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.
Copyright (c) 2009 Wiley-Liss, Inc.