R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

Working with medical scan data 41
4.6 Region selected using an increased lower threshold value.
one selected by the user. This results in single anatomical structures being
isolated from neighbouring, but unconnected, structures.
However, this is not as simple as it might fi rst appear. It only requires
one single pixel (representing perhaps 0.25 mm) to connect two regions for
the software to assume that they are the same structure. Therefore, structures
that are separate but in close proximity or contact may need to be
separated manually before region growing will be successful. This may
occur, for example, in joints.
4.1.3 Other techniques
Many other techniques may be available depending on the software being
used. Manual techniques can be used and are similar to those found in
photo-editing software, such as draw, delete, cavity fi ll, etc. These allow the
user to edit data to remove artefacts or connect neighbouring structures.
Other techniques are sophisticated variations on the thresholding
and region growing functions. These may incorporate local variations to