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Fig. 4 Typical CT scanner unit. Patient is placed in alignment with the central axis of the helical
trajectory traced by the X-ray beam source and detectors as they rotate about the patient
multiple layers of internal anatomy to detector banks within the scanner. The X-ray
beam source and detectors rotate about the patient following a helical trajectory.
The beamline is directed toward the patient, who has been placed in alignment with
the central axis of the helix, with detectors positioned on the opposite sides of the
patient. Thus, the X-ray source projects photons through the patient along a con-
tinuous angular progression radial beamline. An example of a CT scanner is shown
in Fig.
4
.
The extent of X-ray attenuation along the beamlines through the patient is
recorded for these radial trajectories, after which complex algorithms for data
reconstruction are used to separate structures along the beamlines and construct an
X-ray attenuation map of the internal elements of the patient
s anatomy [
3
].
A volume source data set is thus derived from the patient, a three-dimensional
entity, as an effective volume map of tissue density. This data is then partitioned
into two-dimensional sections, typically following standardized orthogonal body
planes, and stored for review by physicians who will be involved in the patient
'
s
diagnosis and treatment. An example of this is demonstrated in Fig.
5
, with a single
image from each series of a CT scan of the spine, reformatted into the standardized
planes for clinical interpretation. These anatomic sections have an appearance as if
the body had been cross sectioned, with each sectional surface displayed as an
image. High resolution sectional images in arbitrary scan planes can be created by
'
