2nd semester. physics AEC and exposure systems test 1 Flashcards
advantages of a fixed KVP system-
7
- ⬇️ pt dose
- ⬆️info on image
- ↔️ exposure latitude
- ⬇️ tube wear
- ⬇️ time settings= ⬇️ motion
- consistency
- easy to remember
disadvantages of a fixed KVP system:
⬆️ scatter
⬇️ contrast which is less pleasing to the eye
how much must we adjust our mAs to notice a difference?
30%
what is the purpose of an exposure system?
to provide a method of consistency in the quality of image production
true or false?
A fixed KVP system has many optimal KVP’s for different densities and contrasts.
true
under what circumstances is an optimal KVP changed with a fixed KVP system?
when certain conditions have changed such as pathology or if acceptance limits are changed
describe anatomically programmed systems:
they combine AEC with exposure factors to correspond to specific procedures.
can suggest technique or manually choose it
eliminates mAs selection
we still control ma. KVP. distance
describe variable KVP exposure systems:
kilovoltage is varied depending on part thickness
a mAs value is specified for each body part
disadvantages of variable KVP system:
have to measure for every image
decreased image contrast with higher KVP
advantages of a variable KVP system:
allows small increments of change in exposure to compensate for variation in part thickness
what is the purpose of ionization chambers:?
they measure the exposure to the receptor which eliminates the need for us to set an exposure time.
what factors do we control with AEC systems ?
KVP, mA, backup time and density
how can we determine configuration of AEC chambers?
take an exposure of the IR at low KVP for maximum contrast
describe cell averaging :
an average between the chambers used determines the exposure time
the cell receiving the most radiation contributes the ______.
most
cell dominance
when should density control be applied :
when the patient or part cannot be properly positioned
X-ray beam intensity can be altered by:
mA exp time KVP filtration generator waveform
why should tight collimation be avoided with AEC?
The selected chamber may think the tissue is very dense if it is collimated over….AEC time will increase and image will be overexposed
what are 2 important aspects regarding timing in AEC?
minimum response time and back up time
define minimum response time:
The length of time needed for AEC to respond to the ionization and send a signal to terminate the exposure
in what situation would you decrease your MA to permit longer AEC time?
when you have a high-speed system and a small part
what is the purpose of back up time?
it establishes the maximum exposure time for the system in order to prevent overexposure
The backup timer should be set at ______percent of the anticipated minimal exposure time
150%
when does undercutting occur?
when collimation is too wide and scatter is produced AEC will terminate the exposure while some areas are still underexposed
basic KVP variable formula:
( 2 KVP X part cm) + ____ KVP = new KVP
for 3 phase: add 25 KVP
