Fifty-seventh annual meeting of the American association of physicists in medicine
MO-FG-204-09: High Spatial Resolution and Artifact-Free CT Bone Imaging at Off-Centered Positions: An Application of Model-Based Iterative Reconstruction
Although the anatomy of interest should be positioned as close as possible to the isocenter of CT scanners, off-centering may be inevitable during certain exams in clinical practice such as lumbar spine and elbow imaging. Off-centering degrades image sharpness, generates streak artifacts, and sometimes creates blooming artifacts due to truncation. The purpose of this work was to investigate whether the use of model-based image reconstruction (MBIR) can alleviate the negative impacts of off-centering to achieve high quality CT bone imaging.
Both an anthropomorphic phantom and an ex vivo swine elbow sample were scanned at centered and off-centered positions using clinical CT bone scan protocols. The magnitude of off-centering was determined from localizer radiographs. Both FBP and MBIR reconstructions were performed. For FBP, both standard and Bone Plus kernels commonly used in bone imaging were used. Objective assessment of image sharpness, noise standard deviation, and noise nonuniformity were performed. Additionally, we retrospectively analyzed human subject data acquired under off-centered conditions as a validation study.
In FBP images of the phantom, off-centering by 10 cm led to a 14% increase in noise (p<1e-3) and a 68% increase in noise nonuniformity (p<0.02). A visible drop in bone sharpness was observed. In contrast, no significant difference in the noise magnitude or the noise nonuniformity between the centered and off-centered MBIR images was found. The image sharpness of off-centered MBIR images outperformed that of FBP images reconstructed with the Bone Plus kernel. In images of the swine elbow off-centered by 20 cm, not only was the noise and spatial resolution performance improved by MBIR, truncation artifacts were also elliminated. The human subject study generated similar results, in which the visibility of the off-centered lumbar spine was significantly improved.
High quality CT bone imaging at off-centered positions can be achieved using MBIR.
This work was partially supported by an NIH grant R01CA169331 and GE Healthcare. K. Li, D. Gomez-Cardona: Nothing to disclose. G.-H. Chen: Research funded, GE Healthcare; Research funded, Siemens AX. A. Budde, J. Hsieh: Employee, GE Healthcare.