Computer methods for measuring 3D facial morphology (original) (raw)

The present article reports our first steps in the development of computer methods for processing and analysing three-dimensional facial morphology in children and adults with the purpose of evaluating and predicting soft tissue changes with age or due to operation. Two Minolta VIVID 900 laser optical digitizers placed as a stereo pair were used to obtain 3D facial images of adults and children. Initially, the digitizer calibration procedure was found to be incapable of providing properly aligned raw left and right scanned images of live subjects. This problem was resolved through the use of RapidForm, commercially available reverse modelling software. The image alignment was preceded by garbage and noise removal, cutting of unessential portions and regions that spoil the alignment, surface smoothing, and small-hole filling. The pre-processed images were then registered (aligned) and merged to obtain a single 3D facial model. Based on RapidForm API functionality, special in-house software was created to automate the different stages of image processing. The procedure developed was tested on a plaster cast face and several adults, and was then applied to 40 children (20 males and 20 females), mean age 11 years and 3 months, enrolled in the cranio-facial growth study programme at the University of Wales, College of Medicine. The registered left and right scanned images were found to coincide to within 0.5 mm on the average of 82.2% of the overlapping area (SD = 8.4%) and 1 mm on the average of 95.7% of the overlapping area (SD = 4.7%). For comparison, the respective results for a plaster cast face, which was perfectly still during scanning, were 87.2% and 97.4%. The results obtained show that the scanning equipment and the computerised techniques elaborated allow 3D representation of facial images of living subjects in a reproducible and reliable manner with a clinically acceptable accuracy. 2. INTRODUCTION Three-dimensional laser scanning is known to be a useful tool in the study of facial morphology. The scanning process is non-invasive and normally completes within a few seconds. Three-dimensional laser scanning systems have been used to create databases for normative populations [1], establish cross-sectional growth changes [2], and evaluate the effects of growth and surgical and non-surgical treatment procedures in the facial region [3-6].