Talbot Brett S, Weinberg Eric P
From the School of Medicine and Dentistry, University of Rochester Medical Center-University Medical Imaging, 601 Elmwood Ave, Box 648, Rochester, NY 14642.
Radiographics. 2016 Jan-Feb;36(1):209-25. doi: 10.1148/rg.2016150075. Epub 2015 Nov 20.
Metallic artifact at orthopedic magnetic resonance (MR) imaging continues to be an important problem, particularly in the realm of total joint arthroplasty. Complications often follow total joint arthroplasty and can be expected for a small percentage of all implanted devices. Postoperative complications involve not only osseous structures but also adjacent soft tissues-a highly problematic area at MR imaging because of artifacts from metallic prostheses. Without special considerations, susceptibility artifacts from ferromagnetic implants can unacceptably degrade image quality. Common artifacts include in-plane distortions (signal loss and signal pileup), poor or absent fat suppression, geometric distortion, and through-section distortion. Basic methods to reduce metallic artifacts include use of spin-echo or fast spin-echo sequences with long echo train lengths, short inversion time inversion-recovery (STIR) sequences for fat suppression, a high bandwidth, thin section selection, and an increased matrix. With care and attention to the alloy type (eg, titanium, cobalt-chromium, stainless steel), orientation of the implant, and magnetic field strength, as well as use of proprietary and nonproprietary metal-suppression techniques, previously nondiagnostic studies can yield key diagnostic information. Specifically, sequences such as the metal artifact reduction sequence (MARS), WARP (Siemens Healthcare, Munich, Germany), slice encoding for metal artifact correction (SEMAC), and multiacquisition with variable-resonance image combination (MAVRIC) can be optimized to reveal pathologic conditions previously hidden by periprosthetic artifacts. Complications of total joint arthroplasty that can be evaluated by using MR imaging with metal-suppression sequences include pseudotumoral conditions such as metallosis and particle disease, infection, aseptic prosthesis loosening, tendon injury, and muscle injury.
骨科磁共振成像中的金属伪影仍然是一个重要问题，尤其是在全关节置换领域。全关节置换术后常常会出现并发症，所有植入装置中都有一小部分会出现这种情况。术后并发症不仅涉及骨质结构，还包括相邻的软组织——这在磁共振成像中是一个极具问题的区域，因为金属假体产生的伪影。如果不进行特殊考虑，铁磁植入物产生的磁化率伪影会导致图像质量下降到无法接受的程度。常见的伪影包括平面内变形（信号丢失和信号堆积）、脂肪抑制不佳或缺失、几何变形和层面间变形。减少金属伪影的基本方法包括使用具有长回波链长度的自旋回波或快速自旋回波序列、用于脂肪抑制的短反转时间反转恢复（STIR）序列、高带宽、薄层面选择和增加矩阵。通过小心并注意合金类型（例如钛、钴铬、不锈钢）、植入物的方向、磁场强度，以及使用专利和非专利的金属抑制技术，以前无法诊断的研究可以产生关键的诊断信息。具体而言，诸如金属伪影减少序列（MARS）、WARP（德国慕尼黑西门子医疗公司）、金属伪影校正的层面编码（SEMAC）和可变共振图像组合的多采集（MAVRIC）等序列可以进行优化，以揭示先前被假体周围伪影掩盖的病理状况。使用带有金属抑制序列的磁共振成像可以评估的全关节置换术后并发症包括假瘤性疾病，如金属沉着病和颗粒病、感染、无菌性假体松动、肌腱损伤和肌肉损伤。
