Introduction to imaging: Ionising radiation
In the first part of our new series about medical imaging, John Frank looks in detail at imaging techniques that use ionising radiation
There are four basic methods of imaging the body, using x rays, gamma rays, sound waves, or magnetism. Each method has its own place; the techniques are complementary, not mutually exclusive. In the first part of this series, I concentrate on using ionising radiation.
For isotopes with a short half life given in normal diagnostic doses, the patient or anyone else is not at risk and radiation levels are well within the normal range of background radiation--exposure is equivalent to watching television. Patients who have had a diagnostic scan can go near pregnant women or children without causing them any harm. It is important to inform the patients about this because they may worry needlessly, associating radiation with atomic bombs or Chernobyl.
However, therapeutic administration of isotopes is different. Patients may be given an isotope with a longer halflife, such as iodine-131, in the treatment of thyrotoxicosis and thyroid cancer.