Patent Publication Number: US-2023157569-A1

Title: Mapping System with Real Time Electrogram Overlay

Description:
FIELD OF THE INVENTION 
     The present invention relates to medical systems, and in particular, but not exclusively, to catheter devices. 
     BACKGROUND 
     A wide range of medical procedures involve placing probes, such as catheters, within a patient&#39;s body. Location sensing systems have been developed for tracking such probes. Magnetic location sensing is one of the methods known in the art. In magnetic location sensing, magnetic field generators are typically placed at known locations external to the patient. A magnetic field sensor within the distal end of the probe generates electrical signals in response to these magnetic fields, which are processed to determine the coordinate locations of the distal end of the probe. These methods and systems are described in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and 6,332,089, in PCT International Publication No. WO 1996/005768, and in U.S. Patent Application Publications Nos. 2002/0065455 and 2003/0120150 and 2004/0068178. Locations may also be tracked using impedance or current based systems. 
     One medical procedure in which these types of probes or catheters have proved extremely useful is in the treatment of cardiac arrhythmias. Cardiac arrhythmias and atrial fibrillation in particular, persist as common and dangerous medical ailments, especially in the aging population. 
     Diagnosis and treatment of cardiac arrhythmias include mapping the electrical properties of heart tissue, especially the endocardium and the heart volume, and selectively ablating cardiac tissue by application of energy. Such ablation can cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions. Various energy delivery modalities have been disclosed for forming lesions, and include use of microwave, laser, pulsed field, and more commonly, radiofrequency energies to create conduction blocks along the cardiac tissue wall. In a two-step procedure, mapping followed by ablation, electrical activity at points within the heart is typically sensed and measured by advancing a catheter containing one or more electrical sensors into the heart, and acquiring data at a multiplicity of points. These data are then utilized to select the endocardial target areas at which the ablation is to be performed. 
     Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral vein, and then guided into the chamber of the heart of concern. A typical ablation procedure involves the insertion of a catheter having a one or more electrodes at its distal end into a heart chamber. A reference electrode may be provided, generally taped to the skin of the patient or by means of a second catheter that is positioned in or near the heart. RF (radio frequency) current is applied between the tip electrode(s) of the ablating catheter, and the reference electrode, flowing through the media between the electrodes it, i.e., blood and tissue. The distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to its electrical resistance. The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue which is electrically non-conductive. 
     Therefore, when placing an ablation or other catheter within the body, particularly near the endocardial tissue, it is desirable to have the distal tip of the catheter in direct contact with the tissue. The contact can be verified, for example, by measuring the contact between the distal tip and the body tissue. U.S. Patent Application Publication Nos. 2007/0100332, 2009/0093806 and 2009/0138007, whose disclosures are incorporated herein by reference describe methods of sensing contact pressure between the distal tip of a catheter and tissue in a body cavity using a force sensor embedded in the catheter. 
     A number of references have reported methods to determine electrode-tissue contact, including U.S. Pat. Nos. 5,935,079; 5,891,095; 5,836,990; 5,836,874; 5,673,704; 5,662,108; 5,469,857; 5,447,529; 5,341,807; 5,078,714; and Canadian Patent Application 2,285,342. A number of these references, e.g., U.S. Pat. Nos. 5,935,079, 5,836,990, and 5,447,529 determine electrode-tissue contact by measuring the impedance between the tip electrode and a return electrode. As disclosed in the &#39;529 patent, it is generally known than impedance through blood is generally lower that impedance through tissue. Accordingly, tissue contact has been detected by comparing the impedance values across a set of electrodes to premeasured impedance values when an electrode is known to be in contact with tissue and when it is known to be in contact only with blood. 
     U.S. Pat. No. 9,168,004 to Gliner, at al., which is herein incorporated by reference, describes using machine learning to determine catheter electrode contact. The &#39;004 patent describes cardiac catheterization being carried out by memorizing a designation of a contact state between an electrode of the probe and the heart wall as an in-contact state or an out-of-contact state, and making a series of determinations of an impedance phase angle of an electrical current passing through the electrode and another electrode, identifying maximum and minimum phase angles in the series, and defining a binary classifier adaptively as midway between the extremes. A test value is compared to the classifier as adjusted by a hysteresis factor, and a change in the contact state is reported when the test value exceeds or falls below the adjusted classifier. 
     US Patent Publication 2013/0085416 of Mest, which is herein incorporated by reference, describes a method for the in vivo re-calibration of a force sensing probe such as an electrophysiology catheter which provides for the generation of an auto zero zone. The distal tip of the catheter or other probe is placed in a body cavity within the patient. Verification that there is no tissue contact is made using electrocardiogram (ECG) or impedance data, fluoroscopy or other real-time imaging data and/or an anatomical mapping system. Once verification that there is no tissue contact made, the system recalibrates the signal emanating from the force sensor setting it to correspond to a force reading of zero grams and this recalibrated baseline reading is used to generate and display force readings based on force sensor data. 
     SUMMARY 
     There is provided in accordance with an embodiment of the present disclosure, a medical system, including a catheter configured to be inserted into a chamber of a heart of a living subject, and including a distal end including catheter electrodes configured to contact tissue at respective locations within the chamber of the heart, at least one position sensor configured to provide at least one position signal indicative of a position of the distal end, a display, and processing circuitry configured to compute the position of the distal end of the catheter responsively to the at least one position signal, render to the display a three-dimensional (3D) anatomical map of the chamber of the heart and a 3D representation of the distal end of the catheter, and render to the display over at least part of the anatomical map, at least one intracardiac electrogram (IEGM) trace representing electrical activity in the tissue that is sensed by at least one of the catheter electrodes. 
     Further in accordance with an embodiment of the present disclosure the processing circuitry is configured to render to the display over at least part of the anatomical map, multiple IEGM traces representing electrical activity in the tissue that is sensed by respective ones of the catheter electrodes. 
     Still further in accordance with an embodiment of the present disclosure the processing circuitry is configured to receive signals from the catheter, and in response to the signals assess a respective quality of contact of each of at least a sub-set of the catheter electrodes with the tissue, and render to the display multiple IEGM traces representing electrical activity in the tissue that is sensed by respective ones of the catheter electrodes responsively to the respective quality of contact of each of the respective ones of the catheter electrodes with the tissue of the heart at the respective locations. 
     Additionally in accordance with an embodiment of the present disclosure the processing circuitry is configured to render to the display the multiple IEGM traces representing electrical activity in the tissue that is sensed by respective ones of the catheter electrodes responsively to the respective quality of contact of each of the respective ones of the catheter electrodes with the tissue of the heart at the respective locations exceeding a threshold quality of contact. 
     Moreover in accordance with an embodiment of the present disclosure the processing circuitry is configured to render to the display the multiple IEGM traces representing electrical activity in the tissue that is sensed by n respective ones of the catheter electrodes responsively to the respective quality of contact of each of the n respective ones of the catheter electrodes with the tissue of the heart being among n highest qualities of contact of the at least sub-set of the catheter electrodes. 
     Further in accordance with an embodiment of the present disclosure the processing circuitry is configured to receive a user input selecting the sub-set of the catheter electrodes. 
     Still further in accordance with an embodiment of the present disclosure the processing circuitry is configured to receive a user input selecting a region of the anatomical map, and render to the display the multiple IEGM traces representing electrical activity in the tissue that is sensed by respective ones of the catheter electrodes responsively to the respective ones of the catheter electrodes being located in proximity to the selected region of the anatomical map, and the respective quality of contact of the respective ones of the catheter electrodes with the tissue of the heart at the respective locations. 
     Additionally in accordance with an embodiment of the present disclosure the processing circuitry configured to move a position of the at least one IEGM trace rendered on the display to follow the movement in the position of the distal end of the catheter. 
     Moreover in accordance with an embodiment of the present disclosure the processing circuitry configured to execute a first software program configured to compute the position of the distal end of the catheter responsively to the at least one position signal, and render to the display the anatomical map of the chamber of the heart and the representation of the distal end of the catheter, and output data indicative of the at least one IEGM trace representing electrical activity in the tissue that is sensed by the at least one of the catheter electrodes, and a second software program configured to receive the data output by the first software program, and render to the display over the at least part of the anatomical map, the at least one IEGM. 
     Further in accordance with an embodiment of the present disclosure the processing circuitry is configured to render the at least one IEGM trace as a progressing IEGM trace representing current electrical activity in the tissue. 
     Still further in accordance with an embodiment of the present disclosure the processing circuitry is configured to render the at least one IEGM trace as a static IEGM trace representing recorded electrical activity in the tissue. 
     Additionally in accordance with an embodiment of the present disclosure the processing circuitry is configured to render the at least one IEGM trace as a progressing IEGM trace representing recorded electrical activity in the tissue. 
     Moreover, in accordance with an embodiment of the present disclosure the processing circuitry is configured to receive a user input selecting a point on the anatomical map, and render to the display the at least one IEGM trace responsively to the user input. 
     There is also provided in accordance with another embodiment of the present disclosure, a medical system, including a catheter configured to be inserted into a chamber of a heart of a living subject, and including a distal end including catheter electrodes configured to contact tissue at respective locations within the chamber of the heart, at least one position sensor configured to provide at least one position signal indicative of a position of the distal end, a display, and processing circuitry configured to compute the position of the distal end of the catheter responsively to the at least one position signal, assess a respective quality of contact of each of at least a sub-set of the catheter electrodes with the tissue, render to the display a three-dimensional (3D) anatomical map of the chamber of the heart and a 3D representation of the distal end of the catheter, and render to the display multiple intracardiac electrogram (IEGM) traces representing electrical activity in the tissue that is sensed by respective ones of the catheter electrodes responsively to the respective quality of contact of each of the respective ones of the catheter electrodes with the tissue of the heart at the respective locations. 
     Further in accordance with an embodiment of the present disclosure the processing circuitry is configured to render to the display the multiple IEGM traces representing electrical activity in the tissue that is sensed by respective ones of the catheter electrodes responsively to the respective quality of contact of each of the respective ones of the catheter electrodes with the tissue of the heart at the respective locations exceeding a threshold quality of contact. 
     Still further in accordance with an embodiment of the present disclosure the processing circuitry is configured to render to the display the multiple IEGM traces representing electrical activity in the tissue that is sensed by n respective ones of the catheter electrodes responsively to the respective quality of contact of each of the n respective ones of the catheter electrodes with the tissue of the heart being among n highest qualities of contact of the at least sub-set of the catheter electrodes. 
     Additionally in accordance with an embodiment of the present disclosure the processing circuitry is configured to receive a user input selecting the sub-set of the catheter electrodes. 
     Moreover in accordance with an embodiment of the present disclosure the processing circuitry is configured to receive a user input selecting a region of the anatomical map, and render to the display the multiple IEGM traces representing electrical activity in the tissue that is sensed by respective ones of the catheter electrodes responsively to the respective ones of the catheter electrodes being located in proximity to the selected region of the anatomical map, and the respective quality of contact of the respective ones of the catheter electrodes with the tissue of the heart at the respective locations. 
     There is also provided in accordance with still another embodiment of the present disclosure, a medical method, including providing at least one position signal indicative of a position of a distal end of a catheter inserted into a chamber of a heart of a living subject, computing the position of the distal end of the catheter responsively to the at least one position signal, rendering to a display a three-dimensional (3D) anatomical map of the chamber of the heart and a 3D representation of the distal end of the catheter, and rendering to the display over at least part of the anatomical map, at least one intracardiac electrogram (IEGM) trace representing electrical activity in tissue of the chamber that is sensed by at least one catheter electrode of the catheter. 
     There is also provided in accordance with still another embodiment of the present disclosure, a medical method, including providing at least one position signal indicative of a position of a distal end of a catheter inserted into a chamber of a heart of a living subject, computing the position of the distal end of the catheter responsively to the at least one position signal, assessing a respective quality of contact of each of at least a sub-set of catheter electrodes of the catheter with tissue of the chamber, rendering to a display a three-dimensional (3D) anatomical map of the chamber of the heart and a 3D representation of the distal end of the catheter, and rendering to the display multiple intracardiac electrogram (IEGM) traces representing electrical activity in the tissue that is sensed by respective ones of the catheter electrodes responsively to the respective quality of contact of each of the respective ones of the catheter electrodes with the tissue of the heart at respective locations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood from the following detailed description, taken in conjunction with the drawings in which: 
         FIG.  1    is a schematic, pictorial illustration of a catheter tracking system constructed and operative in accordance with an embodiment of the present invention; 
         FIG.  2    is a flowchart including steps in a first method of operation of the system of  FIG.  1   ; 
         FIG.  3    is a schematic view of a representation of a catheter in an anatomical map rendered in the system of  FIG.  1   ; 
         FIG.  4    is a flowchart including steps in a second method of operation of the system of  FIG.  1   ; and 
         FIG.  5    is a schematic view of the representation of the catheter in the anatomical map of  FIG.  3    with multiple electrograms overlaying the map. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Overview 
     As mentioned previously, in a two-step procedure, mapping followed by ablation, electrical activity at points within the heart is typically sensed and measured by advancing a catheter containing one or more electrodes into the heart, and acquiring data at a multiplicity of points. These data are then utilized to select the target areas at which the ablation is to be performed. 
     In particular, the electrical activity is typically displayed as intracardial electrogram (IEGM) traces for analysis by a physician in order to find sources of arrhythmia. A catheter electrode, which is not in contact with tissue in the heart, generally measures some electrical signal from the heart tissue and a far field signal. When the catheter electrode is in contact with the heart tissue, the amplitude of the signal is mainly based on tissue conductivity, while the far field is minor. Therefore, the physician is generally interested in analyzing the IEGM traces of electrodes in contact with the tissue. 
     For focal catheters with one or two electrodes, a single IEGM trace is typically displayed for a physician to analyze. A physician can quickly determine based on the form of the signal whether the catheter electrode providing the signal is in contact with the tissue. However, multi-electrode catheters simultaneously capturing electrical activity from different tissue locations may provide data for a plurality of IEGM traces to be displayed at the same time on a single display. In some cases, the number of IEGM traces may be too numerous for the physician to easily determine which of the IEGM traces are provided by electrodes in contact with the tissue, and which are not. 
     An example of a multielectrode catheter is the Octaray® catheter, with in excess of 48 electrodes, produced by Biosense Webster Inc., of Irvine, Calif., USA. The Octaray includes eight deflectable arms disposed at the distal end of a shaft, with each of the deflectable arms including six electrodes. Details of such catheter can be found in U.S. patent Ser. No. 11/058,315, which is incorporated by reference herein. Some catheters may include more electrodes, for example, but not limited to, 120 electrodes. 
     In addition to the need to determine electrode contact during mapping discussed above, the physician performing an ablation procedure monitors the contact of electrodes with tissue as effective ablation generally requires sufficient contact between the ablation electrode(s) and the tissue. Recently, ultra-fast ablation treatment technologies such as irreversible electroporation (IRE) have been introduced into the market. The speed as well as the ease at which the treatment may be executed may be improved by helping the physician focus on the clinically relevant input during the procedure. 
     Embodiments of the present invention solve at least some of the above problems during a medical procedure such as a mapping or ablation procedure, by presenting a physician with one or more IEGM traces (e.g., voltage versus time graphs) of signals acquired by electrodes of a catheter, overlaying the representation of the catheter and anatomical map so that the IEGM trace(s) are visible in the region of the screen where the physician is generally concentrating. In some embodiments, the IEGM trace(s) may move on the screen to follow movement of the catheter to allow the IEGM trace(s) to stay in the region of the screen where the physician is now concentrating. 
     In some embodiments, a main mapping software application may process signals provided by the catheter and body surface electrodes and provide other mapping functions such a generating and rendering the anatomical map and the representation of the catheter to a display. A secondary software application may receive data (for example, a position of the distal end of the catheter on the display, and IEGMs captured by the catheter electrodes) from the main mapping software application. The secondary software application may then display the IEGMs overlaying the anatomical map, typically centered around the distal end of the catheter. In this manner, the main mapping software application does not need to be changed, or undergoes minor changes, while other functionality is provided by the secondary software application. In other embodiments, the functionality provided herein may be implemented with a single software application. 
     In some embodiments, instead of showing all the IEGM traces of signals acquired by all the electrodes of the catheter, the number of IEGM traces displayed may be reduced to select one or more of the IEGM traces more relevant to the physician. 
     In some embodiments, the IEGM traces selected for display may be captured by groups of electrodes selected by the physician. For example, the physician may be more interested in certain groups of electrodes, such as electrodes at the distal tip of the catheter or electrodes around an equator of a basket or balloon distal end of the catheter. In some embodiments, the IEGM traces selected for display may be those electrodes in sufficient contact with tissue of a given region of the heart. The region of the heart may be a named region, which is selected by the physician (e.g., pulmonary vein, right atrium, left atrium, right ventricle, left ventricle), or a region selected on the anatomical map using a pointing device such as a mouse, stylus, or a finger. 
     Additionally, or alternatively, the number of IEGM traces displayed may be limited based on a quality of contact of the respective electrodes with tissue of the heart. For example, IEGM traces of electrodes having a sufficient quality of contact greater than a threshold quality of contact may be displayed, or the IEGM traces of the n electrodes having the highest quality of contact among the electrodes may be displayed. 
     In the above discussion, sufficiency of tissue contact is used to decide whether or not to display the IEGM traces. A quality of contact may be assessed based on different methods including impedance measurements, force or pressure measurements, or from analysis of IEGM traces, as will now be described in more detail. 
     The displayed may be current IEGM traces being currently captured by the electrodes or recorded IEGM traces which may be displayed as progressing IEGMs (in which different time windows of electrical activity of the tissue is shown over time) or static IEGMs (in which one or more time-windows of electrical activity of the tissue is shown without changing the IEGM data being displayed). 
     In response to signals provided by the catheter, processing circuitry assesses the respective quality of contact of each of the catheter electrodes with the tissue in the heart. Any one of the catheter electrodes may be in full or partial contact with the tissue of the heart. In some cases, any one of the catheter electrodes may be in contact with the tissue via another fluid such as blood of various thicknesses. The quality of contact (full or partial contact, or contact via another liquid) of any one of the catheter electrodes with the tissue may be assessed based on the signals provided by the catheter. 
     The term “quality of contact” as used in the specification and claims is defined herein as a quantitative indicator of the degree of contact between one of the catheter electrodes and the tissue. The “quality of contact” may be expressed directly, for example in terms a measured electrical impedance, or indirectly, for example in terms of contact force, pressure or IEGM amplitude, as will now be described below in more detail. In some embodiments, the “quality of contact” may be expressed as a measurement from the respective electrode to the tissue based on computing the position of the electrode as located in the generated anatomical map and the known location of the tissue given by the generated anatomical map. 
     In some embodiments, the catheter may provide signals which provide an indication of impedance between the catheter electrodes and body surface electrodes. The indication of the impedance provides an indication of a quality of contact, such that a higher value of impedance between one of the catheter electrodes and the body surface electrodes indicates a higher quality of contact between that catheter electrode and the tissue. A value of impedance may be selected to define a minimum quality of contact considered to represent sufficient contact between any one of the catheter electrodes and the tissue. 
     In some embodiments, the impedance between one of the catheter electrodes and another one of the electrodes on the catheter may be used as a measure of quality of contact. As disclosed in the &#39;529 patent mentioned in the background section above, it is generally known that impedance through blood is generally lower than impedance through tissue. Accordingly, tissue contact may be assessed by comparing impedance values across a set of electrodes to premeasured impedance values when an electrode is known to be in sufficient contact with tissue and when it is known to be in contact only with blood. 
     In some embodiments, the method of U.S. Pat. No. 9,168,004 to Gliner, at al., which is herein incorporated by reference, may be used to assess quality of contact using a machine learning based method. 
     In some embodiments, the catheter may provide signals from force or pressure sensors. The indication of force or pressure provides an indication of a quality of contact, such that a higher value of force or pressure indicates a higher quality of contact between a catheter electrode and the tissue. A value of force or pressure may be selected to define a minimum quality of contact considered to represent sufficient contact between any one of the catheter electrodes and the tissue. 
     In some embodiments, the generated IEGM traces may be used to assess the quality of contact between any one of the catheter electrodes and the tissue. The maximum amplitude of the IEGM trace associated with one of the catheter electrodes is indicative of the quality of contact between that catheter electrode and the tissue, such that a higher value of the maximum amplitude of the IEGM trace indicates a higher quality of contact between that catheter electrode and the tissue. An amplitude value of the IEGM trace may be selected to define a minimum quality of contact considered to represent sufficient contact between any one of the catheter electrodes and the tissue. 
     System Description 
     Reference is now made to  FIG.  1   , which is a schematic, pictorial illustration of a catheter tracking system  20 , in accordance with an embodiment of the present invention. The system  20  includes a catheter  40  configured to be inserted into a body part (e.g., a chamber of a heart  26 ) of a living subject (e.g., a patient  28 ) seen in detail in inset  25 . A physician  30  navigates the catheter  40  (for example, a basket catheter produced by Biosense Webster, Inc. of Irvine, Calif., USA), seen in detail in inset  45 , to a target location in the heart  26  of the patient  28 , by manipulating a deflectable segment of an insertion tube  22  of the catheter  40 , using a manipulator  32  near a proximal end  29  of the insertion tube  22 , and/or deflection from a sheath  23 . In the pictured embodiment, physician  30  uses catheter  40  to perform anatomical mapping of a cardiac chamber. 
     The catheter  40  includes a distal end  33 . The distal end  33  of the catheter  40  includes an assembly  35  (e.g., a basket assembly as shown in  FIG.  1    or a balloon assembly or any suitable distal end assembly, e.g., grid, flexible splines or a focal catheter) on which at least one (e.g., multiple) catheter electrode(s)  48  (only some labeled for the sake of simplicity) are disposed. The electrodes  48  are configured to contact tissue at respective locations with the chamber of the heart. The assembly  35  is disposed distally to the insertion tube  22  and may be connected to the insertion tube  22  via a coupling member of the insertion tube  22  at the distal end  33 . The coupling member of the insertion tube  22  may be formed as an integral part of the rest of the insertion tube  22  or as a separate element which connects with the rest of the insertion tube  22 . 
     The assembly  35  further comprises multiple flexible strips  55  (only two labeled for the sake of simplicity), to each of which are coupled the electrodes  48 . The assembly  35  may include any suitable number of electrodes  48 . In some embodiments, the assembly  35  may include ten flexible strips  55  and 120 electrodes, with twelve electrodes disposed on each flexible strip  55 . 
     The catheter  40  includes a pusher  37 . The pusher  37  is typically a tube that is disposed in a lumen of the insertion tube  22  and spans from the proximal end  29  to the distal end  33  of the insertion tube  22 . A distal end of the pusher  37  is connected to distal ends of the flexible strips  55 , typically via a coupling member of the pusher  37 . The coupling member of the pusher  37  may be formed as an integral part of the rest of the pusher  37  or as a separate element which connects with the rest of the pusher  37 . The distal end of the insertion tube  22  is connected to proximal ends of the flexible strips  55 , typically via the coupling member of the distal end  33 . The pusher  37  is generally controlled via the manipulator  32  to deploy the assembly  35  and change an ellipticity of the assembly  35  according to the longitudinal displacement of the pusher  37  with respect to the insertion tube  22 . The actual basket assembly  35  structure may vary. For example, flexible strips  55  may be made of a printed circuit board (PCB), or of a shape-memory alloy, or any suitable material. 
     Embodiments described herein refer mainly to a basket distal-end assembly  35 , purely by way of example. In alternative embodiments, the disclosed techniques can be used with a catheter having a balloon-based distal-end assembly or of any other suitable type of distal-end assembly. 
     Catheter  40  is inserted in a folded configuration, through sheath  23 , and only after the catheter  40  exits sheath  23  is catheter  40  able to change shape by retracting pusher  37 . By containing catheter  40  in a folded configuration, sheath  23  also serves to minimize vascular trauma on its way to the target location. 
     The distal end  33  of the catheter  40  comprises magnetic coil sensors  50 A and  50 B. The magnetic coil sensor  50 A is shown in inset  45  at the distal edge of insertion tube  22  (i.e., at the proximal edge of basket assembly  35 ). The sensor  50 A may be a Single-Axis Sensor (SAS), or a Double-Axis Sensor (DAS) or a Triple-Axis Sensor (TAS). Similarly, the sensor  50 B may be a SAS, DAS, or TAS. Magnetic coil sensors  50 A and  50 B and electrodes  48  are connected by wires running through insertion tube  22  to various driver circuitries in a console  24 . 
     In some embodiments, system  20  comprises a magnetic-sensing sub-system to estimate an ellipticity of the basket assembly  35  of catheter  40 , as well as its elongation/retraction state, inside a cardiac chamber of heart  26  by estimating the elongation of the basket assembly  35  from the distance between sensors  50 A and  50 B. Patient  28  is placed in a magnetic field generated by a pad containing multiple magnetic field generator coils  42 , which are driven by a unit  43 . The magnetic field generator coils  42  are configured to generate respective alternating magnetic fields, having respective different frequencies, into a region where a body-part (e.g., the heart  26 ) of a living subject (e.g., the patient  28 ) is located. The magnetic coil sensors  50 A and  50 B are configured to output electrical signals responsively to detecting the respective magnetic fields. For example, if there are nine magnetic field generator coils  42  generating nine respective different alternating magnetic fields with nine respective different frequencies, the electrical signals output by the magnetic coil sensors  50  will include components of the nine different frequency alternating magnetic fields. The magnitude of each of the magnetic fields varies with distance from the respective magnetic field generator coils  42  such that the location of the magnetic coil sensors  50  may be determined from the magnetic fields sensed by the magnetic coil sensors  50 . Therefore, the transmitted alternating magnetic fields generate the electrical signals in sensors  50 A and  50 B, so that the electrical signals are indicative of position and orientation of the magnetic coil sensors  50  in the heart chamber. 
     The generated signals are transmitted to console  24  and become corresponding electrical inputs to processing circuitry  41 . The processing circuitry  41  may use the signals to compute: the elongation of the basket assembly  35 , in order to estimate basket ellipticity and elongation/retraction state from the calculated distance between sensors  50 A and  50 B; and compute a relative orientation between the axes of the sensors  50 A and  50 B to estimate a shape of the expandable distal end assembly  35  (e.g., a basket shape) responsively to the relative orientation, as described in more detail below. 
     The bow of the flexible strips  55  and/or the positions of the electrodes  48  (or other features) on the flexible strips  55  with respect to a fixed point on the catheter  40  (such as the distal tip of the insertion tube  22 ) may be measured for various distances between the magnetic sensors  50 A,  50 B and for various relative orientation angles between the magnetic sensors  50 A,  50 B. For example, the positions of the electrodes  48  with respect to the fixed point on the catheter  40  may be measured for every 0.2 mm movement of the pusher  37  with respect to the insertion tube  22  and for every 1 degree of relative orientation between the magnetic sensors  50 A,  50 B (up to a maximum sideways movement of the assembly  35 ). At each different distance/relative-orientation combination, the computed distance and computed relative orientation angle between the magnetic sensors  50 A,  50 B is recorded along with the position data of the electrodes  48 . This data may then be used to estimate the bow of the flexible strips  55  and/or the positions of the electrodes  48  (or other features) on the flexible strips  55  with respect to a fixed point on the catheter  40  (such as the distal tip of the insertion tube  22 ) responsively to the computed distance and relative orientation angle between the magnetic sensors  50 A,  50 B. 
     Additionally, or alternatively, the bow of the flexible strips  55  may be estimated based on the following assumptions: (a) each of the flexible strips  55  is of a fixed and known length; (b) each of the flexible strips  55  is connected to the pusher  37  via a coupler, with the distal ends of the flexible strips  55  being substantially perpendicular (within an error of plus or minus 10 degrees) to the longitudinal axis of the insertion tube  22 ; (c) each of the flexible strips  55  is connected to the insertion tube  22  via a coupler, which couples the proximal ends of the flexible strips  55  to the insertion tube  22 , substantially parallel (within an error of plus or minus 10 degrees) to the longitudinal axis of the insertion tube  22 . Based on the above assumptions (a)-(c), and the computed positions of the couplers based on the computed positions of the magnetic sensors  50 A,  50 B, the bow of each of the flexible strips  55  may be computed using a third-degree polynomial. In some embodiments, the bow of the flexible strips  55  and/or the positions of the electrodes  48  (or other features) on the flexible strips  55  with respect to a fixed point on the catheter  40  (such as the distal tip of the insertion tube  22 ) may be computed based on the computed distance and orientation between the magnetic sensors  50 A,  50 B and a model of the catheter  40  which provides the bow of the flexible strips  55  and/or the positions of the electrodes  48  for the computed distance based on the mechanical properties and dimensions of the flexible strips  55 . 
     A method of position and/or direction sensing using external magnetic fields and magnetic coil sensors, such as sensors  50 A and  50 B, is implemented in various medical applications, for example, in the CARTO® system, produced by Biosense-Webster, and is described in detail in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and 6,332,089, in PCT Patent Publication WO 96/05768, and in U.S. Patent Application Publications 2002/0065455 A1, 2003/0120150 A1 and 2004/0068178 A1. 
     In some embodiments, the processing circuitry  41  uses position-signals received from the electrodes  48  or body surface electrodes  49 , and the magnetic sensor  50  to estimate a position or orientation of the assembly  35  inside a body part, such as inside a cardiac chamber. In some embodiments, the processing circuitry  41  correlates the position signals received from the electrodes  48 ,  49  with previously acquired magnetic location-calibrated position signals, to estimate the position of the assembly  35  inside the body part. The position coordinates of the electrodes  48  may be determined by the processing circuitry  41  based on, among other inputs, measured impedances, voltages or on proportions of currents distribution, between the electrodes  48  and the body surface electrodes  49 . 
     The method of position sensing using current distribution measurements and/or external magnetic fields is implemented in various medical applications, for example, in the Carto® system, produced by Biosense Webster Inc. (Irvine, Calif.), and is described in detail in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612, 6,332,089, 7,756,576, 7,869,865, and 7,848,787, in PCT Patent Publication WO 96/05768, and in U.S. Patent Application Publications 2002/0065455 A1, 2003/0120150 A1 and 2004/0068178 A1. 
     The Carto®3 system applies Active Current Location (ACL) which is a hybrid current-distribution and magnetic-based position-tracking technology. In some embodiments, using ACL, the processing circuitry  41  estimates the positions of the electrodes  48 . In some embodiments, the signals received from the electrodes  48 ,  49  are correlated with a current-to-position matrix (CPM) which maps current distribution ratios (or another electrical value) with a position that was previously acquired from magnetic location-calibrated position signals. The current distribution ratios are based on measurements of the body surface electrodes  49  of current flowing from the electrodes  48  to the body surface electrodes  49 . 
     In some embodiments, to visualize catheters which do not include a magnetic sensor, the processing circuitry  41  may apply an electrical signal-based method, referred to as Independent Current Location (ICL) technology. In ICL, the processing circuitry  41  calculates a local scaling factor for each voxel of the volume in which catheters are visualized. The factor is determined using a catheter with multiple electrodes having a known spatial relationship, such as a lasso-shaped catheter. However, although yielding accurate local scaling (e.g., over several millimeters), ICL is less accurate when applied to a volume of a whole heart chamber, whose size is in the order of centimeters. The ICL method, in which positions are calculated based on current distribution proportions can have errors and may yield a distorted shape of the assembly  35 , due to the non-linear nature of the current-based ICL space. In some embodiments, the processing circuitry  41  may apply the disclosed ICL method to scale ICL space and the assembly  35  shape into a correct one, based on known smaller scale distances between electrodes of a lasso-shaped catheter, for example, as well as based on larger scale distances, themselves based on the known distance between the electrodes  48  at the ends of the assembly  35 . 
     Processing circuitry  41 , typically part of a general-purpose computer, is further connected via a suitable front end and interface circuits  44 , to receive signals from body surface-electrodes  49 . Processing circuitry  41  is connected to surface-electrodes  49  by wires running through a cable  39  to the chest of patient  28 . The catheter  40  includes a connector  47  disposed at the proximal end  29  of the insertion tube  22  for coupling to the processing circuitry  41 . 
     In some embodiments, processing circuitry  41  renders to a display  27 , a representation  31  of at least a part of the catheter  40  and an anatomical map or body-part, (e.g., from a mapping process or from a scan (e.g., CT or MRI) of the body-part previously registered with the system  20 ), responsively to computed position coordinates of the insertion tube  22  and the flexible strips  55 . 
     Processing circuitry  41  is typically programmed in software to carry out the functions described herein. The software may be downloaded to the computer in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory. The system  20  may also include a memory  51  used by the processing circuitry  41 . 
     The example illustration shown in  FIG.  1    is chosen purely for the sake of conceptual clarity.  FIG.  1    shows only elements related to the disclosed techniques for the sake of simplicity and clarity. System  20  typically comprises additional modules and elements that are not directly related to the disclosed techniques, and thus are intentionally omitted from  FIG.  1    and from the corresponding description. The elements of system  20  and the methods described herein may be further applied, for example, to control an ablation of tissue of heart  26 . 
     Reference is now made to  FIGS.  2  and  3   .  FIG.  2    is a flowchart  100  including steps in a first method of operation of the system  20  of  FIG.  1   .  FIG.  3    is a schematic view of a representation  59  of the catheter  40  in an anatomical map  61  rendered in the system  20  of  FIG.  1   . 
     As previously described with reference to  FIG.  1   , the position of the distal end of the catheter  40  inside a chamber of the heart may be found using a variety of methods, for example, based on signals provided by at least one position sensor, which may include the magnetic coil sensors  50  and/or the electrodes  48  and/or the body surface electrodes  49 . The position sensor(s)  50 ,  48 ,  49  are configured to provide at least one position signal indicative of a position or orientation of the distal end with reference to a 3D anatomical map of the chamber of the heart. In some embodiments, the position of the distal end of the catheter  40  may be found using imaging techniques such as ultrasonic scanning and suitable processing of the ultrasound images. The processing circuitry  41  is configured to compute the position of the distal end of the catheter  40  responsively to the position signal(s) provided by the position sensor(s)  50 ,  48 ,  49  (block  102 ). That is, circuitry  41  computes the position of the distal end of the catheter from the at least one position signal to define the position and orientation of the distal end or electrodes of the catheter with respect to a chamber of the heart and thereby render to the display a three-dimensional (3D) anatomical map of the chamber of the heart and a 3D representation of the location and orientation of the distal end of the catheter as referenced to the 3D anatomical map. By providing the 3D anatomical map and the 3D representation of the catheter, the physician is able to identify where the position of the distal end of the catheter (and its electrodes) are located with reference to the chamber of the heart and move the distal end of the catheter within the heart to specific locations in the heart chamber by viewing the 3D representations of the heart and catheter. 
     The processing circuitry  41  is configured to render to the display  27  the three-dimensional (3D) anatomical map  61  of the chamber of the heart  26  and the 3D representation  59  of the distal end of the catheter  40  (block  104 ) as positioned or orientated with respect to the 3D anatomical map. The anatomical map  61  may be generated using any suitable anatomical map generation method, for example, but not limited to, Fast Anatomical Mapping (FAM). FAM is described in U.S. Pat. No. 10,918,310 to Cohen, et al. In FAM, a smooth shell is generated around a three-dimensional (3D) cloud of data points, such as a cloud of computed electrode positions of the electrodes  48  so that the position and orientation of the distal end and electrodes  48  with respect to the chamber of the heart can be graphically represented in the 3D anatomical map  61  of the heart. 
     In some embodiments, the processing circuitry  41  is configured to receive signals from the catheter  40 , and in response to the signals, assess a respective quality of contact of each of (at least a sub-set of) the catheter electrodes  48  with the tissue (block  106 ). 
     Any one of the catheter electrodes  48  may be in full or partial contact with the tissue of the heart  26 . In some cases, any one of the catheter electrodes  48  may be in contact with the tissue via another fluid such as blood of various thicknesses. The quality of contact (full or partial contact, or contact via another liquid) of any one of the catheter electrodes  48  with the tissue may be assessed based on the signals provided by the catheter  40 . 
     As previously mentioned, the term “quality of contact” is a quantitative indicator of the degree of (electrical) contact between one of the catheter electrodes  48  and the tissue. The “quality of contact” may be expressed directly, for example in terms a measured electrical impedance, or indirectly, for example in terms of contact force, pressure or IEGM amplitude, as will now be described below in more detail. The “quality of contact” may also be expressed in terms of distance from the electrodes to the tissue based on computed positions of the electrodes  48  and the anatomical map  61 . 
     In some embodiments, the catheter  40  may provide signals which provide an indication of impedance between the catheter electrodes  48  and the body surface electrodes  49 . The indication of the impedance provides an indication of a quality of contact, such that a higher value of impedance between one of the catheter electrodes  48  and the body surface electrodes  49  indicates a higher quality of contact between that catheter electrode  48  and the tissue. A value of impedance may be selected to define a minimum quality of contact considered to represent sufficient contact between any one of the catheter electrodes  48  and the tissue. 
     In some embodiments, the impedance between one of the catheter electrodes  48  and another one of the electrodes on the catheter  40  may be used as a measure of quality of contact. As disclosed in the &#39;529 patent mentioned in the background section above, it is generally known that impedance through blood is generally lower than impedance through tissue. Accordingly, tissue contact may be assessed by comparing impedance values across a set of electrodes to premeasured impedance values when an electrode is known to be in sufficient contact with tissue and when it is known to be in contact only with blood. 
     In some embodiments, the method of U.S. Pat. No. 9,168,004 to Gliner, at al., which is herein incorporated by reference, may be used to assess quality of contact. The &#39;004 patent describes using machine learning to determine catheter electrode contact. The &#39;004 patent describes cardiac catheterization being carried out by memorizing a designation of a contact state between an electrode of the probe and the heart wall as an in-contact state or an out-of-contact state, and making a series of determinations of an impedance phase angle of an electrical current passing through the electrode and another electrode, identifying maximum and minimum phase angles in the series, and defining a binary classifier adaptively as midway between the extremes. A test value is compared to the classifier as adjusted by a hysteresis factor, and a change in the contact state is reported when the test value exceeds or falls below the adjusted classifier. 
     In some embodiments, the catheter  40  may provide signals from force or pressure sensors (not shown), disposed at different locations on the flexible strips  55 , that provide an indication of force or pressure exerted by the catheter electrodes  48  on the tissue. The indication of force or pressure provides an indication of a quality of contact, such that a higher value of force or pressure indicates a higher quality of contact between that catheter electrode  48  and the tissue. A value of force or pressure may be selected to define a minimum quality of contact considered to represent sufficient contact between any one of the catheter electrodes  48  and the tissue. These embodiments, may use any suitable force or pressure sensors as well as any suitable method for measuring the force or pressure, including any of the patents or Patent Publications mentioned in the background section including the method described in US Patent Publication 2013/0085416 of Mest, which is herein incorporated by reference, and describes a method for the in vivo re-calibration of a force sensing probe such as an electrophysiology catheter which provides for the generation of an auto zero zone. The distal tip of the catheter or other probe is placed in a body cavity within the patient. Verification that there is no tissue contact is made using electrocardiogram (ECG) or impedance data, fluoroscopy or other real-time imaging data and/or an anatomical mapping system. Once verification that there is no tissue contact made, the system recalibrates the signal emanating from the force sensor setting it to correspond to a force reading of zero grams and this recalibrated baseline reading is used to generate and display force readings based on force sensor data. 
     In some embodiments, intracardiac electrogram (IEGM) traces generated by the processing circuitry  41  may be used to assess the quality of contact between any one of the catheter electrodes  48  and the tissue. The maximum amplitude of the IEGM trace associated with one of the catheter electrodes  48  is indicative of the quality of contact between that catheter electrode  48  and the tissue, such that a higher value of the maximum amplitude of the IEGM trace indicates a higher quality of contact between that catheter electrode  48  and the tissue. An amplitude value of the IEGM trace may be selected to define a minimum quality of contact considered to represent sufficient contact between any one of the catheter electrodes  48  and the tissue. 
     In some embodiments, the steps of the methods of  FIGS.  2  and  4    are executed via a single software program. In some embodiments, the method described with reference to  FIG.  2    is executed by a first software program and the method described with reference to  FIG.  4    is executed by a second software program. 
     In some embodiments, the processing circuitry  41  is configured to execute a main mapping software application  108  (also referred herein as a “first software program”) to perform the steps of blocks  102 - 106 , while a secondary software application  110  ( FIG.  4   ) (also referred herein as a “second software program) may receive data (for example, a position of the distal end of the catheter  40  on the display  27 , and IEGMs of the catheter electrodes  48 ) from the main mapping software application. The steps performed by the secondary software application are described with reference to  FIG.  4   . In this manner, the main mapping software application does not need to be changed, or undergoes minor changes, while other functionality is provided by the secondary software application. In other embodiments, the steps described with reference to  FIGS.  2  and  4    may be implemented with a single software application. 
     Therefore, in some embodiments, the main mapping software application  108  running on the processing circuitry  41  is configured to output data indicative of the IEGM trace(s) representing electrical activity in the tissue that is sensed by the catheter electrode(s)  48 , and a position of the distal end of the catheter  40  on the display  27  (block  112 ), for example using a TCP-based communication protocol. 
     Reference is now made to  FIG.  4   , which is a flowchart  120  including steps in a second method of operation of the system  20  of  FIG.  1   . Reference is also made to  FIG.  3   . 
     As previously mentioned, the steps described with reference to  FIG.  4    may be performed by the secondary software application  110 . Therefore, the processing circuitry  41  is configured to execute the secondary software application  110  to receive the data output by the main mapping software application  108  (block  122 ), for example using a TCP-based communication protocol. In other embodiments, the steps described with reference to  FIGS.  2  and  4    may be implemented with a single software application. 
     The physician  30  is able to select a region of, and/or a point on, the anatomical map  61 , and/or a sub-set of the electrodes  48  as criteria in rendering one or more IEGMs to the display  27 , as described in more detail below with reference to  FIG.  5   . In some embodiments, the processing circuitry  41  is configured to receive a user input selecting a sub-set of the catheter electrodes (block  124 ). The sub-set may be selected from predefined sub-sets. For example, one sub-set may include electrodes at the distal tip of a basket-shaped catheter or electrodes around an equator of a basket or balloon-shaped catheter. In some embodiments, the processing circuitry  41  is configured to receive a user input selecting a region  63  of the anatomical map  61  (block  126 ). The region may be selected from a predefined list of regions, such as pulmonary vein, right atrium, left atrium, right ventricle, left ventricle, or the region  63  may be selected by delineating the region on the anatomical map  61  using a pointing device such as a mouse, stylus, or finger, as shown in  FIG.  3   . In some embodiments, the processing circuitry  41  is configured to receive a user input selecting a point  65  on the anatomical map  61  (block  128 ). 
     Reference is now made to  FIG.  5   , which is a schematic view of the representation  59  of the catheter  40  in the anatomical map  61  of  FIG.  3    with multiple intracardiac electrograms (IEGM) traces  67  overlaying the map  61 . Reference is also made to  FIG.  4   . 
     The processing circuitry  41  is configured to render to the display  27 , over at least part of the anatomical map  61  (and/or over at least part of the representation  59  of the catheter  40 ), one or more IEGM traces  67  representing electrical activity in the tissue of the heart  26  that is sensed by one or more of the catheter electrodes  48  (block  130 ). For example, if the physician  30  selected the point  65  in the step of block  128 , the processing circuitry  41  may be configured to render to the display one IEGM trace  67  which represents electrical activity closest to the point  65 . The rendered IEGM trace  67  may represent current electrical activity captured by one of the electrodes  48  at, or near, the point  65 , or previously captured electrical activity at, or near, the point  65 . Therefore, in some embodiments, the processing circuitry  41  is configured to render one IEGM trace  67  at least partially over the anatomical map  61  responsively to receiving the user input selecting the point  65  on the anatomical map  61 . 
     In some embodiments, the processing circuitry  41  is configured to render to the display  27  over at least part of the anatomical map  61 , multiple IEGM traces  67  representing electrical activity in the tissue of the heart  26  that is sensed by respective catheter electrodes  48 . 
     The number of IEGM traces  67  rendered to the display  27  may be dependent on the quality of contact of each electrode  48  or a sub-set of electrodes  48  (for example, the sub-set of electrodes  48  selected in the step of block  124 ) so that the more relevant IEGM traces  67  are rendered to the display  27 . Therefore, in some embodiments, the processing circuitry  41  is configured to render to the display  27  (over at least part of the anatomical map  61 ) multiple IEGM traces  67  representing electrical activity in the tissue that is sensed by respective catheter electrodes  48  responsively to the respective quality of contact of each respective catheter electrode  48  with the tissue of the heart at the respective locations. In some embodiments, the processing circuitry  41  is configured to render to the display  27  (over at least part of the anatomical map  61 ) the multiple IEGM traces  67  representing electrical activity in the tissue that is sensed by respective catheter electrodes  48  responsively to the respective quality of contact of each respective catheter electrode  48  with the tissue of the heart at the respective locations exceeding a threshold quality of contact. In other words, the IEGM traces  67  of the electrodes  48  (or the selected sub-set of the electrodes  48 ) having a quality of contact exceeding the threshold quality of contact are rendered to the display  27  over at least part of the anatomical map  61  by the processing circuitry  41 . 
     The number of IEGM traces  67  rendered to display  27  may be limited to n IEGM traces  67  so that the IEGM traces  67  of n corresponding electrodes  48  (or n electrodes  48  of the selected sub-set of the electrodes  48 ) closest to the tissue (measured by the quality of contact) are rendered to the display  27 . Therefore, in some embodiments, the processing circuitry  41  is configured to render to the display  27  n IEGM traces  67  representing electrical activity in the tissue that is sensed by n respective catheter electrodes  48  (e.g., n electrodes  48  from all the electrodes  48  or of the selected sub-set of electrodes  48 ) responsively to the respective quality of contact of each of the n respective catheter electrodes  48  with the tissue of the heart being among n highest qualities of contact of the electrodes  48  or the sub-set of the catheter electrodes  48 . The value n may be set to any suitable number by the physician  30 . The value n may depend on the number of electrodes  48  and/or the size of the display  27 . 
     In some embodiments, the IEGM traces  67  may be limited to the IEGM traces  67  captured by respective electrodes  48  from one or more selected regions  63  of the heart  26 . Therefore, in some embodiments, the processing circuitry  41  is configured to render to the display  27  multiple IEGM traces  67  representing electrical activity in the tissue that is sensed by respective catheter electrodes  48  responsively to: the respective catheter electrodes  48  being located in proximity to the selected region  63  of the anatomical map  61 ; and optionally the respective quality of contact of the respective catheter electrodes  48  with the tissue of the heart  26  at the respective locations (exceeding a threshold quality of contact). 
     The IEGM traces  67  may be progressing signals (i.e., dynamically change with time) or static signals of current, or previously recorded, electrical activity captured from the tissue of the heart  26 . Therefore, in some embodiments, the processing circuitry  41  is configured to render the IEGM trace(s)  67  as progressing IEGM trace(s) representing current electrical activity in the tissue. In some embodiments, the processing circuitry  41  is configured to render the IEGM trace(s)  67  as static IEGM trace(s) representing recorded electrical activity in the tissue. In some embodiments, the processing circuitry  41  is configured to render the IEGM trace(s)  67  as progressing IEGM trace(s) representing recorded electrical activity in the tissue. 
     In some embodiments, the processing circuitry  41  is configured to move a position of the IEGM trace(s)  67  rendered on the display  27  to follow movement in the position of the distal end of the catheter  40  (block  132 ), as provided by the step of block  102  of  FIG.  2   . 
     As used herein, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein. More specifically, “about” or “approximately” may refer to the range of values ±20% of the recited value, e.g., “about 90%” may refer to the range of values from 72% to 108%. 
     Various features of the invention which are, for clarity, described in the contexts of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment may also be provided separately or in any suitable sub-combination. 
     The embodiments described above are cited by way of example, and the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.