Point of interest (POI) maps for arrhythmia diagnosis

Abstract

A system includes a display and a processor. The processor is configured to receive a cardiac anatomical surface, and receive a plurality of electrophysiological (EP) data points including (i) respective locations on the cardiac anatomical surface, and (ii) respective values of arrhythmia indicating EP parameters at the locations, and apply respective criteria to the values of the EP data points. For each EP data point whose value satisfies a respective criterion, the processor is configured to graphically encode the EP data point to generate a point of interest (POI), overlay POIs of at least two types of arrhythmia indicating EP parameters on the anatomical surface to generate a POI map reflecting a potentially arrhythmic surface location, and map the POIs of the at least two types of arrhythmic indicating EP parameters on the anatomical surface. And visualizing the POI map to a user on the display.

Description

Technical Field

[0001] The present disclosure generally relates to cardiac electrophysiology (EP) mapping, and more particularly to cardiac EP maps. Background Art

[0002] Previously, EP maps generated from EP signals obtained from catheters have been described in the patent literature. For example, U.S. Patent Application Publication No. 2022 / 0211314 describes a method that includes receiving (i) a modeled surface of at least a portion of the heart, and (ii) a plurality of EP values measured at a plurality of corresponding locations in the heart. A plurality of regions are defined on the modeled surface, and for each region, a confidence level of the EP values whose locations fall within that region is estimated. The modeled surface is presented to the user, including (i) the EP values superimposed on the modeled surface, and (ii) the confidence levels visually represented graphically in each region of the modeled surface.

[0003] As another example, U.S. Patent No. 11,160,485 describes a method that includes storing an anatomical map of at least a portion of the surface of the heart. Storing the corresponding electrogram (EGM) signal amplitudes measured at corresponding locations on the surface of the heart. Based on the EGM signal amplitudes, one or more first regions of the surface where the EGM signal amplitudes are fractionated and one or more second regions of the surface where the EGM signal amplitudes are non-fractionated are defined. A first surface representation is generated for the fractionated EGM signal amplitudes in the first region. Propagation times are extracted from the non-fractionated EGM signal amplitudes in the second region and a second surface representation of the propagation times is derived. The first surface representation and the second surface representation of the corresponding first and second regions of the surface are presented simultaneously superimposed on the anatomical map.

[0004] Julien S. et al. describe in a paper titled "Atrial Fibrillation (AF) Ablation Guided by Spatiotemporal Electrogram Dispersion Without Pulmonary Vein Isolation" (JACC, Vol. 69, No. 3, 2017) how to use EP mapping to indicate AF drivers by clustering intracardiac electrograms exhibiting spatiotemporal dispersion.

[0005] In conjunction with the accompanying drawings, the present disclosure will be more fully understood from the following detailed description of an example of the present disclosure, wherein: Brief Description of the Drawings

[0006] Figure 1 is a schematic illustration of a catheter-based electrophysiology (EP) mapping and ablation system according to an example of the present disclosure;

[0007] Figure 2 is a schematic diagram of a point of interest (POI) mapping graph according to an example of the present disclosure;

[0008] Figure 3 is a schematic diagram of a POI mapping graph according to another example of the present disclosure; and

[0009] Figure 4 is a flowchart schematically illustrating a method for generating, editing, and presenting a POI mapping graph according to an example of the present disclosure. Detailed Description

[0010] Overview

[0011] A probe-based (e.g., multi-electrode catheter-based) cardiac diagnostic and treatment system can measure a large number of intracardiac electrophysiological (EP) signals, such as electrograms (EGMs), during an invasive procedure. Typically, the analysis of such a large amount of EP information is facilitated by generating and presenting to a user (e.g., a physician or a clinical application specialist) one or more EP mapping graphs. Each such EP mapping graph can display typical EP parameters for the procedure. Examples of EP parameters that can be presented include arrhythmia-indicating EP parameters selected from a list that includes cycle length, percentage of regional ripples, local activation time (LAT), bipolar potential, activation wave speed, and complex fractionated atrial electrograms (CFAE).

[0012] A physician performing a cardiac arrhythmia diagnosis and / or planning treatment typically switches between different EP mapping graphs to examine various cardiac tissue properties. Thus, diagnosis and planning (e.g., selecting ablation locations to eliminate arrhythmias) are typically based on the cognitive integration of information from multiple EP mapping graphs, each of which displays one or more of the above EP parameters. A physician switching between different EP mapping graphs may get lost in the details and confusing indications and may thus fail to prioritize the tissue locations for treatment.

[0013] Examples of the present disclosure described herein provide algorithms and visualizations for advanced and fully automated EP data point acquisition and / or selection for display.

[0014] In some examples, a user or a processor sets acquisition criteria to acquire only data points that meet these criteria for analysis. Such criteria include a minimum predefined number of electrodes for a multi-electrode catheter (e.g., a group of electrodes that cover a minimum continuous tissue area at one time), and stability acquired within a minimum predefined time period (e.g., 2.5 seconds).

[0015] The disclosed technology can use a GUI to select several types of EP parameters and the corresponding criteria applied to the acquired data points. Using the EP selection, the processor analyzes and displays a Point of Interest (POI) map, as described below. Using one or more of the disclosed POI maps, a physician can overcome difficulties such as those described above in prioritizing tissue locations for ablation.

[0016] In some examples, the processor displays an anatomical map overlaid with POIs graphically encoded (e.g., marked). To do this, the processor receives a plurality of EP data points, which include corresponding locations on the cardiac anatomical surface and the corresponding values of arrhythmia-indicating EP parameters at those locations.

[0017] The processor applies the corresponding criteria to the values of the EP data points. For each EP data point whose value meets the corresponding criteria, the processor graphically encodes the EP data point to generate a Point of Interest (POI).

[0018] The processor superimposes POIs of at least two types of arrhythmia-indicating EP parameters on the anatomical surface to generate a POI map reflecting the surface locations that may be arrhythmogenic and visualizes the POI map to the user on a display.

[0019] In one example, to reflect the surface locations that may be arrhythmogenic, the processor divides the cardiac anatomical surface into unit regions of predefined size and shape and, for each unit region or a given portion of a unit region, determines the count of differently encoded POIs therein and graphically indicates that count at the unit region.

[0020] The graphical indication (e.g., a marker) can be shaped and / or color-coded to indicate the EP parameter it represents. The disclosed POI map does not indicate the value of each of these EP parameters, only the locations in the anatomical map where the EP parameter values meet the criteria. Using the disclosed POI map, tissue showing arrhythmogenic behavior can be marked with multiple markers or with a special marker indicating multiple markers.

[0021] The marker can be a thumbtack or a color mosaic on the anatomical map. The graphical indication can be embedded in the surface itself, such as in a wavefront displayed using a continuous color code, e.g., as done when using a coherent EP map and a spatio-temporal dispersion map. The anatomical map can be a modeled map (Fast Anatomical Map, FAM) or a 3D image of a part of the heart.

[0022] In this way, the physician can obtain an overview of the POIs on the anatomical mapping diagram. As described above, the processor can divide the anatomical mapping diagram into unit areas of predefined size and shape, and in each unit area, a combined marker indicating multiple markers among different markers of different EP parameters is generated. For example, if the markers are stripes of different colors, the processor can generate a complex stripe pattern representing different colors therein.

[0023] In an example of the POI mapping diagram, the processor displays an EP mapping diagram, such as a spatio-temporal dispersion mapping diagram (sequential activation of consecutive bipolars of a multi-electrode catheter, with the maximum derivative exceeding 85% (70%-90%) of the defined threshold over the atrial fibrillation cycle length). On this EP mapping diagram, the processor adds prominent color-coded pushpins to indicate other parameters of interest for arrhythmia. Specifically, the processor can generate a POI mapping diagram of atrial fibrillation (AFib) in this way, which will help the physician determine where to ablate the tissue. The user can change the height and / or width of the pushpins according to the criteria they choose to represent.

[0024] An example scheme for color-coded prominent pushpins is as follows:

[0025] ● A red pushpin indicates a location with a regular cycle length, for example, as a point within the range of [minimum cycle length, minimum cycle length + 10 milliseconds]

[0026] ● A blue pushpin indicates a location with a regular STD cycle length, for example, as an STD point within the range of [minimum STD cycle length, minimum STD cycle length + 5 milliseconds]

[0027] ● A brown pushpin indicates the location of a point with CFAE (showing fractionated signals)

[0028] ● A purple pushpin indicates the location of the regional ripple percentage, and the purple pushpin appears at a point higher than 0.75 *

[0029] the maximum regional ripple percentage

[0030] For another example, a POI mapping diagram with a color scale is provided to the physician, and this color scale classifies regions according to the number of parameters indicating arrhythmia therein. The physician can select from a list of parameters used to construct the mapping diagram. For example, the physician can select five parameters. The scale on the mapping diagram shows the number of these selected parameters, for example, ranging from 0 to 5, and these parameters affect a given region of the mapping diagram. The physician may consider the region showing 5 as a candidate region for ablation.

[0031] The physician can select different EP parameters from the list to count in the EP parameter scale. Additionally, the physician can assign weights to the parameters.

[0032] Finally, the processor is used to train a machine learning model using a sufficient number of POI mapping diagrams to build an expert application that can generate one or more optimized POI mapping diagrams.

[0033] System Description

[0034] Figure 1 is a schematic illustration of a catheter-based electrophysiology (EP) mapping and ablation system 10 according to an example of the present disclosure.

[0035] System 10 may include a plurality of catheters that are inserted by a physician 24 through the patient's vascular system via the skin into the chambers or vascular structures of the heart 12. In the illustrated example, a delivery sheath catheter is inserted into the left atrium or right atrium near the desired location in the heart 12. Then, a plurality of catheters may be inserted into the delivery sheath catheter to reach the desired location. The plurality of catheters may include catheters dedicated to sensing intracardiac electrogram (IEGM) signals, catheters dedicated to ablation, and / or catheters dedicated to both sensing and ablation. An example EP mapping catheter 14 configured to sense IEGM is illustrated herein. The physician 24 places the distal end 28 (hereinafter also referred to as "distal end assembly 28") of the catheter 14 in contact with the heart wall for sensing a target site in the heart 12. For ablation, the physician 24 similarly brings the distal end of the ablation catheter to the target site for ablation.

[0036] Catheter 14 is an exemplary catheter that includes one (and preferably a plurality of) electrodes 26 optionally distributed above a plurality of splines 22 at the distal end 28 and configured to sense IEGM signals. Catheter 14 may additionally include a position sensor 29 embedded in or near the distal end 28 for tracking the position and orientation of the distal end 28. Optionally and preferably, the positioning sensor 29 is a magnetic-based positioning sensor that includes three magnetic coils for sensing three-dimensional (3D) position and orientation.

[0037] The magnetic-based positioning sensor 29 may operate in conjunction with a position pad 25 that includes a plurality of magnetic coils 32 configured to generate a magnetic field in a predefined workspace. The real-time position of the distal end 28 of the catheter 14 may be tracked based on the magnetic field generated by the position pad 25 and sensed by the magnetic-based positioning sensor 29. Details of magnetic-based position sensing techniques are described in U.S. Patents Nos. 5,539,199, 5,443,489, 5,558,091, 6,172,499, 6,239,724, 6,332,089, 6,484,118, 6,618,612, 6,690,963, 6,788,967, and 6,892,091.

[0038] System 10 includes one or more electrode patches 38 that are positioned in contact with the skin of patient 23 to establish a position reference for impedance-based tracking of position pad 25 and electrodes 26. For impedance-based tracking, current is directed toward electrodes 26 and sensed at the electrode-skin patches 38 such that the position of each electrode can be triangulated via the electrode patches 38. Details of impedance-based position tracking techniques are described in U.S. Patent Nos. 7,536,218, 7,756,576, 7,848,787, 7,869,865, and 8,456,182.

[0039] Recorder 11 displays an electrogram 21 captured using body surface ECG electrodes 18 and an intracardiac electrogram (IEGM) captured using electrodes 26 of catheter 14. Recorder 11 may include pacing capabilities for pacing the heart rhythm and / or may be electrically connected to an independent pacemaker.

[0040] System 10 may include an ablation energy generator 50 that is adapted to conduct ablation energy to one or more electrodes at the distal end of a catheter configured for ablation. The energy generated by ablation energy generator 50 may include, but is not limited to, radiofrequency (RF) energy or pulsed field ablation (PFA) energy (including monopolar or bipolar high voltage DC pulses that can be used to effect irreversible electroporation (IRE)), or a combination thereof.

[0041] Patient Interface Unit (PIU) 30 is an interface configured to enable electrical connectivity between a catheter, electrophysiology equipment, a power source, and a workstation 55 for controlling the operation of System 10. The electrophysiology equipment of System 10 may include, for example, a plurality of catheters, position pad 25, body surface ECG electrodes 18, electrode patches 38, ablation energy generator 50, and recorder 11. Optionally and preferably, PIU 30 additionally includes processing capabilities for performing real-time position calculations of the catheter and for performing ECG calculations.

[0042] Workstation 55 includes a memory 57, a processor unit 56 with a memory or storage device having appropriate operating software loaded therein, and user interface capabilities. Workstation (55) may provide a variety of functions, optionally including (1) three-dimensional (3D) modeling of endocardial anatomy and rendering a model or POI map 20 for display on display device 27; (2) displaying on display device 27 activation sequences (or other data) compiled from the recorded electrograms 21, which activation sequences include representative visual indicia or images in the rendered POI map 20; (3) displaying the real-time position and orientation of multiple catheters within the heart chambers, and (4) displaying on display device 27 sites of interest, such as locations where ablation energy has been applied. A commercial product embodying the elements of System 10 may be available as CARTOTM obtained by the 3 system and available from Biosense Webster, Inc., 31A Technology Drive, Irvine, CA 92618.

[0043] Point of Interest (POI) Cardiac Mapping Diagram

[0044] Figure 2 is a schematic diagram of a POI mapping graph 200 according to an example of the present disclosure. The POI mapping graph 200 can be Figure 1 the POI mapping graph 20 shown in

[0045] The POI mapping graph 200 includes an anatomical mapping graph 202, which in the shown case is an anatomical diagram of the left atrium. The POI mapping graph 200 also includes EP data points encoded graphically (e.g., marked). The data POIs are used for a given unit area on the mapping graph, and at least two EP parameters are superimposed on the mapping graph. The marks can be shaped graphically and / or color-coded to indicate the parameters they represent. The disclosed POI mapping graph does not indicate the value of each EP parameter among the EP parameters, but only indicates the positions where the EP parameter values in the anatomical mapping graph exceed a threshold.

[0046] In the example of the shown POI mapping graph 200, the processor displays prominent color-coded pushpins indicating additional parameters of interest for arrhythmias such as atrial fibrillation (AFib).

[0047] Examples of the color-coding scheme for highlighting the pushpins include:

[0048] ● The red pushpin 204 indicates the position of a regular cycle length, e.g., as a point within the range [minimum cycle length, minimum cycle length + 10 milliseconds]

[0049] ● The blue pushpin 206 indicates the position of a regular STD cycle length, e.g., as an STD point within the range [minimum STD cycle length, minimum STD cycle length + 5 milliseconds]

[0050] ● The brown pushpin 208 indicates the position of a point with CFAE (showing fractionated signals)

[0051] ● The purple pushpin 210 indicates the position of the regional ripple percentage, and the purple pushpin appears at points higher than 0.75 * the maximum regional ripple percentage

[0052] As further seen, the pushpin 212 includes rings of different colors to mark the positions where the indications of the pushpins 204, 206, and 208 overlap each other.

[0053] The EP wavefront can also be color-coded (214) on the mapping diagram, such as is done when using a coherent EP mapping diagram.

[0054] If the analysis shows that the degree of spatio-temporal dispersion in the region exceeds a given slope, one or more regions can be graphically coded (215) on the EP mapping diagram. Such dispersion can be determined if a sufficient number of electrodes cover the region under test for a sufficient duration.

[0055] Finally, additional indicators, such as spheres 216, can be included, which represent, for example, that the point potential duration (PM) is greater than a defined threshold.

[0056] Figure 3 is a schematic diagram of a POI mapping diagram 300 according to another example of the present disclosure. The POI mapping diagram 300 can be Figure 1 the POI mapping diagram 20 shown in. The POI mapping diagram 300 includes an anatomical mapping diagram 302, which, in the case shown, is an anatomical diagram of the left atrium.

[0057] The physician is provided with a POI mapping diagram 300 having a color scale that classifies regions according to the number of EP parameters indicating arrhythmia. The physician can select from a list 304 of EP parameters for constructing the POI mapping diagram 300. For example, the physician can select five EP parameters from a list of arrhythmia-indicating EP parameters, such as the cycle length, percentage of regional ripples, local activation time (LAT), bipolar potential, activation wave velocity, spatio-temporal dispersion slope, and complex fractionated atrial electrogram (CFAE) described above. The scale 306 on the mapping diagram shows the number of these selected EP parameters that affect a given region of the mapping diagram, for example, ranging from 0 to 5. The physician may consider a region 308 showing 5 to be a candidate region for ablation.

[0058] The physician can select different EP parameters from the list 304 to be counted in the EP parameter scale 306. Additionally, the physician can assign weights to the EP parameters.

[0059] Figure 4 is a flowchart schematically illustrating a method for generating, editing, and presenting a POI mapping diagram (such as mapping diagrams 200 and 300) according to an example of the present disclosure. According to the example presented, the algorithm performs the following process, which starts with the processor 28 receiving (e.g., uploading) a cardiac anatomical surface (such as anatomical mapping diagrams 202 and 302) at the anatomical surface upload step 402.

[0060] Next, at the EP data point receiving step 404, the processor receives a plurality of EP data points on the anatomical surface, each of which corresponds to (belongs to) one EP parameter among a plurality of EP parameters.

[0061] At the standard application step 406, the processor applies the corresponding (i.e., for each EP parameter) EP standard to the EP data points. These can include EP values that cross a threshold or fall within a range. The EP parameters can be taken from the above-mentioned arrhythmia-indicating EP parameters (cycle length, regional ripple percentage, local activation time (LAT), bipolar potential, activation wave speed, spatio-temporal dispersion slope, and complex fractionated atrial electrogram (CFAE)).

[0062] At the graphical step 408, the processor graphically encodes each EP data that complies with the standard in order to generate points of interest.

[0063] At the POI mapping generation step 410, the processor graphically indicates the POI (e.g., as shown by the thumbtack 212 in Figure 2 ) at the location where at least two or more EP parameters meet the corresponding predefined criteria; and / or graphically indicates the POI according to a scale that determines the number of differently encoded POIs (e.g., as shown by the scale 306 in Figure 3 ), up to 5), and graphically indicates the count at the unit area. In this way, the processor enables the POI mapping to provide an indication of the surface locations that may be arrhythmogenic.

[0064] Finally, at the POI mapping display step 412, the processor displays the POI mapping to the user, such as displaying the mapping 20 on the display device 27.

[0065] Examples

[0066] Example 1

[0067] A system (10) includes: a display (27) and a processor (56). The processor is configured to: receive a cardiac anatomical surface (202, 302), and receive a plurality of electrophysiological (EP) data points that include (i) corresponding locations on the cardiac anatomical surface, and (ii) corresponding values of arrhythmia-indicating EP parameters at these locations, and apply corresponding criteria to these values of the EP data points. For each EP data point whose value meets the corresponding criteria, the processor is configured to: graphically encode (204, 206, 208, 210, 212) the EP data point to generate a point of interest (POI), superimpose the POIs of at least two types of arrhythmia-indicating EP parameters on the anatomical surface in order to generate a POI mapping that reflects the surface locations that may be arrhythmogenic, and visualize the POI mapping to the user on the display (27).

[0068] Example 2

[0069] The system (10) according to Embodiment 1, wherein the types of these arrhythmia-indicating EP parameters are selected from a list including at least two of the following: cycle length, percentage of regional ripples, local activation time (LAT), bipolar potential, activation wave speed, spatio-temporal dispersion slope, and complex fractionated atrial electrogram (CFAE).

[0070] Example 3

[0071] The system (10) according to any one of Embodiments 1 and 2, wherein the processor (56) is configured to visualize the POI mapping diagram by: dividing the cardiac anatomical surface (202, 302) into unit regions of predefined size and shape, and for each unit region, determining the count of differently encoded (204, 206, 208, 210) POIs in the unit region, and graphically indicating (306) the count at the unit region.

[0072] Example 4

[0073] The system according to any one of Embodiments 1 to 3, wherein for a given unit region, the processor is configured to: graphically indicate (204, 206, 208, 210) the count (306) by generating a new graphical indication reflecting the count of differently graphically encoded POIs in the given unit region.

[0074] Example 5

[0075] The system according to any one of Embodiments 1 to 3, wherein for a given unit region, the processor is configured to: reflect the count (306) by combining differently graphically encoded (204, 206, 208, 210) into a single graphically encoded (212) POI to indicate each of the differently graphically encoded POIs in the given unit region.

[0076] Example 6

[0077] A method, comprising: receiving a cardiac anatomical surface (202, 302); receiving a plurality of electrophysiological (EP) data points, each EP data point including (i) a corresponding location on the cardiac anatomical surface and (ii) a corresponding value of an arrhythmia-indicating EP parameter at these locations; applying corresponding criteria to the values of these EP data points; for each EP data point whose value meets the corresponding criteria, graphically encoding (204, 206, 208, 210, 212) the EP data point to generate a point of interest (POI); superimposing POIs of at least two types of arrhythmia-indicating EP parameters on the anatomical surface so as to generate a POI map reflecting surface locations that may be arrhythmogenic; and visualizing the POI map to a user.

[0078] It should be understood that the above embodiments are cited by way of example, and the present disclosure is not limited to what is specifically shown and described above. Instead, the scope of the present disclosure includes combinations and sub-combinations of the various features described above, as well as their variations and modifications, which will occur to those skilled in the art upon reading the above description and which are not disclosed in the prior art. Documents incorporated by reference into this patent application are considered an inseparable part of this application, unless any terms defined in these incorporated documents conflict with the definitions expressly or implicitly given in this specification, in which case only the definitions in this specification shall be considered.

Claims

1. A system, comprising: A display; And A processor configured to: Receive a cardiac anatomical surface; Receive a plurality of electrophysiological (EP) data points, the plurality of EP data points including (i) corresponding locations on the cardiac anatomical surface, and (ii) corresponding values of arrhythmia-indicating EP parameters at the locations; Apply corresponding criteria to the values of the EP data points; For each EP data point whose value meets the corresponding criteria, graphically encode the EP data point to generate a point of interest (POI); Overlay POIs of at least two types of arrhythmia-indicating EP parameters on the anatomical surface so as to generate a POI map reflecting surface locations that may be arrhythmogenic; and Visually present the POI map to a user on the display.

2. The system according to claim 1, wherein, The types of the arrhythmia-indicating EP parameters are selected from a list including at least two of the following: cycle length, regional fractionation percentage, local activation time (LAT), bipolar potential, activation wave speed, spatio-temporal dispersion slope, and complex fractionated atrial electrogram (CFAE).

3. The system according to claim 1, wherein, The processor is configured to visually present the POI map by: dividing the cardiac anatomical surface into unit regions of predefined size and shape, and for each unit region, determining the count of differently encoded POIs in the unit region and graphically indicating the count at the unit region.

4. The system according to claim 3, wherein For a given unit region, the processor is configured to: graphically indicate the count by generating a new graphical indication reflecting the count of the differently encoded POIs in the given unit region.

5. The system according to claim 3, wherein For a given unit region, the processor is configured to; reflect the count by combining the differently encoded POIs into a single graphically encoded POI to indicate each of the differently encoded POIs in the given unit region.

6. A method, comprising: Receiving a cardiac anatomical surface; Receiving a plurality of electrophysiological (EP) data points, the plurality of EP data points including (i) corresponding locations on the cardiac anatomical surface, and (ii) corresponding values of arrhythmia-indicating EP parameters at the locations; Applying corresponding criteria to the values of the EP data points; For each EP data point whose value meets the corresponding criteria, graphically encoding the EP data point to generate a point of interest (POI); Overlaying POIs of at least two types of arrhythmia-indicating EP parameters on the anatomical surface so as to generate a POI map reflecting surface locations that may be arrhythmogenic; and Visually presenting the POI map to a user.

7. The method according to claim 6, wherein, The types of the arrhythmia-indicating EP parameters are selected from a list including at least two of the following: cycle length, regional fractionation percentage, local activation time (LAT), bipolar potential, activation wave speed, and complex fractionated atrial electrogram (CFAE).

8. The method according to claim 6, wherein, Visualizing the POI mapping diagram includes: dividing the cardiac anatomical surface into unit regions of a predefined size and shape, and for each unit region, determining the count of POIs with different encodings in the unit region and graphically indicating the count at the unit region.

9. The method according to claim 8, wherein For a given unit region, graphically indicating the count includes: generating a new graphical indication reflecting the count of the POIs encoded in different graphical ways in the given unit region.

10. The method according to claim 8, wherein For a given unit region, reflecting the count includes: combining the POIs encoded in different graphical ways into a single graphically encoded POI to indicate each of the POIs encoded in different graphical ways in the given unit region.

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