Abstract
PurposeTo evaluate the influence of different scan parameters for single-energy CT and dual-energy CT, as well as the impact of different material used in a TKA prosthesis on image quality and the extent of metal artifacts.MethodsEight pairs of TKA prostheses from different vendors were examined in a phantom set-up. Each pair consisted of a conventional CoCr prosthesis and the corresponding anti-allergic prosthesis (full titanium, ceramic, or ceramic-coated) from the same vendor. Nine different (seven dual-energy CT and two single-energy CT) scan protocols with different characteristics were used to determine the most suitable CT protocol for TKA imaging. Quantitative image analysis included assessment of blooming artifacts (metal implants appear thicker on CT than they are, given as virtual growth in mm in this paper) and streak artifacts (thick dark lines around metal). Qualitative image analysis was used to investigate the bone–prosthesis interface.ResultsThe full titanium prosthesis and full ceramic knee showed significantly fewer blooming artifacts compared to the standard CoCr prosthesis (mean virtual growth 0.6–2.2 mm compared to 2.9–4.6 mm, p < 0.001). Dual-energy CT protocols showed less blooming (range 3.3–3.8 mm) compared to single-energy protocols (4.6–5.5 mm). The full titanium and full ceramic prostheses showed significantly fewer streak artifacts (mean standard deviation 77–86 Hounsfield unit (HU)) compared to the standard CoCr prosthesis (277–334 HU, p < 0.001). All dual-energy CT protocols had fewer metal streak artifacts (215–296 HU compared to single-energy CT protocols (392–497 HU)). Full titanium and ceramic prostheses were ranked superior with regard to the image quality at the bone/prosthesis interface compared to a standard CoCr prosthesis, and all dual-energy CT protocols were ranked better than single-energy protocols.ConclusionsDual-energy CT and ceramic or titanium prostheses reduce CT artifacts and provide superior image quality of total knee arthroplasty at the bone/prosthesis interface. These findings support the use of dual-energy CT as a solid imaging base for clinical decision-making and the use of full-titanium or ceramic prostheses to allow for better CT visualization of the bone–prosthesis interface.
Highlights
Common complications of total knee arthroplasty implants (TKA) are loosening of the prosthesis or infection [3, 4, 18]
We found significantly less virtual growth for the following anti-allergic models compared to the standard CoCr models: L CS® (4.0 mm (p < 0.001)); ACS® (0.3 mm (p = 0.019)); LegionTM (1.3 mm (p < 0.001)); NexGen® LPS (1.7 mm (p < 0.001)); and BPK-S (1.4 mm (p < 0.001))
The scan protocol with the lowest virtual growth was observed for scan protocol 5, with a mean of 3.3 mm over all prostheses
Summary
Common complications of TKA are loosening of the prosthesis or infection [3, 4, 18]. Postoperative care of TKAs usually includes periodic physical examinations, as well as radiographic follow-up [17]. In the presence of abnormal findings in postoperative follow-up examinations, e.g., suspicious loosening or osteolytic lesions, further work-up includes scintigraphy [20] and computed tomography (CT) [10, 19]. The latter provides excellent spatial resolution of the bones, soft-tissue, and prosthetic material, but it has. Several methods have been proposed to reduce metal artifacts [6, 12, 16, 24, 26], which are the result of photon starvation and beam-hardening of the metal components of the prosthesis [2]. These methods include changes in scan parameters, such as higher tube voltage, and the use of image post-processing algorithms [13, 14, 23]
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