Patent Application
20140125653
The present invention relates generally to graphic displays, and specifically to combining two or more three-dimensional (3D) surfaces to produce a single 3D display.
While the surface of a three-dimensional (3D) element may be mapped, by a variety of procedures, in a single mapping operation, there are many situations where two or more mapping operations are performed on different portions of the element. In these latter cases the surfaces mapped in the different operations need to be combined in order to produce a more complete 3D map of the element. A method for efficiently combining the surfaces would be advantageous.
An embodiment of the present invention provides a method for mapping, including:
measuring coordinates of a first set of points on a first surface of a first portion of a three-dimensional (3D) element;
generating a first volume enclosed by the first set of points;
measuring coordinates of a second set of points on a second surface of a second portion of the 3D element;
generating a second volume enclosed by the second set of points;
connecting the first and second volumes to form a combined volume; and
generating coordinates of a third set of points on a third surface of the combined volume to form a 3D surface map of the element.
Typically, connecting the first and second volumes includes forming a union of the first volume with the second volume. Generating the coordinates of the third set of points may include covering the union with the third surface.
In a disclosed embodiment an intersection of the first volume and the second volume includes a non-null set.
In an alternative embodiment generating the first volume includes forming a first surface from the first set of points and filling a first space enclosed by the first surface, and generating the second volume includes forming a second surface from the second set of points and filling a second space enclosed by the second surface. Typically, filling the first space includes closing at least one first opening in the first surface to form a closed first surface, and filling the second space includes closing at least one second opening in the second surface to form a closed second surface.
In the alternative embodiment generating the coordinates of the third set of points may include covering a union of the first and second volumes to form the third surface, and opening the at least one first opening and the at least one second opening in the third surface to form the 3D surface map.
Typically, the 3D element includes at least a part of an organ of a human person. The organ may include a heart.
There is further provided, according to an embodiment of the present invention, apparatus for mapping, including:
a probe which is configured to measure coordinates of a first set of points on a first surface of a first portion of a three-dimensional (3D) element, and to measure coordinates of a second set of points on a second surface of a second portion of the 3D element; and
a processor which is configured to:
generate a first volume enclosed by the first set of points,
generate a second volume enclosed by the second set of points,
connect the first and second volumes to form a combined volume; and
generate coordinates of a third set of points on a third surface of the combined volume to form a 3D surface map of the element.
The present disclosure will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings, in which:
An embodiment of the present invention provides a method for efficiently combining three-dimensional (3D) surfaces. The surfaces combined are typically partial 3D surfaces of an object, such as of at least a part of an organ of the human body. In the following description the surfaces being combined are assumed, by way of example, to comprise two partially mapped surfaces of the right atrium of the heart.
To generate a first partially mapped surface, coordinates of a first set of points on the right atrium are measured. A first volume is formed by filling the space enclosed by the first set of points. Similarly, to generate a second partially mapped surface, coordinates of a second set of points on the right atrium are measured and a second volume is formed by filling the space enclosed by the second set of points.
The two volumes are formed as respective sets of volume elements or voxels. The two volumes are connected, typically by forming a union of the two sets, to form a combined volume. Usually, the two volumes have a significant overlap, i.e., the intersection of the two volumes is not a null set, so that the number of voxels in the union is less than a sum of the numbers of voxels in the two separate volumes.
Once the combined volume has been formed, it is used to generate coordinates of a third set of points of a third surface covering the combined volume. The third surface effectively combines the first and second surfaces, and forms a 3D surface map of the object.
Combining surfaces by the method described herein is an efficient process for combining partial surfaces of an object. The method may be performed more simply than prior art methods of combining surfaces, such as those which stitch surfaces together, with no loss of accuracy.
Reference is now made to
For simplicity and clarity, the following description, except where otherwise stated, assumes an investigative procedure wherein system 20 performs measurements on a human body organ 34, herein assumed to comprise a heart, using a probe 24.
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.
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 which displays a three-dimensional (3D) map 50 of the heart. The screen typically displays other items 52 of auxiliary information related to the heart and superimposed on the map, while the heart is being investigated, such as the positions of catheters used by professional 28.
Professional 28 is able to use pointing device 39 to vary parameters of the frame of reference, so as to display the resultant map in a selected orientation and/or at a selected magnification.
Screen 48 typically also presents a graphic user interface to the user.
Processor 40 uses software, including a probe tracker module 30 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.
Probe tracker module 30 tracks both the location and orientation of distal end 32 of probe 24, within the heart of subject 26. The location and orientation coordinates are assumed to be stored in a mapping module 56. 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
The Carto® system produced by Biosense Webster, of Diamond Bar, Calif., uses such a tracking method. Alternatively or additionally, tracker module 30 may track distal end 32 by measuring impedances between an electrode on the distal end and electrodes on the skin of subject 26. The Carto3® system produced by Biosense Webster uses both magnetic field transmitters and impedance measurements for tracking. By way of example tracking module 30 is assumed to be used to map in three dimensions portions of the surface of an element 36 of heart 34. For clarity, in the following description element 36 is considered to be the right atrium, which is mapped as a first right atrium portion 36A and a second right atrium portion 36B.
After generating surface 108, the processor checks if the surface is closed, i.e., if the surface is topologically equivalent to a closed surface such as a sphere. Typically, surface 108 is not closed, having one or more openings. The openings in surface 108 may be those which naturally occur in the organ, such as the superior vena cava, or the inferior vena cava of the right atrium. Such openings are herein referred to as natural openings. Additionally, there may be openings in surface 108, herein referred to as artificial openings, because the organ has not been fully mapped.
In the event that surface 108 is not closed, the processor closes the surface by adding further surface elements until the surface is closed. The surface produced by closing surface 108 is herein referred to as closed surface 116. In one embodiment an opening is closed by adding an oriented bounding box that surrounds the opening, the box having a minimal volume. The box is then treated as part of the surface.
Surface 116 is assumed to have a defining equation:
S
1(x,y,z)=0 (1)
where S1 is a function.
In the description herein surface 116 is also referred to as surface S1.
Volume V1 may be defined according to expression (2):
V
1
={V(x,y,z)|S1(x,y,z)<0} (2)
where V(x, y, z) represents a voxel 122 centered on (x, y, z), and V1 is the volume formed by voxels 122.
Volume 120 is also referred to herein as volume V1.
S
2(x,y,z)=0 (3)
where S2 is a function.
Surface 154 is also referred to herein as surface S2.
From equation (3), an expression for volume 156, the volume filling the space enclosed by surface S2, is given by:
V
2
={V(x,y,z)|S2(x,y,z)<0} (4)
where V(x, y, z) represents a voxel 162 centered on (x, y, z), and V2 is the volume formed by voxels 162.
Volume 156 is also referred to herein as volume V2.
In a first step 202, processor 40 acquires coordinates of a first set of points, herein assumed to be set 100 of portion 36A. In a parallel first step 204, the processor acquires coordinates of a second set of points, herein assumed to be set 148 of portion 36B. The acquisition is typically as described above with reference to
In a surface generation step 206, the processor transforms the set of points acquired in step 202 into a closed surface, substantially as described with reference to
In surface generation steps 206 and 208, the processor records any openings in surface 108 and in surface 152 that need to be closed in order to generate closed surface 116 and closed surface 154. The surfaces are closed, typically by adding bounding boxes to any openings present, as described above.
In a filling step 210, processor 40 fills the space enclosed by the surface generated in step 206, to form a first volume in the form of a first set of voxels. The first volume includes any bounding boxes that have been used to close the surface. As described above with reference to
In a connecting step 214, illustrated by
V=V
1
UV
2 (5)
where V is the union of volume V1 with volume V2.
Volume V, corresponding to V1UV2, is also referred to herein as composite volume 170. The union of the two volumes V1, V2, means that volume V comprises voxels 172 that only occur in volume V1, voxels 174 that only occur in volume V2, and voxels 176 that are common to volume V1 and volume V2. It will be understood that the common voxels (illustrated in
Typically, the intersection V1∩V2 is not a null set of voxels, i.e., there is at least one voxel present in the intersection. Since in practice the two volumes being combined are based on two surfaces which typically have a relatively large overlap, the intersection V1∩V2 also comprises relatively large numbers of voxels. However, embodiments of the present invention include cases where the intersection is a null set, i.e., where there is no physical intersection.
Processor 40 uses equations (2) and (3), which define the sets of voxels in each volumes V1 and V2 according to their (x, y, z) coordinates, in order to find the voxels in the union.
The upper part of
In a surface generating step 216, once the union of the two volumes has been formed, processor 40 generates sets of points on a closed surface 180 (
While the description above relates generally to combining two surfaces, those of ordinary skill in the art will be able to adapt the description, without undue experimentation, for the combination of three or more surfaces. Embodiments of the present invention thus include the combination of two or more surfaces to generate a complete surface for the multiple surfaces.
It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.
