X-Ray, CT and PET Scan Flashcards
What is ionising radiation?
Ionising radiation is radiation that causes ionisation (esentially takes or add electrons off and become charged particles) when it interacts with matter
Why do we use ionising radiation?
Ionising radiation is used as they can penetrate through the body through different mediums/tissue) and be captured on our imaging detectors
What are the two ways ionising radiation can act?
- Indirect action (radiation will break up water and produce free radicals)
- Direct action (directly impact DNA inside a cell)
Describe the indirect action of ionising radiation
- Majority of our body is water
- Ionising radiation can break up water and result in the production of free radicals and hydrogen peroxide
- H• OH• HO2• H2O2
- Free radicals are highly reactive and break down DNA
Describe the direct action of ionising radiation
Direct impact of the DNA inside our cells
Direct effect of radiation damage
- Threshold effect (very high level of radiation exposure/ doses needed, beyond the threshold level, in order to see those effects)
- E.g Erythema and hair loss
What are the indirect effects of radiation damage?
- Indirect effects can increase risk of the cancer induction
- Risk of genetic change in subsequent population
- Effect is proportional to radiation dose, no threshold
- All radiation has risk (the higher the radiation the higher the risk that radiation will cause cancer)
What are positrons?
Posotively charged electrons which interact with matter to create gamma rays
How are positrons formed?
They are emitted following the radioactive decay of an unstable nucleus
What are positrons used in
PET scanning (Positron Emission Tomography)
What are gamma rays
Are a type of penetrating electromagnetic radiation emitted following the radioactive decay of an unstable nucleus
What are gamma rays used in?
Gamma camera imaging e.g SPECT
What are X-rays?
Spectrum of electcomagnetic radiation
How are X-rays produced?
They are produced artificially in an X-ray tube
What are X-rays used in?
X-ray imagine
CT and radiographs
What does X-ray attenuation mean?
As the high-energy photons pass through material, their energy is decreasing
Essentially there is a reduction in the intensity of an X-ray beam as it traverses matter
What factors affect attenuation?
Attenuation increases with
- Higher atomic number
- Higher density
What is used for transmission imaging and what is used for emission imaging?
Transmission Imaging → X-Ray
Emission Imaging → Gamma Rays
What is transmission imaging?
- A patient will lie between an X-ray tube and detector
- Radiation will be directed through the patient
- A transmission map is collected (attenuation map)
- Maps all the tissues that either block the signal or not
- Good at showing structure, especially between tissues of different densities or atomic number
Describe emission imaging?
- Radiation is administered to the patient in the form of a tracer (radioactive material injected)
- Patient will emit radiation (e.g gamma rays)
- These will be detected outside the patient
What is an X-Ray tube composed of?
- Filament, Target (anode), tube (evacuated), Voltage difference between two terminals (filament and target) to accelarate electrons
How does an X-ray work? How are the X-rays produced?
- A current will flow through a heating circuit which will cause electrons to be fired from the filament to the target (anode)
- The electrons will accelerate through the voltage and hit the target (anode)
- Upon hitting the target (metal tungsten), those electrons will produce a beam of X-rays
How do we have the abillity to control X-rays?
- Operators can control the X-rays by changing the voltage setting
- X-rays are only produced when the tube is in action (can be switched on/off)
- High voltage and current can be used to control the amount and energy of X-rays produced
What is the effect of X-ray on bone?
Bone has a high atomic number and high density so therefore blocks most of the X-ray signal (high attenuation) hence appears white
Soft tissue has a lower atomic number and lower density so therefore allows more X-rays through = blacker appearance