Method and apparatus for large field of view imaging and detection and compensation of motion artifacts

Abstract

A method and apparatus are provided to improve large field of view CT image acquisition by using at least two scanning procedures: (i) one with the radiation source and detector centered and (ii) one in an offset configuration. The imaging data obtained from both of the scanning procedures is used in the reconstruction of the image. In addition, a method and apparatus are provided for detecting motion in a reconstructed image by generating a motion map that is indicative of the regions of the reconstructed image that are affected by motion artifacts. Optionally, the motion map may be used for motion estimation and/or motion compensation to prevent or diminish motion artifacts in the resulting reconstructed image. An optional method for generating a refined motion map is also provided.

1 . An apparatus for acquiring tomographic projection data at a plurality of angular positions relative to an object disposed in an examination region, the apparatus comprising:
 a radiation source;   a radiation sensitive detector which detects radiation emitted by the source that has traversed the examination region; and   a reconstructor;   wherein the apparatus is adapted to perform at least two scanning procedures of an object;   wherein at least a first scanning procedure is a centered geometry scanning procedure, wherein a center of the radiation sensitive detector is aligned with a center of rotation of the source and detector;   wherein at least a second scanning procedure is an offset geometry scanning procedure; wherein a center of the radiation sensitive detector is displaced by a distance of approximately half a width of the detector or more from the center of rotation of the source and detector;   wherein projection data is acquired during the at least two scanning procedures including centered geometry projection data during the centered geometry scanning procedure and offset geometry projection data during the offset geometry scanning procedure; and   wherein the reconstructor reconstructs the projection data acquired during the at least two scanning procedures together to generate volumetric data indicative of the object.   
     
     
         2 . (canceled) 
     
     
         3 . The apparatus of  claim 1 , wherein the reconstruction performed by the reconstructor combines the projection data acquired during the at least two scanning procedures to form a data set corresponding to an imaging scan performed by a single virtual detector in one position with respect to the source. 
     
     
         4 . The apparatus of  claim 1 , wherein the radiation sensitive detector is a flat detector, and wherein the center of the radiation sensitive detector is transversely displaced from the center of rotation in the transaxial plane during the at least one offset geometry scanning procedure. 
     
     
         5 . (canceled) 
     
     
         6 . The apparatus of  claim 1 , wherein a faded weighting technique and an averaging technique are applied to an overlap region of the projection data acquired during the at least two scanning procedures during reconstruction. 
     
     
         7 . The apparatus of  claim 1 , wherein a lower dose of radiation is administered during the at least one offset geometry scanning procedure than during the at least one centered geometry scanning procedure. 
     
     
         8 . The apparatus of  claim 7 , wherein the dose of radiation administered during the at least one offset geometry scanning procedure is less than half of the radiation administered during the at least one centered geometry scanning procedure. 
     
     
         9 . The apparatus of  claim 1 , wherein the apparatus is a cone-beam computed tomography imaging device. 
     
     
         10 . The apparatus of  claim 1 , further comprising a mechanical drive for moving the radiation sensitive detector with respect to the radiation source. 
     
     
         11 . The apparatus of  claim 1 , further comprising an image processor, a user interface and a user input, and wherein the image processor processes the volumetric data for display on the user interface. 
     
     
         12 . A computed tomography imaging method, comprising the steps of:
 performing at least two scanning procedures of an object, including:   acquiring projection data during at least one centered geometry scanning procedure in which a center of the radiation sensitive detector is aligned with a center of rotation of the source and detector; and   acquiring projection data during at least one offset geometry scanning procedure in which a center of the radiation sensitive detector is displaced from the center of rotation of the source and detector by a distance of approximately half a width of the detector or more;   acquiring projection data during the at least two scanning procedures including centered geometry projection data during the centered geometry scanning procedure and offset geometry projection data during the offset geometry scanning procedure; and   reconstructing the projection data acquired during the at least two scanning procedures together to generate volumetric data indicative of the object.   
     
     
         13 . (canceled) 
     
     
         14 . The method of  claim 12 , wherein the reconstruction combines the projection data acquired during the at least two scanning procedures to form a data set corresponding to an imaging scan performed by a single virtual detector in one position with respect to the source. 
     
     
         15 . The method of  claim 12 , wherein the radiation sensitive detector is a flat detector, and further comprising transversely displacing the center of the radiation sensitive detector from the center of rotation in the transaxial plane during the at least one offset geometry scanning procedure. 
     
     
         16 . (canceled) 
     
     
         17 . The method of  claim 12 , wherein a faded weighting technique and an averaging technique are applied to an overlap region of the projection data acquired during the at least two scanning procedures during reconstruction. 
     
     
         18 . The method of  claim 12 , further comprising administering a lower dose of radiation during the at least one offset geometry scanning procedure than during the at least one centered geometry scanning procedure. 
     
     
         19 . The method of  claim 18 , wherein the dose of radiation administered during the at least one offset geometry scanning procedure is less than half of the radiation administered during the at least one centered geometry scanning procedure. 
     
     
         20 . An apparatus for generating a motion map, the apparatus comprising:
 a radiation source;   a radiation sensitive detector which detects radiation emitted by the source that has traversed an examination region; and   a reconstructor an image processor;   wherein the radiation source and the radiation sensitive detector are used to acquire projection data at a plurality of angular positions relative to an object disposed in the examination region;   wherein the reconstructor is used to generate a reference image from the projection data;   wherein reference projection data is obtained from a forward projection of the reference image;   wherein differences between the acquired projection data and the reference projection data are computed to determine line integral differences; and   wherein the image processor uses the line integral differences to generate a motion map indicative of the regions of a corresponding image reconstructed from the projection data that are affected by motion.   
     
     
         21 . The apparatus of  claim 20 , wherein the image processor applies a windowing process to refine the motion map. 
     
     
         22 . The apparatus of  claim 20 , wherein the image processor applies a normalization process to refine the motion map. 
     
     
         23 . The apparatus of  claim 20 , wherein the image processor applies a volumetric median filter to refine the motion map. 
     
     
         24 . The apparatus of  claim 20 , wherein the image processor applies a Gaussian blur to refine the motion map. 
     
     
         25 . The apparatus of  claim 20 , wherein the apparatus is a cone-beam computed tomography imaging device. 
     
     
         26 . The apparatus of  claim 20 , wherein the image processor processes the volumetric data for display on a user interface. 
     
     
         27 . The apparatus of  claim 20 , wherein the motion map indicates the amount of motion correction to be applied to an image. 
     
     
         28 . The apparatus of  claim 27 , wherein the image processor uses the motion map in a motion-compensated image reconstruction. 
     
     
         29 . The apparatus of  claim 28 , wherein the image processor performs a reconstruction as a weighted average between a motion corrected reconstruction and a reconstruction not corrected for motion, wherein the weights are provided by the motion map. 
     
     
         30 . The apparatus of  claim 27 , wherein the motion displacement in a motion-corrected reconstruction is adapted according to the motion map. 
     
     
         31 . A method for generating a motion map, the method comprising the steps of:
 acquiring projection data at a plurality of angular positions relative to an object disposed in an examination region;   reconstructing from the projection data to generate a reference image;   obtaining reference projection data from a forward projection of the reference image;   computing differences between the acquired projection data and the reference projection data to determine line integral differences; and   using the line integral differences to generate a motion map indicative of the regions of a corresponding image reconstructed from the projection data that are affected by motion.   
     
     
         32 . The method of  claim 31 , further comprising the step of applying a windowing process to refine the motion map. 
     
     
         33 . The method of  claim 31 , further comprising the steps of refining the motion map by normalizing the motion map, applying a volumetric median filter to the motion map, and applying a Gaussian blur to the motion map. 
     
     
         34 . The method of  claim 31 , further comprising the step of using the motion map in conjunction with the corresponding image reconstructed from the projection data to detect regions of the reconstructed image that are affected by motion. 
     
     
         35 . The method of  claim 31 , further comprising the step of using the motion map in conjunction with a motion correction technique to compensate for the effects of motion in the corresponding image reconstructed from the projection data. 
     
     
         36 . The method of  claim 35 , further comprising compensating for motion only in regions of the corresponding image that are indicated to have been affected by motion by the motion map. 
     
     
         37 . The method of  claim 35 , further comprising compensating for motion by applying a weighted value of motion correction to regions of the corresponding image reconstructed from the tomographic projection data, the weighted value being calculated for each region based upon a quantitative amount of motion indicated for each image region by the motion map.