R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

10 Medical modelling
2.1 A CT image of the head.
the density difference between soft tissues and air is great allowing, for
example, the nasal airways to be clearly seen. However, the density difference
between different soft tissue structures is not great and therefore it
may be diffi cult to distinguish between different adjacent organs in a CT
image. Artifi cial contrast agents that absorb X-ray energy may be introduced
into the body, which makes some structures stand out more strongly
in CT images.
As CT uses ionising radiation in the form of X-rays, it is called a noninvasive
modality, but exposure should be minimised, particularly to sensitive
organs such the eyes, thyroid and gonads. The X-rays are generated
and detected by a rotating circular array through which a moving table can
travel. Typically, the patient lies on their back and is passed through the
circular aperture in the scanner. The detector array acquires cross sections
perpendicular to the long axis of the patient. The images acquired are,
therefore, usually termed the axial or transverse images.
The scanner, therefore, performs a spiral around the long axis of the
patient. This innovation enables three-dimensional CT scanning to be