Fat-suppressed MR Imaging of the Spine for Metal Artifact Reduction at 3T: Comparison of STIR and Slice Encoding for Metal Artifact Correction Fat-suppressed T₂-weighted Images

Abstract

Purpose:To compare short tau inversion recovery (STIR) images with slice encoding for metal artifact correction (SEMAC)-corrected magnetic resonance imaging (MRI) of spectral presaturation with inversion recovery (SPIR) or inversion recovery (IR) at 3T in patients with metallic spinal instrumentation.Methods:Following institutional review board’s approval, 71 vertebrae with interbody fixation in 26 patients who underwent transpedicular spondylodesis with spinal metallic prostheses were analyzed with SEMAC spinal MRI. All the fixated vertebrae were examined with STIR, and 41 vertebrae of 15 patients were scanned with SEMAC-SPIR T2-weighted MRI. The remaining 30 vertebrae of 11 patients were scanned with SEMAC-IR T2-weighted MRI. Two musculoskeletal radiologists compared the image sets and qualitatively analyzed the images with a five-point scale that included artifact reduction around the metallic implant and visualization of the rod and pedicle. Quantitative assessments were performed by calculating the signal intensity ratio of the fixated vertebra and non-metallic vertebra and by calculating the signal-to-noise ratios (SNRs) of the vertebrae. A paired t-test was used for the statistical analyses.Results:The SEMAC-IR MRI had a significant decrease in the metallic artifact area (P < 0.05), while the SEMAC-SPIR MRI yielded significantly increased artifact areas (P < 0.05). However, the signal intensity ratios (i.e., metal-induced signal pile-up) were not significantly different (P > 0.05) between the STIR and SEMAC MRI. The SNR of the SEMAC MRI was significantly lower than the SNR of the STIR (P < 0.05). The metal artifact reduction scores were significantly higher in the SEMAC-SPIR MRI (P < 0.05).Conclusion:Despite the relatively larger artifact size and lower SNRs, the SEMAC-SPIR MRI was superior to the other types of fat-suppressed MRI of SEMAC-IR or T2-weighted STIR MRI. However, the drawbacks of high signal pile-up, large artifact size, and relatively low SNRs require further investigation to determine the best method for fat-suppressed MRI of metallic implants.

Improved Visualization of Juxtaprosthetic Tissue Using Metal Artifact Reduction Magnetic Resonance Imaging

“…Standard SEMAC sequences (without CS) had been frequently acquired with 6 to 12 SESs. [7][8][9][36][37][38] Therefore 11,19,and 27 SESs were assessed in this study. More SESs were associated with higher SNR, reduced metal artifacts, and improved imaged quality, but images showed more severe ripple artifacts and had longer acquisition and reconstruction times; 19 SESs were identified to be sufficient for optimal artifact reduction.…”

Advances in MRI around metal

“…Failure of fat saturation is another major problem encountered in the presence of metal implants . The most commonly used spectral fat saturation is dependent on a homogenous magnetic field.…”

“…SEMAC sequences enabled significantly improved periprosthetic visualization of the pedicles, vertebral body, dural sac, and neural foramina . Still, acquisition of MARS spine images with diagnostically sufficient SNR and contrast is challenging . STIR sequences sometimes fail to detect bone marrow edema, and therefore evidence of bone marrow edema should be assessed with caution in the presence of metal .…”

MSVAT-SPACE-STIR and SEMAC-STIR for Reduction of Metallic Artifacts in 3T Head and Neck MRI

“…Such long acquisition times are not applicable to in vivo head and neck imaging because different weightings as well as pre-and postcontrast images are typically used in clinical protocols. An in vivo study of Lee et al 13 noted only a minor artifact reduction of 17.8% using SEMAC-STIR instead of TSE-STIR for spine imaging. Once again, this can be explained by less spectral coverage in terms of slice-encoding steps compared with Zho et al but still more than we used in our study: 11 (Lee et al) versus 36 (Zho et al) versus 4 in our study.…”

“…[7][8][9][10][11][12] These new techniques for artifact reduction were predominantly developed and tested for orthopedic and neurosurgical applications. 13,14 Until now, little attention has been paid to the head and neck area. Moreover, results of previous studies are of limited transferability because the amount of material, shape, and materials is different in the head and neck area compared with orthopedic or neurosurgical implants, and all these characteristics influence artifact size.…”