Abstract:
A method for displaying information, including receiving measurements, with respect to an invasive probe inside a body of a subject, of probe parameters consisting of a force exerted by the probe on tissue of the subject and temperatures measured by sensors of the probe. The method further includes, responsively to the measurements, displaying in a single map on a display screen a graphical representation of a distribution of the temperatures in a vicinity of the probe and superimposing thereon a vector representation of the force.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to graphic displays, and specifically to displays related to the temperature and force measured by a catheter. 
       BACKGROUND OF THE INVENTION 
       [0002]    PCT/US2012/059131 Patent Application to Ghaffari et al., whose disclosure is incorporated herein by reference, describes an apparatus for medical diagnosis. The disclosure provides a series of screen shots of an example graphical user interface demonstrating a variety of conditions simulated with the apparatus. 
         [0003]    U.S. Patent Application 2003/0153905 to Edwards, et al. whose disclosure is incorporated herein by reference, describes systems for ablation of hollow organs. The disclosure describes a temperature map in which the temperature data may be used to monitor and control ablation. 
         [0004]    U.S. Patent Application 2006/0253116 to Avitall, et al. whose disclosure is incorporated herein by reference, describes catheters, systems, and methods for performing medical procedures such as tissue ablation. The disclosure describes a graphical representation of an internal anatomical structure, which may be displayed in a display window of a monitor. 
         [0005]    U.S. Patent Application 2007/0293792 to Sliwa, et al. whose disclosure is incorporated herein by reference, describes prostate probe systems comprising either a force or pressure sensor mounted on or in a rectally insertable probe or a temperature sensor mounted on or in a rectally insertable probe, or both. The disclosure describes a thermographic or temperature mapping capability. 
         [0006]    U.S. Patent Application 2012/0226130 to De Graff, et al. whose disclosure is incorporated herein by reference, describes systems that integrate stretchable or flexible circuitry, including arrays of active devices for enhanced sensing, diagnostic, and therapeutic capabilities. The disclosure describes a graphical presentation and mapping functionality. 
         [0007]    U.S. Patent Application 2012/0232388 to Curra, et al. whose disclosure is incorporated herein by reference, describes ultrasound systems and methods for real-time noninvasive spatial temperature estimation. The disclosure claims that strain and spectral information can be compounded and correlated with both strain-based and spectral-based temperature calibration maps. 
         [0008]    U.S. Patent Application 2013/0079650 to Turgeman, et al. whose disclosure is incorporated herein by reference, describes a graphic user interface for physical parameter mapping. The disclosure describes receiving a selection from a user of a value in a parameter sub-range and displaying a candidate location for further measurement. 
         [0009]    Endosense, of Geneva, Switzerland, produce a “Tactisys Quartz” system. The system is claimed to allow visualization of contact force between a catheter tip of the system and a heart wall. 
         [0010]    Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered. 
       SUMMARY OF THE INVENTION 
       [0011]    An embodiment of the present invention provides a method for displaying information, including: 
         [0012]    receiving measurements, with respect to an invasive probe inside a body of a subject, of probe parameters consisting of a force exerted by the probe on tissue of the subject and temperatures measured by sensors of the probe; and 
         [0013]    responsively to the measurements, displaying in a single map on a display screen a graphical representation of a distribution of the temperatures in a vicinity of the probe and superimposing thereon a vector representation of the force. 
         [0014]    Typically, the vector representation includes a first indication of a magnitude of the force and a second indication of a force-direction of the force. 
         [0015]    In a disclosed embodiment the vector representation includes an arrow, the first indication includes a width of the arrow, and the second indication includes a combination of a length of the arrow and a direction of the arrow. 
         [0016]    In a further disclosed embodiment the vector representation includes an arrow and a text box associated with the arrow, the first indication includes text within the text box, and the second indication includes a combination of a length of the arrow and a direction of the arrow. 
         [0017]    In a yet further disclosed embodiment the vector representation includes a first circle having a first center, the graphical representation of the distribution includes a second circle having a second center, the first indication includes a diameter of the first circle, and the second indication consists of a combination of a distance between the first and second centers and a direction therebetween. 
         [0018]    In an alternative embodiment the method includes calculating a center of the graphical representation, and displaying the center in the single map. 
         [0019]    There is further provided, according to an embodiment of the present invention embodiment of the present invention, apparatus for displaying information, including: 
         [0020]    a probe, configured to be inserted into a body of a subject; 
         [0021]    a force sensor attached to the probe, coupled to provide a force signal indicative of a force exerted by the probe on tissue of the subject; 
         [0022]    temperature sensors attached to the probe, coupled to provide temperature signals of temperatures in a vicinity of the probe; 
         [0023]    a display screen; and 
         [0024]    a processor coupled to receive the force signal and the temperature signals, to display in a single map on the display screen a graphical representation of a distribution of the temperatures, and to superimpose thereon a vector representation of the force. 
         [0025]    The present disclosure will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a schematic illustration of an invasive medical procedure, according to an embodiment of the present invention; 
           [0027]      FIGS. 2A ,  2 B, and  2 C schematically illustrate a distal end of a probe used in the procedure of  FIG. 1 , according to an embodiment of the present invention; 
           [0028]      FIG. 3A  is a schematic diagram illustrating a temperature distribution in the vicinity of a distal end of the probe, as displayed on a screen, according to an embodiment of the present invention; 
           [0029]      FIG. 3B  is a schematic diagram illustrating a vector representation of the force exerted by the distal end, as displayed on the screen, according to an embodiment of the present invention; 
           [0030]      FIG. 3C  and  FIG. 3D  are respective illustrations of a first single combined force-temperature map and a second single combined force-temperature map, according to embodiments of the present invention; 
           [0031]      FIG. 4A  is a schematic diagram illustrating a vector representation of the force exerted by distal the end  22 , as displayed on the screen, according to an alternative embodiment of the present invention; 
           [0032]      FIG. 4B  and  FIG. 4C  are respective illustrations of single combined force-temperature maps, according to alternative embodiments of the present invention; 
           [0033]      FIG. 5A  is a schematic diagram illustrating a vector representation of the force exerted by the distal end, according to a further alternative embodiment of the present invention; 
           [0034]      FIG. 5B  and  FIG. 5C  are respective illustrations of single combined force-temperature maps, according to further alternative embodiments of the present invention; 
           [0035]      FIG. 6A  and  FIG. 6B  are respective illustrations of single combined force-temperature maps, according to disclosed embodiments of the present invention; 
           [0036]      FIG. 7A  and  FIG. 7B  are respective illustrations of single combined force-temperature maps, according to further disclosed embodiments of the present invention; and 
           [0037]      FIG. 8A  and  FIG. 8B  are respective illustrations of single combined force-temperature maps, according to yet further disclosed embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0038]    In the following description, like elements in the drawings are identified by like numerals, and the like elements are differentiated as necessary by appending a letter to the identifying numeral. 
         [0039]      FIG. 1  is a schematic illustration of an invasive medical procedure  10  using apparatus  12 , according to an embodiment of the present invention. The procedure is performed by a medical professional  14 , and, by way of example, procedure  10  is assumed to comprise ablation of a portion of a myocardium  16  of the heart of a human patient  18 . In order to perform the ablation, professional  14  inserts a probe  20  into a lumen of the patient, so that a distal end  22  of the probe enters the heart of the patient. Distal end  22  comprises electrodes mounted on the outside of the distal end, the electrodes contacting respective regions of the myocardium. Probe  20  has a proximal end  28 . Distal end  22  of the probe is described in more detail below with reference to  FIGS. 2A and 2B . 
         [0040]    Apparatus  12  is controlled by a system processor  46 , which is located in an operating console  48  of the apparatus. During the procedure, processor  46  typically tracks a location and an orientation of distal end  22  of the probe, using any method known in the art. For example, processor  46  may use a magnetic tracking method, wherein magnetic transmitters external to patient  18  generate signals in coils positioned in the distal end. The Carto® system produced by Biosense Webster, of Diamond Bar, Calif., uses such a tracking method. 
         [0041]    The software for processor  46  may be downloaded to the processor in electronic form, over a network, for example. Alternatively or additionally, the software may be provided on non-transitory tangible media, such as optical, magnetic, or electronic storage media. The track of distal end  22  is typically displayed on a three-dimensional representation  60  of the heart of patient  18  on a screen  62 . 
         [0042]    In order to operate apparatus  12 , processor  46  communicates with a memory  50 , which has a number of modules used by the processor to operate the apparatus. Thus, memory  50  comprises a temperature module  52 , an ablation module  54 , and a force module  56 , the functions of which are described below. Memory  50  typically comprises other modules, such as a tracking module for operating the tracking method used by processor  46 , and an irrigation module allowing the processor to control irrigation provided for distal end  22 . For simplicity, such other modules, which may comprise hardware as well as software elements, are not illustrated in  FIG. 1 . 
         [0043]    Processor  46  uses results of measurements of temperature and force, acquired by modules  52  and  56 , to display on screen  62  a combined force-temperature map  64 . Embodiments of force-temperature map  64  are described in more detail below. 
         [0044]      FIGS. 2A ,  2 B, and  2 C schematically illustrate distal end  22  of probe  20 , according to an embodiment of the present invention.  FIG. 2A  is a sectional view along the length of the probe,  FIG. 2B  is a cross-sectional view along a cut IIB-IIB that is marked in  FIG. 2A , and  FIG. 2C  is a perspective view of a section of the distal end. An insertion tube  70  extends along the length of the probe and is connected at the termination of its distal end to a conductive cap electrode  24 A, which is assumed herein to be used for ablation.  FIG. 2C  is a schematic perspective view of cap electrode  24 A. Cap electrode  24 A has an approximately plane conducting surface  84  at its distal end and a substantially circular edge  86  at its proximal end. Conductive cap electrode  24 A is herein also termed the ablation electrode. Proximal to ablation electrode  24 A there are typically other electrodes such as electrode  24 B. Typically, insertion tube  70  comprises a flexible, biocompatible polymer, while electrodes  24 A,  24 B comprise a biocompatible metal, such as gold or platinum, for example. Ablation electrode  24 A is typically perforated by an array of irrigation apertures  72 . 
         [0045]    An electrical conductor  74  conveys radio-frequency (RF) electrical energy from ablation module  54  ( FIG. 1 ), through insertion tube  70 , to electrode  24 A, and thus energizes the electrode to ablate myocardial tissue with which the electrode is in contact. Module  54  controls the level of RF power dissipated via electrode  34 A. During the ablation procedure, cooling fluid flowing out through apertures  72  may irrigate the tissue under treatment. 
         [0046]    Temperature sensors  78  are mounted within conductive cap electrode  24 A at locations that are arrayed around the distal tip of the probe, both axially and circumferentially. In this example, cap  24 A contains six sensors, with one group in a distal location, close to the tip, and the other group in a slightly more proximal location. This distribution is shown only by way of example, however, and greater or smaller numbers of sensors may be mounted in any suitable locations within the cap. Sensors  78  may comprise thermocouples, thermistors, or any other suitable type of miniature temperature sensor. These sensors are connected by leads running through the length of insertion tube  70  to provide temperature signals to temperature module  52 . 
         [0047]    In a disclosed embodiment cap  24 A comprises a side wall  73  that is relatively thick, on the order of 0.5 mm thick, in order to provide the desired thermal insulation between temperature sensors  78  and the cooling fluid inside a central cavity  75  of the tip. The cooling fluid exits cavity  75  through apertures  72 . Sensors  78  are mounted on rods  77 , which are fitted into longitudinal bores  79  in side wall  73 . Rods  77  may comprise a suitable plastic material, such as polyimide, and may be held in place at their distal ends by a suitable glue  81 , such as epoxy. U.S. patent application Ser. No. 13/716,578, which is incorporated herein by reference, describes a catheter having temperature sensors mounted in a similar configuration to that described above. The arrangement described above provides an array of six sensors  78 , but other arrangements, and other numbers of sensors, will be apparent to those having ordinary skill in the art, and all such arrangements and numbers are included within the scope of the present invention. Another arrangement of sensors  78  is described in U.S. patent application Ser. No. 13/716,578, referenced above. 
         [0048]    In addition to the temperature sensors, distal end  22  comprises a force sensor  90 , which is configured to measure the force exerted by the distal end on tissue contacted by the distal end. Force sensor  90  generates signals in response to the measured force, and the signals are transferred to force module  56 , which operates the sensor and which calculates a value for the magnitude, as well as a value for the direction, of the force exerted. The direction of the force exerted is measured with respect to an axis  92 , typically the axis of symmetry, of distal end  22 . 
         [0049]    In the description herein, distal end  22  is assumed to define a set of xyz orthogonal axes, where axis  92  corresponds to the z axis of the set, and orthogonal x and y axes are in any convenient xy plane orthogonal to the z axis. For simplicity, the xy plane is herein assumed to correspond to the plane defined by circle  86 , the origin of the xyz axes is assumed to be the center of the circle. 
         [0050]    Force sensor  90  may comprise any convenient sensor of force or pressure known in the art. By way of example, herein force sensor  90  is assumed to operate by measuring the deflection, parallel to z axis  92  and orthogonal to the axis, i.e., in an xy plane, of a cylindrically shaped spring  94 . The deflection of spring  94  may be measured by transmitting an alternating magnetic field from a magnetic transmitter  96  located in proximity to the distal end of the spring, and measuring the received magnetic field in magnetic receivers  98  located at the proximal end of the spring. Typically transmitter  96  and receivers  98  are coils, transmitter  96  being located on axis  92 , and receivers  98  being distributed symmetrically around the axis. In force sensor  90  there are three receivers  98  (two are shown in the figure). Operating signals between force module  90  and the transmitter and the receivers are transferred by conductors  100 , and enable the force module to generate a unique value for the magnitude of a given force, as well as a unique value for the direction of the force with respect to the xyz axes of distal end  22 . Force sensors similar to force sensor  90  are described in U.S. Patent Applications 2009/0306650 to Govari et al., 2011/0130648 to Beeckler et al., and 2012/0253167 to Bonyak et al., all of which are incorporated herein by reference. 
         [0051]    Typically, distal end  22  contains other functional components, which are outside the scope of the present disclosure and are therefore omitted for the sake of simplicity. For example, the distal end of the probe may contain steering wires, as well as sensors of other types, such as a position sensor. Probes containing components of these kinds are described, for example, in U.S. Patent Applications 2009/0306650 and 2011/0130648, referenced above. 
         [0052]      FIG. 3A  is a schematic diagram illustrating a temperature distribution in the vicinity of distal end  22 , as displayed on screen  62 , according to an embodiment of the present invention. Using measurements provided by temperature sensors  78 , as well as knowledge of the positions of the sensors with respect to each other and with respect to the xyz axes of distal end  22 , processor uses temperature module  52  to generate a two-dimensional (2D) temperature map  100 . 2D map  100  is a graphical representation of the three-dimensional (3D) distribution of the temperatures of the external surface of electrode  24 A, and is assumed to be drawn as a 2D projection with respect to the xyz axes defined above for distal end  22 . Map  100  is drawn as a circular map, a bounding circle  102  of the map corresponding with edge  86  of electrode  24 A. The generation of 2D map  100  from measurements of sensors  78  typically uses interpolation and extrapolation from the measurements, as is known in the art. 
         [0053]    As stated above, 2D map  100  is a 2D projection of a 3D distribution of temperatures. One type of projection that may be used, based on angles subtended by a line through the origin of the xyz axes to the z-axis ( FIG. 2A ), is described in more detail with respect to  FIG. 3B , which illustrates a projection used to represent the direction of a force vector. As is assumed in the following description, the same type of projection may be used to represent the temperature distribution and the force vector. However, there is no necessity that the projections are the same, and in some embodiments the projections are different. 
         [0054]    2D map  100  is typically a color map showing the different temperatures of the external surface of electrode  24 A, and a legend  104  may be displayed with the map showing values of the temperatures for the different colors. (In the figures different colors are schematically illustrated by different shadings.) In some embodiments the numerical values measured by each of sensors  78  may also be displayed on map  100 . For simplicity, the display of such numerical values is not illustrated in  FIG. 3A . 
         [0055]      FIG. 3B  is a schematic diagram illustrating a vector representation  108  of the force exerted by distal end  22 , as displayed on screen  62 , according to an embodiment of the present invention. As explained above force sensor  90  is able to generate signals which may be used by force module  56  and processor  46  to find a magnitude of the force exerted by distal end  22 , as well as a direction of the force. The direction of the force may be measured relative to the xyz axes of distal end  22 . Starting with a 3D vector representation of the force, the 3D direction may be represented on a 2D surface such as that of screen  62  by any convenient projection of a 3D direction. By way of example, a projection used herein is similar to a polar stereographic projection, generating a circular map  110 . Map  110  has a bounding circle  112 , which represents directions orthogonal to the z-axis referred to above. A center  114  of map  110  represents directions along the z-axis. In the exemplary projection illustrated herein, a broken circle  116  corresponds to a direction at 60° to the z-axis, and a broken circle  118  corresponds to a direction at 30° to the z-axis. Circles representing angles to the z-axis, such as circles  116  and  118 , are also herein termed angular circles. By way of example, in the projection assumed herein a diameter of an angular circle is in direct proportion to the angle it represents, so that circles  112 ,  116 , and  118  have diameters in the ratio of 3:2:1. 
         [0056]    Representation  108  comprises a variable length arrow  120  representing the direction of the force exerted by distal end  22 , which has been drawn on map  110 . Arrow  120  has a start point corresponding with the center of circle  112 , and an end point corresponding to the angle subtended by the distal end force to the z-axis, so that a length of the arrow is a function of the angle of the force measured with respect to the z-axis. Thus in  FIG. 3B , the distal end force is in a direction that is approximately 40° to the z-axis. In representation  108  arrow  120  has a direction with respect to the xy axes corresponding to a projection of a 3D representation of the force vector on the xy plane.  FIG. 3B  illustrates arrow  120  as subtending an angle of approximately −70° with respect to the x-axis. 
         [0057]    In order to represent the magnitude of the force in representation  108 , in a disclosed embodiment a width of arrow  120  is varied according to the magnitude. By varying the width of the arrow, representation  108  is a complete vector representation of the magnitude and the direction of the force exerted by distal end  22 . 
         [0058]      FIG. 3C  and  FIG. 3D  are respective illustrations of a single combined force-temperature map  64 A and a single combined force-temperature map  64 B, according to embodiments of the present invention. In the following description, elements indicated by the same reference numerals in  FIGS. 3A ,  3 B,  3 C, and  3 D are generally similar in function. Maps  64 A and  64 B are formed by having circles  102  and  112  ( FIGS. 3A and 3B ) the same diameter, and superimposing the resulting circular temperature map  100  and force representation  108  on each other, so as to form single maps  64 A and  64 B on screen  62 . Thus combined force-temperature map  64 A displays both the temperature distribution in the vicinity of distal end  22  and the force exerted by the distal end. For a different case, combined force-temperature map  64 B also displays the temperature distribution and the force. In both maps the force is displayed as an arrow, and a color of the arrow is selected so that the arrow is easily differentiated from the temperature distribution. 
         [0059]    In the presentation of single map  64  on screen  62 , an operator of the system may choose to display all, some, or none of the xyz axes and the angular circles. By way of example, in the examples illustrated herein, angular circles, but not the xyz axes, are displayed. 
         [0060]    Single maps  64 A and  64 B have the same temperature distribution, and the force is in the same direction (approximately 40° to the z-axis and −70° to the x-axis). However, the magnitudes of the force in the two maps is different, the difference being presented on screen  62  as different widths of an arrow  120 A in map  64 A and an arrow  120 B in map  64 B. Usually a width of the arrow representing the force is configured to be proportional to, and typically directly proportional to, a magnitude of the force.  FIGS. 3C and 3D  show that arrow  120 B (map  64 B) is wider than arrow  120 A (map  64 A), Thus, for example, the force in map  64 A may be 2 g, and the force in map  64 B may be 3 g. 
         [0061]      FIG. 4A  is a schematic diagram illustrating a vector representation  128  of the force exerted by distal end  22 , as displayed on screen  62 , according to an alternative embodiment of the present invention. Apart from the differences described below, vector representation  128  ( FIG. 4A ) is generally similar to representation  108  ( FIG. 3B ), and elements indicated by the same reference numerals in both representations are generally similar in function and in properties. 
         [0062]    Rather than using an arrow to represent the force exerted by distal end  22 , representation  128  uses a circle  130 . A center  132  of the circle, measured with respect to center  114  and the xy axes, represents the direction of the force exerted by the distal end.  FIG. 4A  has been drawn assuming the force on distal end  22  is the same as that illustrated in  FIG. 3B . Thus in  FIG. 4A , angular circles  116  and  118  indicate that center  132  is in a direction that is approximately 40° to the z-axis, and an imaginary line between centers  114  and  132  subtends an angle of approximately −70° with respect to the x-axis. 
         [0063]    In order to represent the magnitude of the force in representation  128 , in a disclosed embodiment a diameter of circle  130  is varied according to the magnitude. By varying the diameter of the circle, representation  128  is a complete vector representation of the magnitude and the direction of the force exerted by distal end  22 . 
         [0064]      FIG. 4B  and  FIG. 4C  are respective illustrations of a single combined force-temperature map  64 C and a single combined force-temperature map  64 D, according to alternative embodiments of the present invention. In contrast to maps  64 A and  64 B, maps  64 C and  64 D are formed by superimposing temperature map  100  ( FIG. 3A ) and force representation  128  ( FIG. 4A ) on each other, and displaying the resulting combined force-temperature map on screen  62 . Thus combined force-temperature map  64 C displays both the temperature distribution in the vicinity of distal end  22  and the force exerted by the distal end. For a different case, combined force-temperature map  64 D also displays the temperature distribution and the force. In both maps the force is displayed as a circle, and a color of the circle is selected so that the circle is easily differentiated from the temperature distribution. 
         [0065]    Single maps  64 C and  64 D have the same temperature distribution, and the force is in the same direction (approximately 40° to the z-axis and −70° to the x-axis), as is indicated by the same positions of centers  132 A and  132 B in their respective circles. However, the magnitudes of the force in the two maps is different, the difference being presented on screen  62  as different diameters of a circle  130 A in map  64 C and a circle  130 B in map  64 D. Usually a diameter of the circle representing the force is configured to be proportional to, and typically directly proportional to, a magnitude of the force.  FIGS. 4B and 4C  show that circle  130 B (map  64 D) has a larger diameter than circle  130 A (map  64 C), Thus, for example, the force in map  64 C may be 2 g, and the force in map  64 D may be 3 g. 
         [0066]      FIG. 5A  is a schematic diagram illustrating a vector representation  138  of the force exerted by distal end  22 , as displayed on screen  62 , according to a further alternative embodiment of the present invention. Apart from the differences described below, vector representation  138  ( FIG. 5A ) is generally similar to representation  108  ( FIG. 3B ), and elements indicated by the same reference numerals in the two representations are generally similar in function and in properties. 
         [0067]    Rather than using a variable length arrow having a variable width (as described above for representation  108 ) to represent the force exerted by distal end  22 , representation  138  uses a variable length arrow  140  with a constant width. Except that it is invariant with regard to width, arrow  140  is generally similar to arrow  120  ( FIG. 3B ), so that a length of arrow  140  is a function of the angle subtended by the force with the z-axis.  FIG. 5A  has been drawn assuming the force on distal end  22  is the same as that illustrated in  FIG. 3B . Thus, in  FIG. 5A , the end or length of arrow  140  indicates that the force is in a direction that is approximately 40° to the z-axis, and the direction of the arrow indicates that the force subtends an angle of approximately −70° with respect to the x-axis. 
         [0068]    In order to represent the magnitude of the force in representation  138 , in a disclosed embodiment a text box  142  is “attached” to arrow  140  and a value corresponding to the force magnitude is entered into the text box. By way of example, text box  142  is attached to the head of arrow  140 , but in other embodiments text box  142  may be in any convenient position with respect to the arrow. Text within the text box gives a magnitude of the force, so that representation  138  is a complete vector representation of the force on distal end  22 . 
         [0069]      FIG. 5B  and  FIG. 5C  are respective illustrations of a single combined force-temperature map  64 E and a single combined force-temperature map  64 F, according to further alternative embodiments of the present invention. Except for the following differences, maps  64 E and  64 F are generally similar to maps  64 A and  64 B. However, in contrast to maps  64 A and  64 B, maps  64 E and  64 F are formed by superimposing temperature map  100  ( FIG. 3A ) and force representation  138  ( FIG. 5A ) on each other, and displaying the resulting combined force-temperature map on screen  62 . Thus combined force-temperature map  64 E displays both the temperature distribution in the vicinity of distal end  22  and the force exerted by the distal end. For a different case, combined force-temperature map  64 F also displays the temperature distribution and the force. In both maps the direction of the force is displayed as an arrow. 
         [0070]    Single maps  64 E and  64 F have the same temperature distribution, and the force is in the same direction (approximately 40° to the z-axis and −70° to the x-axis), as is indicated by the same directions and lengths of arrows  140 A and  140 B. However, the magnitudes of the force in the two maps are different, the difference being presented on screen  62  as a text box  142 A in map  64 E and as a text box  142 B in map  64 F. Thus, for example, the force in map  64 E is 2 g, and the force in map  64 F is 3 g. 
         [0071]      FIG. 6A  and  FIG. 6B  are respective illustrations of a single combined force-temperature map  64 G and a single combined force-temperature map  64 H, according to embodiments of the present invention. Except for the following differences, maps  64 G and  64 H are generally similar to maps  64 E and  64 F. Maps  64 E,  64 F,  64 G, and  64 H are all combined force-temperature maps, using the embodiment illustrated in  FIGS. 5A-5C , with the same temperature distribution. However, while maps  64 E,  64 F illustrate the force as having the same direction and a different magnitude, maps  64 G,  64 H illustrate the force as having the same magnitude of 2 g, but different force directions. Thus map  64 G illustrates the force as subtending approximately 30° to the z-axis, and −20° to the x-axis, and map  64 H illustrates the force as subtending approximately 60° to the z-axis, and −70° to the x-axis. 
         [0072]      FIG. 7A  and  FIG. 7B  are respective illustrations of a single combined force-temperature map  64 J and a single combined force-temperature map  64 K, according to embodiments of the present invention. Except for the following differences, maps  64 J and  64 K are generally similar to maps  64 A and  64 B. Maps  64 A,  64 B,  64 J, and  64 K are all combined force-temperature maps, using the embodiment illustrated in  FIGS. 3B-3D , with the same temperature distribution. However, while maps  64 A,  64 B illustrate the force as having the same direction and a different magnitude, shown by the different arrow widths, maps  64 J,  64 K illustrate the force as having the same magnitude, since arrows  120 C and  120 D have the same widths. However, the forces in the two maps have different directions. Thus map  64 J illustrates the force as subtending approximately 30° to the z-axis, and −90° to the x-axis, and map  64 K illustrates the force as subtending approximately 70° to the z-axis, and −90° to the x-axis. 
         [0073]    By presenting the force (in magnitude and direction) together with the temperature distribution in a single map, embodiments of the present invention facilitate the ablation process performed by a physician, by enabling the physician to see the relative alignment between the force and the temperature distribution. For example, during the ablation process, the physician may desire that the force is directed to the hottest part of the temperature distribution, so that the force “aligns” with the temperature. This is typically the desired state during ablation of a single region. Alternatively, the physician may desire that the force is directed in a particular direction away from the hottest part of the temperature distribution. This is typically the desired state during ablation along a line. Embodiments of the present invention facilitate these types of alignment by allowing the physician to mark a “center” of the temperature, which enables the physician to compare the direction of the force, and the “direction” of the temperature distribution. 
         [0074]      FIG. 8A  and  FIG. 8B  are respective illustrations of a single combined force-temperature map  64 L and a single combined force-temperature map  64 M, according to embodiments of the present invention. The two maps have the same temperature distribution, but in map  64 L the force is represented as a circle  130 C with a center  132 C, as described above with respect to  FIG. 4A , and in map  64 M the force is represented as an arrow  140 C with an attached text box  142 C, as described above with respect to  FIG. 5A . 
         [0075]    A center of the temperature distribution is calculated by any means known in the art. For example, the center may correspond to a weighted center of gravity of regions of the distribution, where the weights are according to the temperatures of each of the regions. In map  64 L a temperature distribution center  150  is indicated by an X on the map; in map  64 M a temperature distribution center  152  is indicated by cross-hairs on the map. In map  64 L the force direction is shown as aligning with temperature distribution center  150 , in a “bullseye” type of display, which may be the desired situation for ablation of a single region. In contrast, in map  64 M the force does not align with temperature distribution center  152 , and this may be the desired situation for ablation along a line. 
         [0076]    It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations 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.