MR imaging after spinal fusion using Slice Encoding for Metal Artifact Correction (SEMAC)

INTRODUCTION: Failed Back Surgery Syndrome (FBSS) is a relatively common complication of lumbar spine surgery, occurring in between 5-10% of cases, and resulting in severe, chronic, and debilitating pain. MRI is often of limited value in these patients due to the significant metal artifact occurring around orthopedic hardware, particularly at higher field strengths (Fig. 1). Slice Encoding for Metal Artifact Correction (SEMAC) is an MRI technique that corrects for spatial distortions by performing extra slice encoding and using view-angle tilting [1,2]. Clinical use of SEMAC has previously been limited by the long acquisition time. Patients with significant back or leg pain in particular found it extremely difficult to remain still for the duration of the scan. However, the use of parallel imaging with autocalibrating reconstruction (ARC), reduced FOV and partial Fourier acquisition, has allowed the acquisition of SEMAC in clinically feasible scan times [3]. The purpose of our study was to determine whether SEMAC could successfully be used in the investigation of patients with residual or recurrent back pain and radicular symptoms following instrumented spinal fusion.