Download RAD 254 Computed Tomography

RAD 254 –Chapt 23 Mulitslice 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.
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
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
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!)
Major components of CT
• Gantry – tube-receptor array, collimators (prepatient 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)
Spiral CT
Sprial
Helical
16 slice
Slip Ring CT
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
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
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
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
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
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