1. RAD 254 –Chapt 23 Mulit-slice Computed Tomography
In short – CT is a thin band (fan) of radiation directed toward the patient and the remnant radiation emitted from the patient is measured by a receptor and the response transmitted to a computer.

2. Dates/activities to remember
1970 Dr. Godfrey Hounsfield demonstrated the technique – “EMI” unit
1982 – Dr. Hounsfield and Dr. Alan Cormack share the Nobel Peace Prize in physics

3. CT Generations and important items
1st – translate-rotate – pencil beam – one rotation for 1 image – Head only – 5 min/image
2nd – translate-rotate, but with a fan beam – produced increased intensiity at the edge of the beam – “bow-tie” filter used to remedy this. 30 sec image time

4. Generations con’t
3rd used array of detectors - produced “ring artifacts”
4th rotate – stationary, fan beam, detector array, short image time and no re-con time
5th Is now here! “spiral/slip ring” (it is slip ring technology that has enabled this latest generation!)

5. Major components of CT
Gantry – tube-receptor array, collimators (pre-patient and pre-detector), generator, patient couch
Computer – microprocessor – recon time a big issue until recently
Operating console – usually two monitors – one for RIS/HIS information and the second for the imaging portion (often times a remote monitor is set up for the radiologist – can be a hassle)

9. Sprial Helical 16 slice Slip Ring CT
Spiral CT
Sprial
Helical
16 slice
Slip Ring CT

10. Interpolation Algorithms
Interpolation – information along the axis within established values
Extrapolation – information outside axis values established, but an estimated value if parameters continue as previously meassured

11. Spiral Terms
Pitch – (pitch ratio) relationship between couch movement and x-ray beam collimation
Increasing pitch ratio enables much more of the patient to be imaged in one breath hold

12. Slip Ring Technology (Made spiral possible – like brushes on s starter motor)
Three slip rings in the gantry (usually)
One for hi voltage power to the tube and hi voltage generator
Low voltage power to the rotating gantry
Transfer of digital data from gantry receptors

13. Multi slice CT Multi detector arrays
Two at once with one beam = two slices per 360 degrees
With “spiral” enable two detectors to produce 16 slices
Envision a person on the table/couch in a screw/nut fashion going through the gantry

14. Maximum Intensity Projection
Pre selecting pixel levels to be viewed AFTER obtaining a “rubic’s cube of information”
Then exhibit only those at the pre-determined value – like MRA/CTA

15. Spiral Advantages over Conventional
Motion blur is reduced/fewer artifacts
Lowered imaging time (fewer breath holds required/less motion/miss-representation)
Larger volumes can be imaged with less part overlap artifacts