Medical Physics - Medical Applications

This GCSE Physics quiz looks at medical applications. A knowledge and understanding of physics is widely used in medical applications to provide better treatment and prevention of illness and ailments. Probably the first to spring to mind is the use of X-rays for examining broken bones, but there are many more such as Computerised Tomography (CT) scanning machines and endoscopes. Radioisotopes can be injected or swallowed and their radioactivity can be measured from outside of the body. This enables doctors to follow how the body is working. Medical radioisotopes have short half-lives and do not emit alpha particles. Inside the human body, alpha particles are the most damaging form of radiation.

For the GCSE, you are required to know about X-rays and ultrasound for scanning, and about using light for image formation with lenses and endoscopes.

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You could be tested on your knowledge of the structure of the eye and how lenses can be used to correct sight defects; you may have to draw and interpret ray diagrams to work out what type of image is formed; you might be challenged to compare the medical uses of any of these applications or even evaluate the advantages and disadvantages of different applications, so make sure you have revised them well.

X-rays are high energy electromagnetic waves that can pass easily through soft tissue like skin, the heart and lungs, however, it is harder for them to pass through solids like bones and teeth. This makes X-rays very useful for dentists, also for doctors who are treating broken bones as they can see exactly what needs doing. Soft tissue isn't completely transparent to X-rays and the method of Computerised Tomography provides enough data to produce a detailed view of soft tissue as well as bones. During a CT scan, many images are taken from different angles and combined using a powerful computer. Since the images are computer generated, they can be used to give three dimensional images of the internal organs. Doctors can then look at any of the organs in great detail from any angle. This is extremely useful to surgeons operating on cancer tumours as they can see the exact size and shape of a tumour before operating.

The disadvantage of X-rays is that they are ionising radiation and therefore could harm the patient and radiographers (medical staff who operate X-ray machinery). Applications using light or ultrasound are non-ionising, ultrasound is safe enough to use on pregnant women to check on the progress of the baby. Light cannot penetrate the body deeply enough to see beyond the skin but it is used for endoscopes. An endoscope is used to look inside body cavities and is used to examine the oesophagus, inside of the stomach, the intestines and trachea.

Endoscopes have also enabled surgeons to develop keyhole surgery. This is so-called because the surgeon makes only a small incision (cut) and works using an endoscope. In normal surgery, a large incision is made and the surgeon looks directly at what they are doing. The biggest advantage of keyhole surgery is that it is less damaging to the patient who will therefore recover faster. Light is shone down the endoscope for illumination. The light reflects off the surrounding tissue and travels back up to a camera, through which the surgeon can see what they are doing. The endoscope is constructed from a bundle of optical quality glass fibres which transmit the light very efficiently by total internal reflection.

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  1. Which of the following is NOT an advantage of a CT scanner over an X-ray?
    A CT scan involves taking many images using X-rays so a greater dose of radiation passes through the patient
  2. Radioisotopes are used in medical imaging to view how the body is functioning, but how are radioisotopes selected to be used in this kind of imaging process?
    When radioisotopes emit their radiation, we can detect the radiation with accurate detectors allowing us to track the path of the substance in the body
  3. Which of the following radiation used in medical physics is non-ionising?
    It can be used to examine a foetus as it will not harm its cells
  4. What does a CT scanner usually consist of?
    This enables three-dimensional images of the patient to be built up
  5. Which type of lens would be used to correct short-sightedness?
    In short sight, the lens of the eye bends the light too much so the focal point is in front of the retina. The use of a concave lens moves the focal point so that it is exactly on the retina and therefore the image is in focus
  6. Which of the following would be used to obtain an image of a person's bone structure?
    X-rays do not pass through solids as easily as soft tissue
  7. Which type of lens would be used to correct long-sightedness?
    The focal point in long-sightedness is behind the retina, using a convex lens in front of the eye's own lens shortens the focal length, bringing the light to a focus exactly on the retina
  8. Which type of radiation is used to sterilise foods and medical equipment?
    The high energy of gamma rays is able to kill off bacteria which could cause illness or reduce the time a product stays fresh
  9. Which of the following radiation used in medical physics is ionising?
    Ionising radiation can damage the DNA within cells
  10. What are possible dangers of using X-rays in medical physics?
    Radiographers need to be protected from the X-rays. Potentially, because they use the X-ray machine several times each day, they could be exposed to harmful amounts of radiation

Author: Martin Moore

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