GCSE AQA Physics 3 Medical Applications

X-rays in medicine
1. How do X-rays work?
  1. High frequency, short wavelength EM waves
  2. Transmitted by healthy tissue, absorbed by bones & metal
    1. Affect photographic film in same way as light
      1. Images can be formed electronically using charge-coupled devices (CCDs)
        Silicon chips that produce electronic signals - form high resolution images
2. CT scans use X-rays
  1. Computerised axial tomography (CT) scans produce high resolution images of soft & hard tissue
  2. Beam fired through body from X-ray tube - picked up by detectors (rotated during scan)
  3. Forms image of 2D slice through body - put multiple scans together --> 3D image
3. Treating cancer
  1. Cause ionisation - kill cancer cells
    1. Radiographers wear lead aprons, stand behind lead screen or leave the room
Ultrasound
1. Higher frequency than upper limit of human hearing - 20000 Hz
2. Wave passes from one medium to another
  1. Some reflected off boundary - partial reflection
    1. Time it takes to reach detector - measure how far away boundary is
3. Oscilloscope traces: distance = speed x time
  1. Then divide by 2
4. Uses
  1. Breaking down kidney stones - turn hard masses into small particles
  2. Pre-natal scanning of a fetus - waves reflected off fetus
Medical imaging
1. Safe?
  1. Ultrasound: non-ionising - safe
  2. X-rays: ionising - can cause cancer, not for babies
  3. CT Scans: more ionising - should only use if really needed
2. Image quality?
  1. Ultrasound: fuzzy
  2. X-rays: clear images of bones & metal
  3. CT Scans: detailed, high resolution images - 3D

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GCSE AQA Physics 3 Medical Applications

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