Combined use of virtual monochromatic images and projection-based metal artifact reduction methods in evaluation of total knee arthroplasty.

OBJECTIVES: To evaluate the effect of the combined use of virtual monochromatic imaging (VMI) and projection-based metal artifact reduction (PB-MAR) methods on further artifact reduction and image quality in total knee arthroplasty (TKA) patients. METHODS: Fifty-seven knee joints from 36 patients who had a previous history of TKA for bilateral or unilateral knee joints were included in this study. Four sets of images were compared between non-MAR, PB-MAR, VMI, and VMI + PB-MAR. For quantitative analysis, the area, mean attenuation, artifact index (AI), and contrast-to-noise ratio (CNR) were calculated for each protocol. Regarding qualitative analysis, overall artifact and depiction of soft tissue and bony structure were compared using relative visual grading analysis. RESULTS: In the femoral region, the VMI + PB-MAR protocol showed the best MAR performance in quantitative measures including area, mean attenuation, and AI (p < .001). However, MAR protocols with VMI showed significantly lower CNRs than did the protocols without VMI in the tibial region (p < .001). On qualitative analysis, VMI + PB-MAR also showed fewer overall artifacts than did the other two MAR protocols. Soft tissue was best depicted in VMI + PB-MAR protocol, and PB-MAR showed the best performance for the depiction of bony structure (p < .001). CONCLUSIONS: The combined use of VMI and PB-MAR showed better MAR performance than did PB-MAR or VMI alone. In areas with severe metal artifacts, the VMI + PB-MAR and PB-MAR protocols were useful for the evaluation of soft tissue and bone structure, respectively. KEY POINTS: • The combination of artifact reduction methods is effective in reducing metal artifacts in CT. • Soft tissue was best depicted in the combined protocol of projection- and dual-energy-based methods, and projection-based protocol showed the best performance for the depiction of bone structure in case of severe metal artifacts.