MEASURING FACIAL SWELLING USING 3-DIMENSIONAL IMAGING

Requirements exist clinically for quantitative analysis of facial swel ling. A quick and non-invasive measurement of facial volume is desirab le. The acquisition of three-dimensional images, corresponding to spat ial models of patients' facial surfaces, has been facilitated using a Spatial Vision System (SVS) developed by Thorn EMI Central Research La boratories (UK). The SVS acquires four video images (two stereo pairs) and constructs a three-dimensional surface representation using stere o matching of spatial features acquired using 'speckled' illumination. Pre-and post-operative binary volumetric images are then spatially al igned using surface matching algorithms. Accuracy of registration is o ptimized using Match Volume Excavation. Segmentation of post-operative swelling is achieved by volume differencing in combination with morph ological erosion. Volumetric quantification is achieved using a method of three-dimensional region growing, giving the number of connected v oxels in the image volume from a user selected seed point. Accuracy of image acquisition has been quantified by imaging a range of hemispher ical phantoms of known volumes. The mean error in repeated measurement of volume was found to be within 3.5%. The perception of temporal cha nges in facial swelling is highly subjective. Further work is being un dertaken to develop an Enhanced Reality visualization tool in which gr aphical swelling annotations are combined with real-time patient image s.