Basic principles of CT scanning

• Basic theory of CT 

1.  - What's inside the gantry ? 
2.  - Data acquisition
3.  - Image reconstruction

• Variations is scanner design

1.   - Generation
2.   - Detector type
3.   - Number of Projections and detectors 
4.   - Slip-ring scanning 

basics of CT scanning

basic principles of CT scanning

back projection

ct scanning

filtered back projection

filtered back projection

filtered back projection

 

filtered back projection
ct scanning

re-binning fan beam data

Data transmission and power cables in old scanners meant start - stop rotation
Change of direction at end of rotation to rewind, then unwind cables
Series of images acquired by rotating clockwise and anti-clockwise for subsequent scans
scan times as fast as ~1 s 

Stop-start gantry

Slip rings introduced in 1990 allowed continuous rotation
Power and signals transmitted to rotating gantry using ‘brushes’ on static rings
no need to start and stop rotation
scan times as fast as 0.3 s

Slip rings

Faster conventional axial scanning

Inter-scan delay governed only by time taken for table to move to new position (~ 1 s)

Continuous rotation allows:

Continuous imaging (Real time CT, CT Fluoroscopy)

Helical scanning
Continuous movement of the patient through the gantry while imaging
Eliminates the irradiate – move patient – irradiate etc cycle of sequential imaging