Biomedical Engineering Reference
In-Depth Information
Re-slicing of the CT Data
CT images are generally obtained as a series of two-dimensional
transverse sections
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in adjacent parallel planes. It is extremely helpful
(Goitein and Abrams, 1983) to view the same data resorted into
sagittal and coronal planes - and even oblique planes. In early CT
studies the spatial resolution along the superior-inferior axis was
poor; slice thicknesses and spacings of the order of half to one centi-
meter were typical. The coarse superior-inferior spatial resolution
resulted in “blocky” sagittal and coronal images. This problem has
largely disappeared due to scanners with the ability to rapidly accu-
mulate many thin slices with millimeter-scale resolution.
It is particularly helpful to view simultaneously the three orthogonal
views; transverse, sagittal and coronal and to identify the planes of
intersection on all three images. An example of such a display,
including an overlaid dose distribution, is shown in Figure 6.6 of
Chapter 6.
Four-dimensional CT (4DCT)
Radiotherapists have known since X-rays were first employed that the
patient and his or her internal anatomy are mobile and vary with time.
For decades, X-ray fluoroscopy was the best method of evaluating
such temporal changes - provided that the region of interest was
directly or indirectly identifiable.
In recent years, a major advance in CT imaging has allowed one to
synchronize scans with a timing signal (such as a signal at some phase
of the respiratory cycle) and to produce CT data sets which show the
patient's anatomy at several different times (e.g., at several different
phases of the respiratory cycle). Figure 3.8 shows a sequence of such
scans for a patient with a lung tumor. This technology allows a quan-
titative assessment of the degree of motion, and permits tailoring
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The principal anatomic planes for imaging purposes are:
transverse
planes, perpendicular to the long axis of the body which divide the body
into top (superior or cephelad) and bottom (inferior or caudad) parts;
sagittal
planes, perpendicular to transverse planes which divide the body
into left and right parts; and
coronal
planes, perpendicular to both trans-
verse and sagittal planes which divide the body into front (anterior) and
back (posterior) parts. Examples of such sections are: transverse - Figure
3.7; sagittal - Figure 3.11; and coronal - Figure 3.8.
