A new method to reduce helical artifacts in the reconstructed image from direct filtered backprojection

In helical scan protocol, direct filtered back projection method introduces helical artifacts in the reconstructed volume. Especially, the helical artifacts become severer when a large two dimensional planar detector array is employed. In this work, we proposed a method to reduce the helical artifacts in the reconstructed volume. The proposed algorithm proceeds in two sequential parts: bone induced artifacts reduction part and soft tissue induced artifacts reduction part. Since artifacts induced by bones are more severe, the bone image are segmented from the initial reconstructed image, and then the bone induced artifacts are generated by conducting the forward projection and filtered back projection on the segmented bone image. The difference between the segmented bone image and reconstructed bone image is calculated, which is subtracted from the initial reconstructed image. In the same manner, the soft tissue induced artifacts are generated from the bone induced artifacts corrected image, and the final correction image is acquired by subtracting the soft tissue induced artifacts from the bone induced artifacts corrected image. The proposed algorithm was verified for extended cardiac-torso (XCAT) simulation. Performance of the proposed algorithm was quantitatively evaluated for uncorrected images, bone corrected images and bone-and-soft tissue corrected images by normalized mean square error (NMSE) and structure similarity index (SSIM). The results showed that the bone artifacts reduction part effectively reduced the helical artifacts, and soft tissue artifacts reduction part further reduced residual artifacts remained in the bone corrected images. The proposed algorithm can reduce helical artifacts without compromising the existing FBP's computational advantages.