12. AEC

Question 1

What is the defenition of AEC?

Answer 1

Terminates the exposure when the IR recieves the proper amount of radiation (mAs) and measures the RR.

Question 2

When do we use AEC?

Answer 2

When doing bucky work and with larger body parts

Question 3

Where is the AEC detector located?

Answer 3

After the grid and before the IR

Question 4

What things does AEC compensate for?

(To produce the same mAs and relatively same DI value)

Answer 4

1. SID
2. Body thickness
3. Desired mA
4. kVp
5. Laterally decentering the tube

Question 5

What techniques can we select for falling load generators with AEC?

Answer 5

Only kVp

Question 6

What techniques can we select for most x ray generators with AEC?

Answer 6

1. kVp
2. mA

Question 7

What happens when we select more than one AEC detector?

Answer 7

The system averages out the exposure

Question 8

What are the two goals of the detector?

Answer 8

1. Consistent exposure/I to IR
2. Less repeats/patient expsosure

Question 9

What are the 3 types of detectors?

Answer 9

1. Ion chambers
2. Solid state detectors
3. Photomultiplier tubes (not ussually used)

Question 10

What is the ion chamber made of?

Answer 10

Gas atoms

Question 11

What happens to the detectors (ionization chambers) during an exposure?

Answer 11

1. X rays ionize gas atoms which make free e-
2. The e- strike a positive anode plate
3. A current is created
4. Once a certian change has been created with current, exposure is terminated

Question 12

With larger objects, how would AEC compensate?

Answer 12

1. Increase in time

More absorption would take place, so less RR

Question 13

When would you use the center detector on its own?

Answer 13

For long bones and lateral chest

Question 14

When would you use the lateral/outside detectors?

Answer 14

Chest (concerned with lungs)

Question 15

When would we use all 3 detectors?

Answer 15

Abdominal work

Question 16

What happens if your detector is sup. to the point where you should be centered using AEC?

Answer 16

1. The IR would see more readiation per time, so AEC would shorten time
2. mAs would be lower
3. The DI value would be too low

Question 17

What woudl happen if you have a larger field size than needed when using AEC?

Answer 17

1. More scatter
2. Detector sees more radiation so the time would be shortened
3. The mAs would be too low
4. The DI value would be too low

Question 18

What is the minumum response time for the system?

Answer 18

5ms

Question 19

Define MRT:

Answer 19

The shortest poosible exposure time we can get with any exposure using AEC

Question 20

What would we do if MRT is an issue?

Answer 20

1. Use a lower mA
2. Use a fixed technique

Question 21

What is the back up time used for?

Answer 21

1. System faliure
2. Technologist faliure

Question 22

What is the purpose of the back up time?

two

Answer 22

1. So we don’t overexpose our patient
2. To prevent tube wear (overload)

Question 23

What is the back up time?

Answer 23

2 seconds

Question 24

What is the BT rule of thumb for AEC?

Answer 24

Choose a back up time of 1.5-2x the expected /fixed exposure time, or mAs