Metal Artifacts in Postoperative Spine MRI: Strategies and Limitations

초록

The increasing number of spinal surgeries has made postoperative magnetic resonance imaging (MRI) essential, but metallic implants frequently cause severe artifacts due to inhomogeneity in the main magnetic field (B0). This review summarizes the underlying mechanisms and imaging features of metal artifacts, such as signal loss, signal translation, signal pile-up, and failure of fat suppression, and outlines the contributing factors, including implant material, shape, orientation, and magnetic-field strength. Reduction of metal artifacts in postoperative spine MRI is particularly challenging because of the preference for T2-weighted imaging, bilateral implant placement near critical structures, and limitations of spine coils that exacerbate field inhomogeneity and reduce image quality in comparison with extremity imaging. Reduction strategies include fast spinecho imaging, use of high receiver bandwidths, increased spatial resolution, and fat suppression with short tau inversion recovery or Dixon techniques. Special sequences, such as view angle tilting and three-dimensional (3D) multispectral imaging (Slice Encoding for Metal Artifact Correction and Multi-Acquisition with Variable Resonance Image Combination SeLective), are reviewed, including their limitations. A recommended protocol combining conventional and special sequences is proposed, emphasizing view angle tilting for axial images and 3D multispectral imaging for sagittal images, when feasible. Emerging technologies, such as low-field MRI and artificial intelligence–based reconstruction, represent promising future directions for metal-artifact reduction.

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