Radiology introduction Flashcards
What are x-rays
high energy electromagnetic radiation with a short wavelength = ionising radiation
they consist of photons and travel in straight lines
What does ionising radiation mean
there is enough energy to detach electrons from atoms/molecules
Outline what happens in an x-ray tube
- At the cathode a tungsten filament is heated to emit electrons
- These move to the anode to give tube current
- Higher voltage accelerates the speed of electrons
- Electrons are converted to photons (x-rays)
What is the anode made of
A tungsten target in a copper block surrounded by oil to remove heat
Why is the x-ray tube under vaccuum
So that there is no obstruction by air molecules
What are the 3 x-ray producing collision
- Continuous spectrum = rapid deceleration at target and energy is lost as x-rays
- Characteristic spectrum = energy is specific to each atom
- Combined spectrum = continuous and characteristic
Define attenuation in regards to x-rays
This is where there is lower intensity of the main x-ray beam because there is absorption and scattering
What are the 4 fates of x-rays
- Unmodified Rayleigh scattering
- Photoelectric effect = pure absorption
- Compton effect = scattering and absorption
- Pair production = pure absorption
How are heat producing collisions made
When the incoming electron changes direction by the outer-shell tungsten electron there is energy loss as heat
Excitation and ionisation also results in heat loss
When is a bitewing used
Caries detection
When is a periapical used
- hepathology of tooth apex
- crown and root check ups
When is a dental panoramic used
to look at TMJ and all dentition
When is an occlusal used
to check for root trauma and unerupted teeth
When is a CT used
to get a 3D image
Define radiation absorbed dose
Energy absorbed per unit mass of tissue
Define equivalent dose
Quantity calculated for individual organs
radiation absorbed dose X radiation weighing factor
Define radiation weighing factor
biological effect of radiation shown; when higher there is a greater chance of tissue damage
Define effective dose
whole body dose
Define collective dose
effective dose X population
What are the four types of biological effects with x-rays
- Somatic deterministic (acute) = large dose, small time and immediate problems
- Somatic deterministic (chronic) = long time after exposure; deathly
- Somatic stochastic = by chance and so it has random occurence and there is no threshold
- Genetic stochastic = mutation based
(stochastic effects are prevalent in dentistry)
What is the safe dose
Dose below which stochastic effects do not occur
What direct damage can x-rays cause
Damage to DNA/RNA molecular structure and so information cannot be passed on leading to cell death
In somatic cells this causes radiation induced malignancy
In reproductive cells radiation induced congenital abnormality
What indirect damage can x-rays cause
Ionisation of water molecules producing free radicals which can damage DNA which then leads to cell death
What 3 steps should be considered before taking radiographs
- Justification; benefits > risk
- Optimisation; exposure should be kept low
- Limitation; shouldn’t exceed ICRP guidelines
