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 detector located?

Answer 3

After the grid and before the IR

Question 4

Why can’t we have the detector outlines on the table?

Answer 4

Because the table floats

Question 5

What object will recieve the same amount of radiation regardless?

Answer 5

Detector

Question 6

What things does AEC compensate for?

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

Answer 6

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

Question 7

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

Answer 7

Only kVp

Question 8

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

Answer 8

1. kVp
2. mA

Question 9

What does the central ray always line up with?

Answer 9

The center detector

Question 10

What happens when we select more than one detector?

Answer 10

The system averages out the exposure

Question 11

What are the two goals of the detector?

Answer 11

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

Question 12

What are the 3 types of detectors?

Answer 12

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

Question 13

What is the ion chamber made of?

Answer 13

Gas atoms

Question 14

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

Answer 14

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 15

With larger objects, how would AEC compensate?

Answer 15

1. Increase in time

More absorption would take place, so less RR

Question 16

When would you use the center detector on its own?

Answer 16

For long bones and lateral chest

Question 17

When would you use the lateral/outside detectors?

Answer 17

Chest (concerned with lungs)

Question 18

When would we use all 3 detectors?

Answer 18

Abdominal work

Question 19

For all of the x ray radiographs, describe what would happen to the mAs, DI, and mAs with centering given.

Answer 19

DO IT DO IT DO IT

Question 20

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

Answer 20

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 21

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

Answer 21

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 22

What is the minumum response time for the system?

Answer 22

5ms

Question 23

Define MRT:

Answer 23

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

Question 24

What would we do if MRT is an issue?

Answer 24

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

Question 25

What is the back up time used for?

Answer 25

1. System faliure
2. Technologist faliure

Question 26

What is the purpose of the back up time?

two

Answer 26

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

Question 27

What is the personal MRT?

Answer 27

2 seconds

Question 28

What is the BT rule of thumb for AEC?

Answer 28

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