optimisation in radiography e lec

Question 1

what are the three principles of radiation protection

Answer 1

justification
optimisation
limitation

Question 2

how to reduce dose

Answer 2

is called optimisation- this happens by
selection criteria 
avoiding lapses in quality assurance 
unnecessary duplication of x rays  
equipment and technique factors

Question 3

what is the x ray tube made up from

Answer 3

sealed glass envelope
vacuum
anode(copper) with tungsten inset
cathode filament of tungsten wire

Question 4

where do electrons move

Answer 4

from negative to positive

Question 5

what is the mains supply to the x ray tube

Answer 5

240 volts

Question 6

how do we generate an x ray

Answer 6

we can generate a high potential difference kV to accelerate electrons across the x ray tube using a step up transformer
we can also provide low current to heat up the tube filament using a step down transformer

Question 7

why is a low current needed

Answer 7

to heat up the tube filament

Question 8

what is the low current caused by

Answer 8

by a step down transformer

Question 9

how can we make this more efficient

Answer 9

constant potential or DC unit

Question 10

what is the advantages of using a constant potential

Answer 10

keeps the KV at its peak throughout exposure
more high energy useful x rays produced 
fewer low energy useless x rays produced
shorter exposure time
eliminates the filament warm up time
reduces dose by 0.8

Question 11

what is the disadvantage of a constant potential

Answer 11

decreased contrast

Question 12

what is the effect on dose altering kvp

Answer 12

at a lower dose the photoelectric effect predominates which is pure absorption
lower energy electrons produced which may reach the patient
by increasing the KVP from 50 to 65, it can reduce thr effective dose by half

Question 13

what happens at a lower dose

Answer 13

the photoelectric effect predominates which is pure absorption

Question 14

what tube potential do we use for intraoral radiography tube

Answer 14

no lower than 50 kV

Question 15

what do we do if the tube potential is under 45 kV

Answer 15

withdrawn immediately

Question 16

what should the potential of new equipment be

Answer 16

60-70 kV

Question 17

what haooens when the kV is increased

Answer 17

it reduces the dose to the patient

Question 18

what happens to the film in low kV

Answer 18

a very contrasty film

Question 19

what type of filtration do we have

Answer 19

inherent and added

Question 20

how much aluminium do we need for 70 kv

Answer 20

1.55mm

Question 21

what should be the length of aluminium above 70kV

Answer 21

2.5mm of which 1.5mm should be permanent

Question 22

what happens if you add too much filtration

Answer 22

then the exposure times get too long

Question 23

what does collimation do

Answer 23

shapes and limits the size of the beam

Question 24

what can we use as a collimater

Answer 24

metal disc or cylinder

Question 25

what was previously recommended as a collimater

Answer 25

circular and as 6cm

Question 26

what do we now use as a collimatar

Answer 26

size 2 film rectangular collimation

Question 27

what happens to the dose when you use a rectangular collimater instead of a circular

Answer 27

you can half the dose

Question 28

what is the spacer cone length

Answer 28

dose follows the inverse square law

Question 29

what does the intensity equal

Answer 29

1/d2 where d is the distance

Question 30

how do we reduce magnification

Answer 30

we can reduce magnification by the focal spot to object distance to be as long as possible- but the x ray beam intensity reduces

Question 31

what is the long cone paralleling technique

Answer 31

produces images with minimal distortion

Question 32

what is the minimum focus to skin distance if greater than 60kV

Answer 32

20cm

Question 33

what is the focus to skin distance if it is less than 60kV

Answer 33

10cm minimum

Question 34

what happens to the dose when you have a short cone

Answer 34

if you are greater than 60kV and a short cone it increases the dose by 1.5

Question 35

which spacer cone shape is better

Answer 35

the open ended cone is better than the pointer cone

Question 36

which is the fastest conventional film for intraoral

Answer 36

F speed

Question 37

how much faster is E speed from D speed

Answer 37

twice as fast

Question 38

how much % decrease is digital image receptors

Answer 38

dose reductions of upto 90% but usually in comparison of D speed

Question 39

how much is rare earth intensifying screens reduce dosage in extraoral image receptors

Answer 39

REDUCED BY 50% compared with calcium tungstate

Question 40

what do we use for intra oral x rays

Answer 40

film holders

Question 41

what is the adv of film holders

Answer 41

reduces retakes more reproducible the projection geometry was optimal

Question 42

what is recommended with the panoramic technique

Answer 42

field trimming and sectional option

Question 43

what are diagnostic reference levels

Answer 43

national levels which you can compare equipment on | may have ti set your own standards

Question 44

what is the achievable dose

Answer 44

intraoral radiography 1.8mG on a 70kV with E speed film

Question 45

what is the diagnostic reference level of panoramic x ray

Answer 45

66.7mGy/mm

Question 46

what do we do if we operating at or above the diagnostic reference level

Answer 46

withdraw ASAP doesn't matter about operating kV

Question 47

what do we do if we operating 2x above diagnostic reference level

Answer 47

withdraw immediately doesn't matter about operating kV

Question 48

what is the equivalent background radiation of 2 bitewings

Answer 48

8-16 hrs

Question 49

what is the equivalent background radiation of panoramic

Answer 49

2-5 days

Question 50

what is the equivalent background radiation of the skull

Answer 50

40 hours

Question 51

what is the equivalent background radiation of barium meal

Answer 51

15 months

Question 52

what is the effective dose in microSv for intraoral radiograph

Answer 52

1-8.3 microSv

Question 53

what is the effective dose in microSv for anterior maxillary occlusal

Answer 53

8 microSv

Question 54

what is the effective dose in microSv for panoramic

Answer 54

3.85-30 microSv

Question 55

what is the effective dose in microSv for lateral cephalometric radiograph

Answer 55

2-3 microSv

Question 56

what is the effective dose in microSv for cross sectional tomography

Answer 56

1-189 microSv

Question 57

what is the risk of fatal cancer from a intraoral radiograph

Answer 57

0.02-0.6 per million

Question 58

what is the risk of fatal cancer from a panoramic

Answer 58

0.21-1.9 per million

Question 59

what is the risk of fatal cancer from a anterior maxillary occlusal

Answer 59

0.4 per million

Question 60

what is the risk of fatal cancer from a lateral cephalometric radiograph

Answer 60

0.34 per million

Question 61

what is the risk of fatal cancer from a cross sectional tomography

Answer 61

1-14 per million

Question 62

what is the risk in relation to age under 10

Answer 62

multiplication factor for risk is x3

Question 63

what is the risk in relation to age 10-20

Answer 63

multiplication factor for risk is x2

Question 64

what is the risk in relation to age 20-30

Answer 64

multiplication factor for risk is x1.5

Question 65

what is the risk in relation to age 30-50

Answer 65

multiplication factor for risk is x0.5

Question 66

what is the risk in relation to age 50-80

Answer 66

multiplication factor for risk is x0.3

Question 67

what is the risk in relation to age 80+

Answer 67

negligible risk

Question 68

what are other forms of lead protection

Answer 68

thyroid collar

Question 69

what do we use a thyroid collar for

Answer 69

our lateral cephalometric radiograph

Question 70

why do we use a thyroid collar

Answer 70

the thyroid is in the field of view and the younger patients have multiplicand associated risk

Question 71

what is CBCT

Answer 71

CONE BEAM computed tomography