Zhang Yong, Cheng Jingliang, Bai Jie, Ren Cuiping, Zhang Yan, Gao Xuemei, Cui Xiaolin, Yang Yun Jun
Department of Radiology, First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, PR China.
J Magn Reson Imaging. 2009 Mar;29(3):704-7. doi: 10.1002/jmri.21637.
We report two cases with tiny ferromagnetic intraocular foreign bodies (FBs) that were demonstrated only on magnetic resonance imaging (MRI) and confirmed by subsequent ophthalmologic operation. Both of the patients had a history of ocular trauma and their clinical symptoms were compatible with an intraocular FB. Plain x-ray film, 3 mm slice thickness computed tomography (CT) scans (Toshiba TXT 600 system and GERP22 system), B-scan ultrasonography, and an MRI study (Siemens Impact 1.0 MR system) were acquired. MR examinations were performed using spin-echo (SE) T1, T2, and PD-weighted axial and sagittal or coronal images with 3 mm slice thickness. Plain x-ray film, 3 mm slice thickness CT scans and B-scan ultrasonography all failed to demonstrate any tiny intraocular FBs in these two patients, whereas MRI revealed tiny ferromagnetic FBs due to their characteristic magnetic susceptibility artifact. A ferromagnetic FB was found in the vitreous body of each patient, which were 0.375x0.3x0.15 mm and 0.5x0.4x0.2 mm, respectively, and there was no evidence of MR-induced damage. We suggest that tiny ferromagnetic fragments with a diameter below 0.5 mm, which are too small to be visualized by x-ray plain films and CT images, may be visualized on MR images. These tiny ferromagnetic particles may not be large enough to cause ocular damage during a 1.0T MRI examination. MRI may be a useful tool in the evaluation of tiny intraocular ferromagnetic FBs if other imaging modalities such as plain s-ray, CT scan, and ultrasonography failed to do so. Further evaluation with a large-scale study (in vitro and in vivo animal study) for the safety of detecting tiny (<0.5 mm) intraocular ferromagnetic particles is warranted.
我们报告了两例微小铁磁性眼内异物（FBs）病例，这些异物仅在磁共振成像（MRI）上显示，并经后续眼科手术证实。两名患者均有眼外伤史，其临床症状与眼内FB相符。获取了普通X线平片、层厚3mm的计算机断层扫描（CT）（东芝TXT 600系统和GERP22系统）、B超扫描以及MRI检查（西门子Impact 1.0 MR系统）。MRI检查采用自旋回波（SE）T1、T2和质子密度加权的轴位以及矢状位或冠状位图像，层厚3mm。普通X线平片、层厚3mm的CT扫描和B超扫描均未在这两名患者中显示任何微小的眼内FB，而MRI由于其特征性的磁敏感性伪影显示出微小的铁磁性FB。在每名患者的玻璃体中均发现了一个铁磁性FB，大小分别为0.375×0.3×0.15mm和0.5×0.4×0.2mm，且没有MR诱导损伤的证据。我们认为，直径小于0.5mm的微小铁磁性碎片太小，无法通过X线平片和CT图像显示，但可能在MR图像上显示。这些微小的铁磁性颗粒可能不够大，在1.0T MRI检查期间不会导致眼部损伤。如果普通X线、CT扫描和超声检查等其他成像方式未能检测到微小的眼内铁磁性FB，MRI可能是评估此类FB的有用工具。有必要通过大规模研究（体外和体内动物研究）进一步评估检测微小（<0.5mm）眼内铁磁性颗粒的安全性。
