Imaging Techniques
Physics: AQA A Level, topic 10.6.1
Gamma Ray Imaging
We can use gamma rays to form images.
Gamma camera
- Gamma radiation can be used to form images.
- Gamma ray imaging commonly uses technetium-99m, iodine-131 and indium-111.
- Radioactive substances are introduced into patient and an image is formed by radioactivity leaving the patient.
- The image is created by the differential uptake of the radioactive substance by the body organs.
- The image is formed using a gamma camera.
Technetium Generator
The Molybdenum-Technetium Generator extracts the unstable nuclei which will decay for medical use.
Gamma decay
- Technetium-99 decays radioactively and produces gamma radiation.
- Gamma radiation will pass through soft tissue and can be detected outside of the body.
- Gamma radiation is the least harmful radiation inside the body.
Medical imaging
- The decay of technetium-99 only depends on the technetium nuclei and not the compound or chemical which it is in.
- The technetium can be attached to a biological compound and injected into the body.
- The bloodstream will carry the compound to the correct area of the body before the technetium can fully decay, a gamma camera can then detect radiation and create an image.
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Half life
- The half-life of a sample used for medical imaging needs to be long enough for the bloodstream to take it to the correct place in the body but short enough so that the patient isn't emitting radiation for a long time.
PET scan
A positron emission tomography scan or PET scan detects pairs of gamma rays.
Annihiliation
- When an electron and a positron meet they mutually annihilate creating an identical pair of gamma rays which move in opposite directions to each other.
- These identical pairs of gamma rays can be detected using a gamma camera and form an image inside of the body.
Beta plus decay
- Beta plus decay is used to create the positrons used for a PET scan.
- Beta plus decay is exactly the same as beta decay but produces a positron.
- The positron will annihilate with an electron and produce the gamma rays.
Test yourself on Imaging Techniques
How is radiation introduced into the body for medical imaging?
What is the condition on the half-life of a radioactive substance used for medical imaging?
Which of these statements are true about using medical radiation?
Which type of radiation is the least harmful inside the body?
PET Scan