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Principles of Computer Tomography (CT)

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Principles of
Computer Tomography (CT)
The formation of a CT image is a distinct three phase
process.
1. The scanning phase produces data, but not an image.
2. The reconstruction phase processes the acquired data and forms a
digital image.
3. The visible and displayed analog image (shades of gray) is produced by
the digital-to analog conversion phase.
4.There are adjustable factors associated with each of these phases that
can have an effect on the characteristics and quality of the image.
The formation of a CT image
•
http://tech.snmjournals.org/content/35/3/115.full.pdf+html
JOURNAL OF NUCLEAR MEDICINE TECHNOLOGY • Vol. 35 • No. 3
• September 2007
•
FIGURE 11. Helical CT. Improved body CT was made
possible with advent of helical CT (or spiral CT). Patient table
is moved smoothly through gantry as rotation and data
collection continue. Resulting data form spiral (or helical) path
relative to patient; slices at arbitrary locations.
•
Figure 1. Schematic of a volumetric CT system.
Gupta R et al. Radiographics 2008;28:2009-2022
В©2008 by Radiological Society of North America
FIGURE 10. Fourth-generation scan geometry.
http://tech.snmjournals.org/content/35/3/115.full.pdf+html
•
Measurements
FIGURE 2. x-Ray
transmission
measurements.
Measurements are
obtained at many
points during
translation motion of
tube and detector.
JOURNAL OF NUCLEAR MEDICINE
TECHNOLOGY • Vol. 35 • No. 3 •
September 2007
Figure 3. Photograph of the prototypic volume CT scanner.
Gupta R et al. Radiographics 2008;28:2009-2022
В©2008 by Radiological Society of North America
Figure 2. Photograph of a prototypic flat-panel volume CT scanner, which is based on a
modification of a commercially available gantry (Sensation 16; Siemens Medical Solutions,
Forcheim, Germany).
Gupta R et al. Radiographics 2008;28:2009-2022
В©2008 by Radiological Society of North America
Figure 3. Miliary tuberculosis.
(a) Radiograph of the left lung shows diffuse 2–3-mm nodules, findings that are typically seen in miliary tuberculosis.
(b) High-resolution computed tomographic (CT) scan demonstrates similar
nodules in a random distribution.
•
http://radiographics.rsna.org/content/27/5/1255.full.pdf+html
Figure 4. Parenchymal postprimary tuberculosis.
Chest radiograph demonstrates the characteristic bilateral
upper lobe fibrosis associated with postprimary
tuberculosis.
Figure 5. Parenchymal postprimary tuberculosis.
High-resolution CT scan shows the typical apical cavitation
of postprimary tuberculosis.
Figure 6. Parenchymal postprimary tuberculosis.
High-resolution CT scan demonstrates multiple small,
centrilobular nodules connected to linear branching
opacities. This so-called tree-in-bud appearance is typically
seen in
Tree-in-bud
appearance
Figure 6. Parenchymal
postprimary tuberculosis.
High-resolution CT scan
demonstrates multiple
small, centrilobular
nodules connected to
linear branching
opacities.
This so-called tree-in-bud
appearance is typically
seen in postprimary
tuberculosis.
• Tree-in-bud appearance
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