Automatic exposure control (AEC)

Question 1

What is the function of AEC?

Answer 1

Measures the quantity of x-rays that reach the IR and terminates exposure when radiation intensity has been recieved

Question 2

How does AEC compensate for pt. size

Answer 2

By adjusting time

Question 3

When using AEC the technologist chooses __, __, __, _ on the operating console

Answer 3

1. kVP
2. mA
3. Back up time
4. Photocells

Question 4

Back up time should be __-__ times the expected mAs for the patinet

Answer 4

2-3 times

Question 5

Name the two types of AEC?

Answer 5

1. Ionization chamber

2. Photodiode

Question 6

Which AEC is

most common ?

Answer 6

Ionization chamber

Question 7

Describe the Ionization chamber AEC

Answer 7

1. It is a flat placed between the pt. and IR
2. // to IR
3. Must be radiolucent
4. Ionization causes a charge in the chamber , when enough charge has been reached, system terminates the beam

Question 8

Describe the Photodiode AEC

Answer 8

1. It is a solid state detector that converts light into electric current
2. Current flows in 1 direction that is opposite of the electrons
3. AKA: Rectifiers

Question 9

Why are photodiodes rectifiers?

Answer 9

because they conduct current in 1 direction

Question 10

What is the purpose of calibrating the AEC circuit

Answer 10

to produce the proper image density regardless of pt. size

Question 11

Phototimer is another name for?

Answer 11

Photocells

Question 12

When more than 1 cell is activated , which cell will contribute the greatest electrical signal and have the most influence on density

Answer 12

The cell receiving the most radiation

Question 13

Why is proper positioning important when using AEC?

Answer 13

• Because the cell is selected for anatomical location of the part of interest. If the parts not completely over the cell, the image could be too light or too dark

Question 14

Which cells would be chosen for KUB

Answer 14

All cells

Question 15

What is APR

Answer 15

Anatomically Programmed Radiography

Question 16

Describe APR

Answer 16

Anatomically Programmed Radiography
* IT is an electronic technique for pt. exposure control
-RT selects part to be imaged and Body habitus, OD
Microprocessor pre-selects kVp and mAs automatically

Question 17

___ acts as a timer for the x-ray circuit

Answer 17

AEC circuit

Question 18

Why are back up timers normally set?

Answer 18

In case the AEC fails to terminate

• Prevents damage to x-ray tube
• Prevents overexposure

Question 19

Regulations require that AEC have a __ mAs or ____ sec. safety override

Answer 19

1. 600 mAs

2. 6 second safety override

Question 20

What are advantages of AEC?

Answer 20

• Reproducability
• Less chance of repeats
• Nearly flawless images
• Less chance of over / underexposure

Question 21

What are the 2 most important things to remember when using AEC?

Answer 21

1. Choose the correct photocells

2. Proper positioning

Question 22

an electronic technique for pt. exposure control

Answer 22

APR ( anatomically programmed radiography)