Patent Publication Number: US-2020297239-A1

Title: Biologic delivery system with positional sensing and force sensing

Description:
BACKGROUND 
     a. Field 
     The present disclosure is directed to delivering therapeutic substances to internal tissue via a catheter device. More specifically, the present disclosure is directed to a catheter and delivery system and their method of use, which allow delivery of therapeutic substances to specifically targeted internal tissue locations and injection of the therapeutic substances to a desired depth. 
     b. Background Art 
     Gene therapy is a treatment that involves altering the genes inside cells of a body to stop or counteract disease. Generally, gene therapy replaces a faulty gene or adds a new gene in an attempt to cure disease or improve a body&#39;s ability to fight disease. Gene therapy holds promise for treating a wide range of diseases, including, without limitation, cancer, cystic fibrosis, heart disease and diabetes. 
     The specific procedure incorporating gene therapy depends on the disease being treated. By way of example, gene therapy may include having blood drawn or bone marrow removed. Then, in a laboratory, cells from the blood or bone marrow are exposed to a viral vector or another type of vector that contains the desired genetic material. Once the vector has entered the cells in the laboratory, those cells are injected back into the body via a vein or directly into tissue, where cells take up the vector along with the altered genes. Other vectors include, without limitation, stem cells and Liposomes. An exemplary use of gene therapy is the treatment of Ischemia. 
     Ischemia is a restriction in blood supply to tissues, causing a shortage of oxygen and glucose needed for cellular metabolism. Ischemia is generally caused by problems with blood vessels, with resultant damage to or dysfunction of tissue. Ischemic heart or cardiac ischemia occurs when the heart muscle, or myocardium, receives insufficient blood flow. Gene therapy for the treatment for ischemia and ischemic heart disease involves the delivery of gene therapy substances to tissue (e.g., myocardial heart tissue) to induce angiogenesis. Angiogenesis is a complex biological process that results in the growth of new blood vessels within tissue. Angiogenesis has been induced in heart tissue for reperfusion of tissue compromised by myocardial ischemia. Several growth factors or mediators are known to elicit angiogenic responses, and administration of these mediators promotes revascularization of ischemic tissues. 
     Delivery of gene therapy substances remains a significant challenge as these substances often have a short half-life. Accordingly, it is desirable to inject these substances directly into tissue to be treated to improve uptake of the therapeutic substance/solution. For example, previous application of gene therapy substances to ischemic heart tissue has typically included an open-chest procedure. According to this procedure, the patient&#39;s chest is opened surgically to expose the heart. The solution containing the vector is then delivered to the heart tissue by using a syringe to make a number of injections in a grid-like pattern, with the surgeon keeping track of the location of each injection. Once injected, the vector causes the cells in the target tissue to produce a desired growth factor to induce Angiogenesis. 
     Other delivery methodologies have included the use of catheters to deliver a therapy substance proximate to internal tissue to be treated. In such procedures, a catheter is guided (e.g., fluoroscopically) proximate to internal tissue to be treated and the tissue is bathed in the therapeutic solution expelled from the catheter. While reducing invasiveness, such a catheter procedure fails to directly inject target tissue with the therapeutic solution. This is due, in part, to the inability to specifically identify the location of a catheter within internal tissue and the inability to control the depth of injection of the therapeutic solution at a desired internal location. For instance, when treating cardiac tissue, the therapeutic substance is most commonly targeted to the myocardium, which is muscle tissue of the heart forming a thick middle layer between an outer epicardium layer and the inner endocardium layer. Accordingly, to effectively treat the myocardium, precise control of the injection depth is required. The injection cannot be too deep or too shallow. 
     SUMMARY 
     Various catheters and/or catheter-based systems, are disclosed herein that may include various combinations of features to control the positioning of a catheter relative to an internal tissue location (e.g., target tissue) and to control injection of a therapeutic substance(s) into the target tissue. In various embodiments, a catheter may include an elongate shaft and one or more position sensing electrodes positioned at or near a distal end of the shaft. The position sensing electrodes may include, for example, a tip electrode, one or more ring electrodes and/or button-type or spot electrodes. The catheter may also include one or more contact sensors, such as mechanical/pressure, impedance and/or optical sensors to provide an indication of contact and/or contact forces between the catheter and targeted tissue. Additionally, the catheter includes a therapy delivery needle that is selectively extendable relative to a distal end of the catheter. The needle may be extended a desired distance beyond a distal end or tip of the catheter to deliver therapeutic substances to tissue. In one arrangement, use of the contact sensor(s) allows for confirming insertion of the therapy needle into the target tissue to a desired depth. Once inserted to the desired depth, a therapeutic substance may be injected into the target tissue at the desired depth. 
     According to a first aspect, a system is provided for the delivery and injection of therapeutic substances into internal tissue of a body. The system includes a catheter having a flexible elongated shaft with a proximal end (e.g., handle) and a distal end adapted for insertion within a patient body. A lumen extends through at least a portion of the catheter shaft and exits the catheter shaft at an opening near the distal end. Disposed within the lumen is a therapy delivery needle, which is selectively movable between a retracted position (i.e., disposed within the catheter shaft) and an extended position where a portion of the needle is disposed a predetermined distance beyond the opening of the lumen. The predetermined distance/extension of the needle may correspond to a desired injection depth. The therapy delivery needle is fluidly connected to a supply of therapeutic solution, which may be controllably injected through the needle. The catheter further includes at least a first contact sensor that is disposed proximate to the distal end of the catheter. The contact sensor(s) generates contact outputs that are indicative of contact conditions between the catheter and an internal target tissue. A control unit monitors the contact outputs of the contact sensor. More particularly, the control unit identifies a first contact output where the catheter contacts a target tissue and the therapy delivery needle is in the retracted position within the lumen (i.e., prior to extension through the opening). The control unit compares subsequent contact outputs obtained after the therapy needle is extended a predetermined distance through the opening of the lumen. Based on these comparisons, the control unit determines a degree of needle insertion into the target tissue and may generate an output indicative of the needle insertion. For instance, the control unit may generate an output indicating that therapy needle is fully inserted within the target tissue upon which the therapeutic solution may be injected through the needle into the target tissue. Alternatively, the control unit may generate an output indicating the needle is less than fully inserted within the target tissue which may allow a clinician to adjust the position of the catheter such that the needle is fully inserted within the target tissue. 
     The contact sensor(s) is configured to detect contact between the distal end of the catheter and target tissue. In one arrangement, the contact sensor is a force sensor that allow assessing the degree of mechanical coupling between catheter and the target tissue. Various force sensors may be utilizes and such sensors may generate signals indicative of a change in resistance, voltage, capacitance or a combination thereof. That is, the force sensors may comprise, for example, capacitance sensors that generate a signal indicative of a change in capacitance resulting from application of a force. Alternatively, the force sensors may comprise piezoelectric sensors that include a piezoelectric material (in the form of a wire, film or tubes, for example) and generate a signal indicative of a change in voltage resulting from placing the piezoelectric material under stress. In another embodiment, the force sensors may also comprise pressure transducers such as a pressure sensitive conductive composite (PSCC) sensors where the electrical resistance of the composite varies inversely in proportion to the pressure that is applied to the composite. In another arrangement, the force sensors may comprise optical sensors that detect deflection in the distal end of the catheter. In another arrangement, the contact sensor may comprise an electrode. In such an arrangement, an electrical property of the electrode may change based on its contact with tissue. For instance, the impedance of such an electrode may change based on the degree of contact with tissue. Along these lines, the control unit may be used to resolve an electrode output signal into component parts of impedance at the catheter/tissue interface allowing the control to determine values for one or more components of a complex impedance between the electrode (e.g., tip electrode) and tissue. Such impedance components or values may be correlated to know contact conditions. 
     In a further arrangement, the system includes a positioning system allows for identifying the location of the catheter relative to a model of an internal tissue location including the target tissue. In this arrangement, the catheter includes one or more position sensors attached to the catheter proximate to the distal end. These position sensors generate position output signals in response to applied signals. A navigation system receives the position outputs from the position sensors and locates a catheter within the coordinate system including the target tissue. Additionally, the navigation system includes a display that is configured to display a representation of the catheter relative to a model of the internal tissue location. Such a navigation and positioning system allows a clinician to visualize the catheter relative to an internal tissue location and/or adjust the position of the catheter relative to the internal tissue location to target one or more tissue targets for therapy injection. In one arrangement, the position sensors are coils that generate outputs in response to magnetic fields. In another arrangement, the position sensors are electrodes that generate outputs in response to electric fields. 
     In a further arrangement, sensors may be attached to the therapy delivery needle. In such an arrangement, a force sensor may be attached to the therapy delivery needle to identify forces applied to the distal tip of the needle. In a further arrangement, electrical wiring may be attached to the therapy delivery needle such that the therapy delivery needle forms an electrode such as an impedance sensor. In such an arrangement, impedance of the needle may change as the needle is extended beyond the catheter and/or inserted into target tissue. In a further arrangement, the catheter may include a sensor that identifies the extension of the needle beyond the lumen opening. Such sensors may include magnetic sensors that identify passage of magnetic strips attached to the therapy delivery needle. 
     In another aspect, a method is provided for delivering an injectable therapeutic substances into internal tissue of a body. The method includes receiving position outputs from position sensors attached proximal to a distal end of a catheter disposed within the body. The position outputs are utilized to generate a display of the catheter relative to a model of the internal tissue region where the catheter is disposed. Such a display may be utilized to position the catheter proximate to one or more target tissue locations. Once positioned at a target location, a first contact condition is identified between the catheter and the target tissue. Once correctly positioned and the first contact condition is identified, a therapy needle may be advanced a predetermined distance relative to the distal end of the catheter. After advancement of the therapy needle, a second contact condition between the catheter and target tissue is identified. Based on the first and second contact conditions, a degree of needle insertion may be identified. The degree of needle insertion may be output to a clinician allowing the clinician to determine if the needle is fully inserted into the target tissue or if the needle is less than fully inserted into the target tissue. If the needle is fully inserted, the clinician may inject a therapeutic substance through the needle. If the needle is not fully inserted, the clinician may reposition the catheter until the needle is fully inserted 
     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 a diagrammatic illustration of an exemplary catheter system which may be implemented to access internal patient tissue for injection of therapeutic substances. 
         FIG. 2  illustrates a display of the exemplary catheter system. 
         FIGS. 3A and 3B  illustrates one embodiment of an injection catheter with a retracted injection needle and an extended injection needle, respectively. 
         FIG. 4  illustrates an introducer sheath and catheter. 
         FIGS. 5A-5D  illustrate insertion of a needle into tissue. 
         FIG. 6  illustrates one process that may be performed by the catheter system. 
         FIGS. 7A and 7B  illustrates another embodiment of an injection catheter with a retracted injection needle and an extended injection needle, respectively. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made to the accompanying drawings, which at least assist in illustrating the various pertinent features of the presented disclosure. The following description is presented for purposes of illustration and description and is not intended to limit the disclosed systems, apparatuses and methods to the forms disclosed herein. Consequently, variations and modifications commensurate with the following teachings, and skill and knowledge of the relevant art, are within the scope of the presented disclosure. The embodiments described herein are further intended to explain the best modes known of practicing the disclosed systems, apparatuses and methods and to enable others skilled in the art to utilize the disclosed systems, apparatuses and methods in such, or other embodiments and with various modifications required by the particular application(s) or use(s). 
     The present disclosure is directed to a catheter-based therapeutic delivery system and method that utilizes positional sensing and contact sensing to ensure delivery of a therapeutic substance to a desired internal location (e.g., target tissue) and to a desired injection depth. Generally, the system uses one or more position sensors to spatially locate a catheter supported therapy delivery needle relative to targeted internal tissue. Once the therapy delivery needle is located at a desired internal location, the needle may be inserted into the target tissue. Use of contact sensing provides confirmation that the therapy delivery needle is inserted into the target tissue to a desired depth prior to injection of the therapeutic substance. The disclosed system and method have application in the controlled delivery of gene therapy as well as other substances (e.g., drugs). 
       FIG. 1  illustrates a system  10  for diagnosis or treatment of tissue  12  in a body  14  in accordance with one embodiment of the present disclosure. In the illustrated embodiment the tissue  12  comprises cardiac tissue and the body  14  comprises a human body. It should be understood, however, that a system  10  in accordance with the present teachings may find application in connection with procedures for the diagnosis or treatment of a variety of tissues in human and non-human bodies. The system  10  may include a medical device position and navigation system  16 , one or more medical devices including, for example, an electrophysiological (EP) mapping catheter  18  and a therapy injection catheter  20 , a supply of a therapeutic substance  44  (e.g., gene therapy solutions, drugs, etc.), a display system  24 , and an electronic control unit (ECU)  26 . 
     The medical device position and navigation system  16  is provided to determine the position and orientation of medical devices within the body  14  such as catheters  18 ,  20  and may also be used to generate an electrophysiological map of a region of interest. The system  16  may display geometries or models of a region of interest in the body  14  on a display such as display system  24  along with representations of the catheters  18 ,  20  indicative of the position of the catheters  18 ,  20  relative to the region of interest. See, e.g.,  FIG. 2 . 
     Referring again to  FIG. 1 , the system  16  may comprise a system that employs electric fields to detect the position of the catheters  18 ,  20  within the body  14  and may, for example, comprise the system available under the trademark “ENSITE NAVX” (a/k/a EnSite Classic as well as other versions of the EnSite™ system denoted as ENSITE VELOCITY′ and ENSITE PRECISION′) by St. Jude Medical, Inc. and generally shown in, for example, U.S. Pat. No. 7,263,397 titled “Method and Apparatus for Catheter Navigation and Location Mapping in the Heart,” the entire disclosure of which is incorporated herein by reference. This embodiment of the system  16  is based on the principle that when low amplitude electrical signals are passed through the thorax, the body  14  acts as a voltage divider (or potentiometer or rheostat) such that the electrical potential or field strength measured at electrodes on the catheters  18 ,  20  may be used to determine the position of the electrode, and therefore the catheters  18 ,  20 , relative to a pair of external patch electrodes using Ohm&#39;s law and the relative location of a reference electrode (e.g. in the coronary sinus). 
     In one configuration, the system  16  includes three pairs of patch electrodes  28  (namely  28   X1 ,  28   X2 ,  28   Y1 ,  28   Y2 ,  28   Z1 ,  28   Z2 ) that are placed on opposed surfaces of the body  14  (e.g., chest and back, left and right sides of the thorax, and neck and leg) and form generally orthogonal x, y, and z axes as well as a reference electrode/patch (not shown) that is typically placed near the stomach and provides a reference value and acts as the origin of a coordinate system  30  for the system  16 . The electrodes  28  are used to create axes specific electric fields within the body  14 . Electrodes  28   X1 ,  28   X2  may be placed along a first (x) axis. Similarly, electrodes  28   Y1 ,  28   Y2  may be placed along a second (y) axis, and electrodes  28   Z1 ,  28   Z2  may be placed along a third (z) axis. Each of the electrodes  28  may be coupled to a multiplex switch  32 . The ECU  26  is configured through appropriate software to provide control signals to the switch  32  and thereby sequentially couple pairs of electrodes  28  to a signal generator  34 . Sinusoidal currents are driven through each pair of patch electrodes  28  to generate an electromagnetic field within the body  14  and voltage measurements for one or more position sensors (e.g., electrodes) associated with the catheters  18 ,  20  are obtained. The measured voltages are a function of the distance of the position sensors from the patch electrodes  28 . The measured voltages are compared to the potential at the reference electrode and a position of the position sensors within the coordinate system  30  of the navigation system  16  is determined. 
     In an alternative embodiment, the system  16  may comprise a system that employs magnetic fields to detect the position of the catheters  18 ,  20  within the body  14  such as the system available under the trademark “GMPS” or “MEDIGUIDE” by St. Jude Medical, Inc. and generally shown and described in, for example, U.S. Pat. No. 6,233,476 titled “Medical Positioning System,” U.S. Pat. No. 7,197,354 titled “System for Determining the Position and Orientation of a Catheter,” and U.S. Pat. No. 7,386,339 titled “Medical Imaging and Navigation System,” the entire disclosures of which are incorporated herein by reference or the system available under the trademark “CARTO XP” by Biosense Webster, Inc. and generally shown and described in, for example, U.S. Pat. No. 5,391,199 titled “Apparatus and Method for Treating Cardiac Arrhythmias,” U.S. Pat. No. 5,443,489 titled “Apparatus and Method for Ablation,” U.S. Pat. No. 5,558,091 titled “Magnetic Determination of Position and Orientation,” U.S. Pat. No. 6,498,944 titled “Intrabody Measurement,” U.S. Pat. No. 6,788,967 titled “Medical Diagnosis, Treatment and Imaging Systems,” and U.S. Pat. No. 6,690,963 titled “System for Determining the Location and Orientation of an Invasive Medical Instrument,” the entire disclosures of which are incorporated herein by reference. In such a system, a magnetic field generator may be employed having three orthogonally arranged coils, arranged to create a magnetic field within body  14  and to control the strength, orientation, and frequency of the field. The magnetic field generator may be located above or below the patient (e.g., under a patient table) or in another appropriate location. Magnetic fields are generated by the coils and current or voltage measurements for one or more position sensors (e.g., coils) associated with the catheters  18 ,  20  are obtained. The measured currents or voltages are proportional to the distance of the sensors from the coils thereby allowing a position of the sensors within the coordinate system  30  of the system  16 . In yet another alternative embodiment, system  16  may comprise a combination electric-field and magnetic-field based system. 
     In one arrangement, an EP mapping catheter  18  may be provided for use in gathering EP data associated with the tissue  12 . The mapping catheter  18  includes a plurality of EP mapping electrodes  36 . The electrodes  36  are placed in the body  14  (e.g., within the heart) within electrical fields created by exciting the patch electrodes  28 . The electrodes  36  experience voltages that are dependent on the location between the patch electrodes  28  and the position of the electrodes  36  relative to the surface of the tissue  12 . Voltage measurement comparisons made between the electrodes  36  can be used to determine the position of the electrodes  36  relative to the tissue  12 . Movement of the electrodes  36  within the heart (e.g., within a heart chamber) or other internal tissue location produces information regarding the geometry of the internal region of interest. That is, the system  16  collects electrical data from the catheter(s)  18  and uses this information to track catheter movement and construct three-dimensional (3-D) models of the heart chamber or other internal tissue location in which the catheter is positioned. Additionally a physician may sweep the catheter(s)  18  across the heart chamber during data collection to outline the structures and relay the signals to the computer system, which generates the 3-D model. The resulting model may then be utilized to, for example, guide the therapy catheter  20  to one or more internal tissue locations where treatment is needed. Such a system allows for the creation of detailed internal models at the time of study and/or performance of an internal procedure. That is, the system is operative to generate substantially real-time models. The EP catheter  18  may be a non-contact mapping catheter such as the catheter available from St. Jude Medical, Atrial Fibrillation Division, Inc. under the registered trademark “ENSITE ARRAY.” It should be understood, however, that the presented systems, apparatuses and methods may also be used with contact mapping systems in which measurements are taken through contact of electrodes with the tissue surface. In any arrangement, a map or model of the tissue  12  may be generated and this map/model may be utilized for subsequent delivery of a therapeutic substance to one or more target locations. 
     The representative therapy injection catheter  20  is provided for the injection of therapeutic substances into internal body tissues such as tissue  12  at desired locations and at desired depths. The injection catheter  20  includes an injection needle  58 , which may be controllably extended and withdrawn though an internal lumen  64  of the catheter  20 . See, for example,  FIGS. 3A and 3B . In the illustrated embodiment, the internal lumen extends directly through the distal end of the catheter along a central axis of the catheter, though this is not a requirement. The needle is fluidly connected to a supply  44  of therapeutic solution via fluid connector attached to a rearward portion of the needle (See  FIG. 1 ). That is, the needle may be connected to a fluid line that passes through the lumen  64  of the injection catheter  20 . In such an arrangement, a short relatively rigid needle may attach to a flexible fluid lumen. In other embodiments, the therapeutic solution may be contained within an internal reservoir within the catheter. Therapeutic substances within the supply may be displaced through the needle by use of a pump device  46  (e.g., an electrically or robotically actuated pump or manual syringe barrel). 
     The injection catheter  20  may include a cable connector or interface  48 , a handle  50 , a shaft  52  having a proximal end  54  and a distal end  56  (as used herein, “proximal” refers to a direction toward the end of the catheter near the clinician, and “distal” refers to a direction away from the clinician and (generally) inside the body of a patient), the extendable needle  58 , one or more position sensors  60  and one or more contact sensors  62 . The catheter  20  may also include other conventional components not illustrated herein such as a temperature sensor, additional electrodes, and corresponding conductors or leads. The catheter  20  may further include signal processing circuitry and may include a memory accessible upon connection to the ECU  26  or another means for providing identifying information for catheter  20  (e.g., catheter manufacturer, model or type, potential configurations for catheter  20 , etc.) to the ECU  26 . The connector  48  provides mechanical, fluid and electrical connection(s) for various cables and lumens at a proximal end of catheter  20 . 
     The handle  50  provides a location for the clinician to hold a region of interest in the body  14  catheter  20  and may further provide means for steering or guiding the shaft  52  within the body  14 . For example, the handle  50  may include means to move a guidewire extending through the catheter  20  to the distal end  56  of the shaft  52  to steer the distal end  56 . The handle  50  is also conventional in the art and it will be understood that the construction of the handle  50  may vary and may be absent in a fully-robotic implementation of the system. 
     The shaft  52  is an elongated, flexible member configured for movement within the body  14 . As illustrated, the shaft  52  supports the extendable therapy needle  58 , position sensors  60 , contact sensors  62 , associated conductors, and possibly additional electronics used for signal processing or conditioning. The shaft  52  may also permit transport, delivery, and/or removal of fluids (including irrigation fluids and bodily fluids), medicines, and/or surgical tools or instruments. The shaft  52  may be made from conventional materials such as polyurethane and typically defines one or more lumens configured to house and/or transport electrical conductors, fluids, or surgical tools. Depending on its intended use, the shaft  52  may be introduced into a blood vessel or other structure within the body  14  through a conventional introducer sheath. Once introduced, the shaft  52  may then be steered or guided through the body  14  to a desired location such as tissue  12  using guide wires or with pullwires or other means known in the art including remote catheter guidance systems (RCGS) such as a system or systems described and illustrated in U.S. Published Patent Application No. 20090247942 published Oct. 1, 2009 and titled “Robotic Catheter Manipulator Assembly”; U.S. Published Patent Application No. 20090247944 published Oct. 1, 2009 and titled “Robotic Catheter Rotatable Device Cartridge”; U.S. Published Patent Application No. 20090247993 published Oct. 1, 2009 and titled “Robotic Catheter System”; U.S. Published Patent Application No. 20090248042 published Oct. 1, 2009 and titled “Model Catheter Input Device”; International Published Patent Application No. WO 2009/120982 published Oct. 1, 2009 and titled “Robotic Catheter System With Dynamic Response”; U.S. Published Patent Application No. 20100256558 published Oct. 7, 2011 and titled “Robotic Catheter System”; and U.S. patent application Ser. No. 12/933,063 filed Sep. 16, 2010 and titled “Robotic Catheter System Input Device”, the entire disclosures of which are incorporated herein by reference. 
     The position sensors  60  are provided to indicate the position and orientation of the catheter  20  within the coordinate system  30  defined by the medical positioning system  16 . In the illustrated embodiment, the position sensors  60  comprise electrodes that are placed within the body  14  (e.g., within the heart) and within electrical fields created by exciting the patch electrodes  28 . In the illustrated embodiment, the position sensors  60  are button-type electrodes. However, it will be appreciated that other electrodes type may be utilized including, without limitation, ring electrodes and/or a tip electrode (e.g., distal tip  38 ). The sensors  60  experience voltages that are dependent on the location between the patch electrodes  28  and the position of the sensors  60  relative to the surface of the heart. Voltage measurement comparisons made between the sensors  60  can be used to determine the position of the sensors  60  within body  14 . It should also be understood that the type of position sensor used will be dependent on the type of medical positioning system used. For example, other conventional position sensing systems could be used including magnetic positioning systems such as the system available under the trademark “GMPS” or “MEDIGUIDE” from St. Jude Medical, Inc. or the system available under the trademark “CARTO” from Biosense Webster, Inc. in which the case the position sensors  60  may comprise magnetic sensors such as coils. 
     To better control the depth at that therapeutic substances are injected into the internal target tissue, the injection catheter  20  may further include means for sensing contact between the catheter  20  and the tissue  12 . That is, the injection catheter  20  may include one or more contact sensors  62  configured to detect, for example, a force applied to, for example, a distal tip  38  of the catheter  20  resulting from contact by the distal tip with the tissue  12 . Such force sensing sensors allow assessing the degree of mechanical coupling between catheter  20  and tissue  12 . Along these lines, the sensors  62  may generate signals indicative of a change in resistance, voltage, capacitance, impedance or a combination thereof. In one embodiment illustrated in  FIGS. 3A and 3B , sensors  62  are disposed in the distal end  56  of the catheter  20  between the distal tip  38  and the shaft  52 . It should be understood, however, that the exact location of the sensors  62  may vary provided that they are located so as to sense movement of the catheter  20  in response to contact with tissue  12 . 
     The contact sensors  62  may comprise, for example, capacitance sensors that generate a signal indicative of a change in capacitance resulting from application of a force. The force sensors  62  may also comprise piezoelectric sensors that include a piezoelectric material (in the form of a wire, film or tubes, for example) and generate a signal indicative of a change in voltage resulting from placing the piezoelectric material under stress. In another embodiment, the force sensors  62  may also comprise pressure sensitive conductive composite (PSCC) sensors (including, but not limited to, quantum tunneling conductive composite (QTC) sensors) in which the electrical resistance of the composite varies inversely in proportion to the pressure that is applied to the composite. Additional information on exemplary sensor embodiments usable with the disclosed systems, apparatuses and methods may be found in U.S. Published Patent Application No. 2011/0022045 tilted “Ablation Electrodes With Capacitive Sensors for Resolving Magnitude and Direction of Forces Imparted to a Distal Portion of a Cardiac Catheter,” U.S. Published Patent Application No. 2008/0161796 titled “Design of Ablation Electrode With Tactile Sensor,” U.S. Published Patent Application No. 2008/0015568 titled “Dynamic Contact Assessment for Electrode Catheters,” U.S. Published Patent Application No. 2007/0123764 titled “Systems and Methods for Assessing Tissue Contact,” and U.S. Published Patent Application No. 2007/0100332 titled “Systems and Methods for Electrode Contact Assessment,” the entire disclosures of which are incorporated herein by reference. 
     The catheter  20  may include one or more contact sensors  62  disposed in a plane perpendicular to a longitudinal axis  140  of the catheter  20 . Where multiple sensors are used, the sensors may be disposed about the axis with regular or irregular spacing. The use of a multiple sensors  62  enables force detection in a plurality of dimensions including, for example, along the longitudinal axis  140  (stretching and compression) and laterally (bending). The sensor or sensors  62  may be mounted on a support structure within catheter  62  and may be in direct physical contact with the therapy needle or indirect contact. 
     In another embodiment, a pair of optically interactive elements (not shown) provides the means for sensing contact force between the catheter  20  and tissue  12 . In such an embodiment, one or more optical sensors work in combination with an optically interactive surface (not shown) supported within the catheter. The optical sensor may include one or more optic fibers configured to emit and receive light energy from the electromagnetic spectrum. The optically interactive surface has a known position relative to the distal end/tip of the catheter such that a change in position, configuration and/or orientation of surface causes a change in the plane of reflection and a change in a characteristic of light (e.g., intensity, wavelength, phase, spectrum, speed, optical path, interference, transmission, absorption, reflection, refraction, diffraction, polarization and scattering) indicative of a force applied to the distal end by, for example, contact with tissue. Additional information on exemplary optical sensing assemblies usable with the present disclosure may be found in U.S. Published Patent Application No. 2008/0249522 titled “Irrigated Catheter With Improved Fluid Flow,” U.S. Published Patent Application No. 2008/0275428 titled “Optic-Based Contact Sensing Assembly and System,” and International (PCT) Published Patent Application No. WO 2010/078453 titled “Optic-Based Contact Sensing Assembly and System,” the entire disclosures of which are incorporated herein by reference. 
     In any embodiment, the contact sensors  62  generate signals which may be transmitted to the ECU. For instance, such signals may be transmitted along conductors connected to the force sensors  62  and extending through shaft  52  of catheter  20 . The signals may, in some embodiments, be compared to signals generated by a reference electrode coupled to the tissue  12  or electrical ground. ECU  26  may use the information generated by sensors  62  to among other things, determine the force applied to the catheter by target tissue. 
     The display system  24  is provided to convey information to a clinician to assist in diagnosis and/or treatment. As shown, the display system  24  may comprise one or more conventional computer monitors or other display devices. Display system  24  may provide a graphical user interface (GUI) to the clinician. The GUI may include a variety of information including, for example, an image of the geometry of a region of interest in body  14 , associated electrophysiology data, therapy delivery maps and images of catheters  18 ,  20  and other medical devices and related information indicative of the position of catheters  18 ,  20  and other devices relative to the region of interest. See  FIG. 2 . Examples of the type of information that may be displayed are shown in commonly assigned U.S. Pat. No. 7,263,397 titled “Method and Apparatus for Catheter Navigation and Location and Mapping in the Heart,” the entire disclosure of which is incorporated herein by reference. 
     The ECU  26  provides a means for, at least in part, controlling the delivery of therapeutic substances from the extendable needle  58 . The ECU  26  may also be a component of position and navigation system  16  and thereby provide a means for determining the geometry of a region of interest in body  14 , physiologic characteristics of the region of interest and the position and orientation of catheters  18 ,  20  relative to the region of interest. The ECU  26  also provides a means for generating display signals used to control display system  24 . ECU  26  may comprise one or more programmable microprocessors or microcontrollers or may comprise one or more ASICs. ECU  26  may include a central processing unit (CPU) and an input/output (I/O) interface through which ECU  26  may receive a plurality of input signals including signals generated by electrodes on catheters  18 ,  20  and feedback signals from position and navigation system  16  and generate a plurality of output signals including those used to control and/or provide data to catheters  18 ,  20 , display system  24  and/or pump device  46 . Although a single ECU  26  is shown in the illustrated embodiment for use with catheters  18 ,  20  and system  16 , it should be understood that catheters  18 ,  20  and system  16  may be configured with individual ECUs. 
     In controlling the delivery of therapeutic substances from the extendable needle  58 , the ECU  26  may further be configured to determine a degree of coupling (e.g., contact condition) and/or contact force between the distal tip  38  of the catheter and the tissue  12  and/or determine a degree of coupling/force between the needle  58  and tissue (e.g., in an embodiment where one or more force sensors are attached to the needle). Based on the degree of coupling and/or force, in conjunction with a known extension of the needle relative to the distal end of the catheter, the ECU may determine if the needle is inserted to a desired depth within the tissue. Typically, the ECU  26  may determine the degree of coupling responsive to signals indicative of contact forces between catheter  20  and tissue  12  including, for example, signals generated by the force sensors  62  described hereinabove. Additionally or alternatively, the ECU  26  may determine the degree of coupling responsive to signals indicative of impedance between a distal tip electrode  38  and tissue. As discussed in U.S. Published Patent Application No. 2010/0228247 titled “Assessment of Electrode Coupling of Tissue Ablation,” U.S. Published Patent Application No. 2009/0163904 titled “System and Method for Assessing Coupling Between an Electrode and Tissue,” and U.S. Published Patent Application No. 2010/0168735 titled “System and Method for Assessing Coupling Between and Electrode and Tissue,” the entire disclosures of which are incorporated herein by reference, the ECU  26  may enable generation of an excitation signal from a signal source (not shown) across a path from an electrode (e.g., tip electrode  38 ) on the catheter  20  comprising a positive polarity connector SOURCE(+) to a return electrode located, for example, on catheter  20  or body  14  comprising a negative polarity connector SOURCE(−). This signal induces a response signal along a path from the catheter electrode which also comprises a positive polarity connector SENSE(+) to another return electrode on catheter  20  or body  14  comprising a negative polarity connector SENSE(−) that is dependent on the complex impedance at the catheter/tissue interface. Conventional circuits may be used to resolve this signal into component parts for the complex impedance at the catheter/tissue interface allowing ECU  26  to determine values for one or more components of a complex impedance between the electrode (e.g., tip electrode) and tissue  12 . These components may including a resistance between the electrode and the tissue  12 , a reactance there between, an impedance magnitude there between and/or an impedance phase angle there between. The ECU  26  may further compute a coupling index responsive to these components and possibly other measurements that is indicative of the degree of coupling (e.g., mechanical/force coupling), which is presented to the clinician on display system  24  or is otherwise made available for use in controlling delivery of an injectable therapeutic substance. Such impedance measurements provide measurements of contact between the electrode and tissue and may be correlated to contact forces. 
       FIG. 4  illustrates the injection catheter as inserted within an introducer sheath  6 . The sheath  6  is a tubular structure defining at least one lumen or longitudinal channel. The sheath  6  is used to introduce and guide the catheter  14  to a targeted internal tissue area. The catheter  14 , however, may be used alone or with other guiding and introducing type devices depending on the particular procedure being performed. As shown in  FIG. 4 , the shaft  52  of the catheter  20  forms a tubular body extending from the proximal handle  50 , through the sheath  6  and extending out of the distal end of the sheath  6 . As noted the proximal handle  50  may be omitted and a proximal portion of the shaft  52  may be connected to a robotic actuator. In the particular system configuration of  FIG. 4 , the sheath  8  is configured to receive and guide the catheter  20  within an internal lumen to a location in the heart or other internal tissue location once the sheath  8  is pre-positioned in an appropriate location. At such time, the distal end of the catheter may extend beyond the distal end of the sheath for subsequent guidance to target locations for injection of therapeutic substances. In addition, the sheath provides a number of additional ports  4  that allow for insertion of various instruments and/or fluids into the internal lumen of the sheath and/or an internal lumen of the catheter. In one arrangement, the needle  58  may include a flexible shaft and may be inserted through a separate port. However, this is not a requirement. 
     The present disclosure is based, in part, on the realization that contact between the distal end of a catheter and target tissue can adversely affect an intended insertion depth of a needle. During an internal injection procedure, the injection catheter  20  is initially guided to a target location/target tissue. This is illustrated in  FIG. 2 , which shows the 24 distal tip of the injection catheter  20  being positioned relative to a first internal target location  80   a . More specifically, the ECU may generate a model of a region of interest (e.g., heart tissue  12 ; shown in 2D for purposes of discussion) on a display  24  along with a representation of the injection catheter  20 . Based on the output of the position sensors  60 , the position of the injection catheter  20  is shown relative to the region of interest. Accordingly, a clinician may guide the distal end of the catheter  20  to one or more target locations  80   a - 80   n , which may be user selected targets or computer generated targets (e.g., grid targets). The distal end of the catheter is typically positioned such that it is brought into contact with the target location (e.g.,  80   a ) prior to advancing the needle  58  to inject a therapeutic substance. This is also illustrated in  FIG. 5A . However, once the catheter is disposed against the tissue surface, advancement of the injection needle  58  may result in both a deflection of the tissue surface  80  and/or displacement of the distal tip of the catheter away from the tissue surface  80 . See  FIG. 5B . Either the displacement of the tissue or the displacement of the distal end of the catheter  20  relative to the tissue (i.e., in response to needle advancement) can result in the needle failing to insert or failing to insert to a desired depth within the tissue. As such, injection of a therapeutic substance may be too shallow. Alternatively, if the distal end of the catheter is compressed too far into the tissue, insertion of the needle may be too deep. See  FIG. 5C . Accordingly, the presented systems and methods utilize contact sensing to confirm proper insertion of a needle at an internal tissue target location. 
     A first process using force sensing to confirm proper needle insertion is illustrated in  FIG. 6 . In this process  200 , a force between the catheter and internal target location is compared (e.g., by the ECU) before and after advancement of the needle to confirm the injection catheter remains in contact with the target tissue after needle insertion. Initially, the injection catheter  20  is positioned  202  against an internal target location. Once positioned at a desired target location, a first contact measurement (e.g., force, impedance etc.) is obtained  204 , which is indicative of contact between the catheter and the internal target location. See, e.g.,  FIG. 5A . After obtaining the first force measurement, which confirms the injection catheter  20  is in contact with the target tissue, the needle  58  is advanced  206  a desired distance beyond the injection catheter  20 . After needle advancement, a second contact measurement is obtained  208 , which is again indicative of the contact between the injection catheter and internal target location. The first and second contact measurements are compared  210  to determine if the second force corresponds to the first force. That is, a comparison is made to determine if the forces are equal or within a predetermined amount of one another (e.g., substantially equal). Substantially equal contact measurements confirm the injection catheter  20  remains in contact with the tissue after needle insertion and confirms insertion of the needle  58  to the desired depth within the tissue. See, e.g.,  FIG. 5D . At this time, the therapeutic substance may be injected  214  through the needle into the tissue. Alternatively, if the contact measurements are different (e.g., a second force is less than a first force by more than a predetermined amount) the advancement of the needle has displaced the tissue and/or displaced the injection catheter from the tissue. See, e.g.,  FIG. 5B . Accordingly, the position of the injection catheter may be adjusted  212  (e.g., advanced) to bring the injection catheter back into contact with the target tissue. That is, the position of the injection catheter may be adjusted until the second contact measurement corresponds to the first contact measurement. Once the second contact measurement corresponds to the first contact measurement, the injection catheter has reestablished the initial contact with the tissue and the needle is inserted to the desired depth within the tissue. Accordingly a therapeutic substance may be injected  214  through the needle. 
     In a variation of the process of  FIG. 6 , the system allows for establishing sufficient contact between the distal end of the injection catheter and the tissue to insure proper needle insertion. That is, a minimum contact may be established between the injection catheter and the target tissue location prior to needle insertion. In this regard, the contact sensors of the injection catheter provide a measurement of a magnitude of the contact between the catheter and the target tissue and the ECU determines if this contact is sufficient for subsequent needle insertion. However, it has been recognized that the sufficiency of contact between the catheter and the target tissues changes for tissues with different mechanical properties, such as tissue compliance. For example, the compliance of the relatively more compliant smooth atrial wall is different from relatively less compliant myocardial tissue. Thus, different force or contract levels may be required for different tissues. 
     In one embodiment, the ECU include a database or memory of contact and/or force values for use in determining sufficiency of contact between the catheter and the tissue. Such values may depend on various system parameters such as the size of the catheter, size/gauge of the needle, needle insertion depth and/or the tissue being injected. In an exemplary embodiment, contact conditions corresponding to various measurements (optical, pressure, impedance, etc.) may be predetermined, e.g., during testing for any of a wide range of tissue types for a variety of operating parameters. These predetermined force or contact measurements may be stored in memory, e.g., as tables or other suitable data structures. The processor ECU may then access the tables in memory and determine if a current contact measurement is adequate prior to needle insertion. By way of example, the ECU may receive a contact measurement and correlate that measurement based on current parameters to determine the adequacy of contact prior to needle insertion. An indication of adequate contact for needle insertion may be output to a user/clinician (e.g., at display device) upon which the needle may be advanced (e.g., manually or robotically). If the contact is inadequate, an appropriate output may be generated to allow, for example, application of additional contact force or reduction of contact force. 
       FIGS. 7A and 7B  illustrate a further embodiment of an injection catheter  20 . In this embodiment, the injection catheter  20  again includes an injection needle  58  and one or more position sensors  60 . However, in this embodiment, a force sensor  62  is connected to the needle  58  rather than between the distal tip  38  and shaft  52  of the catheter (all electrical connections are omitted for clarity). This embodiment allows for monitoring the force applied to the needle  58  as the needle is inserted into internal tissue. Typically, the force applied to the tip of the needle will be a zero or null value when the needle is in the retracted position as shown in  FIG. 7A . The force applied to the needle will increase as the needle extends into tissue. When extended to desired depth, the force on the needle returns to zero or near zero. Accordingly, such information may allow for monitoring insertion of the needle into the internal tissue. In a further embodiment, the distal tip  38  may form an impedance electrode that allows for identifying contact with the tissue. Accordingly, an output from the tip electrode  38  may be monitored in conjunction with the output of the force sensor  62  attached to the needle to monitor needle insertion. In a further embodiment, additional force sensors (not shown) may be incorporated into the shaft of the catheter and utilized in conjunction with the needle force sensor. In a further arrangement, the needle may form an impedance electrode. Accordingly, the impedance of the needle may be monitored as it is advanced. The change in the environment around the needle (e.g., insertion into tissue) will result in a change in the monitored impedance. Such a needle impedance value may, in an alternate embodiment, be utilized alone or in conjunction with additional contact measurements to confirm needle insertion. 
     As illustrated in  FIGS. 7A and 7B , a flexible sheath  88  is disposed around the lumen extending between the needle  58  and the supply of therapeutic solution (not shown). The sheath  88  allows for applying force to the needle from a proximal location (e.g., catheter handle). Such a sheath may be incorporated into any of the catheter embodiments. The illustrated catheter also includes a needle extension sensor  84  attached to the tip of the injection catheter  20 . The sensor  84  is configured to identify markings  86  disposed at known locations along the length of the needle  58 . In one embodiment, the sensor  84  is a magnetic sensor and the markings  86  are magnetic bands applied about the needle  58  however, it will be appreciated that different sensors may be utilized including, for example, an impedance-based sensor. In any embodiment, the sensor  84  allows for monitoring the extension of the needle  58  relative to the catheter  20 . When utilizing a catheter having the needle extension sensor  84 , the ECU can generate an output that allows the clinician to monitor needle extension providing fine needle depth control. Alternatively, in a robotically controlled system, the ECU may robotically control extension of the needle to a desired extension beyond the distal end of the catheter based on the sensor output. Alternatively or in addition, markings may be provided on proximal portions of the sheath  88  and/or the needle lumen that provide an indication of the relative position of the needle to the distal end of the catheter. Such markings may allow manual or robotic needle extension. Such markings may be incorporated into any of the catheter embodiments. 
     Although various embodiments of the disclosed systems, apparatuses and methods 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 spirit or scope of this disclosure. For example, different arrangements exist for determining the position of a distal end of a catheter and for determining a force between a contact surface of a catheter and patient tissue. Further, additional arrangements exist for determining the displacement of a catheter-borne needle relative to a distal end of a catheter and/or patient tissue. Further it will be appreciated that 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 present invention, and do not create limitations, particularly as to the position, orientation, or use of the disclosed systems, apparatuses and methods. 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 limiting. Changes in detail or structure may be made without departing from the spirit of the disclosed systems, apparatuses and methods as defined in the appended claims.