what is ionising radiation?
radiation that causes ionisation when it interacts with matter (causes electrons to be knocked out of matter)
where do gamma rays come from?
nucleus of the atom
where do X-rays come from?
movement of electrons
why do we use ionising radiation?
can penetrate through the body and be captured on image detectors
indirect interaction of radiation with matter
radiation interacts with water in our bodies and splits up water molecules into free radicals, free radicals have an impact on the cell structure
direct interaction of radiation with matter
radiation can directly impact on DNA strand, cause breaks, they have an effect on cell structure
radiation damage (direct)
visible effects after a threshold is reached; erythema, hair loss
radiation damage (indirect)
- risk of cancer induction
- risk of genetic change in subsequent population
- (effect is proportional to radiation dose but there is no threshold)
what is dose?
the amount of radiation that has been imparted to the patient
principles of positron emission tomography
patients injected with positrons; interact with electrons in our body, cancel each other out & penetrating gamma rays are detected
attenuation of X-rays
attenuation increases with higher atomic number, higher density
X-rays are an attenuation map: bone stops X-rays that muscles and lungs wouldn’t
Transmission imaging
- radiation directed through the patient
- transmission map collected
- good at showing structure between tissues of different densities or atomic number
Emission imaging
- radiation is administered to a patient in the form of a tracer
- emitted radiation is detected outside the patient
how are x-rays controlled?
- high voltage controls the energy of the x-rays
- current controls the amount of x-rays
x-ray set up
x-ray and x-ray film detector, with the patient in between
- x-ray beam penetrates through the patient
- don’t see bony tissues, just bony structures
uses of x-ray
- diagnostic x-ray: fracture
- dental radiology
- normal chest x-ray
- mammography
how fluoroscopy is used in real-time x-ray
catheter fed inside artery & radio opaque dye is injected
shows the blood flow inside vessels (can show any areas that have been blocked)
limitations of planar x-ray
- cant distinguish between overlying tissues
- overlying tissues reduce the contrast between different layers
CT scanner
X-ray tube & detector rotates around the patient, obtain 3D slices
gamma camera
- Uses single photon emitting radionuclides
- Can operate in 2D (planar) or 3D (SPECT)
nuclear medicine imaging
- only shows function
- make an image distribution of the radioactive tracer
half-life
time taken for radioactivity to reduce 50%
metabolism of FDG
FDG is a glucose analogue which enters cells in the same way as glucose: good reflection of the distribution of glucose uptake
PET scanner
ring of detectors, photos emitted and recorded
