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.

The WEBD project: a research of new methodologies for a distant-learning 3D system prototype.

OBJECTIVES: To create and to spread a new interactive multimedia instrument, based upon virtual reality technologies, that allows both the running simulation of machines and equipment and the reproduction via Web of complex three-dimensional (3D) anatomical models such as the skull. METHODS: There were two main aspects of the project, one of design engineering and the other biomedical engineering, for the creation of "artificial" and anatomical objects. The former were made with 3D Studio Max R4 by Autodesk, San Rafael, CA, while the latter were created starting from real bones scanned with a CT system or a surface scanner and elaborated with different programs (3D Studio Max R4, Scenebuilder by Viewpoint, New York, NY and Spinfire by Actify, San Francisco, CA). The 3D models were to be integrated into web modules and had to respect file limits while preserving a sufficient definition. Two systems of evaluation were used, a questionnaire on a selected sample and an external evaluation by a different university. RESULTS: The Viewpoint format offers the best interactivity and size reduction (up to 96% from the original 3D model). The created modules included production of radiological images, rapid prototyping, and anatomy. The complete "3D Distant Learning Prototype" is available at www.webd.etsii.upm.es. CONCLUSIONS: The software currently available permits the construction of interactive modules. The verification on the selected sample and the evaluation by the University of Naples show that the structure is well organized and that the integration of the 3D models meets the requirements.