Floating volume-of-interest in multilayer volume ray casting

1. A method, comprising:

receiving vertices of a mesh, wherein the mesh represents a volume of interest (VOI) from an original volume;

performing a transformation operation on the mesh, wherein the transformation operation transforms vertices of the mesh, wherein the transformed vertices of the mesh can be anywhere in three-dimensional (3D) space so that a bounding box used in ray-layer buffer generation considers the transformed vertices;

obtaining sampling locations of the original volume using the transformed vertices;

performing an inverse transformation on the transformed vertices of the mesh and the sampling locations;

rendering a cut-out of the VOI twice in each depth-peeling pass for creating a ray layer buffer, the first time as a static VOI and the second time as a floating VOI; and

once the ray layer buffer is created, performing a ray casting on the original volume to produce an image, wherein the ray casting uses the transformed vertices and a result of the inverse transformation to define transformed starting positions of ray segments corresponding to regions inside the VOI.

2. The method of claim 1 , wherein the transformation operation includes a translation, rotation, scaling, shearing, or mirroring.

3. The method of claim 1 , further comprising:

duplicating the vertices of the mesh to represent first and second VOIs of identical shapes;

rendering the first VOI with a color lookup table full of zeros so that the first VOI represents an empty region;

rendering the second VOI with the same color lookup table as a region outside the second VOI;

transforming the mesh of the second VOI so that it moves away from an original position and orientation; and

calculating sampling locations, which are used for rendering the second VOI, from the transformed mesh of the second VOI followed by an inverse transformation, so that these sampling locations are the same as those computed from an untransformed version of the mesh of the second VOI.

4. The method of claim 1 , further comprising:

duplicating the vertices of the mesh to represent first and second VOIs of identical shapes;

rendering the first VOI with a color lookup table different from voxels outside the first VOI;

rendering the second VOI with the same color lookup table as the first VOI:

transforming the mesh of the second VOI so that it moves away from an original position and orientation; and

calculating sampling locations, which are used for rendering the second VOI, from the transformed mesh of the second VOI followed by an inverse transformation, so that these sampling locations are the same as those computed from an untransformed version of the mesh of the second VOI.

5. A system, comprising:

a memory device for storing a program;

a processor in communication with the memory device, the processor operative with the program to:

receive vertices of a mesh, wherein the mesh represents a volume of interest (VOI) from an original volume;

perform a transformation operation on the mesh, wherein the transformation operation transforms vertices of the mesh, wherein the transformed vertices of the mesh can be anywhere in three-dimensional (3D) space so that a bounding box used in ray-layer buffer generation considers the transformed vertices;

obtain sampling locations of the original volume using the transformed vertices;

perform an inverse transformation on the transformed vertices of the mesh and the sampling locations;

render a cut-out of the VOI twice in each depth-peeling pass for creating a ray layer buffer, the first time as a static VOI and the second time as a floating VOI; and

once the ray layer buffer is created, perform a ray casting on the original volume to produce an image, wherein the ray casting uses the transformed vertices and a result of the inverse transformation to define transformed starting positions of ray segments corresponding to regions inside the VOI.

6. The system of claim 5 , wherein the transformation operation includes a translation, rotation, scaling, shearing, or mirroring.

7. The system of claim 5 , wherein the processor is further operative with the program to:

duplicate the vertices of the mesh to represent first and second VOIs of identical shapes;

render the first VOI with a color lookup table full of zeros so that the first VOI represents an empty region;

render the second VOI with the same color lookup table as a region outside the second VOI;

transform the mesh of the second VOI so that it moves away from an original position and orientation; and

calculate sampling locations, which are used for rendering the second VOI, from the transformed mesh of the second VOI followed by an inverse transformation, so that these sampling locations are the same as those computed from an untransformed version of the mesh of the second VOI.

8. The system of claim 5 , wherein the processor is further operative with the program to:

duplicate the vertices of the mesh to represent first and second VOIs of identical shapes;

render the first VOI with a color lookup table different from voxels outside the first VOI;

render the second VOI with the same color lookup table as the first VOI;

transform the mesh of the second VOI so that it moves away from an original position and orientation; and

calculate sampling locations, which are used for rendering the second VOI, from the transformed mesh of the second VOI followed by an inverse transformation, so that these sampling locations are the same as those computed from an untransformed version of the mesh of the second VOI.

9. A computer program product, comprising:

a non-transitory computer readable storage medium having computer readable program code embodied therewith, the computer readable program code comprising:

computer readable program code configured to perform the steps of:

receiving vertices of a mesh, wherein the mesh represents a volume of interest (VOI) from an original volume;

performing a transformation operation on the mesh, wherein the transformation operation transforms vertices of the mesh, wherein the transformed vertices of the mesh can be anywhere in three-dimensional (3D) space so that a bounding box used in ray-layer buffer generation considers the transformed vertices;

obtaining sampling locations of the original volume using the transformed vertices;

performing an inverse transformation on the transformed vertices of the mesh and the sampling locations;

rendering a cut-out of the VOI twice in each depth-peeling pass for creating a ray layer buffer, the first time as a static VOI and the second time as a floating VOI; and

once the ray layer buffer is created, performing a ray casting on the original volume to produce an image, wherein the ray casting uses the transformed vertices and a result of the inverse transformation to define transformed starting positions of ray segments corresponding to regions inside the VOI.

10. The computer program product of claim 9 , wherein the transformation operation includes a translation, rotation, scaling, shearing, or mirroring.

11. The computer program product of claim 9 , wherein the computer readable program code is further configured to perform the steps of:

duplicating the vertices of the mesh to represent first and second VOIs of identical shapes;

rendering the first VOI with a color lookup table full of zeros so that the first VOI represents an empty region;

rendering the second VOI with the same color lookup table as a region outside the second VOI;

transforming the mesh of the second VOI so that it moves away from an original position and orientation; and

calculating sampling locations, which are used for rendering the second VOI, from the transformed mesh of the second VOI followed by an inverse transformation, so that these sampling locations are the same as those computed from an untransformed version of the mesh of the second VOI.

12. The computer program product of claim 9 , wherein the computer readable program code is further configured to perform the steps of:

duplicating the vertices of the mesh to represent first and second VOIs of identical shapes;

rendering the first VOI with a color lookup table different from voxels outside the first VOI;

rendering the second VOI with the same color lookup table as the first VOI;

transforming the mesh of the second VOI so that it moves away from an original position and orientation; and

calculating sampling locations, which are used for rendering the second VOI, from the transformed mesh of the second VOI followed by an inverse transformation, so that these sampling locations are the same as those computed from an untransformed version of the mesh of the second VOI.