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RAD 354 Chapt. 23 Multi-slice CT In short – CT is a thin band (fan) of radiation directed toward the pt. and the remnant radiation emitted from the pt.

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Presentation on theme: "RAD 354 Chapt. 23 Multi-slice CT In short – CT is a thin band (fan) of radiation directed toward the pt. and the remnant radiation emitted from the pt."— Presentation transcript:

1 RAD 354 Chapt. 23 Multi-slice CT In short – CT is a thin band (fan) of radiation directed toward the pt. and the remnant radiation emitted from the pt. is measured by a receptor and the response transmitted to a computer for reconstruction of the image(s)

2 “Slip rings”

3 Dates/Activities to Remember 1970 – Sir Godfrey Hounsfield,Ph.D.., demonstrated the technique of CT scanning – “EMI” head unit

4 Dates/Activities Con’t Dr. Hounsfield and Dr. Alan Cormack share the Nobel Peace Prize in physics CT Generations and important items: – 1 st – translate-rotate; “pencil beam” - one full rotation for 1 image; head only; 5 min. per image! – 2 nd – translate-rotate, but with a “fan” beam; produced INCREASED INTENSITY at the edge of the beam – “bow-tie” filter used to remedy this; 30 sec. image time

5 Generations con’t. – 3 rd – used ARRAY of DETECTORS – produced “ring artifacts” – 4 th rotate – stationary, fan beam, detector array; short image time and NO re-con time! – 5 th is NOW here! “Spiral/slip ring” (It is slip ring technology that has enabled this latest generation!)

6 Major Components of CT Gantry – tube-receptor array, collimators (pre- pt. and pre-detector), generator, pt. couch Computer – microprocessor – recon time was a BIG issue until recently Operating console – usually two monitors – one for RIS/HIS and the second for the imaging portion (often times a “remote” monitor is set up at the radiologist’s desk – can really be a hassle)

7 Radiation Dose Comparisons

8 Current – 5 th Generation Terms Spiral Helical 16/32/64 slice Slip Rings CT

9 Interpolation/Extrapolation Interpolation – information ALONG the axis WITHIN established values Extrapolation – information OUTSIDE axis values established, BUT an ESTIMATED value based upon previously measured parameters IF they continue

10 “Spiral” Terms Pitch – relationship between couch movement and x- ray beam collimation (pitch ratio) – Increasing pitch ratio enables much MORE of the pt. to be imaged in ONE BREATH HOLD! Breath holds = misrepresentation of the images. Slip ring technology made “spiral CT” possible 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 portion – Transfer of digital data from gantry receptors to the computer

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

12 Spiral/slip ring

13 Tube (fan beam)/receptors

14 Z-axis

15 Maximum Intensity Projection (MIP) Pre selecting pixel levels to be viewed AFTER obtaining a “rubic’s cube of information” – Then only exhibit those at the PRE-DETERMINED value – like an MRA or CTA

16 Spiral Advantages of Conventional CT Motion blur is reduced – fewer artifacts Lowered imaging time (fewer breath holds required = less motion and less mis- representation) Larger volumes can be imaged with LESS part overlap artifacts


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