Objective: To evaluate the impact of radiation dose reduction on image quality in patients with metal-on-metal total hip arthroplasties (THAs) using model-based iterative reconstruction (MBIR) combined with orthopaedic metal artefact reduction (O-MAR).
Materials and methods: Patients with metal-on-metal THAs received a pelvic CT with a full (FD) and a reduced radiation dose (RD) with -20%, -40%, -57%, or -80% CT radiation dose respectively, when assigned to group 1, 2, 3, or 4 respectively. FD acquisitions were reconstructed with iterative reconstruction, iDose4. RD acquisitions were additionally reconstructed with iterative model-based reconstruction (IMR) levels 1-3 with different levels of noise suppression. CT numbers, noise and contrast-to-noise ratios were measured in muscle, fat and bladder. Subjective image quality was evaluated on seven aspects including artefacts, osseous structures, prosthetic components and soft tissues.
Results: Seventy-six patients were randomly assigned to one of the four groups. While reducing radiation dose by 20%, 40%, 57%, or 80% in combination with IMR, CT numbers remained constant. Compared with iDose4, the noise decreased (p < 0.001) and contrast-to-noise ratios increased (p < 0.001) with IMR. O-MAR improved CT number accuracy in the bladder and reduced noise in the bladder, muscle and fat (p < 0.01). Subjective image quality was rated lower on RD IMR images than FD iDose4 images on all seven aspects (p < 0.05) and was not related to the applied radiation dose reduction.
Conclusion: In RD IMR with O-MAR images, CT numbers remained constant, noise decreased and contrast-to-noise ratios between muscle and fat increased compared with FD iDose4 with O-MAR images in patients with metal-on-metal THAs. Subjective image quality reduced, regardless of the degree of radiation dose reduction.
Keywords: CT; Hip prosthesis; IMR; MBIR; Metal artifacts; Metal-on-metal; O-MAR; Radiation dose reduction; Total hip arthroplasty.