Img Aec Automatic Exposure Control System

Front 1

what are the 2 parts of the AEC?

Back 1

• Detector
• Comparator

Front 2

What is the Function of AEC Systems

Back 2

to monitor the amount of radiation reaching
the image receptor, and to terminate the
exposure at a preset level
normally measure product of intensity (I) and
time (t)

Front 3

Ionisation chamber measures radiation exposure ____ it reaches the image receptor

Back 3

before

Front 4

Photo-timers/Scintillator Counters are exit-type devices, meaning,

Back 4

they measure radiation exposure after it passes through cassette

Front 5

where is the Photo-timers/Scintillator Counters commonly found?

Back 5

Commonly found in
fluoroscopic units

Front 6

What type of external mode is this?

Back 6

side on

Front 7

What type of external mode is this?

Back 7

head on

Front 8

Spectral sensitivity of
photocathode MUST match
wavelength of light from
scintillator crystal for optimal
conversion

Back 8

Only 10-30% of photons
cause emission of electrons

Front 9

) As radiation passes
through the chamber,
the gas becomes
____. Ion-pairs form.
Negative electrons flow
to the _____. Current
generated.

Back 9

ionised; anode

Front 10

Study

Back 10

study

Front 11

difference between ion chamber & fluorescent screen

Back 11

ion chamber & fluorescent screen

Front 12

where is the detector placed?

Back 12

Placed between patient and
film

Front 13

advantages of detector

Back 13

• Allows actual mAs used to be displayed immediately after
exposure
• Allows radiographer to become more familiar with manual
exposure techniques
• Use it to verify exposure charts in department
• If image is suboptimal, allows of adjustment of exposure
using manual technique

Front 14

what is Minimum Response Time (M.R.T.)?

Back 14

• the length of time necessary for the AEC to respond to the
ionisation & send a signal to terminate the exposure.
• Between 3 – 30 milliseconds may elapse before all the
electronics & relays actually stop the exposure.

Front 15

what are Guard/Backup timers?

Back 15

• all AEC devices are fitted with a guard timer
• A safety device which prevents the patient from receiving an
excessive dose of radiation should the automatic timer fail due to
mechanical or operator errors.
• These terminate exposures that exceed 600mAs above 50kVp, and
2000mAs at lower potentials.

Front 16

for density settings:

Back 16

-2: 50% decrease in density from 0 (Neutral)
-1: 25% decrease in density
+1: 25% increase in density
+2: 50% increase in density

Front 17

the dominant zone is where ________.

Back 17

Positioning where a specific patient part (ROI)
should be placed over the detectors

Front 18

If the sensor is under a body part for which k is
incorrect, then an over or ______-exposure will result

Back 18

under

Front 19

one of the largest sources of error in using AEC devices is ____.

Back 19

poor positioning

Front 20

Sufficient collimation demonstrates that as you increase the amount of
collimation and shielding, the amount of scattered radiation
reaching the detector _____, resulting in a darker
diagnostic radiograph.

Back 20

decreases