Patent Publication Number: US-2013241929-A1

Title: Selectably transparent electrophysiology map

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to graphic displays, and specifically to displaying of electrophysiological data in a map. 
     BACKGROUND OF THE INVENTION 
     In medical procedures, such as mapping the electrical activity of the heart, there is typically a large amount of information that may be presented to a professional performing the mapping, and/or performing a procedure using the mapping. The large amount of information presented may lead to difficulties in comprehension of the information. A system to improve the comprehension of the information would be beneficial. 
     SUMMARY OF THE INVENTION 
     There is provided, according to an embodiment of the present invention, a method for mapping a body organ, including: 
     receiving a three-dimensional (3D) map of the body organ together with items of auxiliary information having respective location coordinates in a frame of reference of the 3D map; 
     apportioning the items into a plurality of sub-groups; 
     assigning to a selected sub-group a visibility parameter indicative of a relative visibility of the selected sub-group in relation to the map and to other sub-groups; and 
     displaying the 3D map of the body organ in a selected orientation while selectively superimposing on the 3D map one or more of the items in the selected sub-group responsively to the orientation, the respective location coordinates of the items, and the assigned visibility parameter. 
     Typically, the items of auxiliary information include a further 3D map of a portion of the body organ, and the further 3D map is assigned a further-3D-map visibility parameter. The further-3D-map visibility parameter may cause the further 3D map to be locally transparent, so that all elements of the further 3D map are visible while the further 3D map is opaque with respect to the 3D map. 
     In an embodiment the further 3D map is disjoint from the 3D map. 
     In an alternative embodiment the further 3D map intersects the 3D map. 
     The body organ may include a heart, and the selected sub-group may include local activation times (LATs) of the heart. Typically, the LATs include measured LATs, and the LATs may include interpolated LATs derived from the measured LATs. 
     In a further alternative embodiment the relative visibility includes a transparency of the selected sub-group. 
     In a yet further alternative embodiment the relative visibility includes at least one of a color and a shading applied to the selected sub-group. 
     Typically, the sub-groups are selected from a set consisting of an ablation site, a catheter type, and a catheter measurement. 
     The relative visibility of an element in the selected sub-group may be a function of the location coordinates of the element. Alternatively or additionally, the relative visibility of an element in the selected sub-group may be a function of a proximity of the element to another element in the sub-group. 
     In a disclosed embodiment the relative visibility of an element in the selected sub-group is a function of a proximity of the element to another element in the other sub-groups. 
     In another disclosed embodiment the relative visibility of an element in the selected sub-group is a function of a time of the mapping of the body organ. 
     There is further provided, according to an embodiment of the present invention, apparatus for mapping a body organ, including: 
     a processor which is configured to: 
     receive a three-dimensional (3D) map of the body organ together with items of auxiliary information having respective location coordinates in a frame of reference of the 3D map, 
     apportion the items into a plurality of sub-groups, and 
     assign to a selected sub-group a visibility parameter indicative of a relative visibility of the selected sub-group in relation to the map and to other sub-groups; and 
     a screen, coupled to the processor, which is configured to display the 3D map of the body organ in a selected orientation while the processor selectively superimposes on the 3D map one or more of the items in the selected sub-group responsively to the orientation, the respective location coordinates of the items, and the assigned visibility parameter. 
     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 
         FIG. 1  is a schematic illustration of a physiological mapping system, according to an embodiment of the present invention; 
         FIGS. 2 and 3  are schematic illustrations of typical three-dimensional charts that may be presented on a screen of the system of  FIG. 1 , according to embodiments of the present invention; 
         FIG. 4  is a flowchart of steps performed for mapping a body organ such as a heart, according to an embodiment of the present invention; and 
         FIG. 5  and  FIG. 6  are schematic examples of charts produced by following the steps of the flowchart, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     An embodiment of the present invention provides a method and system for mapping a body organ, by selectively changing the relative visibility of elements of a chart of the body organ, as imaged on a screen. The imaged body organ, typically the heart of a patient, is presented in a three-dimensional (3D) format, and comprises a map of the organ upon which are superimposed one or more items of auxiliary information. The items of auxiliary information are classified into sub-groups, and one or more sub-groups are assigned respective visibility parameters which are indicative of respective relative visibilities of the sub-group. Sub-groups of the items may comprise, for example, location coordinates of points on a surface of the organ, measurements made on regions of the surface, actions performed on the regions, and types of instruments such as catheters associated with the body organ. 
     The chart of the body organ, comprising the map and the sub-groups of items, may be displayed on the screen in a selected orientation. The display superimposes on the 3D map one or more selected sub-groups responsively to the selected orientation, respective location coordinates of the one or more selected sub-groups, and assigned values of the respective visibility parameters of the one or more selected sub-groups. 
     By implementing selective relative visibilities of elements of the chart displayed on the screen, embodiments of the present invention considerably improve comprehension of the chart. 
     System Description 
     Reference is now made to  FIG. 1 , which is a schematic illustration of a physiological mapping system  20 , according to an embodiment of the present invention. System  20  may be configured to map substantially any physiological parameter or combinations of such parameters. In the description herein, examples of mapped parameters are assumed to comprise local activation times (LATs) derived from intra-cardiac electrocardiogram (ECG) potential-time relationships. The measurement and use of LATs are well known in the electrophysiological arts. System  20  may map other physiological parameters, such as the location and/or size of cardiac lesions, the force applied to a region of the heart wall by a catheter, and the temperature of the heart wall region. 
     For simplicity and clarity, the following description, except where otherwise stated, assumes an investigative procedure wherein system  20  senses electrical signals from a heart  34 , using a probe  24 . A distal end  32  of the probe is assumed to have an electrode  22  for sensing the signals. Those having ordinary skill in the art will be able to adapt the description for multiple probes that may have one or more electrodes, as well as for signals produced by organs other than a heart. 
     Typically, probe  24  comprises a catheter which is inserted into the body of a subject  26  during a mapping procedure performed by a user  28  of system  20 . In the description herein user  28  is assumed, by way of example, to be a medical professional. During the procedure subject  26  is assumed to be attached to a grounding electrode  23 . In addition, electrodes  29  are assumed to be attached to the skin of subject  26 , in the region of heart  34 . 
     System  20  may be controlled by a system processor  40 , comprising a processing unit  42  communicating with a memory  44 . Processor  40  is typically mounted in a console  46 , which comprises operating controls  38 , typically including a pointing device  39  such as a mouse or trackball, that professional  28  uses to interact with the processor. Results of the operations performed by processor  40  are provided to the professional on a screen  48 . The screen displays a three-dimensional (3D) map  50  of heart  34 , together with items  52  of auxiliary information related to the heart and superimposed on the map, while the heart is being investigated. In the description and in the claims, an item of auxiliary information comprises any property or element that is, or that can be, associated with a region of the organ under consideration. In the examples described herein, the organ comprises heart  34 . Examples of items  52  are provided below. 
     The combination of map  50  and items  52  is herein termed a chart  54  of the heart. Chart  54 , comprising map  50  and items  52 , is typically drawn on screen  48  relative to a frame of reference  58  of the map, and professional  28  is able to use pointing device  39  to vary parameters of the frame of reference, so as to display the chart in a selected orientation and/or at a selected magnification. 
     In addition to being able to have its orientation and magnification selected, chart  54 , and its constituent parts: map  50  and items  52 , may be presented on screen  48  in a number of different forms described below. In the description herein different forms of the chart and its parts are differentiated by having a letter, or a letter and a number, appended to the identifying numerals  50 ,  52 , and  54 . The different charts, maps and items are respectively referred to generically as charts  54 , maps  50 , and items  52 . 
     Screen  48  typically also presents a graphic user interface to the user, and/or a visual representation of the ECG signals sensed by electrode  22 . 
     Processor  40  uses software, including a probe tracker module  30  and an ECG module  36 , stored in memory  44 , to operate system  20 . The software may be downloaded to processor  40  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. 
     ECG module  36  is coupled to receive electrical signals from electrode  22  and electrodes  29 . The module is configured to analyze the signals and may present the results of the analysis in a standard ECG format, typically a graphical representation moving with time, on screen  48 . 
     Probe tracker module  30  tracks sections of probe  24  while the probe is within subject  26 . The tracker module typically tracks both the location and orientation of distal end  32  of probe  24 , within the heart of subject  26 . In some embodiments module  30  tracks other sections of the probe. The tracker module may use any method for tracking probes known in the art. For example, module  30  may operate magnetic field transmitters in the vicinity of the subject, so that magnetic fields from the transmitters interact with tracking coils located in sections of the probe being tracked. The coils interacting with the magnetic fields generate signals which are transmitted to the module, and the module analyzes the signals to determine a location and orientation of the coils. (For simplicity such coils and transmitters are not shown in  FIG. 1 .) The Carto® system produced by Biosense Webster, of Diamond Bar, Calif., uses such a tracking method. Alternatively or additionally, tracker module  30  may track probe  24  by measuring impedances between electrode  23 , electrodes  29  and electrodes  22 , as well as the impedances to other electrodes which may be located on the probe. (In this case electrodes  22  and/or electrodes  29  may provide both ECG and tracking signals.) The Carto3® system produced by Biosense Webster uses both magnetic field transmitters and impedance measurements for tracking. 
     Using tracker module  30  processor  40  is able to measure locations of distal end  32 , and form location coordinates of the locations in frame of reference  58  for construction of map  50 . The location coordinates are assumed to be stored in a mapping module  56 . In addition, mapping module  56  is assumed to store location coordinates of items  52  of auxiliary information associated with heart  34 , and the procedure being performed on the heart. 
     Examples of items  52  and associated information of the items that mapping module  56  is able to store, include, but are not limited to, those given in Table I below. For each item  52 , mapping module  56  stores, as appropriate, location coordinates associated with the item. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                   
                 Examples of Auxiliary 
               
               
                   
                   
                 information associated with 
               
               
                   
                 Item 
                 item 
               
               
                   
                   
               
             
            
               
                   
                 Local activation time (LAT) 
                 Time at which a cardiac 
               
               
                   
                   
                 activation wave arrives at 
               
               
                   
                   
                 the LAT location 
               
               
                   
                 Ablation site 
                 power dissipated, force 
               
               
                   
                   
                 applied, temperature 
               
               
                   
                   
                 reached, time at site 
               
               
                   
                 Catheter type 
                 straight, lasso, multi- 
               
               
                   
                   
                 electrode, multi-prong; 
               
               
                   
                 Catheter measurement 
                 potential (at catheter 
               
               
                   
                   
                 electrode or electrodes); 
               
               
                   
                   
                 force; temperature; rate of 
               
               
                   
                   
                 irrigation; energy, such as 
               
               
                   
                   
                 X-ray or ultrasound energy, 
               
               
                   
                   
                 flux. 
               
               
                   
                   
               
            
           
         
       
     
     Tracker module  30  measures location coordinates for all items  52 . Other modules in processor  40  measure auxiliary information associated with specific items  52 . For example, ECG module  36  measures LATs. For clarity and simplicity, other modules measuring the auxiliary information, such as force, temperature, irrigation rate and energy flux modules, are not shown in  FIG. 1 . 
       FIGS. 2 and 3  are schematic illustrations of typical 3D charts that may be presented on screen  48 , according to embodiments of the present invention. In the disclosure, charts are drawn on sets of xyz orthogonal axes. The illustrations of  FIGS. 2 and 3  are herein shown as gray-scale images, whereas typically the images are presented on screen  48  as color images. 
     In  FIG. 2 , a chart  54 A illustrates parameters of a section of the heart that are drawn assuming that the heart is completely opaque, i.e., that the walls of the heart are non-transparent. Chart  54 A is based on a first 3D map  50 A of the walls of the section being illustrated, the first 3D map being constructed from measured location coordinates of points on the walls. Typically, to construct the first 3D map, a mesh of the measured points is produced, and 3D location coordinates of points between the measured points are determined by interpolation. The location coordinates of the measured and interpolated points are then used to produce a 3D continuous surface which is represented by 3D map  50 A. 
     By way of example, first 3D map  50 A is registered with a second 3D map  50 B of the section. Map  50 B is typically produced in a substantially similar manner to the method used for producing the first 3D map. However, this is not a requirement, so that in some embodiments the two maps may be produced from different sources. For example, one of the maps may be produced using magnetic resonance imaging (MRI) or by computerized tomography (CT). 
     In the embodiment described herein, the two maps are assumed to intersect so that part of map  50 B covers  50 A. An approximate intersection of the two maps is illustrated by a broken line  51 . Nevertheless, there is no need that the two maps intersect, and in some embodiments the two maps have no intersection whatsoever, i.e., they are disjoint. Furthermore, in some embodiments one of the disjoint maps may enclose the other map. 
     The two registered maps are herein referred to as a combined 3D map  50 C. In  FIG. 2  both maps  50 A and  50 B are configured to be completely opaque, so that in combined 3D map  50 C map  50 B and only part of map  50 A are visible. 
     Superimposed on combined map  50 C are selected items  52  of auxiliary information, so as to form chart  54 A. By way of example, items  52  that have been superimposed are:
         Items  52 A, comprising estimated values of the LATs at location coordinates of the walls. Items  52 A are herein also termed estimated LATs  52 A. The superposition of estimated LATs  52 A on map  50 A is implemented by applying a gray scale according to the value of the estimated LAT, each level of gray corresponding to a numerical value of the estimated LAT.   Items  52 B, comprising measured values of the LATs at respective location coordinates of the walls, and herein also termed measured LATs  52 B. Measured LATs  52 B are superimposed on map  50 C by incorporating the respective LAT numerical measured value in proximity to a respective point, representative of the location coordinate where the LAT is measured into the map. By way of example, specific measured values  52 B 1  and  52 B 2  of LATs are indicated in  FIG. 2 .   Items  52 C, comprising sites having information related to the procedure being performed, and herein drawn as spheres. Different types of information may be denoted by the size and/or color of the spheres. For example, red spheres may denote ablation sites, and a yellow sphere may denote the site of the His bundle. For simplicity, in the disclosure items  52 C are assumed to be sites at which ablation has been performed, and are herein termed ablation sites  52 C. Some of ablation sites  52 C are only partially visible because of the opacity of map  50 C. By way of example, specific ablation sites  52 C 1 ,  52 C 2 ,  52 C 3 , the latter two of which are partially obscured by opaque portions of map  50 A, are shown in  FIG. 2 .   Items  52 D, herein termed icons  52 D and comprising icons representing the locations of distal ends of catheters being used during a procedure on the heart. In  FIG. 2 , while more than one catheter distal end may be present, only one distal end icon  52 D 1 , of a lasso catheter, is visible. In the figure lasso catheter distal end icon  52 D 1  is only partly shown because of the opacity of map  50 C.       

     In  FIG. 3 , a chart  54 B illustrates similar parameters to the section of the heart shown in  FIG. 2 . Thus, as for chart  54 A, chart  54 B is based on the intersection of first 3D map  50 A and second 3D map  50 B, to form combined 3D map  50 C. However, in contrast to chart  54 A, chart  54 B assumes that both the first and the second maps are transparent, so that all parts of both maps are visible. 
     As for chart  54 A, estimated LATs  52 A, measured LATs  52 B, ablation sites  52 C, and icons  52 D are superimposed on chart  54 B. Because of the transparency of both maps, all items that are visible in chart  54 A are also visible in chart  54 B. In addition, because of the transparency, in chart  54 B further estimated LATs  52 A, measured LATs  52 B, ablation sites  52 C, and all icons  52 D are visible. For example, measured LAT  52 B 3 , ablation sites  52 C 4 ,  52 C 5 , and a multi-probe catheter distal end icon  52 D 2  are now visible. In addition, parts of elements that were not visible in chart  64 A, such as ablation sites  52 C 2 ,  52 C 3 , and icon  52 D 1 , are now shown. 
     Comparison of  FIGS. 2 and 3  shows that for chart  54 A the information presented is relatively clear, but that there may be missing information. Conversely, in chart  54 B while there may be no missing information, the information presented is extremely cluttered and “noisy.” 
       FIG. 4  is a flowchart  100  of steps performed for mapping a body organ such as heart  34 , and  FIGS. 5 and 6  are schematic examples of charts produced by following the steps of the flowchart, according to embodiments of the present invention. 
     In a definition step  102 , elements of a chart that is to be displayed on screen  48  are apportioned and classified into sub-groups. Referring back to  FIGS. 2 and 3 , sub-groups of a chart are assumed to comprise one or more maps of the body organ. The sub-groups also comprise items of auxiliary information such as those exemplified above in Table I. 
     In a visibility step  104 , at least one sub-group generated in step  102  is assigned a respective visibility parameter, a value of which is applied to elements of the sub-group. Typically, two or more sub-groups are each assigned visibility parameters. For a selected sub-group, the value of its visibility parameter determines a relative visibility of the sub-group in relation to the other sub-groups, including the map or maps of the displayed chart. The relative visibility comprises one or more visual characteristics, such as a transparency, of the sub-group. 
     In some embodiments the visibility parameter may also determine other visual characteristics of the sub-group, such as a color or shading to be applied to the sub-group. Typically, although not necessarily, all elements of a given sub-group are assigned the same visibility parameter. However, in some embodiments, the visibility parameter for an element of a given sub-group may be a function of factors of the element other than its membership in the given sub-group. For example, the visibility parameter of an element may be a function of its location coordinates, and/or its proximity to elements of the same or of another sub-group. 
     In a disclosed embodiment a given sub-group may comprise one given map used in the mapping, and all elements associated with the given map. In this case the visibility parameter may be assigned to the given map and its associated elements. 
     In an optional display step  106 , typically implemented at the start of a procedure, a chart comprising all the elements of all the sub-groups is displayed on screen  48 . Elements of sub-groups that have not had visibility parameters assigned are rendered visible. For sub-groups that have been assigned visibility parameters, the values of the parameters are set so that all the elements of these sub-groups are initially at least partially visible. 
     In a filter selection step  108 , for each sub-group having an assigned visibility parameter, professional  28  assigns values for the visibility parameters until a desired visibility of each element of each sub-group is achieved. The assignment may be via professional  28  interacting with a graphic user interface on screen  48 , using pointing device  39 , or by any other convenient type of interaction. The chart displays on screen  48  according the relative visibility that has been set for each element. The chart, and the elements of its constituent sub-groups, is also displayed according to an orientation selected for the chart by professional  28 , as well as according to the location coordinates of each of the elements of the chart. 
     As an example of the implementation of filter step  108 , in the disclosed embodiment referred to above the visibility parameter assigned to the given sub-group may cause elements of the sub-group to be “locally” transparent. In the disclosure and in the claims, the phrase “locally transparent” as applied to a given map is to be understood as meaning that the given map and its associated elements may be considered to be mounted on a transparent surface, so that all features of the map, as well as its elements are visible. However, the locally transparent visibility parameter prevents the transparency extending beyond the given map, so that with respect to other maps in a chart, the given map is opaque. 
     Thus, if there is a second map behind the given map, the only features of the second map that are visible are those which are not shadowed by the given map. In other words the transparent characteristic of the given map does not apply from the point of view of the second map. Rather, as described above, with respect to the second map, the given map is opaque. 
       FIG. 5  illustrates a first application of flowchart  100  to produce a chart  54 C. In chart  54 C map  50 A has had its relative visibility set so that the map is opaque, and map  50 B has been set so that it is transparent. In addition, elements of a sub-group of catheter type items have had respective relative visibilities set according to the types of catheter in the sub-group, so that multi-probe catheters are visible. Thus icon  52 D 2  shows in chart  54 C. 
       FIG. 6  illustrates a second application of flowchart  100  to produce a chart  54 D. For clarity, maps in chart  54 D are assumed to be simple geometrical shapes. In chart  54 D a map  50 D is a sphere, and a map  50 E is a plane, parallel to the xy plane, which has been tessellated with diamond shapes. The plane is behind and disjoint from the sphere, so that the z values of all points on the sphere are greater than the z value of the plane. The visibility parameter of map  50 D has been set so that the map and its elements are locally transparent. Map  50 D comprises lines of latitude and longitude, and because of the local transparency of the map the rear sections of the lines are visible, as well as the front sections. However, since map  50 D is opaque with respect to map  50 E, because of the local transparency of map  50 D, there are no diamond shapes visible in sections  120 ,  122  of map  50 D. 
     It will be appreciated that charts other than those described above, with elements having other relative visibilities, may be implemented as embodiments of the present invention. For example, ablation sites  52 C 4  and  52 C 5  ( FIG. 3 ) may be added to chart  54 C ( FIG. 5 ) by appropriate definition of the visibility parameter of ablation sites  52 C. Such a definition may incorporate, for example, a region of the chart wherein ablation sites are to be rendered visible, and/or a region wherein ablation sites are not to be visible. Alternatively or additionally, the visibility parameter may include a time component. For example, ablation sites which have been produced within a predefined time range of a procedure are rendered visible, but may or may not be visible outside the range, typically depending on a choice made by professional  28 . 
     The description above has referred to forming a chart from two maps, by assigning a visibility parameter to elements of at least one of the maps. Those having ordinary skill in the art will be able to adapt the description to form the chart from three or more maps, while assigning a visibility parameter to elements of at least one of the maps. 
     It will thus 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.