Measuring facial swelling using three-dimensional imaging

Requirements exist clinically for quantitative analysis of facial swelling. A quick and non-invasive measurement of facial volume is desirable. The acquisition of three-dimensional images, corresponding to spatial models of patients' facial surfaces, has been facilitated using a Spatial Vision System (SVS) developed by Thorn EMI Central Research Laboratories (UK). The SVS acquires four video images (two step pairs) and constructs a three-dimensional surface representation using stereo matching of spatial features acquired using 'speckled' illumination. Pre- and post-operative binary volumetric images are then spatially aligned using surface matching algorithms. Accuracy of registration is optimized using Match Volume Excavation. Segmentation of post-operative swelling is achieved by volume differencing in combination with morphological erosion. Volumetric quantification is achieved using a method of three-dimensional region growing, giving the number of connected voxels in the image volume from a user selected seed point. Accuracy of image acquisition has ben quantified by imaging a range of hemispherical phantoms of known volumes. The mean error in repeated measurement of volume was found to be within 3.5%. The perception of temporal changes in facial swelling is highly subjective. Further work is being undertaken to develop and Enhanced Reality visualization tool in which graphical swelling annotations are combined with real-time patient images.