The in vivo assessment of thoracic vertebral shape from MRI data using a shape model

Abstract

Study design Feasibility study on characterising thoracic vertebral shape from magnetic resonance images using a shape model. Objectives Assess the reliability of characterising thoracic vertebral shape from magnetic resonance images and estimate the normal variation in vertebral shape using a shape model. Summary of background data The characterisation of thoracic vertebrae shape is important for understanding the initiation and progression of deformity and in developing surgical methods. Methods for characterising shape need to be comprehensive, reliable and suitable for use in vivo. Methods Magnetic resonance images of the thoracic vertebrae were acquired from 20 adults. Repeat scans were acquired, after repositioning the participants, for T4, T8 and T12. Landmark points were placed around the vertebra on the images and used to create a shape model. The reliability was assessed using relative error (E%) and intra-class correlation (ICC). The effect of vertebral level, sex and age on vertebral shape was assessed using repeated measures analysis of variance. Results Five modes of variation were retained from the shape model. Reliability was excellent for the first two modes (mode 1: E% = 7, ICC = 0.98; mode 2: E% = 11, ICC = 0.96). These modes

described variation in the vertebral bodies, the pedicle width and orientation, and the facet joint position and orientation with respect to the pedicle axis. Variation in vertebral shape was found along the thoracic spine and between individuals, but there was little effect of age and sex. Conclusions Magnetic resonance images and shape modelling provides a reliable method for characterising vertebral shape in vivo. The method is able to identify differences between vertebral levels and between individuals. The use of these methods may be advantageous for performing repeated measurements in longitudinal studies.