27 PET Flashcards
What radio site is used in PET
Positron emission tomography, hence the radialitpe must decay by beta plus to produce positron
Fluiroine 18 is used which decays to produce positrons by beta plus , neutron and electorn neutirno
What is the thinking behind emitting positrons
About 1mm away from emission, the positrons will ANNHILATE with an electron, where one positron anhilates with one electron , and this produces TWO GAMMA PHOTONS
These gamma photons must be travelling OPPSITE each other to conserve momentum
- these gamma photons are highly peoentrating so leave the body and are detected by detectors.
- the time lag between the gamma photons can then be used and processed by computer to work out the exact postiom of emission
Note it’s not the GAMMA photons produced by the decay of fluorine 18 rather by annihilation of positron and electron
What medical travel is used in PETA SCANS and why
Pet scans use molecule which body treats as if it were glucose, where one atom is replaced with the fluorine 18 isotopes.
This is useful because cna now image the function of things requiring high amounts of glucose, such as the brain
Why is USIGN dog and flrion 18 good for modelling tumours then?
Tumours have a HIGH RATE OF RESPIRATION
Thus absorb hella glucose, and consequently fdg, and hence fdg is perfect for looking for tumours , as it will show high concentrations of emission at that point
How does a PET SCAN work COMPLETLEY
Patient lies on a horixntsl tray , and is injected with FDG
- the fluorine 18 decays, producing a positron
- this annihilates with an electron only 1mm away from emission, producing TWO GAMMA PHOTONS travelling in oppsite directions to conserve momentum
2) the Patient is surrounded by a RING OG GAMMA CAMERAS, all with scinetallrod and photomultiper tubes
- these detect the gamma photons, and send signals to a high speed computer
BASED ON THE LAG TIME BETWEEN photons ! The computer can work out exactly the point of emission, can process an image modelling function of organ / tumour whatever
Why no collimator
Beta sue the angle is consistent by BITH photons not needed, and as they are coming at different angles this is long
Advantages of a PET scan
- 1) 3d image of functioning organs can be used ( whereas gamma was 2D) , and CROSS SECTION TOO but resolution is trash
2) models the function of the thing, good for that rather than anatomy - no high dosage of radiator
- non invasive tehcnieuq used to identity tumours
Insane disadvantage PET scan
The flurione 18 must be produced onsite or close by with specialist particle accelerators equipment.
This means only select hospitals are able to carry out PET scans
Hence doctors will need to mark a choice on who gets it and not, and this could be hard, and also patients may have to travel far distances to get a scan, or not get one at all
2) also this is just EXPENSIVE, so doctors have to pick who gets it
3) images low resolution
4) and gamma radiation is involved so always some ionisation risk
Why does flurione produced onsite again
Onsite because half life low
As particle accelerator used this hellllla expensive
Pet vs
Pet vs gamma
= pet can produce 3d images of function and slice, whereas gamma only 2D
- gamma uses technetium
- pet uses flurione which mst be produced onsite due to short half life, but particle accelerator hence expensive so only select hospitals hsbe these facial ties
Pet vs cat
- both produce 2D and thus 3d models
- cat is anatomy , pet is function
- cat uses high dosage , pet not so much
- cat still
Life
