Radiology Flashcards
what is a radiograph?
an image produced by radiation, commonly by x-rays
what is the difference between radiography and radiology?
radiography is the technique of taking radiographs
radiology is the interpretation of radiographs
what are the main types of radiograph in dentistry?
bitewings
periapicals
OPG
wavelength and frequency of x-rays
short wave lengths with a high frequency
what determines whether x-rays are penetrated or passed through?
penetrates liquids, solids and gases. composition of substance determines whether x-rays penetrate or pass through or absorbed.
what is ionisation capability?
x-rays interact with materials they penetrate and cause ionisations.
what is fluorescence capability?
x-rays can cause certain substances to fluoresce or emit radiation in longer wavelengths (e.g., visible light and ultraviolet light)
how do x-rays travel?
in straight lines but can be deflected or scattered
are x-rays waves or particles?
they are waves and energy. the packets of energy that x-rays travel in are called photons.
what are photons?
the packets of energy that x-rays travel in
what is needed to create an x-ray?
a power source, and a circuit
which way do electrons flow in the circuit?
from negative side of battery around the tube to create x-ray
what is needed to create an x-ray?
a power source, and a circuit
which way are the filament and anode connected?
filament is connected to negative side of battery
anode on positive side of battery
what is x-ray tube made out of?
glass, vacuum inside it
what is the filament made of and why?
tungsten due to its very high melting point
what is the anode made out of and why?
tungsten mounted on copper
copper is used as a conduction metal for electricity and heat. allows heat to dissipate so it doesnt get too hot and melt.
process? how are electrons converted into x-ray photons?
electrons heat up the filament and they build up in vacuum (at negative side). they boil off the filament. anode is positive, so electrons fly across the vacuum and hit it, flying at high speeds. when hitting tungsten on other side they are converted into heat. anodes rotate so electrons don’t constantly hit the same part. all in oil sealed container to aid heat dissipation. produces x-ray photons.
what is the anode made out of and why?
tungsten mounted on copper
copper is used as a conduction metal for electricity and heat. allows heat to dissipate so it doesnt get too hot and melt.
how is the x-ray beam created?
whole tube is held in a lead casing with a little window where electrons can flow out and create the x-ray beam.
what is the braking effect?
electron gets attracted to a nucleus and swings around it, producing a heat causing collision by hitting the outer shell electrons. it swings around and exits the other side. it slows down to the stop because electron has a lot of kinetic energy as it comes around but it is lost as it swings around the nucleus of the atom. kinetic energy is lost and transferred in/and produces an x-ray photon.
what happens if the electron does not swing all the way around?
it sometimes does not swing all the way around but changes direction slightly. this produces an x-ray photon but with not as much energy.
do short or long wavelengths correlate to high energy?
long wavelength = low energy
short wavelength = high energy
which electrons produce short wavelength photons?
electrons that slow down more, lose more energy, so photon released has more energy, producing a shorter wavelength and more of them
which electrons produce long wavelength photons?
electrons that are slightly deflected can lose more energy and create more photons by interacting with more nuclei. produces more lower energy long wavelength photons.
what is characteristic radiation?
electron smashes into an inner electron. both electrons go off in different electrons, creating a hole in the inner shell. an outer shell electron will drop down into the inner shell etc. this creates a release of energy when it drops down, creating a photon. occurs again when electrons drop down again to another shell, but further out is less so lower energy and photons are not detectable. it is characteristic of specific elements - always same wavelength and energy for that element.
which shell electrons have the highest energy?
K shell has the highest energy
which shell, when filled, produces the highest energy photons?
K shells
their electrons have the highest energy so when an electron in K shell is filled, they produce higher energy photons
what is the combined spectrum?
combining bremsstrahlung and characteristic radiation
what are the 4 situations that can occur when photons interact with matter?
- absorbed with total loss of energy
- scattered with some absorption and loss of energy
- scattered but no loss of energy
- pass through unchanged
energy/directional changes
what is scattering?
change in direction of a photon with or without a loss of energy
what is absorption?
deposition of energy, loss of energy from the photon
what is attenuation?
reduction in the intensity of the main x-ray caused by absorption and scattering
what is ionisation?
removal of an electron from a neutral atom, producing a positively charged atom
how does ionisation occur?
short wavelength, high energy x-rays (anything above it in the EMS, e.g., gamma)
energy deposited into atoms is deposited into electrons in the shells. when there is more energy than the energy holding the negative electron to the positive nucleus, it results in that electron being hoisted out of the cell, resulting in a positively charged ion.
what is the photoelectric effect? (summary)
complete absorption - x-ray photon hits the matter and is completely absorbed. mechanism of absorption = photoelectric effect.
what is compton scattering? (summary)
absorption and scatter. as the x-ray photon passes out of the material, it has changed in photon energy. travels in with the same energy as photon 1, but interaction that happens in the matter results in a change in direction and a loss of energy of that photon.
describe the photoelectric effect
incoming photon collides with an electron in the inner shell, so it is bounced out and displaced. this displaced electron is the photoelectron. it has a high energy and will go on to eject other electrons from other adjacent atoms and cause further ionisation. thus complete absorption results in ionisation.
what type of electrons predominate the photoelectric effect?
the photoelectric effect predominates with low energy electrons. x-ray photon energy = binding energy of electron
low energy photons can displace more inner shells.
what happens to the photoelectric effect as Z increase?
as atomic number increases, number of inner shell electrons increase, so more photoelectric interactions, meaning more absorption.
the probability of photoelectric interactions occurring is proportional to?
atomic number^3
the probability of photoelectric interactions occurring is inversely proportional to?
(energy of the x-ray beam)^3
(as energy of x-ray beam increases, photoelectric effect decreases)
describe the compton effect
x-ray photon comes in and interacts with an outer shell electron. it collides but the photon still has more energy to impar. the outer shell electrons are less tightly bound so do not need as much energy to be released from their shell. so compton scattered electron is produced as well as a photon scattered in the form of an x-ray.
does the compton effect result in ionisation? why?
yes because atom has lost an electron.
what happens to the incoming photon from the compton effect?
the incoming photon is attenuated. lower energy photon leaves the matter in an altered direction - it is scattered.
the incoming photon energyv > binding energy of the photon, thus the excess energy is released in the form of another photon
where are scattered photons deflected?
any direction
what happens if scattered photons are deflected to a different area of the x-ray film?
they cause noise in the final image
which photons produce more forward and backward scatter?
high energy photons produce more forward scatter (forward through the matter); low energy photons produce back scatter
what is detected in radiography?
transmission
which parts are white and black in radiographs?
anything absorbed is white. x-rays pass through the bits through the teeth so show up as black.
does the photoelectric effect occur inside teeth?
yes - so teeth absorb x-rays
putting a detector (plate) behind the matter, we can detect the x-rays/photons that pass through. we want to detect transmission. what is white and black?
white bit is where transmission is blocked
black is where x-rays transmit through
what direct damage occurs to cells?
direct hit on DNA or RNA from a photon radiation disrupts chemical bonds causing molecular changes, e.g., mutations
what indirect damage occurs to cells?
formation of free radicals, ions and ejected photoelectrons which bring about molecular changes
are direct and indirect damage micro or macroscopic effects?
microscopic effects
what are deterministic effectss?
they will definitely happen in the threshold of a high dose of radiation is reached
what happens with deterministic effects of radiation?
eg sunburn
skin redness, mucositis, xerostomia, blood and gut changes, cataract formation
what is stochastic effect?
no known threshold dose. every time you expose to ionising radiation, you have a chance of causing damage to the tissues.
probability: the lower the dose the lower the probability of causing cell damage. the lower the number of x-rays, the lower the probability of causing cell damage.
which effects are dentistry affected by?
stochastic - each time we take a dental radiograph, we have a chance of causing a stochastic change. no deterministic effect since dose of radiation is low.