A patient is given a radionuclide tracer that accumulates in tumour cells. Describe what happens to the tracer inside the patient's body and explain how a gamma camera produces an image of the tumour.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
The tracer is taken up by tumour cells, concentrating there more than in healthy tissue.
The radionuclide emits gamma photons from inside the body.
The photons pass through the body and are detected by the gamma camera.
The camera records a higher count rate from the tumour region.
The resulting count map is displayed as an image showing the tumour’s location and shape.
The radionuclide emits gamma photons from inside the body.
The photons pass through the body and are detected by the gamma camera.
The camera records a higher count rate from the tumour region.
The resulting count map is displayed as an image showing the tumour’s location and shape.
Examiner tips
- Use the word "concentrate" or "accumulate" for uptake. Mention "gamma photons" and that they are detected. Show that higher counts give a brighter area on the image.
Common mistakes
- Confusing beta with gamma radiation. Failing to state that the camera records a higher count rate. Describing the image as a photograph rather than a count map.
Mark scheme (5 marks)
- The tracer is taken up / absorbed / concentrated in the tumour cells (more than in surrounding healthy tissue)
- The radionuclide emits gamma radiation from inside the body
- Gamma radiation passes out of the body and is detected by the gamma camera
- The camera detects more gamma radiation / counts from where the tracer has accumulated (the tumour)
- This produces an image showing the location / position / shape of the tumour
Key terms in this question
radionuclide tracer · gamma camera · accumulate
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →