2. • Computed tomography (or
computerized axial tomography) is
an examination that uses X-ray and
computer to obtain a cross-
sectional images of the human
body.
3. • The first commercially viable CT scanner
was invented by Godfrey Newbold
Hounsfield in Hayes, England at Thorn
EMI Central Research Laboratories using
X-rays.
• Hounsfield conceived his idea in 1967,
and it was publicly announced in 1972.
5. The gantry assembly is the largest of these systems. It is
made up of all the equipment related to the patient,
including the patient support, the positioning couch, the
mechanical supports, and the scanner housing. It also
contains the heart of the CAT scanner, the x-ray tube, as
well as detectors that generate and detect x rays.
7. • Two types of detectors are used
• Scintillation Detectors
• Gas Filled Detectors
• Scintillation Detectors
• Materials Used
• Sodium Iodide
• Bismuth Germanium Oxide
• Cesium Iodide
• Cadmium Tungstate Scintillator
Crystal
Photo Multiplier
Detector
Rings
8. Gas Filled Detectors
• Materials Used
• Xenon
• Krypton
• Xenon + Krypton
Since 90% of 50 is 45, the output is same. The overall efficiency
of both the detectors is same.
Gas Filled Detectors Scintillation Detectors
Sensitive face: 100%
Detection Efficiency: 45%
Sensitive face: 50%
Detection Efficiency: 90%
9. • The DAS consists of the following parts
• X-ray photons come on the detector.
• The detector detects the intensity in form of current.
• The current is converted into voltage.
• The analog integrator removes spikes.
• The analog signal is converted into digital form.
• This signal can now be processed and reconstructed in
the computer.
Detector
Current to
Voltage
Convertor
Pre
Amplifier
Analog
Integrator
Analog to
Digital
Convertor
Computer
10. • After enough transmission measurements (detector)
• Sent to the computer for processing
• A software called Fourier Slice Transform is used.
• More than 250,000 reconstruction algorithms are used
(example: algebraic reconstruction technique) to compute
the image.
11. • The operating console is the master
control center of the CAT scanner.
• It is used to input all of the factors related to taking a
scan.
• Typically, this console is made up of a computer, a
keyboard, and multiple monitors.
• Often there are two different control consoles, one used
by the CAT scanner operator, and the other used by the
physician.
• The operator's console controls such variables as the
thickness of the imaged tissue slice, mechanical
movement of the patient couch, and other radiographic
technique factors.
12.
13. generation configuration detector beam Min scan time
first Translate -rotate 1-2 Pencil thin 2.5min
second Translate -rotate 3-52 Narrow fan 10sec
Third
Rotate- rotate 256-1000 Wide fan 0.5sec
fourth Rotate- fixed 600-4800 Wide fan 1sec
fifth Electron beam 1284 Wide fan
electron beam
33ns
Generations of CT scan
14. Advantages
First ,CT completely eliminates the
superimposition of images of structures outside
the area of interest.
Second, because of the inherent high-contrast
resolution of CT, differences between tissues
that differ in physical density by less than 1%
can be distinguished.
Third, data from a single CT imaging
procedure consisting of either multiple
contiguous or one helical scan can be viewed
as images in the axial, coronal, or sagittal
planes, depending on the diagnostic task. This
is referred to as multiplanar reformatted
imaging.
15. CT scanning is painless, non- invasive and
accurate.
A major advantage of CT is its ability to image bone,
soft tissue and blood vessels all at the same time.
Unlike conventional x-rays, CT scanning provides
very detailed images of many types of tissue as well
as the lungs, bones, and blood vessels.
CT examinations are fast and simple; in emergency
cases, they can reveal internal injuries and bleeding
quickly enough to help save lives.
CT has been shown to be a cost-effective imaging
tool for a wide range of clinical problems.
CT is less sensitive to patient movement than MRI.
Benefits Vs.
Risks
