Preliminary experience with black bone magnetic resonance imaging for morphometry of the mandible and visualisation of the facial skeleton

Children with orofacial deformity may require repeated imaging of the facial skeleton. To test the feasibility and accuracy of “black bone” magnetic resonance imaging (MRI) for assessing facial deformity in children. Three-dimensional (3-D) black bone gradient echo sequences (flip angle 5°, submillimetre spatial resolution) from 10 children (median age: 13 years, range: 2–16 years), who underwent MRI of the temporomandibular joints, were evaluated with multiplanar reconstruction and 3-D rendering tools. Intra- and inter-reader agreement was investigated for measuring the height of the mandibular ramus and condyle, basal length of the mandible, gonion angle and mandibular inclination angle by intraclass correlation coefficient (ICC) and Bland–Altman analysis. Absolute percentage error was calculated with the average of all measurements serving as reference. Sixty linear and 40 angle measurements were obtained on reformatted multiplanar black bone images with excellent inter-reader agreement (ICC > 0.99, agreement bias < 1.4 mm/ < 1.5°) and small error (median absolute error < 3%). The black bone images required inversion of the signal intensity and removal of air before they could be processed with standard volume rendering tools. The diagnostic utility of 3-D views for assessing the facial skeleton was sufficient except for assessing dental relationship. Morphometric measurements of the mandible can be obtained from black bone MRI with comparable inter-rater agreement to that reported for cone beam computed tomography (CT). With improvements of 3-D rendering techniques and software, black bone MRI may become a radiation-free alternative to CT in children with facial deformities.