Describe how a digital X-ray image of a patient's chest is produced, from the X-ray tube to the final image.

AQA A-Level Physics (7408) — 3.10.5 X-ray Imaging · Describe · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

X‑rays are produced by an X‑ray tube and emitted towards the patient.
X‑rays pass through soft tissue but are absorbed by denser materials such as bone.
A charge‑coupled device (CCD) or other detector records the X‑rays that reach it.
The CCD/detector converts the X‑ray data into electrical signals and then into digital data.
The digital data is processed by a computer to produce a visible image, where areas that absorb more X‑rays appear lighter/white.

Examiner tips

  • Use the exact sequence: tube → patient → detector → conversion → processing. Mention the key components (X‑ray tube, soft tissue vs bone, CCD/detector, digital conversion, image processing).
  • Show the relationship between absorption and image brightness (more absorption = lighter).

Common mistakes

  • Confusing the direction of X‑ray travel (treating the detector as the source). Forgetting to mention the conversion of X‑ray data into digital signals. Describing the image as darker where more X‑rays are absorbed, rather than lighter.

Mark scheme (5 marks)

  1. X-rays are produced by / emitted from an X-ray tube
  2. X-rays pass through soft tissue but are absorbed by denser materials such as bone
  3. A charge-coupled device (CCD) / detector detects the X-rays that pass through the patient
  4. The CCD/detector converts the X-ray data into electrical signals / digital data
  5. The digital data is processed by a computer to produce a visible image, where areas that absorb more X-rays appear lighter/white

Key terms in this question

X-ray tube

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