Metal Artifact Reduction by Using Limited EPID Projections and Deformable Registration in Prostate Seed Localization

摘要

A novel metal artifact reduction technique has been introduced. It uses image deformable registration between a kilovoltage cone-beam computed tomography (kV-CBCT) image set and a megavoltage cone-beam CT (MV-CBCT) image set. The kV-CBCT image set (IS-1) is obtained with full projections, but the MV-CBCT image set (IS-2) is reconstructed with a, limited number of projected views by using an electronic portal imaging device (EPID). The overall procedure consists of four steps. First, for each image set, an intensity threshold value is applied to extract images having artifact streaks from the IS-1 and seed only images from the IS-2. Second, seed clusters it) the IS-2 that do not have clear corresponding clusters in the IS-1 are eliminated. Third, both IS-1 and IS-2 are registered with deformation to generate a deformation grid. Finally, the original kV-CBCT image is re-sampled according to the deformation grid. The effectiveness of this method was studied using a test phantom designed to simulate various complex seed positions. A total of 91 dummy seeds (diameter of I mm and length of 5 mm) were placed for this test. Using the current method, the metal artifact was greatly reduced. Quantitatively, the ratio of the artifact-included seed volume to the physical seed volume was reduced from 9.72 to 6.45. The results of this study demonstrated the effectiveness of this procedure for metal artifact reduction. This improvement may help to increase the accuracy of implant dosimetry. The proposed method can be easily implemented in most clinics.