Radiographic Doses

Question 1

what is the effect of using an alternating current on the overall dose.

compare this with the dose using a direct current that generates a constant potential

Answer 1

a constant potential/ direct current unit = keeps the kV at its PEAK as soon as you turn the machine on and throughout x-ray production= more efficient therefore

AND

direct current= eliminates filament warm up time = reduces dose from 260–> 170.

AND
direct current= more high energy useful x-ray photons are made and fewer low energy/ harmful x-rays are made.

Question 2

a direct current is better than an alternating current.

BUT what is the disadvantage of using direct current over alternating?

Answer 2

REDUCED contrast

Question 3

why are low energy photons bad?

Answer 3

they do not contribute to the final image and are may reach the pt and cause harm.

Question 4

what are the current regulations on the operating Kvp for optimal diagnosis potential?

Answer 4

60-70 kV

Question 5

what is the effect on dose by increasing kvp?

Answer 5

lowers the dose.

Question 6

what is the effect on contrast by increasing kvp?

Answer 6

reduces contrast

Question 7

what is the purpose of filtration?

Answer 7

remove all the low energy photons= optimise dose

Question 8

there is both inherent and added filtration. what is the legal regulation of filtration?

Answer 8

1. 5mm of Al for 70kv

2. 5mm of Al if above 70kv

Question 9

what is the downside of too much filtration?

Answer 9

increase exposure time= movement artefacts= degrade image

Question 10

what is a collimator/spacer cone? what shape is currently used

Answer 10

a colimator is put over the x-ray beam and it regulates the size of the beam. it used to be circular but now it is rectangle to match the size of the film. it is also open ended

Question 11

what is the effect of using a rectangle shaped collimator on the dose

Answer 11

it reduces the dose.

Question 12

focal spot to object distance (fsd) needs to be as long as possible. why

Answer 12

minimise magnification/ image distortion (but we are reducing the intensity of the x-ray beam)

Question 13

what is the minimum recommended fsd?

Answer 13

200mm if more than 60kv

100mm if less than 60kv

Question 14

for extra oral image receptors, which one reduces dose: the rare earth intensifying screens or calcium tungstate?

Answer 14

the rare earth intensifying screens

Question 15

how would technique for intra-orals effect the overall dose?

Answer 15

1. use film holder
2. reduce the reason for repeats
3. ensure the geometry is optimal

Question 16

what are the ‘diagnostic reference levels’ / DRL

Answer 16

national levels which are used to generate a graph. from the graph, the 3rd quartile tells you the reference your practise equipment should follow.

Question 17

what is the DRL for panoramic?

Answer 17

66.7 mGy

Question 18

what is the DRL for intra-orals?

Answer 18

1.8 mGy

Question 19

can lead aprons reduce dose in dentistry?

Answer 19

no, there is a scatter which cannot be stopped by the use of a lead apron

Question 20

2 bitewings are equivalent to how much background radiation?

Answer 20

8-16 hours

Question 21

1 panoramic is equivalent to how much background radiation?

Answer 21

2-5 DAYS

Question 22

the risk from radiation is related to AGE. if under 10, the risk factor increases by ….

Answer 22

x3.