Tiny ferromagnetic intraocular foreign bodies detected by magnetic resonance imaging: A report of two cases

Abstract

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 0.375 ϫ 0.3 ϫ 0.15 mm and 0.5 ϫ 0.4 ϫ 0.2 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 (Ͻ0.5 mm) intraocular ferromagnetic particles is warranted.

An investigation into the accuracy of orbital X-rays, when using CR, in detecting ferromagnetic intraocular foreign bodies

“…More recently, Zhang et al 14 reported two cases where patients with tiny ferromagnetic IOFBs (0.375x0.3x0.15mm and 0.5x0.4x0.2mm) underwent MRI examinations with no apparent resultant MR-induced damage. In both cases, plain X-ray films failed to allow the visualisation of the IOFBs.…”

“…However, the risk of an MRinduced injury is dependent on several factors including the shape, location, composition, and orientation of the ferromagnetic objects 15,16 . If a foreign body is located near important neural or vascular structures or other soft tissues, MR examinations must be avoided 14 . Approximately onethird of the orbit is occupied by the globe while the rest of the orbit is composed of fat, nerves, muscles, and vasculature 17 .…”

Penetrating ocular trauma associated with blank cartridge

“…However, the sensitivity of CT for detecting clinical occult open-globe injuries varied from 56% to 68%, depending on the observer [10]. Glass fragment of 0.5 mm were detected 48% by CT [9], and Zhang et al [11] reported that CT can fail to detect metal fragments less than 0.5 mm. Moreover, a recent case report describes even 4 mm glass intraocular foreign body that was not identified at 1-mm collimation CT scanning [12].…”

Evaluation of intraorbital prosthetic pigmentation using 0.3 and 1.5Tesla magnetic resonance imaging and computed tomography

“…Various publications have reported advanced imaging susceptibility artifacts as well as techniques to reduce these artifacts . In a recent case report, a brown‐pigmented intraorbital prosthetic caused a significant susceptibility artifact on MR images that precluded adequate visualization of intracranial structures in a patient with neurologic disease .…”

“…1 Various publications have reported advanced imaging susceptibility artifacts as well as techniques to reduce these artifacts. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] In a recent case report, a brown-pigmented intraorbital prosthetic caused a significant susceptibility artifact on MR images that precluded adequate visualization of intracranial structures in a patient with neurologic disease. 18 Since this publication, to the authors' knowledge, no studies have evaluated the effects of other commonly used intraorbital prosthetics on MRI or CT images or potential techniques to reduce this artifact.…”