# US 5,708,691 A · X-ray computed tomographic imaging device and x-ray computed tomographic method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,708,691 A - Document ID: US5708691A - Status: Granted - Kind: A - Application number: 08/675,833 - Filed: 1996-07-05 - Granted: 1998-01-13 - Earliest claimed: 1996-07-05 - Assignees: Kabushiki Kaisha Toshiba - Inventors: Ilan Zmora - Web page: https://patentgrep.com/patent/US5708691A ## CPC - A61B 6/032: {Transmission computed tomography [CT]} - A61B 6/027: {characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral} - Y10S 378/901: Computer tomography program or processor - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) - Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS ## Abstract A computed tomography method and system where a voxel of a subject irradiated with x-rays is divided into an plurality of sub-voxels, and backprojection data is obtained for the sub-voxels. Projection data for the sub-voxels can be weighted before backprojecting, or the projection data can be backprojected and then weighted. With the method according to the invention, instead of backprojecting data on a straight line passing through the center of a voxel, the beam passing through the entire voxel is backprojected. Also, the method and system weights the sub-voxels using a space-variant function. The weighting can be applied to discrete sub-voxels or integration can be used with infinitely thin sub-voxels. The present invention is a more accurate method and can take into account of spreading of the x-ray beam. ## Claims ### Claim 1 A computed tomography system, comprising: an x-ray source; a detector array having a plurality of detector elements; a projection data circuit connected to said detector array; a sub-voxel circuit connected to said projection data circuit; and a backprojection circuit connected to said projection data circuit. ### Claim 2 (depends on 1) A system as recited in claim 1, comprising: a weighting circuit connected to at least one of said sub-voxel circuit and said backprojection circuit. ### Claim 3 (depends on 1) A system as recited in claim 1, comprising: an interpolation circuit connected to said projection data circuit. ### Claim 4 (depends on 1) A system as recited in claim 1, wherein said sub-voxel circuit comprises: means for determining a plurality of points within a voxel of a subject being irradiated by an x-ray beam; means for determining respective x-ray paths from said x-ray source through said plurality of points to said detector array. ### Claim 5 (depends on 4) A system as recited in claim 4, wherein said backprojection circuit performs backprojection for each of said plurality of points and produces a respective plurality of backprojection data, said system comprising: means for weighting said plurality of backprojection data; and means for determining backprojection data for said voxel based upon said weighted plurality of backprojection data. ### Claim 6 (depends on 2) A system as recited in claim 2, wherein said weighting circuit comprises: means for weighting projection data based upon a position of an intersection of an x-ray beam, through a sub-voxel, on one of said plurality of detector elements. ### Claim 7 (depends on 6) A system as recited in claim 6, wherein said means for weighting weights based also upon a position of said sub-voxel. ### Claim 8 (depends on 2) A system as recited in claim 2, wherein said weighting circuit comprises means for weighting and adding projection data prior to said backprojection circuit performing backprojection. ### Claim 9 (depends on 2) A system as recited in claim 2, wherein said weighting circuit comprises: means for weighting projection data corresponding to a voxel having a contribution from only two of said detector elements as: ##EQU13## where W.sub.A and W.sub.B are weights associated with detector elements A and B, t.sub.A and t.sub.B are predetermined positions in said detector elements A and B, respectively, N is a number of sub-voxels within said voxel, D.sub.t is a spacing between said predetermined positions, and t.sub.i is a position of the an x-ray beam through a sub-voxel on detectors A and B. ### Claim 10 (depends on 2) A system as recited in claim 2, wherein said weighting circuit comprises: means for weighting projection data corresponding to a voxel having a contribution from only three adjacent ones of said detector elements as: ##EQU14## for beams I incident between predetermined positions of detector elements A and B, where t.sub.B is said predetermined positions in said detector element B, N is a number of sub-voxels within said voxel, D.sub.t is a spacing between said predetermined positions, and t.sub.i is a position of the an x-ray beam through a sub-voxel on detector elements A and B; for beams I incident between a predetermined position in detector element C and said predetermined position in detector element B; and as ##EQU15## for beams I incident on between said predetermined positions in detector elements A,B and B,C, respectively. ### Claim 11 (depends on 1) A system as recited in claim 1, comprising: means for determining an x-ray path for a plurality of paths at a plurality of points in a voxel; and means for interpolating projection data for each of said plurality of points; wherein said backprojection circuit back-projects interpolation data and produces back-projection data for each of said plurality of points. ### Claim 12 A computed tomography system, comprising: an x-ray source; a detector array having a plurality of detection elements and disposed to receive x-rays emitted from said x-ray source; and a projection data circuit connected to said detector array; a space-variant weighting circuit connect to said projection data circuit; and a sub-voxel backprojection circuit connected to said projection data circuit. ### Claim 13 (depends on 12) A system as recited in claim 12, wherein said sub-voxel backprojection circuit comprises: means for determining a plurality of points within a voxel of a subject being irradiated by an x-ray beam; means for determining respective x-ray paths from said x-ray source through said plurality of points to said detector array. ### Claim 14 A method of operating a computed tomography system, comprising: obtaining projection data; and backprojecting said projection data using a plurality sub-voxels. ### Claim 15 (depends on 14) A method as described in claim 14, wherein said system includes an x-ray source, said method comprising: dividing a voxel of a subject irradiated by said x-ray source into a plurality of sub-voxels; and obtaining sub-voxel projection data for the sub-voxels; and backprojecting using said sub-voxel projection data. ### Claim 16 A method of operating a computed tomographic system, comprising: dividing a voxel of a subject in to a plurality of sub-voxels; and obtaining backprojection data for said plurality of sub-voxels. ### Claim 17 (depends on 16) A method as recited in claim 16, wherein said method includes an x-ray source and an x-ray detector, and dividing said voxel comprises: determining a plurality of points within said voxel about a center point of said voxel corresponding to said plurality of sub-voxels; determining a plurality of x-ray paths from said x-ray source through said plurality points to said detector, respectively; and backprojecting each of said sub-voxels. ### Claim 18 (depends on 17) A method as recited in claim 17, wherein backprojecting said sub-voxels comprises: obtaining projection data; interpolating sub-voxel projection data for said sub-voxels from said projection data; and backprojecting said sub-voxel projection data. ### Claim 19 (depends on 18) A method as recited in claim 18, wherein interpolating said sub-voxel projection data comprises: interpolating said sub-voxel data from 2N rows of said projection data, where N is an integer greater than 1. ### Claim 20 (depends on 16) A method as recited in claim 16, wherein obtaining backprojection data comprises: obtaining sub-voxel backprojection data for each of said sub-voxels; and weighting said sub-voxel backprojection data.