Are Magnetic Resonance Imaging-Generated 3Dimensional Models Comparable to Computed Tomography-Generated 3Dimensional Models for Orbital Fracture Reconstruction? An In-Vitro Volumetric Analysis

Abstract

Background: Magnetic resonance imaging (MRI) is being increasingly considered as an alternative for the evaluation and reconstruction of orbital fractures. No previous research has compared the orbital volume of an MRI-imaged, three-dimensional (3D), reconstructed, and virtually restored bony orbit to the gold standard of computed tomography (CT).

Purpose: To measure the orbital volumes generated from MRI-based 3D models of fractured bony orbits with virtually positioned prebent fan plates in situ and compare them to the volumes of CT-based virtually reconstructed orbital models.

Study design: This retrospective in-vitro study used CT and MRI data from adult patients with orbital trauma assessed at the Royal Brisbane and Women's Hospital Outpatient Maxillofacial Clinic from 2011 to 2012. Only those with orbital blowout fractures were included in the study.

Predictor variable: The primary predictor variable was imaging modality, with CT- and MRI-based 3D models used for plate bending and placement.

Main outcome variable: The primary outcome variable was the orbital volume of the enclosed 3D models.

Covariates: Additional data collected was age, sex, and side of fractured orbit. The effect of operator variability on plate contouring and orbital volume was quantified.

Analyses: The Wilcoxon signed rank test was used to assess differences between orbital volumes with a significance level P < .05.

Results: Of 11 eligible participants, six patients (four male and two female; mean age 31 ± 8.6 years) were enrolled. Two sets of six CT-based virtually restored orbits were smaller than the intact contralateral CT models by an average of 1.02 cm³ (95% CI -0.07 to 2.11 cm³; P = .028) and 0.99 cm³ (95% CI 0.07 to 1.91 cm³; P = .028), respectively. The average volume difference between the MRI-based virtually restored orbit and the intact contralateral MRI model was 0.97 cm³ (95% CI -1.08 to 1.94 cm³; P = .75). Imaging modality did affect orbital volume difference for 1 set of CT and MRI models (0.63 cm³; 95% CI -0.11 to 1.29 cm³; P = .046) but not the other (0.69 cm³; 95% CI -0.11 to 1.23 cm³; P = .075). Single operator variability in plate bending did not result in significant (P = .75) volume differences.

Conclusions: MRI can be used to reconstruct orbital volume with a clinically acceptable level of accuracy.