Patent ID: 7366278

Claim:
A method of generating a DRR (digitally reconstructed radiograph) from 3D scan data of an object so as to increase the visibility within the DRR of one or more structures in the object, the DRRs representing a radiographic projection image of the object that would be obtained with a 2D imaging beam of a known intensity, origination position, and angle if the object were positioned as shown in the 3D scan data, the method comprising: providing 3D scan data of the object, the 3D scan data resulting from a 3D scan conducted at a 3D scan energy level, wherein the 3D scan data comprise a plurality of CT numbers representing the image intensity of corresponding 3D CT voxels, each CT voxel representing a corresponding volume element of the object, each CT number representing the attenuated intensity of an x-ray CT beam that has been generated at a CT scan energy level and that has traversed the corresponding volume element of the object; modifying the 3D scan data to compensate for a difference between the attenuation of the one or more structures at the scan energy level and the attenuation of the one or more structures at the known intensity of the 2D imaging beam; casting a plurality of hypothetical rays through the modified 3D scan data from the known intensity, the known origination position, and angle of the 2D imaging beam; and integrating the 3D scan data along each hypothetical ray, and projecting the integrated value of the 3D scan data onto an imaging plane, wherein the act of modifying the CT numbers comprises performing a mathematical operation derived from a non-linear x-ray attenuation model and given by: C ( x,y,z )=a C 0 ( x,y,z ) e bC0(x,y,z) where C(x,y,z) represents the modified CT number of a 3D CT voxel having a location (x,y,z); a and b represent weighting coefficients; and C 0 (x,y,z) represents the un-modified CT number, based on a linear attenuation model, of a 3D CT voxel having a location (x,y,z).