A morphological methodology for three-dimensional human face soft-tissue landmarks extraction: a preliminary study.

Assessment of facial soft tissues could be implemented using only anatomical landmarks. These points are so significant in the medical context because are able to provide significant information about the human face morphology and dimensions. At present their detection and location is made by expert physicians using palpation. Even if this procedure normally provides reliable information, the reliability of the results is proportional to the expertise of the physician. Considering that at present many physicians are beginning to use 3D scanners that provide three-dimensional data of the human face, it is possible to implement a robust and repeatable methodology that supports the physician's diagnosis. To reach this goal it is necessary to implement a methodology based on geometrical codification of landmarks and which mathematically formalizes the physician's visual and palpation analyses of the real patient.

Reconstruction of facial morphology from laser scanned data. Part I: reliability of the technique.

OBJECTIVES: The aim of this study was to evaluate the effects of scanning parameters on the precision of the data acquired using a facial laser scanner and to assess the reliability of automatic model recording in humans. METHODS: Data were acquired using a laser scanner (Cyberware 3030RGB); analysis and measurements were performed with Rapid Form 2004 software. A mannequin and six volunteers were scanned to investigate the effects of environmental conditions, positioning, head orientation, and software procedures. Precision and accuracy of the data were evaluated comparing six linear measures calculated on scanned data with those obtained directly. Two sessions with different head inclination were performed. The reliability of repeated scans was also assessed measuring the distance between the surfaces reconstructed from two separate scans of the same subject, at 12 anatomical points, in 5 subjects, during two sessions using a different head inclination. Differences were analysed using paired t-tests or analysis of variance (ANOVA). RESULTS: The accuracy of scanning was +/-0.65 mm. The development of a specific protocol resulted in a mean scanning error of 1-1.2 mm and a recording error of 0.3-0.4 mm on repeated scans of human subjects. CONCLUSIONS: This study indicates that scanning of the human face may be hampered by errors and artefacts, mainly due to movements. While the effect of trembling and involuntary movements during the exam may be minimized using faster scanning devices, comparative observation over time may be affected by unreal differences due to the uncertainty of facial expression. The overall error is, however, in the range useful for most clinical studies.