1. X-Ray Production Flashcards
How are x-rays produced in the x-ray tube
What happens on the cathode side
the tungsten filament is heated and produces e- through thermionic emission
How are x-rays produced in the x-ray tube
What happens on the anode side
e- produced at the anode side accelerate towards the anode and hits the metal target
what type of electrode is the cathode
what is the role of the cathode in x-ray production
its a negative electrode
its the source of e-
what type of electrode is the anode
what is the role of the anode in x-ray production
positive electrode
e-s attracted to the positive charge and accelerate towards it where they are stopped/decelerated
what occurs at the anode in terms of energy that produces x-rays
what else does the process produce
kinetic energy of e- transferred to the anode (when e- strike target it loses energy which is the kinetic energy)
x-rays and heat are produced
what material is the center of the anode made of
tungsten
where do the x-rays leave the x-ray tube from
the window
what does the vacuum in the x-ray tube prevent and do
it makes sure that the e- energy is undissipated so produces x-rays and prevents energy from being lost as heat
what are the 2 types of anodes
stationary and rotating
what is the limitation of the stationary anode and what is the benefit of the rotating anode
stationary = compact but wears and creates heat
rotating = larger and longer life as can tolerate higher mAs and dissipate more heat
what 2 components make up the cathode
filament (large and small) and focusing cup
what is the filament and what is its role in x-ray production
coiled tungsten wire
source of e- during x-ray production
filament current heats the tungsten filament and causes thermionic emission
what is the focusing cup and what is its role in x-ray production
surrounds filament and open at one end to allow e- to flow from cathode to anode
purpose is the focus the e- stream, it does this with its negative charge which prevents the filaments emitted e- from spreading apart
what are the 3 components of the rotating anode and how are they arranged in a x-ray tube
target, stator and rotor
rotor attached to target and the stator is found either side of the rotor
what is the purpose of the anode target
metal that abruptly decelerates/stops e- in the tube current
either rotational or stationary
what is the purpose of the stator and rotor
electric motor that turns the rotor
the rotor is connected to the target through the molybdenum anode stem
what components of the x-ray tube prevent overheating
insulating oil
which 2 types of interactions produce x-ray photons
bremsstrahlung and characteristic interactions
in terms of the incident e- and x-ray production what occurs in bremsstrahlung interactions
incident e- is attracted to the nucleus but doesnt eject any e-s
incident e- loses energy and changes direction
excess energy is emitted as a photon
which 2 factors impact the photon energy produced from a bremsstrahlung interaction
proximity to nucleus
atomic number
how does increased proximity of the incident e- to the nucleus impact the photon energy produced from a bremsstrahlung interaction
closer = incr attractive forces = more energy lost = incr photon energy
how atom size impact the photon energy produced from a bremsstrahlung interaction
larger atom = incr attractive force = incr photon energy
is the range of energy produced for photons from bremsstrahlung interactions discrete or continuous
continuous
what is a bremsstrahlung interaction
projectile e- completely avoids the orbital e- of the tungsten atom and travels very close to its own nucleus
the strong electrostatic force of the nucleus causes the e- to slow down
e- loses energy and change direction and energy lost produces an x-ray photon
in the diagnostic energy range most of the interactions are characteristic/bremsstrahlung
bremsstrahlung interaction
in terms of the incident e- and x-ray production what occurs in characteristic interactions
incident e- removes an e- from the inner k shell of the orbit via repulsion
other e-s in the orbit falls form outer shell to inner shell to replace the removed e-
x-rays are emitted in this process due to the energy difference created
is the range of energy produced for photons from characteristic interactions discrete or continuous
discrete specific energies due to specific orbits
Is there a difference in x-rays produced by bremsstrahlung and characteristic interactions at the same energy level
no they are the same simply produced by different processes
the x-ray spectrum has what on its y and x axis
y = x-ray intensity
x = energy (keV)
what is the x ray quantity and how is this show on the spectrum
total number of x-ray photons
area under whole curve
what is x-ray quality
average energy of x-ray photons contained in x-ray beam/spectrum
is the x-ray spectrum representative of the average energy
no
why is there a lower and upper limit on the bremsstrahlung interactions on the x-ray spectrum
upper = cant produce more energy than it had to start with (need to apply more voltage to increase the upper limit)
lower = doesnt go to 0 as its filtered by the x-ray tube and the tube components
what is the tube current
the mA is the current of e- flowing from cathode to anode in the x-ray tube
what is the space charge effect
e- from the filament during thermionic emission form a cloud around the filament called space charge
tendency to prevent more e- boiled off the filament (number of e- is limited)
what aspect of the e- in the tube current does kV control
speed at which they move
in terms of quality and quantity what does the kV affect and how
quantity and quality
higher quality = high energy and greater penetrability
in terms of quality and quantity what does the mA affect and how
quantity, doesnt affect quality or energy
more e- in the tube current the more x-ray produced
what effect does exposure time have on the x-ray quantity
longer exposure time results in more e- moving in the tube current from cathode to anode
more x-rays produced
what is the anode heel effect
x-ray beams have higher intensity (number of x-rays) on cathode side but lower intensity on anode side
why is the anode heel effect present
the x-rays produced leave in many directions and the x-rays produced at the anode side have further to travel and some are absorbed by the anode itself
this reduces the x-ray numbers compared to the to photon produced in the direction of the cathode
how can the anode heel effect be used advantageously
place cathode over thicker anatomy to produce a more even exposure
what is the line focus principle
relationship between the actual focal spot and the effective focal spot
by angling the anode target the actual focal spot can remain large and effective fs can be reduced in size (greater heat capacity and greater image quality achieved)
what is the actual focal spot and what does it depend on
size of area on anode target that is exposed to e- from tube current
depends on the filament size producing the e- stream
what is the effective focal spot
focal spot size as measured directly under the anode target
what is the difference between using small and large focal spots in terms of quality and exposures
large fs can withstand large exposures
small fs can give better image quality
the larger the anode angle, the larger/smaller the effective focal spot
larger
In terms of the line focus principle what does biased and non biased mean for the voltage
Biased = voltage applied
Non-biased = same voltage everywhere
Effective focal spot is smaller/bigger near cathode & smaller/bigger near anode
cathode = bigger
anode = smaller
the smaller the anode target angle the smaller/bigger the effective focal spot size
smaller
Total filtration in the x-ray beam includes which 2 types of filtration
inherent and added filtration
the intensity of the x-ray beam is greater on the ___ side of the tube
cathode
the clouds of e- that forms before x-ray production is referred to as ___ ____
space charge
what % of kinetic energy is converted to heat when moving e-strike the anode target
99%
