing advantages. For example only and without limitation, because a surface coating is applied to an electrode and an opening is made to expose a portion of the conductive material of the electrode, the manufacturing tolerances of the conductive material may be reduced. That is, the size of the conductive material does not need to be held to such a tight tolerance because the effective size of the conductive area of the electrode will be determined by the size of the opening in the surface coating. This may allow the use of a common size of conductive material for different applications, wherein the size of the opening is varied for the particular application. This may also reduce manufacturing costs and time. 
     Among other things, the disclosed catheters, with their plurality of partially-masked electrodes, are useful to (1) define regional propagation maps of particularly sized areas (e.g., one centimeter square areas) within the atrial walls of the heart; (2) identify complex fractionated atrial electrograms for ablation; (3) identify localized, focal potentials between the microelectrodes for higher electrogram resolution; and/or (4) more precisely target areas for ablation. These mapping catheters and ablation catheters are constructed to conform to, and remain in contact with, cardiac tissue despite potentially erratic cardiac motion. Such enhanced stability of the catheter on a heart wall during cardiac motion provides more accurate mapping and ablation due to sustained tissue electrode contact. Additionally, the catheters described herein may be useful for epicardial and/or endocardial use. For example, the planar array embodiments depicted herein may be used in an epicardial procedure where the planar array of partially-masked electrodes is positioned between the myocardial surface and the pericardium. Alternatively the planar array embodiments may be used in an endocardial procedure to quickly sweep and/or analyze the inner surfaces of the myocardium and quickly create high-density maps of the heart tissue&#39;s electrical properties. 
     Now with reference to  FIG.  23   , a method of using catheters having the partially-masked electrodes described herein is shown and described. At step  2300 , the method includes tracking the location of at least one of the partially-masked electrodes  42  within a body of a patient. The insulated coating  56  of at least one of the partially-masked electrodes  42  is selected and configured to allow the reception of a localization signal by the conductive material  54 , as described herein. The insulated coating  56  of at least one of the partially-masked electrodes  42  is selected and configured to prevent the reception of at least a significant amount of a far field signal by the conductive material  54 . The method further includes, at step  2302 , placing the upper perimeter  58   p  of the insulated coating  56  of at least one of the partially-masked electrodes  42  in contact with a tissue of interest in the body of the patient, the tissue of interest being proximate a blood pool, such that the insulated coating  56  creates a seal between the blood pool and the contoured opening  58  to inhibit the receipt of the far field signal in the blood pool. 
     Now with reference to  FIGS.  24 A and  24 B , another method of using catheters having the partially-masked electrodes described herein is shown and described. At step  2400 , the method includes tracking the location of one of the partially-masked electrodes  42  within a body of a patient. The insulated coating  56  of the partially-masked electrode  42  is selected and configured to allow the reception of a localization signal by the conductive material  54 , as described in greater detail elsewhere herein. The insulated coating  56  of the partially-masked electrode  42  is selected and configured to prevent the reception of at least a significant amount of a far field signal by the conductive material  54 . At step  2402 , the method further includes placing the upper perimeter  58   p  of the insulated coating  56  of the partially-masked electrode  42  in contact with a tissue of interest at a first location in the body of the patient, the tissue of interest being proximate a blood pool, such that the insulated coating  56  creates a seal between the blood pool and the contoured opening  58  to inhibit the receipt of the far field signal in the blood pool. At step  2404 , the method further includes receiving, by the partially-masked electrode  42 , a first local electrical signal from the first location on the tissue of interest at the contoured opening  58 . The first local electrical signal having a first magnitude, wherein as a result of the seal between the blood pool and the contoured opening the first local electrical signal comprises little or no far field signal. 
     As shown in  FIG.  24 B , the method may continue, at step  2406 , with moving the partially-masked electrode  42  from the first location to a second location in the body of the patient. At step  2408 , the method may further include placing the upper perimeter  58   p  of the insulated coating  56  of the partially-masked electrode  42  in contact with the tissue of interest at the second location in the body of the patient. The tissue of interest being proximate a blood pool, such that the insulated coating  56  creates a seal between the blood pool and the contoured opening  58 , and thereby inhibits the receipt of the far field signal in the blood pool. Then at step  2410 , the method may further include, receiving, by the partially-masked electrode  42 , a second local electrical signal from the second location on the tissue of interest at the contoured opening  58 . The second local electrical signal having a second magnitude, wherein as a result of the seal between the blood pool and the contoured opening the second local electrical signal comprises little or no far field signal. In various embodiments, the second local electrical signal may have a second magnitude different from the first magnitude of the first local electrical signal. Then at step  2412 , the method may further include diagnosing the health of the tissue of interest based on the difference between the first magnitude and the second magnitude. That is, the state (e.g., voltage magnitude) of the tissue can be determined and an assessment of the health of the tissue may be able to be made based on the measured state. 
     In some embodiments consistent with the present disclosure, one or more partially-masked electrodes may be oriented inward (away from the tissue) relative to the catheter. Accordingly, these inward oriented partially-masked electrodes are solely exposed to a blood pool and receives signals from the blood pool indicative of “far field” influences. Controller circuitry may utilize the signal from such inward oriented partially-masked electrodes to filter out such “far field” influences from the signals received from outward facing partially-masked electrodes in contact with the tissue. 
     Although several embodiments of an apparatus, system, and method in accordance with present teachings have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this disclosure. All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise and counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the disclosed embodiments, and do not create limitations, particularly as to the position, orientation, or use of the disclosed embodiments. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not as limiting. Changes in detail or structure may be made without departing from the present teachings as defined in the appended claims. 
     Various embodiments are described herein to various apparatuses, systems, and/or methods. Numerous specific details are set forth to provide a thorough understanding of the overall structure, function, manufacture, and use of the embodiments as described in the specification and illustrated in the accompanying drawings. It will be understood by those skilled in the art, however, that the embodiments may be practiced without such specific details. In other instances, well-known operations, components, and elements have not been described in detail so as not to obscure the embodiments described in the specification. Those of ordinary skill in the art will understand that the embodiments described and illustrated herein are non-limiting examples, and thus it can be appreciated that the specific structural and functional details disclosed herein may be representative and do not necessarily limit the scope of the embodiments, the scope of which is defined solely by the appended claims. 
     Reference throughout the specification to “various embodiments,” “some embodiments,” “one embodiment,” or “an embodiment”, or the like, means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments,” “in some embodiments,” “in one embodiment,” or “in an embodiment”, or the like, in places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Thus, the particular features, structures, or characteristics illustrated or described in connection with one embodiment may be combined, in whole or in part, with the features, structures, or characteristics of one or more other embodiments without limitation given that such combination is not illogical or non-functional. 
     It will be appreciated that the terms “proximal” and “distal” may be used throughout the specification with reference to a clinician manipulating one end of an instrument used to treat a patient. The term “proximal” refers to the portion of the instrument closest to the clinician and the term “distal” refers to the portion located furthest from the clinician. It will be further appreciated that for conciseness and clarity, spatial terms such as “vertical,” “horizontal,” “up,” and “down” may be used herein with respect to the illustrated embodiments. However, surgical instruments may be used in many orientations and positions, and these terms are not intended to be limiting and absolute. 
     Any patent, publication, or other disclosure material, in whole or in part, that is said to be incorporated by reference herein is incorporated herein only to the extent that the incorporated materials does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.