A novel metal artifact reducing method for cone-beam CT based on three approximately orthogonal projections

Metal artifacts remain a challenge for computed tomography (CT) reconstruction, especially for medical CT, in which the radiation dose for patients is strictly limited. This study presents a novel method of reducing the metal artifacts for cone-beam CT by renovating the metal areas in the 2D cone-beam projection. We first calculate the 3D coordinates of all the metallic implants, which will then be projected into the projection images in each angle as the metal seed points (MSPs), increasing the precision of the segmentation of the metal areas. Different from the existing methods of calculating the metal positions with two projection images, we proposed a new method to calculate the 3D coordinates of all the metallic implants using three different projection images that are nearly orthogonal. One is the parallel-beam projection image along the Z-axial direction (i.e. along the rotation axis) calculated by the projection synthesizing method, while the other two are the cone-beam projections at two different views chosen from the scanned data. The three nearly orthogonal views will greatly help to accurately locate the metallic implants when there is more than one implant in the object. Then the MSPs can be located in each projection by geometry calculations. The region growing segmentation method and the bilinear interpolation method are used to modify the projection areas of the metallic implants. Experimental studies demonstrate that this method is accurate in locating MSPs and efficient in reducing metal artifacts.