Computer Tomography

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Computer Tomography
By Moustafa M. Mohamed
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Introduction to Medical Imaging
Uses of medical imaging
NON Invasive
Obtain information about internal body organs or
the skeleton to determine a patients physical
state.
Imaging Modalities
X-ray (plan , Dental, Panorama, Mammo, Angio,
) C.T Ultrasound MRI Gamma
Camera PET SPECT
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Types of image
1) Projections
2) Dimensional 3D 4D
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3) Slices

• Trans axial - plane normal to a vector from
  head to toe.
• Coronal - plane normal to a vector from front
  to back
• Sagittal - plane normal to a vector from left
  to right.
• Oblique - a slice that is not (at least
  approximately) one of the above.

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Principles of X-ray tube
Target (tungsten)
High Voltage supply
Filament
Glass envelope
Anode connection kV

Filament connection
Anode
Focussing cup
Focal Area
Window
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Tomography
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CT Scan

• CAT Scan ---- Computerized Axial Tomography

• CT Scan ---- Computed Tomography

• Produce thin cross-sectional images

• Non-traumatic radiographic technique

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CT Scan
Based on Reconstruction of a tomographic plane of
the body (a slice) from a large number of
collected x-ray absorption measurements taken
during a scan around the bodys periphery.
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Image Reconstruction
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Image Reconstruction
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CT Generations

• 4 Generations

• Based on Tube / Detector setting

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First generation CT-scanner Translate Rotate
Translation
Rotation

• Single Detector Cell
• First Translation then Rotation.

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Second generation CT-scanner Translate Rotate

• Array of Detector Cell ( e.g. 20)
• First Translation then Rotation.
• Scan Time could be reduced to 1/10

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Third generation CT-scanner Rotate Rotate
Rotation movement

• Array of Detector Cell ( e.g. 896)
• NO Translation movement.
• Scan Time Reduced.

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Fourth generation CT-scanner
Tube rotates, Detector is stationary (full ring
of detectors)
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Fifth generation CT-scanner
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Gantry
Consol
Patient Couch
Control Unit
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TUBE
CT Scan General Block Diagram
DAS
Pre-Proc
DETECTOR
Reconstructor
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Tilting (/-20 to /-30)
Emergency Stop
Positioning Lights
Operator Controls
SLIDE
HEIGHT
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Gantry (X-ray path)
Collimator
T
metal plate with a hole Limit x-ray beam
Wedge
Limit x-ray beam Prevent detector overflow
Slit
X-ray beam
defines the slice thickness
Beamtrimmer
Detector
Detector
Limit x-ray beam Used for thin slices (1 3 mm)
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Data Transfer from DAS to Console
In non-continuous rotating system the data is
transferred from the DAS to the Console via
parallel cable.
D.A.S.
CONSOLE
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Data Transfer from DAS to Console

• In continuous rotating system the DAS data is
• converted from parallel to serial,
• transferred (via slipring or optical)
• converted back from serial to parallel.

D.A.S.
Parallel to Serial
Serial to Parallel
CONSOLE
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