Magnetic resonance imaging: an accurate, radiation-free, alternative to computed tomography for the primary imaging and three-dimensional reconstruction of the bony orbit.

PURPOSE To determine the extent to which the accuracy of magnetic resonance imaging (MRI) based virtual 3-dimensional (3D) models of the intact orbit can approach that of the gold standard, computed tomography (CT) based models. The goal was to determine whether MRI is a viable alternative to CT scans in patients with isolated orbital fractures and penetrating eye injuries, pediatric patients, and patients requiring multiple scans in whom radiation exposure is ideally limited. MATERIALS AND METHODS Patients who presented with unilateral orbital fractures to the Royal Brisbane and Women's Hospital from March 2011 to March 2012 were recruited to participate in this cross-sectional study. The primary predictor variable was the imaging technique (MRI vs CT). The outcome measurements were orbital volume (primary outcome) and geometric intraorbital surface deviations (secondary outcome) between the MRI- and CT-based 3D models. RESULTS Eleven subjects (9 male) were enrolled. The patients' mean age was 30 years. On average, the MRI models underestimated the orbital volume of the CT models by 0.50 ± 0.19 cm(3). The average intraorbital surface deviation between the MRI and CT models was 0.34 ± 0.32 mm, with 78 ± 2.7% of the surface within a tolerance of ±0.5 mm. CONCLUSIONS The volumetric differences of the MRI models are comparable to reported results from CT models. The intraorbital MRI surface deviations are smaller than the accepted tolerance for orbital surgical reconstructions. Therefore, the authors believe that MRI is an accurate radiation-free alternative to CT for the primary imaging and 3D reconstruction of the bony orbit.

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