Reliability of slice-encoding for metal artefact correction (SEMAC) MRI to identify prosthesis loosening in patients with painful total hip arthroplasty - a single centre, prospective, surgical validation study

MRI of total hip arthroplasty: technical aspects and imaging findings

Total hip arthroplasty (THA) is the best surgical approach for treating advanced hip degeneration, providing pain relief, and improved function in most cases. In the past, MR imaging quality has been highly compromised by in-plane distortions, inadequate fat saturation, and other artifacts due to metal components of THA. Technological advancements have made pathologic conditions, which were previously hidden by periprosthetic artifacts, outstanding features due to the optimization of several sequences. To date, several short and long-term complications involving bony and soft-tissue structures may be detected through magnetic resonance imaging (MRI). The use of MRI with adapted sequences and protocols may drastically reduce artifacts thereby providing essential pre-operative elements for planning revision surgery of failed THA. This review has the purpose of conveying new insights to musculoskeletal radiologists about the techniques to suppress metal-related artifacts and the hallmark MRI findings of painful THA. CRITICAL RELEVANCE STATEMENT: Advancements in metal-suppression have given radiologists the opportunity to play an emerging role in THA management. This article provides technical and imaging insights into challenges that can be encountered in cases of THA, which may present complications and characteristic imaging findings. KEY POINTS: Imaging total hip arthroplasty requires adapted MRI protocol and awareness of the common complications. We have reported the available metal-suppression sequences for evaluating total hip arthroplasty. Many structures and conditions should be considered when dealing with painful aseptic or septic arthroplasty.

Artifact Reduction Proton Density Magnetic Resonance Imaging Can Better Visualize Unicompartmental Knee Arthroplasty Components but Does Not Improve Measurement Accuracy at 3T: An In Vitro Phantom Study

Background There are no studies of the efficacy of slice encoding for metal artifact correction (SEMAC) magnetic resonance imaging (MRI) at 3T for patients following unicompartmental knee arthroplasty (UKA), although the artifact is expected to increase compared with 1.5T. Purpose To clarify whether SEMAC MRI can better visualize UKA components and improve measurement accuracy at 3T MRI. Materials and methods The phantom consisted of femoral and tibial standard UKA components embedded in agarose gel. The MR images were scanned on a 3T MR system including proton density (PD) MR images. Six orthopedic surgeons blinded to the size and details of the components independently scored the diagnostic value for measurement and measured the lengths of the femoral posterior condyle, femoral peg, anterior-posterior (AP) tibial component, medial-lateral (ML) tibial component, and tibial keel, with and without SEMAC. Visualization scores were stratified as 0 = definitely nondiagnostic, 1 = probably nondiagnostic, 2 = possibly diagnostic, 3 = probably diagnostic, and 4 = definitely diagnostic. In addition, the differences between actual length and 95% confidence intervals of five measurement points were analyzed. Results The diagnostic values of the posterior condyle (2.0; 1.5 vs. 0; 0) and femoral peg (1.5; 1.0 vs. 0; 0) were significantly better in SEMAC-PD MRI than in non-SEMAC-PD MRI (P<0.05). On the other hand, there were no significant differences in the visualizations of AP, ML, and keel of the tibial components. Measurements of the femoral posterior condyle and tibial keel approached the actual length, but were not involved within the 95% confidence interval (actual length, 19.4 mm vs. 95% CI, 15.7-19.1 mm). Conclusion A significant reduction of metal artifacts was observed only around the femoral component in SEMAC-PD MRI. Despite artifact reduction, this sequence did not result in better visualization for measurement.

Advances in Bone Joint Imaging-Metal Artifact Reduction

Numerous types of metal implants have been introduced in orthopedic surgery and are used in everyday practice. To precisely evaluate the postoperative condition of arthroplasty or trauma surgery, periprosthetic infection, and the loosening of implants, it is important to reduce artifacts induced by metal implants. In this review, we focused on technical advances in metal artifact reduction using digital tomosynthesis, computed tomography, and magnetic resonance imaging. We discussed new developments in diagnostic imaging methods and the continuous introduction of novel technologies to reduce metal artifacts; however, these innovations have not yet completely removed metal artifacts. Different algorithms need to be selected depending on the size, shape, material and implanted body parts of an implant. Future advances in metal artifact reduction algorithms and techniques and the development of new sequences may enable further reductions in metal artifacts even on original images taken previously. Moreover, the combination of different imaging modalities may contribute to further reductions in metal artifacts. Clinicians must constantly update their knowledge and work closely with radiologists to select the best diagnostic imaging method for each metal implant.