Download First generation CT

Computer
Tomography
By
Moustafa M. Mohamed
Introduction to Medical Imaging
Uses of medical imaging
NON Invasive
Obtain information about internal body
organs or the skeleton to determine a patient’s
physical state.
Imaging Modalities:
* X-ray (plan , Dental, Panorama, Mammo, Angio, …)
* C.T
* Ultrasound
* MRI
* Gamma Camera
* PET SPECT
Types of image
1) Projections
2) Dimensional
3D & 4D
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.
Principles of X-ray tube
High Voltage
supply
Filament
Glass
envelope
+
Filament
connection
Focussing
cup
Target
(tungsten)
Anode
connection
+ kV
Anode
Focal
Area
Window
• CAT Scan ---- Computerized Axial Tomography
• CT Scan ---- Computed Tomography
• Produce thin cross-sectional images
• Non-traumatic radiographic technique
Based on Reconstruction of a tomographic plane of
the body (a slice) from a large number of collected xray absorption measurements taken during a scan
around the body’s periphery.
Image Reconstruction
X-ray
tube
Detector
Array
Detector cell
Image Reconstruction
CT Generations
• 4 Generations
• Based on Tube / Detector setting
First generation CT-scanner
“Translate – Rotate”
Translation
Rotation
• Single Detector Cell
• First Translation then Rotation.
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
Third generation CT-scanner
“Rotate – Rotate”
• Array of Detector Cell ( e.g. 896)
• NO Translation movement.
• Scan Time Reduced.
Fourth generation CT-scanner
Tube rotates, Detector is stationary (full ring of detectors)
Fifth generation CT-scanner
Main Component of CT scan
Gantry
Consol
Control Unit
Patient Couch
TUBE
CT Scan
General Block Diagram
Pre-Proc
DAS
DETECTOR
Reconstructor
Tilting (+/-20 to +/-30)
Positioning Lights
Operator
Controls
HEIGHT
Gantry (X-ray path)
Collimator
T
TUBE
metal plate with a hole
Limit x-ray beam
Wedge
Limit x-ray beam
Prevent detector overflow
X-ray
beam
Slit
defines the slice thickness
Beamtrimmer
Detector
Detector
Limit x-ray beam
Used for thin slices (1 – 3 mm)
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
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