Physics Unit 3 GCSE AQA X-Rays in Medicine

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X-Ray Images;

  • X-rays are high frequency, short wavelength electromagnetic waves.
  • They pass through healthy tissue but are absorbed by denser materials, like metal or bone.
  • They affect photographic film the same way as they do light .
  • X-Ray photographs can be used to diagnose medical problems and dental problems.
  • X-Ray Images are formed electronically using charged- coupled devices.
  • CCD's are silicon chips divided up into millions of identical pixels.
  • CCD's detect X-rays and produce electronic signals.
  • These signals form high resolution images.
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CT Scans

CT Scans;


  • They use X-rays to produce high resolution images of soft AND hard tissue.
  • The patient is put inside the cylindrical scanner.
  • The X-ray beam is sent through the body from an X-ray tube and picked up by detectors on the opposite side.
  • A computer interprets the signals and is then able to draw a two-dimensional picture which is a slice of the patients body.
  • Multiple two-dimensional pictures are put together to form a three-dimensional image of iinside the body.
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Treating Cancer and Precautions being Taken

X-Rays can cause IONISATION- which kills living cells .

  • If the X-rays are focused they are able to kill cancer cells without harming too many of the healthy living cells.

To Treat Cancer

  • The X-rays and focused on the tumour using a wide beam.
  • The beam is rotated around teh patient, with the tumour in the centre.
  • This minimises the exposure of healthy cells to radiation, and it reduces the chances of damaging the rest of the body

Taking Precautions

  • Radiographers have to take precautions to minimise their X-ray dose.
  • They wear lead aprons, stand behind a lead screen or leave the room whilst the scan is being done.
  • Lead is used as a shield the areas of the patient that aren't being screened.
  • Finally the exposure time to the X-rays are kept to an absolute minimum.
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Ultrasound has a higher frequency than we can hear.

  • Electrical systems can be made which produce ELECTRICAL OSCILLATIONS of any frenquency.
  • These are converted into MECHANICAL VIBRATIONS to produce sound waves of a higher frequency than the upper limit of human hearing-This is an ULTRASOUND

Ultrasound waves are PARTIALLY REFLECTED - This means that when the waves pass from one median to another e.g. air to glass, some of the wave is reflected and some is refracted. This is partial reflection.

  • The time is takes for the reflections to reach a detector can be used to measure how far the boudary is.
  • This is how ultrasound imaging works.
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The Uses of an Ultrasound

There are many uses for ultrasounds but the two most common are BREAKING DOWN KIDNEY STONES and PRE-NATAL SCANNING OF THE FOETUS.

Breaking Down Kidney Stones;

  • Kidney stones are hard masses that block the urinary tract.
  • The ultrasound beam concentrates high-energy waves at the kidney so the hard masses turn to a sand-like substance.
  • This sand-like substance is then passed out of teh body through the urine,

Pre-Natal Scanning of the Foetus;

  • Ultrasound waves can pass through the body but when they pass through two different substances e.g. tissue and bone the waves reflect back and are detected.
  • A computer processes the exact timing in which the waves are reflected (echoed)and are converted into a video image.
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The Compromises of Mecical Imaging

Is it safe?

  • Ultrasound are non-ionising so they are safe.
  • X-Rays are ionising so a lot of exposure to the radiation can mutate the cells and turn tehm cancerous.
  • CT scans have an increased amount of exposure to the radiation so are only used if it is really needed.

Are they good quality?

  • Ultrasound can be a bit fuzzy which can make is difficult to diagnose some medical conditions.
  • X-Rays can produce a clear picture of the bones and metal but nothing else.
  • CT scans give a very detailed picture and make it easier to diagnose complicated medical conditions.
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