Topic 3b - Medical Uses of Radiation Flashcards
How do tracers work?
It is a radioactive substance that is usually injected into the body.
To be useful needs to build up in specific organ.
Some are absorbed directly (iodine) some have to be incorporated into larger molecules that are then absorbed.
Usually a gamma.
Once its had time to build up in correct place a gamma camera detects the gamma rays which builds up an image.
What does PET stand for
positron emission tomography
How do PET scans work
Use tracer that undergoes b+ decay.
When it releases a positron it almost immediately collides with an electron, they annihilate created gamma rays that detected by the PET scanner.
By detecting many pairs the computer is able to build up a 3D image of the body
Why must tracers have a short half life
so the patient is not radioactive after scan.
Despite half life of a few hours they should still avoid pregnant women, babies or young children for a few hours. They must be produced in hospital.
What are the risks/benefits of PET scans
typical PET exposes patient to three years does of background radiation. Provided its only carried out once there is very little risk
key advantage is that it is possible to investigate the extent to which the tracer is being absorbed by different parts of the body. This can induce whether cancer cells are alive or dead
Give an example of a disease that can be deleted by PET scans
cancer
coronary heart disease - shows areas of damaged tissue by detecting areas of decreased blood flow.
What types of ionising radiation is mainly used for radiotherapy
beta, gamma, or x-rays
How does internal radiotherapy work
Works by placing radiation source inside patient, next to tumour.
E.g prostate cancer treated by surgically inserting small radioactive ‘seeds’ into prostate. These sources continually emit radiation that is absorbed locally, gradually killing cells
Thyroid cancer treated by either drinking or injecting iodine-131 which is absorbed by the thyroid and emits beta particles which kills cancer cells in the thyroid
How does external radiotherapy work?
Most radiotherapy applied externally.
Uses gamma source of high frequency x-rays.
Must be carefully targeted at the tumour while avoiding healthy tissues.
Simplest way is to rotate the beam of radiation around patient ensuring beam is always passes through the tumour.
Tumour receives continuos dose whilst healthy tissue surrounding receives only small dose
What is Palliative care
radiotherapy can be used to shrink tumours.
Condition isn’t cured but patient will be in less pain and may enjoy better quality of life
What are the risks and benefits of radiotherapy
patient receives large dose of radiation. if procedure is well designed the dose to healthy tissue should be minimised.
May harm the patient, possibly causing more tumours to develop. can cause hair loss, sickness and skin irritation.
Bowel damage or infertility
Advantage of internal is that source is placed right next to tumour so does not affect as much healthy tissue
What is ultrasound used for
Scanning
destroying kidney stones
measuring blood flow
How can we use ultrasound for prenatal scanning
ultrasound scanner both transmits and receives ultrasound waves.
The waves pass through the body and are partially reflected at boundaries between different tissues
reflected waves detected by scanner and information is processed by a computer to produce an image on a screen
How is ultrasound used for kidney stones
Kidney stones are hard deposits in the kidneys that can be extremely painful.
High intensity ultrasound can be used to break them up by focussing it so it has a very high amplitude at the location of kidney stone
vibrations shatter stone into smaller pieces which are then passed in urine
how is ultrasound used to measure blood flow
works by using doppler effect
when waves reflect from or pass through moving blood it changes their frequency
the scanner can detect the change and provide a measurement of the blood flow speed.
This can provide information about blockages in blood vessels
