Dedicated CT and MRI Techniques for the Evaluation of the Postoperative Knee

Abstract

Advances in surgical techniques, orthopaedic implant design, and higher demands for improved functionality of the aging population have resulted in a high prevalence of patients with metallic implants about the knee. Total knee arthroplasty, knee-replacing tumor prostheses, and osteosynthesis implants create various imaging artifacts and pose special challenges for the imaging evaluation with computed tomography (CT) and magnetic resonance imaging (MRI). CT artifacts can be effectively mitigated with metal artifact reduction reconstruction algorithms, dual-energy data acquisition with virtual monoenergetic extrapolation, and three-dimensional postprocessing techniques, such as volume and cinematic rendering. Artifacts related to metal implants on MRI can be reduced via optimization of the scan parameters and using advanced techniques such as multi-acquisition variable-resonance image combination, and slice encoding for metal artifact correction.

Postoperative Spinal CT: What the Radiologist Needs to Know

“…Metal implant-induced CT artifacts can be further minimized by using advanced techniques, including metal artifact reduction reconstruction algorithms and dual-energy data acquisition with virtual monoenergetic extrapolation postprocessing (14). Although many vendors have their own proprietary reconstruction algorithms and metal artifact reduction software, many use projection completion.…”

“…Although many vendors have their own proprietary reconstruction algorithms and metal artifact reduction software, many use projection completion. With projection completion, inaccurate or missing x-ray projections are replaced by interpolations from adjacent projections (14). Dual-energy CT images can be acquired by using several different methods, most of which involve the use of specialized CT scanner systems (Fig 2) (14,15).…”

“…Image acquisition factors that reduce artifact severity include high peak voltage, high tube current, narrow collimation, and thin sections (11). The peak voltage (Fig 1) affects the ability of an ential mass densities are combined with the mass attenuation coefficients, virtual monoenergetic images can be created (14). The acquisition of virtual monoenergetic images at higher energies reduces the severity of high-attenuation beam-hardening artifacts (Fig 1), but it does not account for other causes of artifacts such as scattering (16).…”

“…Iterative and monoenergetic CT techniques can be used to substantially reduce spine implant-and prosthesis-induced metal artifacts and improve the visibility of bone, soft tissues, and pathologic processes (17)(18)(19). The use of threedimensional postprocessing with multiplanar and curved reformations, as well as volume and cinematic rendering techniques, can further decrease the severity of streak artifacts by averaging the axial data in reformation planes in which true signal and random artifacts are balanced (14,20).…”

Update on Imaging of Knee Arthroplasties: Normal Findings and Hardware Complications

“…11,[13][14][15] The two main methods of metal artifact reduction are projectionbased metal artifact reduction algorithms and dual-energy CT scanning with virtual monochromatic images. 16 Projection-based algorithms are vendor specific and correct for errors due to scatter and photon starvation by interpolating the image appearance from adjacent projections. 17 Metal artifact reduction algorithms may be applied retrospectively; however, the decision to use dual-energy scans must be made before the scan is acquired in most scanners.…”