6. X-Ray Hardware Flashcards
what is beam filtration and what does it do to the beam
filtration hardens the x-ray beam
the standard bremsstrahlung spectrum is formed by which type of filtration
inherent filtration of machine
what is beam hardening
increases average energy of x ray beams by removing the lower energies because of presence of filtrating materials
lead to only higher energy beam passing through so higher quality
why are low energy photons undesirable
Low energy photon very unlikely to exit patient so not contributing to image quality at all so bad for patient as extra energy/radiation without any image benefits
what happens to the k edge of attenuation as you increase keV
increases but at a certain point you match the e- orbital and get extra absorption of photon and more attenuation
contrast between tumor and breast tissue gets smaller with increasing/decreasing kV
increasing
increase kV = lower contrast
what are compensating filters
modifies the x-ray beam intensity across the field of view
what is added filtration
filtration that is added to the port of x-ray tube
what does added filtration do in terms of the photon energy
absorbs more low energy photons while higher energy photons can exit
what are inherent filtration
filtration that is permanently in the path of the x-ray beam
what are the 3 components that contribute to the inherent filtration
envelope of the tube
oil that surrounds the tube
window of tube housing
what is the total filtration
sum of added and inherent filtration
what is compensating filtration
added to the primary beam to alter its intensity
used to image areas that are non-uniform in makeup and assist in producing more consistent exposure to the IR
what is the heat unit
amount of heat produced from any given exposure
what 2 factors does the HU depend on
type of x-ray generator
exposure factors selected
what is the equation for HU
HU = mA x time x kVp x generator factor
what are tube rating charts
gives the max current that you can run through the x-ray tube
what are the 2 factors that need to be satisfied in terms of the machines voltage source
Need to get voltage as high as we need
Need a way to keep voltage constant with the machinery
what are the 2 types of diodes in terms of bias
forwards and reverse bias
what are diodes and what are they made of
Diodes are solid state electrical device, has semi conductor type materials in it
allows current flow in one direction and restricts it in another (acts as a one way switch)
Inside you have 2 materials, one which we made slightly more positive than the other and the other you dope with some positive charge with some insulating material in the middle
what are forward bias diodes and what is their charge distribution
is there conduction
Top positive (where the + charges are) bottom negative (where the - charges are)
Positive charges are repelled downwards and produces a current and allows current to go through so is in the conductive state
e- and holes more across the junction
conduction
what are reverse bias diodes and what is their charge distribution
is there conduction
Top negative (where the + charges are) bottom positive(where the - charges are)
they’re attracted to opposite charge so don’t flow through insulating material and no conduction as stay away from junction in the middle
e- and holes stay away from the junction
no conduction
when the diode acts in a forward bias in a AC current what does the diode become in terms of conduction
becomes conductor
acts like a closed circuit
when the diode acts in a reverse bias in a AC current what does the diode become in terms of conduction
diode does not conduct
no current flow
a diode in a AC circuit produces what
half rectified waveform
what does the diode do to the waveforms in a AC current
Can take signal that’s alternating and makes it completely positive so when its negative there’s no current at all but when its positive it allows current to flow
what are transformers and what do they do in a electrical circuit
transfers electrical energy from one circuit to another
used to step up/down the voltage from an AC power supply
the coils in transformers are not connected so what transfers the power
magnetic field
As each turn creates a magnetic field
for transformers the amount of current produced depends on what
Amount of current you produce depends how many coils on the wire there are
more secondary turns in a transformer than primary turns means there is an increase/decrease in voltage
what has happened to the power
More turns on the right means there is an increase in voltage = steps up the power
Takes the energy and steps it up due to difference in number of turns
you can also do the opposite if needed
what are the 3 circuits in a full x-ray circuit
Primary
filament
secondary
what is the purpose of the primary circuit in the full x-ray circuit
Primary = control parameter and produce power,
what is the purpose of the filament circuit in the full x-ray circuit
Filament circuit controls heating of filaments so release e-
what is the purpose of the secondary circuit in the full x-ray circuit
Secondary circuit allows rectifying and flattening out the waveform
what is Electromagnetic induction
a changing magnetic field induces an electrical potential difference (voltage) in a nearby conductor and also in which a voltage is induced in a conductor moving through a stationary magnetic field.
in Electromagnetic induction the magnitude of the induced voltage is proportional to what factor
The magnitude of the induced voltage is proportional to the rate of change of the magnetic field strength.
what are power ratings
The power rating of an x-ray tube or generator is the maximal power that an x-ray tube focal spot can accept or the generator can deliver.
what is an anode heating chart
shows the anode heat loading for various input powers (kW or HU/s) as the x-ray tube is operating, taking into account the cooling that simultaneously occurs
the anode cooling curve is steeper for larger/smaller anode heat capacities
With larger anode heat capacities, the anode cooling curve is steeper
what does the primary circuit do in terms of the power
supplies power from the mains to the x-ray circuit
why are circuit breaker included in the primary circuit
protect against short circuits and electric shocks
what 2 things does the primary circuit control and what one factor does it monitor
controls tube voltage and exposure time
monitor tube voltage
what are the 6 components of the primary circuit
power supply
mains power switch
circuit breaker
tube voltage selector
voltage meter
exposure timer
what do auto transformers do in the primary circuit
allows selecting of different powers
what are the 4 components of the secondary circuit
step-up transformers
rectifier
current meter
x-ray tube
what does the secondary circuit monitor
tube current (mA)
only monitoring NOT setting it!
what does the secondary circuit do in terms of the power type and voltage
convert AC to DC power
creates potential difference across the x-ray tube (for e- to accelerate)
step up voltage to voltage that is suitable for x-ray production
how many diodes are in the secondary circuit
how many will let current through and how many wont
what do they allow the current to do
4
2 will, 2 wont
allow current to flow in a forward reaction
there is a positive tube voltage when there is a ____ ___ ___
positive input voltage
there is a negative tube voltage when there is a ____ ___ ___
negative input voltage
what does the bridge rectifier in the secondary circuit produce in an AC circuit
what does this mean for the voltage
fully rectified waveform
negative voltage isn’t just removed, it’s also turned into a positive waveform
what is the voltage ripple
how is it dealt with
Ripple = difference between highest and lowest point
Take maximum of each one that’s going out of phase, produce a lower ripple
why do we need to reduce voltage ripple
get a higher quality x ray and higher average x ray that gets rid of lower energy and makes most of characteristic peaks
what does the filament circuit control
how is this accomplished
controls the tube current (mA)
change resistance to change the current
what 3 things does the filament circuit do in terms of the filament
selects the filament to be used
produces a current in the filament
initiate thermionic emission
what % of energy is converted to x-rays
what is the rest converted to
1% = x-rays
99% = thermal energy (heat)
what is the power rating in terms of the focal spot and the generator
max power that a x-ray tube focal spot can accept
max power that x-ray generator can deliver
