The present invention relates to a three dimensional back projection method and an X-ray computed tomography (CT) apparatus. More specifically, the present invention relates to a three dimensional back projection method and an X-ray CT apparatus, in the image reconstruction (referred to as cone beam reconstruction) based on the projection data that is gathered by axial scanning or helical scanning by means of a multidetector system, which allow reconstructions to be performed using the projection data precisely corresponding to the X-ray beam passing through the reconstruction area.
To date, the mainstream X-ray CT apparatus typically uses a filtered back projection technique, which reconstructs an image through processes including gathering data, preprocessing, filtering, back projecting and postprocessing.
FIG. 1 schematically shows projection data gathered at a view angle a “view=0°” by scanning with a multidetector 24 and the position of reconstruction area P.
In the back projection methods of the related art, the projection data gathered by the fifth array of detectors that corresponds to the z-coordinate of the reconstruction area P has been used for the projection data at the view angle “view=0°” for use in the image reconstruction.
FIG. 2 is a schematic enlarged view in z-axis of an X-ray beam passing through the reconstruction area P as shown in FIG. 1(b).
Part A of the X-ray beam passing through the reconstruction area P is incident into the fifth array of detectors d5. There may not be any problem in using the projection data collected by the fifth array of detectors d5 as the projection data at a view angle “view=0°” for the reconstruction.
However, part B of the X-ray beam passing through the reconstruction area P is incident into the sixth array of detectors d6, rather than the fifth array of detectors d5. There may arise a problem of discrepancy if the projection data collected by the fifth array of detectors d5 is used is used for the projection data at the view angle “view=0”, resulting in a so-called corn angle artifact.