Stationary, rotating anodes and KV equipment Flashcards
(37 cards)
what form of anode is used with KV
stationary
what are the advantages of a stationary anode?
- constant stream of x-rays
- constant heat production which can be removed by a cooling system
what is the stationary anode made from?
it is a solid block
what is the focal spot
where the electrons are focused, in which the x-rays are produced
what are the rotating advantages?
- intense and instantaneous x-rays
- clear image
- faster, less likely to include movement
- heat is produced across the whole area obtained when the electrons hit the target
- tungsten is a good heat conductor, rhenium adds flexibility
describe the rotating anode
- rotates at high speeds, if not at the correct speed, little x-rays will be produced
- heat is dissipated by radiation
- minimal heat is conducted due to the stem preventing the transfer of heat backwards
- used in most imaging x-rays times
where is the beam less intense?
away from the CA
where do x-rays come from?
the applicator
name the equipment within a KV machine
- x-ray tube
- applicator system
- mechanical system
- control panel
what is the beam energy for kv equipment
50-300 kVp photons
below this won’t penetrate into the body
what is included within the stationary anode?
- high tension power supply
- cathode
- anode
- evacuated tube
- radiation protection
describe superficial RT
- it is low energy, which won’t penetrate the body, only a few cm deep.
- 50-150 kVp
- SXR = superficial X-ray
- SXT = superficial X-ray therapy
what is the target made from
90% = tungsten
10% = rhenium
why is an insulator used?
to maintain the current
describe the process of the stationary anode
- a current in passes through the wire
- electrons must have enough energy to be free from the wire
- a wire needs to be able to withstand the heat
- a stream of electrons is targeted at the copper block
- electrons form a negative cloud, creating an electrostatic force in all directions
- a current will choose a path of least resistance
- the cathode hood bunches the electrons together so it moves in a forward direction remaining in a one directional region
- remaining in this region causes absorption back into the filament, in order for the electrons to move a more positive area needs to be created (p.d either positive or neutral)
- stationary anode has a vacuum
- when electrons hit the stationary anode, bremsstrahlung occurs
- photons which pass through the edge aren’t absorbed by the anode
- electrons which hit the target will produce EM radiation and heat
- heat is taken away by the copper block and a oil cooling system
what does oil help with?
dissipation of heat by convection
what is the max angle
30 degrees (a greater angle will cause an uneven distribution)
a wider treatment angle?
has a wider width/ beam size at a shorter distance, with the intensity at G and t being lower than the CA
what is the anode heel effect
it is the production of a position photon, at which it will be attenuated and absorbed at the target. Intensity at T is reduced, due to the angle. The g side can be controlled by an external shield
what is thermionic emission?
it is the release of electrons from the cathode (free electrons gains more energy when they are released). Anode allows for heat conduction at the back of the copper block, in where theres an oil system - convection. Radiation will occur at the back of the block through the air.
why is a glass envelope used?
it is used to withstand the heat to a greater extent, in which a ceramic insulator is incorporated at the cathode. this is small, less bulky so can move more easily.
what is the range of energies produced by the glass envelope?
90 kVp - 300kVp
what is perspex?
a tissue equivalent
what is the acceptable beam transmission within the kv applicator?
- beam size needs to reduce the intensity outside the useful beam to 2%
- lead lining walls must not transmit more than 2% of the useful beam