Corrected anatomic map

Abstract

The invention is entitled "Correcting an anatomical map." A system is disclosed that includes a display and a processor. The processor is configured to compute a point P' on a virtual surface representing a point cloud of an anatomical volume by projecting another point P corresponding to a location on an anatomical surface of the anatomical volume onto the virtual surface. The processor is further configured to define a virtual sphere centered on a virtual line connecting P to P' such that P lies on a spherical surface of the virtual sphere and to unfold the point cloud throughout the virtual sphere or exclude the virtual sphere from the point cloud. The processor is further configured to regenerate the virtual surface such that P lies on the virtual surface as a result of having unfolded the point cloud or excluded the virtual sphere and to display the regenerated virtual surface on the display. Other embodiments are also described.

Description

Technical Field

[0001] This invention relates to the field of anatomical mapping. Background Technology

[0002] U.S. Patent Application Publication 2009 / 0148012, granted to Altmann et al., describes a medical imaging method that includes creating an anatomical mapping of the inner walls of cavities within a subject's body by inserting a probe into the body and using the probe to collect data. Based on this mapping, a three-dimensional (3-D) contour is depicted as a 3-D image of the cavity. Summary of the Invention

[0003] According to some embodiments of the present invention, a system including a display and a processor is provided. The processor is configured to calculate a point P' on a virtual surface by projecting another point P, corresponding to a position on an anatomical surface of an anatomical volume, onto a virtual surface representing a point cloud of the anatomical volume. The processor is further configured to define a virtual sphere centered on a virtual line connecting P to P', such that P lies on the spherical surface of the virtual sphere. The processor is further configured to perform operations selected from a group of operations consisting of: unfolding the point cloud over the entire virtual sphere, and excluding the virtual sphere from the point cloud. The processor is further configured to regenerate the virtual surface after performing the operations, such that P lies on the virtual surface since the operations have been performed, and the regenerated virtual surface is displayed on the display.

[0004] In some implementations, the processor is configured to regenerate the virtual surface by applying a sphere pivoting algorithm (BPA) with a sphere radius r to the point cloud, and the processor is configured to define a sphere such that the radius R of the sphere is at least 2r.

[0005] In some implementations, R = 2r.

[0006] In some implementations, the processor is further configured to recognize P in response to input from the user.

[0007] In some implementations, the input indicates the location of the probe within the body.

[0008] In some implementations, the input includes selecting P from the display of the point cloud.

[0009] In some implementations, the anatomical volume includes at least a portion of the chambers of the heart.

[0010] According to some embodiments of the invention, a method is also provided, comprising using a processor to compute a point P' on a virtual surface by projecting another point P, corresponding to a location on an anatomical surface of an anatomical volume, onto a virtual surface of a point cloud representing the anatomical volume. The method further comprises defining a virtual sphere centered on a virtual line connecting P to P', such that P lies on a spherical surface of the virtual sphere. The method further comprises performing operations selected from a group of operations: unfolding the point cloud over the entire virtual sphere, and excluding the virtual sphere from the point cloud. The method further comprises regenerating the virtual surface after performing the operations, such that P lies on the virtual surface because the operations have already been performed.

[0011] According to some embodiments of the present invention, a computer software product is also provided comprising a tangible, non-transitory, computer-readable medium therein storing program instructions. When read by a processor, the instructions cause the processor to calculate a point P' on a virtual surface by projecting another point P, corresponding to a position on an anatomical surface of an anatomical volume, onto a virtual surface representing a point cloud of the anatomical volume. The instructions also cause the processor to define a virtual sphere centered on a virtual line connecting P to P', such that P lies on the spherical surface of the virtual sphere. The instructions further cause the processor to perform operations selected from a group of operations: unfolding the point cloud over the entire virtual sphere, and excluding the virtual sphere from the point cloud. The instructions further cause the processor to regenerate the virtual surface after performing the operations, such that P lies on the virtual surface because the operations have already been performed.

[0012] According to some embodiments of the present invention, a system including an input device and a processor is also provided. The processor is configured to add a plurality of points corresponding to respective locations of a probe within the anatomical volume to a point cloud representing an anatomical volume. The processor is further configured to, after adding points, remove a subset of points from the point cloud in response to input received via the input device. The processor is further configured to, after removing the subset, add additional points corresponding to corresponding subsequent locations of the probe within the anatomical volume to the point cloud.

[0013] In some implementation schemes,

[0014] This input indicates that the probe will be used in point removal mode, and

[0015] The processor is configured to remove a subset by removing points for each point in the subset in response to the detection probe being located at the location corresponding to the point.

[0016] In some implementation schemes,

[0017] This input is the first input, and

[0018] The processor is configured to add additional points to the point cloud in response to a second input indicating that the probe will be used in point-adding mode.

[0019] In some implementations, the processor is configured to remove the point in response to the probe pressing against the surface of the anatomical volume.

[0020] In some implementations, the input indicates a time period, and the subset includes those points added to the point cloud during that time period.

[0021] In some implementations, the time period begins T time units before the time the input is submitted, and the input indicates the time period by indicating T.

[0022] In some implementations, the input indicates an integer N, and the subset includes the N points most recently added to the point cloud.

[0023] In some implementations, the anatomical volume includes at least a portion of the chambers of the heart.

[0024] According to some embodiments of the present invention, a method is also provided, which includes using a processor to add a plurality of points corresponding to corresponding positions of a probe within the anatomical volume to a point cloud representing an anatomical volume. The method further includes, after adding the points, removing a subset of the points from the point cloud in response to input from a user. The method further includes, after removing the subset, adding additional points corresponding to corresponding subsequent positions of the probe within the anatomical volume to the point cloud.

[0025] According to some embodiments of the present invention, a computer software product is also provided, comprising a tangible, non-transitory, computer-readable medium therein storing program instructions. When read by a processor, the instructions cause the processor to add a plurality of points corresponding to corresponding positions of a probe within the anatomical volume to a point cloud representing an anatomical volume. The instructions also cause the processor, after adding points, to remove a subset of points from the point cloud in response to input from a user. The instructions further cause the processor, after removing the subset, to add additional points to the point cloud corresponding to corresponding subsequent positions of the probe within the anatomical volume. Attached Figure Description

[0026] This disclosure will be more fully understood through the following detailed description of embodiments of the invention, taken in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 This is a schematic diagram of an anatomical mapping system according to some exemplary embodiments of the present invention;

[0028] Figure 2 This is a schematic diagram of a technique for generating anatomical mapping maps according to some exemplary embodiments of the present invention;

[0029] Figure 3 This is a flowchart of an algorithm for generating anatomical mapping maps according to some exemplary embodiments of the present invention;

[0030] Figures 4A to 4B This is a schematic diagram of a technique for reconstructing a model according to some exemplary embodiments of the present invention; and

[0031] Figure 5 This is a flowchart of an algorithm for reconstructing a model according to some exemplary embodiments of the present invention. Detailed Implementation

[0032] Overview

[0033] In anatomical mapping of cardiac chambers, a physician moves a probe through the chamber while a tracking system tracks the probe's position. Based on this tracking, a model of the chamber is constructed. This model includes a point cloud and a surface surrounding the point cloud. The point cloud includes multiple points corresponding to the probe's (typically the distal end of the probe) position within the chamber, and the surface represents the tissue surrounding the chamber. This surface can be correlated with the electrical properties of the tissue, which can be derived from electrogram signals acquired by the probe at various locations on the tissue.

[0034] When performing such mapping, a challenge lies in the potential addition of stray points to the model due to respiratory movements or excessive force applied to the tissue by the probe. Conventionally, these points are removed after mapping by modifying the model surface (e.g., using spline deformation and / or surface interpolation) so that the surface passes through points known to correspond to locations on the tissue. (These points are referred to herein as "anchor points" and correspond to those locations where electrogram signals were acquired, as physicians typically take care not to apply excessive force to the tissue when acquiring electrogram signals.) However, this deformation can compromise the accuracy of the model.

[0035] To address this challenge, embodiments of the present invention provide various techniques for removing stray points from a model. After removing the stray points, the surface can be regenerated. Therefore, surface deformation may not be necessary.

[0036] According to one such technique, a point removal mode is provided for manipulating the probe. When the probe is manipulated in this mode, moving the probe to a specific location causes the removal of a point corresponding to that location from the model. Therefore, physicians can correct the model in real time by switching from the usual point addition mode to the point removal mode and then moving the probe to any location corresponding to a stray point.

[0037] According to another such technique, for each anchor point, a virtual sphere is defined that extends through the anchor point (see reference below). Figure 4A(As detailed above), and then remove any points within the sphere from the point cloud. Subsequently, the model surface or at least a portion of the model surface near the anchor points is regenerated, such that the model surface passes through the anchor points. Advantageously, this technique can be performed after acquiring each new anchor point, during or after the construction of the point cloud.

[0038] For cases where the anchor point is outside the point cloud, a variation of the latter technique can be performed. According to this variation, after defining the virtual sphere, the sphere is filled with additional points to enhance the point cloud.

[0039] System Description

[0040] First refer to Figure 1 This is a schematic diagram of an anatomical mapping system 20 according to some embodiments of the present invention.

[0041] System 20 includes an in vivo probe 26 that is proximally connected to console 32. System 20 also includes a processor 34 typically housed within console 32.

[0042] System 20 is used to generate an anatomical mapping 38 of the volume of the heart 24 of the subject 22 (such as at least a portion of the chambers of the heart 24). Mapping 38 includes a point cloud that represents the mapping volume by including a plurality of points corresponding to corresponding locations within the mapping volume. Mapping 38 also includes a virtual surface 46 surrounding the point cloud. The processor may display the mapping on display 36 during and / or after the mapping is generated.

[0043] More specifically, as the physician 30 moves the probe 26 within the volume, the processor 34 continuously probes the sub-volume 27 occupied by the distal end of the probe. For each probed sub-volume 27, the processor also constructs a point cloud by adding one or more points (typically multiple points) corresponding to the sub-volume 27 to the point cloud. (Therefore, each added point corresponds to a specific location of any part of the probe within the mapping volume, specifically the distal end of the probe.) After constructing the point cloud and / or intermittently during point cloud construction, the processor generates a virtual surface 46. (It should be noted that, for ease of description, the sub-volume 27 may be referred to herein as the “probe location.”)

[0044] Typically, the distal end of probe 26 includes at least one sensing electrode 28. As the probe moves within the heart, electrode 28 acquires electrogram signals from cardiac tissue. Processor 34 analyzes these signals and, in response, annotates mapping map 38 (e.g., by coloring the mapping map according to a sliding color scale) to indicate the electrical properties of the tissue. In such embodiments, mapping map 38 may be referred to as an “electroanatomical map” or an “electrophysiological map.”

[0045] In some embodiments, to facilitate probe tracking, one or more electromagnetic coils are coupled to the distal end of the probe and generate a magnetic field near the subject 22. As the probe moves within the heart, the magnetic field induces a position-dependent signal in the coils. Based on this signal, a processor detects the position of each coil in the coils, thereby identifying subvolume 27. Such magnetic-based tracking is disclosed, for example, in U.S. Patents 5,391,199, 5,443,489, and 6,788,967 to Ben-Ham, U.S. Patent 6,690,963 to Ben-Ham et al., U.S. Patent 5,558,091 to Acker et al., and U.S. Patent 6,177,792 to Govari, the corresponding disclosures of which are incorporated herein by reference.

[0046] Alternatively or otherwise, one or more electrodes coupled to the distal end of the probe can transmit current to multiple electrode patches coupled to the subject's body at different corresponding locations. (Typically, these electrodes do not include electrode 28.) Based on the current and the resulting body impedance measurements, the processor can detect the location of each electrode, thereby identifying subvolume 27. A hybrid technique combining such impedance-based tracking with magnetic tracking is described in U.S. Patent 8,456,182 to Bar-Tal et al., the disclosure of which is incorporated herein by reference.

[0047] Alternatively or otherwise, the processor may use any other suitable tracking technique to track the probe, thereby constructing a point cloud.

[0048] Generally, processor 34 may be embodied as a single processor or a group of cooperative networked or clustered processors. In some embodiments, as described herein, the functionality of processor 34 may be implemented solely in hardware, such as using one or more application-specific integrated circuits (ASICs) or field-programmable gate arrays (FPGAs). In other embodiments, the functionality of processor 34 is implemented at least partially in software. For example, in some embodiments, processor 34 is embodied as a programmable digital computing device including at least a central processing unit (CPU) and random access memory (RAM). Program code (including software programs and / or data) is loaded into RAM for execution and processing by the CPU. For example, program code and / or data may be downloaded to the processor electronically via a network. Alternatively or otherwise, program code and / or data may be provided and / or stored on a non-transitory tangible medium, such as magnetic, optical, or electronic memory. Such program code and / or data, when provided to the processor, create a machine or special-purpose computer configured to perform the tasks described herein.

[0049] Generate anatomical mapping

[0050] See now Figure 2 This is a schematic diagram of a technique for generating a calibration map 38 according to some embodiments of the present invention.

[0051] Figure 2 A portion of point cloud 42 is shown, as referenced above. Figure 1 The portion describes the mapping volume of the heart by including a plurality of points 44 corresponding to the respective locations of the intracardiac probe 26. Figure 2 A virtual surface 46 is also shown, which represents the anatomical surface 40 of the mapping volume (i.e., the tissue surrounding the mapping volume).

[0052] Typically, the processor generates the virtual surface 46 by applying the Ball-Pivoting Algorithm (BPA) to the point cloud (described in "The ball-pivoting algorithm for surface reconstruction" by Bernardini, Fausto, et al., IEEE Transactions on Visualization and Computer Graphics 5.4(1999):349-359, which is incorporated herein by reference). This algorithm computes surface 46 as a triangular mesh of points approximately interpolated from the periphery of the point cloud by: (i) finding seed triangles whose vertices are points from the periphery of the point cloud, and then (ii) expanding the triangulation by pivoting a virtual sphere around the edges of the existing triangles until no open edges remain. Alternatively, the processor may use any other suitable surface generation algorithm.

[0053] Figure 2 The leftmost portion shows the situation where the probe 26 pushes the surface 40 outward from its natural position 48 to create a bulge 50 in the surface. Therefore, as... Figure 2 As shown in the middle part, stray points corresponding to one or more locations of the probe within the bulge 50 are added to the point cloud, so that the virtual surface 46 acquires the stray bulge 52.

[0054] To address this issue, embodiments of the present invention provide various techniques for removing a subset of points 44 from the point cloud and then generating the virtual surface 46, such as... Figure 2 The rightmost part is shown. After removing the subset, additional points can be added to the point cloud. This removes stray points during the mapping process, thus reducing the post-processing required for the mapping map.

[0055] Typically, the removal of a subset of points is initiated by the system user. For example, in response to noticing a bulge 52 on display 36 ( Figure 1 Users, such as physicians, can submit input instructing that some points should be removed from the point cloud. Subsequently, in response to this input, the processor can remove a subset of points.

[0056] In some implementations, the probe can be used in two different modes: a point-addition mode and a point-removal mode. When the probe is in point-addition mode, the processor adds a corresponding point for each new location of the probe. Conversely, when the probe is in point-removal mode, the processor removes any points corresponding to a probe location. (Additionally, the probe may have a third inactive mode, in which neither points are added nor removed.)

[0057] In such implementations, the aforementioned input from the user indicates that the probe will be used in point removal mode, and the processor removes points in response to detecting the location of the probe at each point in a subset. For example, after adding a first set of points to the point cloud, the physician may submit input indicating that the probe will be used in point removal mode. The physician may then pass the probe through a previously mapped portion of the patient's anatomy. In response to this input and in response to detecting the probe's location within that portion, the processor can remove points corresponding to those locations. Next, after removing the probe from that portion, the physician may submit another input indicating that the probe will again be used in point addition mode. In response to this input, the processor can add points to the point cloud again.

[0058] To reduce the number of valid points removed from the point cloud, the processor can check whether the probe is pressing against surface 40 before removing a point, for example, by processing a signal from a pressure sensor at the distal end of the probe. In response to detecting that the probe is pressing against the surface, the processor can remove the point; otherwise, the processor can avoid removing the point.

[0059] As an alternative or supplement to operating the probe in point removal mode, other techniques can be used to remove points from the point cloud. For example, the point removal initiation input from the user can indicate a time period, and the subset of points to be removed can include those points added to the point cloud during that time period. As a specific example, the time period can begin T time units (e.g., seconds) before the time the input is submitted, and the input can indicate the time period by indicating T. Alternatively, the input can indicate an integer N, and the subset can include the N points most recently added to the point cloud.

[0060] Generally, users can use any suitable input device to submit the aforementioned input. For example, a user can press console 32 ( Figure 1 One or more buttons or keys on the control handle of the probe or probe. Alternatively or additionally, the display may include a touchscreen, and the user may submit at least some of the input via the touchscreen. Alternatively or additionally, the user may submit at least some of the input using a keyboard and / or mouse. As another option, the user may use a foot switch, for example, to switch back and forth between modes of operating the probe.

[0061] Now for reference Figure 3It is for generating a calibration map 38 according to some embodiments of the present invention. Figure 1 The flowchart of algorithm 54.

[0062] According to Algorithm 54, at the location detection step 56, the processor repeatedly detects the probe's position. After detecting the probe's position, at the first check step 58, the processor checks whether the probe is in point-adding mode. If so, at the point-adding step 60, the processor adds one or more points corresponding to the position to the point cloud. Otherwise, at the second check step 62, the processor checks whether the probe is in point-removing mode. If so, at the point-removing step 64, the processor removes one or more points corresponding to the position. After adding or removing points, or if the probe is neither in point-adding nor point-removing mode (but in an inactive mode), the processor returns to the location detection step 56.

[0063] In parallel with algorithm 54, the processor may execute another algorithm for receiving input from the user and switching back and forth between modes in response. Additionally, in parallel with algorithm 54, the processor may execute an algorithm for intermittently regenerating virtual surface 46. Figure 2 Another algorithm. For example, the processor can intermittently regenerate a portion of a virtual surface at each peripheral part of the point cloud where points have been added or removed.

[0064] Use anchor points

[0065] In some implementations, the processor identifies one or more anchor points known to correspond to locations on the anatomical surface. For each anchor point, the processor may remove a portion of the point cloud located outside the anchor point before generating a virtual surface such that the virtual surface passes through the anchor point. (This technique may be performed as an alternative to or supplement to the point removal technique described above.) Alternatively, the processor may unfold the point cloud such that, after regenerating the virtual surface, the virtual surface passes through the anchor point.

[0066] Typically, the processor responds to user input such as physician 30 ( Figure 1 The input is used to identify each anchor point. For example, as described in the overview above, during mapping, electrogram signals can be acquired at various locations on the anatomical surface. At each of these locations, the physician can position the probe to contact the tissue, typically without pushing the tissue outward, and then submit an input to the processor indicating that the probe is positioned on the tissue. (Generally, the user can use any suitable input device to submit this input, as referenced above.) Figure 2 In response to such input, the processor can identify the point corresponding to the probe position as an anchor point. (It should be noted that since the probe was previously located at the current position, the anchor point may already belong to the point cloud.) Alternatively or otherwise, when on display 36 (… Figure 1 When displaying a point cloud, the user can select one of the points in the point cloud as an anchor point, for example, by using a touchscreen or mouse.

[0067] For further details, see now. Figures 4A to 4B This is a schematic diagram of a technique for reconstructing a model according to some embodiments of the present invention.

[0068] Figure 4A The leftmost part shows the point cloud and thus the virtual surface 46 has been incorrectly unfolded outwards. Figures 4A to 4B The shaded areas correspond to point clouds. In this case, such as... Figure 4A As shown in the middle section, the processor removes points from the point cloud such that the anchor point P corresponding to the position on the anatomical surface is located at the periphery of the point cloud. Subsequently, as... Figure 4A As shown in the rightmost part, the processor regenerates virtual surface 46 such that P lies on the virtual surface because P is located around the point cloud.

[0069] Specifically, after identifying point P, the processor calculates another point P' on the virtual surface by projecting P onto it. In other words, the processor calculates P' as the point on the virtual surface closest to P. (P' can be an initial point belonging to the point cloud, but typically P' is a new point defined by the processor.) The processor then defines a virtual sphere 43 centered on the virtual line 47 connecting P to P' (i.e., having a center 45 on it), such that P lies on the (spherical) surface of the virtual sphere 43. Next, the processor excludes the virtual sphere from the point cloud; that is, the processor removes each point located within the sphere from the point cloud. Finally, the processor regenerates the virtual surface such that, since the virtual sphere has been excluded from the point cloud, P lies on the virtual surface.

[0070] Typically, a virtual surface reconstruction (BPA) is used to regenerate the virtual surface. In such implementations, the radius R of the sphere is at least 2r, where r is the radius of the virtual sphere 49 used for the BPA, allowing the sphere 49 to pivot within the region of the removal point. For example, R can be equal to 2r.

[0071] like Figure 4B As shown, even when the peripheral portion of the anatomical volume is missing during mapping, the above technique can also be used to propagate point clouds and virtual surfaces outwards. In other words, the processor can identify P' and then define a virtual sphere, as described above and as... Figure 4B The leftmost part is shown. Subsequently, the processor can expand the point cloud throughout the entire virtual sphere, that is, fill the portions of the sphere outside the point cloud with new points, as shown... Figure 4B The middle part is shown. (New points can have any suitable spacing between points.) Finally, as... Figure 4BAs shown in the rightmost part, the processor can regenerate the virtual surface as described above, such that P lies on the virtual surface since the point cloud has already been unfolded throughout the virtual sphere.

[0072] See now Figure 5 This is a flowchart of an algorithm 66 for reconstructing a model according to some embodiments of the present invention.

[0073] Algorithm 66 begins with point identification step 68, where the processor identifies anchor point P. Then, in projection step 70, the processor calculates point P' by projecting P onto a virtual surface. Next, in virtual sphere definition step 72, the processor defines a virtual sphere. After defining the virtual sphere, in point cloud modification step 74, the processor modifies the point cloud relative to the virtual sphere (by adding or removing points from the virtual sphere) so that P lies on the periphery of the point cloud. Finally, in regeneration step 76, the processor regenerates the virtual surface so that P subsequently lies on the virtual surface.

[0074] While the above description primarily concerns the mapping of cardiac chambers, it should be noted that the techniques described herein can also be applied to the mapping of any other anatomical volume, such as the ear and pharynx.

[0075] Those skilled in the art will understand that this invention is not limited to what has been specifically shown and described above. Rather, the scope of embodiments of this invention includes both combinations and sub-combinations of the various features described above, as well as variations and modifications outside the scope of the prior art that may occur to those skilled in the art upon reading the foregoing specification. Documents incorporated herein by reference are considered an integral part of this application, except that if any terminology defined in such incorporated documents conflicts with the definitions expressly or implicitly given in this specification, only the definitions in this specification shall be considered.

Claims

1. A system for anatomical mapping, the system comprising: monitor; and Processor, the processor being configured to: A virtual surface is generated around the perimeter of a point cloud, the point cloud representing a mapping volume within an anatomical volume, and the virtual surface representing an anatomical surface surrounding the mapping volume, wherein the point cloud includes a plurality of points corresponding to corresponding mapping locations within the anatomical volume; In response to an input identification point P from the user, where P is known to correspond to a position on the anatomical surface of the anatomical volume; Calculate point P' on the virtual surface, where point P' is the point on the virtual surface that is closest to P. Define a virtual sphere centered on the virtual line connecting P to P', such that P lies on the spherical surface of the virtual sphere. An operation is performed to place P at the periphery of the point cloud, wherein the operation is selected from a group of operations consisting of: expanding the point cloud over the entire virtual sphere, and excluding the virtual sphere from the point cloud, in response to input from the user. The virtual surface is regenerated after the operation is performed, wherein P lies on the regenerated virtual surface, and The regenerated virtual surface is displayed on the monitor.

2. The system of claim 1, wherein the processor is configured to regenerate the virtual surface by applying a sphere pivoting algorithm (BPA) with a sphere radius r to the point cloud, and wherein the processor is configured to define the virtual sphere such that the radius R of the virtual sphere is at least 2r.

3. The system according to claim 2, wherein R = 2r.

4. The system of claim 1, wherein the input indicator probe is located at the said position.

5. The system of claim 1, wherein the input includes selecting P from the display of the point cloud.

6. The system of claim 1, wherein the anatomical volume comprises at least a portion of the chambers of the heart.

7. A method for anatomical mapping, the method comprising: A processor is used to generate a virtual surface around the perimeter of a point cloud, which represents a mapping volume within an anatomical volume, and the virtual surface represents an anatomical surface around the mapping volume, wherein the point cloud includes a plurality of points corresponding to corresponding mapping locations within the anatomical volume. In response to an input identification point P from the user, where P is known to correspond to a position on the anatomical surface of the anatomical volume; Calculate point P' on the virtual surface, where point P' is the point on the virtual surface that is closest to P; Define a virtual sphere centered on the virtual line connecting P to P', such that P lies on the spherical surface of the virtual sphere; An operation is performed to place P at the periphery of the point cloud, wherein the operation is selected from a group of operations consisting of: expanding the point cloud over the entire virtual sphere and excluding the virtual sphere from the point cloud in response to input from the user; as well as The virtual surface is generated again after the operation is performed, wherein P is located on the regenerated virtual surface.

8. The method of claim 7, wherein regenerating the virtual surface comprises regenerating the virtual surface by applying a sphere pivoting algorithm (BPA) with a sphere radius r to the point cloud, and wherein defining the virtual sphere comprises defining the virtual sphere such that the radius R of the virtual sphere is at least 2r.

9. The method according to claim 8, wherein R = 2r.

10. The method of claim 7, wherein the input indicator probe is located at the said position.

11. The method of claim 7, wherein the input includes selecting P from a display of the point cloud.

12. The method of claim 7, wherein the anatomical volume comprises at least a portion of the chambers of the heart.

13. A computer software product comprising a tangible, non-transitory computer-readable medium storing program instructions therein, the instructions, when read by a processor, causing the processor to: A virtual surface is generated around the perimeter of a point cloud, the point cloud representing a mapping volume within an anatomical volume, and the virtual surface representing an anatomical surface surrounding the mapping volume, wherein the point cloud includes a plurality of points corresponding to corresponding mapping locations within the anatomical volume; In response to an input identification point P from the user, where P is known to correspond to a position on the anatomical surface of the anatomical volume; Calculate point P' on the virtual surface, where point P' is the point on the virtual surface that is closest to P. Define a virtual sphere centered on the virtual line connecting P to P', such that P lies on the spherical surface of the virtual sphere. An operation is performed to place P at the periphery of the point cloud, wherein the operation is selected from a group of operations consisting of: expanding the point cloud over the entire virtual sphere, and excluding the virtual sphere from the point cloud, and... The virtual surface is generated again after the operation is performed, such that P is located on the regenerated virtual surface because the operation has already been performed.

14. The computer software product of claim 13, wherein the instructions cause the processor to regenerate the virtual surface by applying a sphere pivoting algorithm (BPA) with a sphere radius r to the point cloud, and wherein the instructions cause the processor to define the virtual sphere such that the radius R of the virtual sphere is at least 2r.

15. The computer software product of claim 13, wherein the input indicator probe is located at the said position.

16. The computer software product of claim 13, wherein the input includes selecting P from the display of the point cloud.

17. The computer software product of claim 13, wherein the anatomical volume comprises at least a portion of the chambers of the heart.

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