AEC

Question 1

History of AEC

Answer 1

1942

Russell Morgan

Question 2

Definition from Bushong

Answer 2

A device that measures the quantity of radiation reaching the IR and automatically terminates the exposure when the IR has received the required radiation intensity.

Question 3

Sterling defines AEC

Answer 3

Radiographic density control device that terminates the exposure when a predetermined amount of radiation has been reached. The AEC is an automatic electronic timing device that replaces the conventional exposure timer.

Question 4

What is the legacy term for AEC

Answer 4

Photo timer

Question 5

What do the definitions refer to this exposure control, to be associated with?

Answer 5

The density or quantity of radiation reaching the IR.

Question 6

How are we controlling the quantity of radiation reaching the IR

Answer 6

By controlling our exposure time.

Question 7

AEC is only as good as? And requires?

Answer 7

The skill of the operator and requires a special understanding on the part of the RT

Question 8

2 purposes of AEC

Answer 8

1. To control the quantity of radiation reaching the IR

2. To consistently achieve properly exposed images, regardless of patient’s size, pathology, etc

Question 9

Advantages over Fixed Time Technique 3

Answer 9

1. Reduces repeats by producing radiographs with proper exposure to the IR
2. Consistent images on all patients
3. Consistency on comparison images of the same patient

Question 10

3 types of AEC

Answer 10

1. photodiode Detector Assembly (less common)
2. Ionization Chamber (more common)
3. Solid State Radiation Detector

Question 11

Photodiode detector assembly

Answer 11

Light sensor located behind the cassette (requires special IR)

Question 12

How does a photodiode detector assembly work?

Answer 12

Radiation is transmitted through the patient and IR to the sensor screen (covered with a phosphor) causing it to fluoresce. The light is picked up by the detector and an electric current is generated in direct proportion to the xRay exposure. The current is fed to an electronic device that terminates the exposure when the proper level of radiation has been reached.

Question 13

Disadvantage of photodiode detector assembly

Answer 13

Can be over sensitive in the 50-60 kVp range

Question 14

How does the ionization chamber control the length of the exposure time

Answer 14

Uses radiation

Question 15

Describe the location of the ionization chamber

Answer 15

Located in front of the Bucky

It’s radiolucent

Question 16

How does the ionization chamber work

Answer 16

A gas is ionized by radiation passing through the chamber. Ionization within the chamber produces a charge that terminates the exposure when a preset level/ charge has been reached.

Question 17

A disadvantage of AEC Ionization Chamber

Answer 17

Can be over sensitive in lower kVp ranges i.e. Mammo.

Question 18

Solid state radiation detectors are used for

Answer 18

Exposure-timer checks

Question 19

Minimum Response Time

Answer 19

The shortest exposure time that the AEC can produce or control. If the minimum response time is greater than the actual time needed for a particular part, the image will be over exposed. Our MA should be low enough so that the exposure time utilized will be longer than the minimum response time.

Question 20

Back-up Time

Answer 20

The maximum permissible exposure time that can be achieved before the exposure circuit is terminated.

Question 21

Why is back up time a safety feature

Answer 21

It limits the maximum exposure possible in case of operator error or equipment failure

Question 22

What should the back up MAS be set at

Answer 22

1.5 times The mAs expected for the part being imaged

Question 23

Regulations require that AEC’s have what

Answer 23

A 600 mAs safety override.

Question 24

Technique considerations re: mA and kVp

Answer 24

The kVp should be at the appropriate level for the part being radiographed

Question 25

Technique considerations re: centering

Answer 25

Centering is crucial, as is proper photocell selection.

Question 26

Technique considerations re: photocells

Answer 26

Photocells can be used individually or in combination with each other. When more than one cell is selected, the electrical charges or averaged, and is the resultant density on the radiograph.

Question 27

Density settings are sometimes called

Answer 27

Density override

Question 28

Density settings are used for

Answer 28

Overriding the AEC for pathologies, or when and increase or decrease in density is required.

Question 29

Technique considerations re: AEC calibrating

Answer 29

AEC must be calibrated for the IR speed in use.

Question 30

With our 400 speed rare earth, we should consider keeping our mA....

Answer 30

Relatively low, so that we avoid minimum response time problems.

Question 31

With photodiode AEC's which use a fluorescent screen, what do we need to remember

Answer 31

Our screens should match the output phosphor. This is called spectral matching.

Question 32

Technique considerations re: collimation

Answer 32

Proper collimation is required to prevent the premature termination of our exposure from scatter.

Question 33

Tech nique charts are recommended and should include

Answer 33

``` mA kVp Backup time Sensor selection OD setting ```

Question 34

4 common errors or problems with AEC's

Answer 34

1. Activating the wrong sensor. 2. Activating the table Bucky instead of the vertical Bucky for an upright exam 3. . Use of AEC with cross table work 4. Improper use of lead over photocell

Question 35

What happens if you activate the table Bucky instead of the chessboard for a chest exam

Answer 35

Generally, you will end up with an over-exposed image here, as the table was waiting for a signal that it never received, so the maximum time was used or mAs.

Question 36

What problem could you have if you use AEC with crosstable work

Answer 36

Quanta reset will always go off. If the fixed time technique selected was appropriate, the image should be OK. The photocell just never received the signal it was waiting for.

Question 37

Oblique ribs upper, use---kVp

Answer 37

Higher

Question 38

Oblique ribs upper. Use --- kVp

Answer 38

Lower

Question 39

APR aka

Answer 39

Anatomically Programmed Radiology | Auto pilot

Question 40

If your 0.03 out of range, what do u do?

Answer 40

1/2 the mAs

Question 41

Reciprocity law

Answer 41

As mA decreases, time increases You can decrease the mA to force the machine to use a longer time