R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

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Medical imaging for rapid prototyping 27
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2.14 Line of sight and viewpoints for scanning the face.
overcome by taking several overlapping scans. The data from each of these
scans can then be aligned using software to give a single coherent data set.
When conducting a series of scans it is, therefore, important that they
overlap so that the individual scans can be put together accurately. Despite
using multiple scans, some areas may remain diffi cult to capture. For
example, it is very diffi cult to capture data from behind the ear and at the
nostrils.
2.4.3 Missing data
Because these techniques use light to calculate the points, transparent or
highly refl ective surfaces can cause problems. Usually human skin performs
very well in this respect, but steps may be required to dry particularly greasy
or moist skin. These effects may also be overcome somewhat by applying
a fi ne powder, such as talcum powder, that will give the object an opaque
matt fi nish. The eyes may cause problems due to their shiny surface and
watering. All optical scanners should be inherently safe; however, care
should be taken when scanning the eyes to ensure that bright light or laser
light does not directly enter the pupil.
Another inherent problem is caused by hair. Hair does not form a coherent
surface and absorbs or randomly scatters the light from the scanner.
However, the fi ne hair present on most body surfaces does not normally
affect the captured data, although excessively thick body hair may reduce
the quality of the data captured. In most cases, the presence of hair will
lead to gaps in the data. Fine or downy body hair often does not cause
signifi cant problems, but there may be little that can be done about a full
head of hair and it would not be normal to consider shaving the head for
such a procedure unless the clinical benefi ts were overwhelming. When
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