Metal artifacts of hip arthroplasty implants at 1.5-T and 3.0-T: a closer look into the B₁ effects

Objective: To evaluate the effect of circular polarization (CP) and elliptical polarization (EP) of the B₁ field on metal implant-induced artifacts of titanium (Ti) and cobalt-chromium (CoCr) hip arthroplasty implants at 1.5-T and 3.0-T field strengths. Material and methods: In vitro Ti and CoCr total hip arthroplasty implants were evaluated using high transmit and receive bandwidth turbo spin echo (HBW-TSE) and slice encoding for metal artifact correction (SEMAC) metal artifact reduction techniques. Each technique was implemented at 1.5-T, which only allows for CP of B₁ field as the system default, as well as 3.0-T, which permitted CP and EP. Manual segmentation quantified the size of the metal artifacts at the level of the acetabular cup, femoral neck, and femoral shaft. Results: In the acetabular cup and femoral neck, 1.5-T CP achieved smaller artifact sizes than 3.0-T CP (28–29% on HBW-TSE, p = 0.002–0.005; 17–34% on SEMAC, p = 0.019–0.102) and 3.0-T EP (25–28% on HBW-TSE, p = 0.010–0.011; 14–36% on SEMAC, p = 0.058–0.135) techniques. In the femoral stem region, 3.0-T EP achieved more efficient artifact suppression than 3.0-T CP (HBW-TSE 44–45%, p < 0.001–0.022; SEMAC 76–104%, p < 0.001–0.022) and 1.5-T CP (HBW-TSE 76–96%, p < 0.001–0.003; SEMAC 138–173%, p = 0.003–0.005) techniques. Conclusion: Despite slightly superior metal reduction ability of the 1.5-T in the region of the acetabular cup and prosthesis neck, 3.0-T MRI of hip arthroplasty implants using elliptically polarized RF pulses may overall be more effective in reducing metal artifacts than the current standard 1.5-T MRI techniques, which by default implements circularly polarized RF pulses.