AEC
eliminates need for for tech to select exposure time and result mAs.
technologist selects?
mA, kVp, detector combinations and sensitivity ( to match patient anatomy with detectors)
technologist loses the ability to set?
Time
When using AEC, the radiographer is responsible for determining
accurate positioning ( very important )
AEC introduced by
Russell H. Morgan
earliest version used photomultiplier tubes (year)
1942
AEC / photomultiplier commonly referred to as
phototiming, in practice
Modern equipment uses ionization chambers designed to improve consistency of image quality
automatic exposure detection (AED)
AEC exposures will produce diagnostic quality results when a radiographer ?
poses good positioning skills
Will result in increased repeat rate when using AEC's
Poor positioning skills
all 3 detectors selected barium located over one of the chambers penetration occurring only at other twi sensors resulting in
image slightly over exposed
only one detector activated barium located over detector little penetration occurring results in
image overexposed ( greatly overexposed )
backup time
150% of exposure time
what does backup time do
protects patient and X-ray tube
when working above 50 kvp law requires automatic termination at?
600 mAs
minimum response time exposure time require for detector to sense radiation terminate exposure.
typically 0.001 seconds or 1/1000 seconds
what errors can occur when using tight collimation
detector chamber clipping
collimation within activated chamber will result ?
overexposed image ( increased IR exposure)
in AEC inadequate collimation may result in?
light image (increased scatter)
computerized exposure system use AEC capabilities provide
exposure techniques based upon body parts
high contrast image of AEC detectors to conform?
locations and sizes
operational amplifier
receives and averages signal from each chamber.
terminates exposure once signals intensity is achieved appropriate voltage for quality is reached.
operational amplifier
modern equipment uses ionization chambers too???
improve consistency of image quality
image receptor exposure controls
permits adjustments of detector sensitivity
exposure control scale manufactures
-3, -2, -1, 0, +1, +2, +3
exposure control scale "increments" indicate ??
% of chance
-3, -2, -1, 0, +1, +2, +3
"0" value indicates what?
detector neutrality/ normal density
should receptor exposure control be used to compensate for changes in part thickness?
No, AEC does this automatically
exposure technique charts are used
for proper AEC usage
when not enough structure of interest is positioned over the activated ionization chamber, the AEC cell will attempt to
produce a ???
diagnostic quality exposure for whatever its over