Extra

Question 1

what is meant by rectification of current

Answer 1

generators within x ray unit modify the alternating current from the mains electricity supply so that it mimics a direct current , which is required by the x ray machine

Question 2

how is intensity of an x ray beam calculated

Answer 2

intensity = 1/ distance from beam ^2
(rearrange to intensity x distance^2 = 1)

Question 3

by what emission are electrons released from the coiled metal wire

Answer 3

thermionic emission

Question 4

what is the cathode filament made of

Answer 4

tungsten

Question 5

what is the cathode focusing cup made of

Answer 5

molybdenum

Question 6

what is the anode target made of

Answer 6

tungsten

Question 7

what is the anode heat dissipating block made of

Answer 7

copper

Question 8

how thick is the alminium sheet used for filtration on x ray machines

Answer 8

1.5mm

Question 9

what is the fsd for machines using more than 60 kV

Answer 9

200mm

Question 10

what is the main purpose of collimation

Answer 10

reduce patient dose

Question 11

heat producing interactions vs x ray producing interactions

Answer 11

heat producing involves outer shell electrons
x ray producing involves inner shell electrons

Question 12

what is the most significant effect of ionising radiation

Answer 12

DNA damage

Question 13

give an example of a highly , a moderate and a low radiosensitive tissue

Answer 13

highly - bone marrow
moderate - skin , lung
low - bone , connective tissue, CNS

Question 14

what does the linear no threshold model estimate

Answer 14

long term biological damage of ionising radiation

Question 15

what are the current diagnostic reference levels for intra oral radiographs
(dose level for typical patient)

Answer 15

solid state 0.9 mGy
phosphor plate and film - 1.2 mGy

child = 0.6 mGy for solid state and 0.7 mGy for phosphor plate and film

Question 16

purpose of diagnostic reference levels

Answer 16

employers must have established doses for typical patient
these can be compared to national reference levels to identify any machines giving higher doses

Question 17

name 2 ways in which patient dose can be minimised

Answer 17

use of collimation
fsd more than or equal to 200mm
kV range of 60 - 70

Question 18

how many ‘bits’ are radiographs typically processed with

Answer 18

8
256 shades of grey

Question 19

how would you know an image has been taken with the receptor the wrong way round

Answer 19

lead foil has a pattern on it that would show on the image

Question 20

why are self developing films not recommended

Answer 20

expensive
poor image quality
image deteriorates over time
no lead foil

Question 21

what are the two methods of processing film radiographs and discuss their pros and cons

Answer 21

manual cycle:
- pros: less expensive
- cons: more prone to error, dark room required
Automated cycle:
- pros: less prone to error, less manual labour, no dark room required, more reliable variables
- cons: expensive