Sparse‐SEMAC: rapid and improved SEMAC metal implant imaging using SPARSE‐SENSE acceleration

Purpose To develop an accelerated SEMAC metal implant MRI technique (Sparse‐SEMAC) with reduced scan time and improved metal distortion correction. Methods Sparse‐SEMAC jointly exploits the inherent sparsity along the additional phase‐encoding dimension and multicoil encoding capabilities to significantly accelerate data acquisition. A prototype pulse sequence with pseudorandom k y ‐k z undersampling and an inline image reconstruction was developed for integration in clinical studies. Three patients with hip implants were imaged using the proposed Sparse‐SEMAC with eight‐fold acceleration and compared with the standard‐SEMAC technique used in clinical studies (three‐fold GRAPPA acceleration). Measurements were performed with SEMAC‐encoding steps (SES) = 15 for Sparse‐SEMAC and SES = 9 for Standard‐SEMAC using high spatial resolution Proton Density (PD) and lower‐resolution STIR acquisitions. Two expert musculoskeletal (MSK) radiologists performed a consensus reading to score image‐quality parameters. Results Sparse‐SEMAC enables up to eight‐fold acceleration of data acquisition that results in two‐fold scan time reductions, compared with Standard‐SEMAC, with improved metal artifact correction for patients with hip implants without degrading spatial resolution. Conclusion The high acceleration enabled by Sparse‐SEMAC would enable clinically feasible examination times with improved correction of metal distortion. Magn Reson Med 78:79–87, 2017. © 2016 International Society for Magnetic Resonance in Medicine