2nd semester. physics AEC and exposure systems test 1

Question 1

advantages of a fixed KVP system-

7

Answer 1

1. ⬇️ pt dose
2. ⬆️info on image
3. ↔️ exposure latitude
4. ⬇️ tube wear
5. ⬇️ time settings= ⬇️ motion
6. consistency
7. easy to remember

Question 2

disadvantages of a fixed KVP system:

Answer 2

⬆️ scatter

⬇️ contrast which is less pleasing to the eye

Question 3

how much must we adjust our mAs to notice a difference?

Answer 3

30%

Question 4

what is the purpose of an exposure system?

Answer 4

to provide a method of consistency in the quality of image production

Question 5

true or false?

A fixed KVP system has many optimal KVP’s for different densities and contrasts.

Answer 5

true

Question 6

under what circumstances is an optimal KVP changed with a fixed KVP system?

Answer 6

when certain conditions have changed such as pathology or if acceptance limits are changed

Question 7

describe anatomically programmed systems:

Answer 7

they combine AEC with exposure factors to correspond to specific procedures.

can suggest technique or manually choose it

eliminates mAs selection

we still control ma. KVP. distance

Question 8

describe variable KVP exposure systems:

Answer 8

kilovoltage is varied depending on part thickness

a mAs value is specified for each body part

Question 9

disadvantages of variable KVP system:

Answer 9

have to measure for every image

decreased image contrast with higher KVP

Question 10

advantages of a variable KVP system:

Answer 10

allows small increments of change in exposure to compensate for variation in part thickness

Question 11

what is the purpose of ionization chambers:?

Answer 11

they measure the exposure to the receptor which eliminates the need for us to set an exposure time.

Question 12

what factors do we control with AEC systems ?

Answer 12

KVP, mA, backup time and density

Question 13

how can we determine configuration of AEC chambers?

Answer 13

take an exposure of the IR at low KVP for maximum contrast

Question 14

describe cell averaging :

Answer 14

an average between the chambers used determines the exposure time

Question 15

the cell receiving the most radiation contributes the ______.

Answer 15

most

cell dominance

Question 16

when should density control be applied :

Answer 16

when the patient or part cannot be properly positioned

Question 17

X-ray beam intensity can be altered by:

Answer 17

mA
exp time
KVP
filtration 
generator waveform

Question 18

why should tight collimation be avoided with AEC?

Answer 18

The selected chamber may think the tissue is very dense if it is collimated over….AEC time will increase and image will be overexposed

Question 19

what are 2 important aspects regarding timing in AEC?

Answer 19

minimum response time and back up time

Question 20

define minimum response time:

Answer 20

The length of time needed for AEC to respond to the ionization and send a signal to terminate the exposure

Question 21

in what situation would you decrease your MA to permit longer AEC time?

Answer 21

when you have a high-speed system and a small part

Question 22

what is the purpose of back up time?

Answer 22

it establishes the maximum exposure time for the system in order to prevent overexposure

Question 23

The backup timer should be set at ______percent of the anticipated minimal exposure time

Answer 23

150%

Question 24

when does undercutting occur?

Answer 24

when collimation is too wide and scatter is produced AEC will terminate the exposure while some areas are still underexposed

Question 25

basic KVP variable formula:

Answer 25

( 2 KVP X part cm) + ____ KVP = new KVP

for 3 phase: add 25 KVP