GCSE AQA Physics 3 Medical Applications

GCSE AQA Physics 3 Medical Applications

1. X-rays in medicine

   • How do X-rays work?
     • High frequency, short wavelength EM waves
     • Transmitted by healthy tissue, absorbed by bones & metal
       • Affect photographic film in same way as light
         • Images can be formed electronically using charge-coupled devices (CCDs)
           • Silicon chips that produce electronic signals - form high resolution images
   • CT scans use X-rays
     • Computerised axial tomography (CT) scans produce high resolution images of soft & hard tissue
     • Beam fired through body from X-ray tube - picked up by detectors (rotated during scan)
     • Forms image of 2D slice through body - put multiple scans together --> 3D image
   • Treating cancer
     • Cause ionisation - kill cancer cells
       • Radiographers wear lead aprons, stand behind lead screen or leave the room

2. Ultrasound

   • Higher frequency than upper limit of human hearing - 20000 Hz
   • Wave passes from one medium to another
     • Some reflected off boundary - partial reflection
       • Time it takes to reach detector - measure how far away boundary is
   • Oscilloscope traces: distance = speed x time
     • Then divide by 2
   • Uses
     • Breaking down kidney stones - turn hard masses into small particles
     • Pre-natal scanning of a fetus - waves reflected off fetus

3. Medical imaging

   • Safe?
     • Ultrasound: non-ionising - safe
     • X-rays: ionising - can cause cancer, not for babies
     • CT Scans: more ionising - should only use if really needed
   • Image quality?
     • Ultrasound: fuzzy
     • X-rays: clear images of bones & metal
     • CT Scans: detailed, high resolution images - 3D