R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

28 Medical modelling
considering scanning the face, gaps are likely to arise from areas of signifi -
cant facial hair, such as beards and moustaches but may also be encountered
around the eyebrows and lashes. These gaps can be clearly seen as
black areas in the surface scan data shown in Fig. 2.15.
2.4.4 Movement
As with other scanning modalities, any patient movement during the scan
will lead to the capture of poor data. The length of time required varies
depending on the exact type and specifi cation of the scanner being used
but may range from a fraction of a second to as much as a minute.
Consequently, it is important that the subject be scanned in a comfortable
and steady posture. This does not normally pose a problem when deal -
ing with co-operative adults and older children, but small children and
babies may be diffi cult to keep still during the scanning. Unlike MR or CT
scanning, it is highly unlikely that sedation would be justifi ed for this type
of scan.
2.15 Scan data of the face of a male subject.