Orthopedic Metal Artifact Reduction Combined with Iterative Reconstruction in CT Imaging after Lumbar Internal Fixation

Objective: Exploring the effect of metal artifact reduction (O-MAR) technology combined with iterative algorithms on the computed tomography (CT) image quality of patients after lumbar spine internal fixation surgery, to provide an accurate basis for postoperative effect evaluation. Methods: CT images were collected from 20 patients who underwent lumbar spine internal fixation surgery. Using O-MAR, filtered back projection (FBP), and iDose4 algorithms, bone (iDose4-1~7 levels) and soft tissue images (iDose4-1~6 levels) were reconstructed. Screws were displayed the best in transverse and sagittal bone reconstructed images. The screw area (center plane) of the transverse soft tissue images of the intervertebral disc was also reconstructed. Noise levels in standard deviation (SD) of bone and muscle were measured, and the artifact index (AI) was calculated. Two radiologists separately rated the metal artifact suppression and diagnostic information in the bone and soft tissue images. The subjective and objective evaluation indicators of the two groups were compared, conducting multiple comparisons between groups. Statistical analyses were further performed on subjective and objective evaluation indicators, including O-MAR comparisons and/or multiple comparisons between groups with different levels of iDose4. Results: In the bone images, the SD and AI of images using O-MAR were significantly lower than those without O-MAR, and the AI values of iDose4 images at different levels gradually decreased as the dose level increased. The subjective score of metal artifacts in O-MAR images significantly improved, and the score of iDose4-5~7 was higher than those of filtered back projection (FBP) and iDose4-1~2. With O-MAR, the diagnostic information score significantly improved. The score of iDose4-2~4 was higher than that of FBP and other iterative levels, with iDose4-3 being the best. In soft tissue images, the SD and AI of images using O-MAR were lower than those without O-MAR. The metal artifact score of images using O-MAR was higher than that of images without, but the diagnostic information score of images not using O-MAR was higher than that of images with O-MAR; For different iteration levels, regardless of whether O-MAR was used or not, no difference was observed in image artifacts and diagnostic information scores. Conclusions: We suggest combining O-MAR technology with intermediate iteration level iDose4-3 for bone image reconstruction. The use of iterative algorithms for image reconstruction using soft-tissue algorithms is not recommended. The images with and without O-MAR should be simultaneously reconstructed for comparative observations.