Computed tomography with increased field of view

Abstract

A volumetric computed tomography system with a large field of view has, in a forward geometry implementation, multiple x-ray point sources emitting corresponding fan beams at a single detector array. The central ray of at least one of the fan beams is radially offset from the axis of rotation of the system by an offset distance D. Consequently, the diameter of the in-plane field of view provided by the fan beams may be larger than in a conventional CT scanner. Any number of point sources may be used. Analogous systems may be implemented with an inverse geometry so that a single source array emits multiple fan beams that converge upon corresponding detectors.

1 . A method of computed tomography comprising: 
 providing multiple x-ray point sources and a detector array;    emitting from the x-ray point sources corresponding fan beams directed at the detector array;    acquiring x-ray data at the detector array; and    rotating the x-ray point sources and the detector array around a rotational axis;    wherein the fan beams have corresponding central rays connecting the corresponding point sources to a midpoint of the detector array, wherein the central ray of at least one of the fan beams is offset from the rotational axis by a substantial offset distance D.    
     
     
         2 . The method of  claim 1  wherein the fan beams have corresponding sets of rays, each ray having a radial offset distance from the rotational axis, wherein the radial offset distances of the rays in the sets are selected such that there is an overlap of radial offset distances between the sets.  
     
     
         3 . The method of  claim 1  wherein at least one of the fan beams has a central ray that is radially offset from the rotational axis by a distance D approximately equal to or greater than a width of the corresponding fan beam near the rotational axis.  
     
     
         4 . The method of  claim 1  wherein a diameter of a field of view provided by the fan beams is larger than an extent of the detector array.  
     
     
         5 . The method of  claim 1  wherein none of the central rays passes through the rotational axis.  
     
     
         6 . The method of  claim 1  wherein the central rays all intersect at a midpoint of the detector array.  
     
     
         7 . The method of  claim 1  wherein rays in one of the fan beams have offset distances from the rotational axis that differ from offset distances of rays in an adjacent one of the fan beams by approximately 2R/N, where R is a radius of a field of view provided by the fan beams and N is the number of point sources.  
     
     
         8 . A computed tomography system comprising: 
 a detector array;    multiple x-ray point sources for generating corresponding fan beams directed at the detector array;    wherein the x-ray point sources and the detector array are capable of being rotated together around a rotational axis; and    wherein the fan beams have corresponding central rays connecting the corresponding point sources to a midpoint of the detector array, wherein the central ray of at least one of the fan beams is offset from the rotational axis by a substantial offset distance D.    
     
     
         9 . The system of  claim 8  wherein the fan beams have corresponding sets of rays, each ray having a radial offset distance from the rotational axis, wherein the radial offset distances of the rays in the sets are selected such that there is an overlap of radial offset distances between the sets.  
     
     
         10 . The system of  claim 8  wherein at least one of the fan beams has a central ray that is radially offset from the rotational axis by a distance D approximately equal to or greater than a width of the corresponding fan beam near the rotational axis.  
     
     
         11 . The system of  claim 8  wherein a diameter of a field of view provided by the fan beams is larger than an extent of the detector array.  
     
     
         12 . The system of  claim 8  wherein none of the central rays passes through the rotational axis.  
     
     
         13 . The system of  claim 8  wherein the central rays all intersect at a midpoint of the detector array.  
     
     
         14 . The system of  claim 8  wherein rays in one of the fan beams have offset distances from the rotational axis that differ from offset distances of rays in an adjacent one of the fan beams by approximately 2R/N, where R is a radius of a field of view provided by the fan beams and N is the number of point sources.