Extra Flashcards
what is meant by rectification of current
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
how is intensity of an x ray beam calculated
intensity = 1/ distance from beam ^2
(rearrange to intensity x distance^2 = 1)
by what emission are electrons released from the coiled metal wire
thermionic emission
what is the cathode filament made of
tungsten
what is the cathode focusing cup made of
molybdenum
what is the anode target made of
tungsten
what is the anode heat dissipating block made of
copper
how thick is the alminium sheet used for filtration on x ray machines
1.5mm
what is the fsd for machines using more than 60 kV
200mm
what is the main purpose of collimation
reduce patient dose
heat producing interactions vs x ray producing interactions
heat producing involves outer shell electrons
x ray producing involves inner shell electrons
what is the most significant effect of ionising radiation
DNA damage
give an example of a highly , a moderate and a low radiosensitive tissue
highly - bone marrow
moderate - skin , lung
low - bone , connective tissue, CNS
what does the linear no threshold model estimate
long term biological damage of ionising radiation
what are the current diagnostic reference levels for intra oral radiographs
(dose level for typical patient)
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
purpose of diagnostic reference levels
employers must have established doses for typical patient
these can be compared to national reference levels to identify any machines giving higher doses
name 2 ways in which patient dose can be minimised
use of collimation
fsd more than or equal to 200mm
kV range of 60 - 70
how many ‘bits’ are radiographs typically processed with
8
256 shades of grey
how would you know an image has been taken with the receptor the wrong way round
lead foil has a pattern on it that would show on the image
why are self developing films not recommended
expensive
poor image quality
image deteriorates over time
no lead foil
what are the two methods of processing film radiographs and discuss their pros and cons
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
