Questions will be limited to consideration of image resolution,…

The idea

This statement defines the scope of comparison questions across imaging techniques such as X-ray, ultrasound, CT, PET and MRI. You are not expected to compare every physical principle in detail; instead, you judge techniques by three practical criteria. Image resolution concerns how small a separation of features can be distinguished, so a technique producing sharp, high-contrast images of fine structure scores well. Convenience covers patient experience and clinical practicality: scan duration, need for stillness, portability, invasiveness and availability. Safety covers ionising radiation dose, heating or cavitation risks, contrast agent reactions and any need to avoid certain patients. A useful method is to name the technique, state the clinical task, then weigh resolution against convenience and safety to justify a choice.

What earns the marks

• Identifies image resolution as the ability to distinguish small, closely spaced features in the resulting image, linking it to the imaging wavelength or reconstruction method where relevant.
• Discusses convenience in terms of scan duration, patient comfort, need to remain still, portability, availability and whether the procedure is invasive.
• Discusses safety in terms of ionising radiation dose, heating or cavitation effects, contrast agent risks and suitability for particular patients such as pregnant women.
• Compares two or more techniques by weighing resolution against convenience and safety for a stated clinical situation rather than listing techniques separately.
• Reaches a justified conclusion that identifies the most suitable technique for the context and acknowledges a trade-off, for example lower resolution but no ionising radiation.

Common mistakes and how to put them right

• Treating resolution as brightness or image size rather than the ability to distinguish fine detail.

  Put it right by defining resolution as the smallest separable feature and linking it to the imaging method.

• Listing advantages and disadvantages of each technique without comparing them.

  Put it right: Explicitly weighing the criteria against each other for the clinical task given.

• Assuming all radiation-based techniques carry equal risk regardless of dose.

  Put it right by distinguishing dose levels and noting that some techniques avoid ionising radiation altogether.

Exam tips

• Read the clinical context carefully and let it drive your judgement, because the best technique depends on the patient and the diagnostic question.
• Use comparative connectives such as whereas and however to show you are weighing criteria rather than describing techniques in isolation.
• State a clear overall recommendation and support it with at least one resolution point, one convenience point and one safety point.