Scintigraphy scans are by far the most common radiation-based medical tests, though they are nowhere near as widespread as X-ray diagnoses. In the OECD countries with higher levels of healthcare, the number of scintigraphy scans went up to 19 per 1000 people in the period between 1996 and 2000. By comparison, X-rays went up to 920 per 1000 people in the same 4 years.
At this level of 19 scintigraphy scans per 1000 people each year, there is a good chance that every inhabitant of a developed country will undergo a nuclear medical test in his lifetime. Positron emission tomography, however, is still relegated to a marginal role in this field, owing to the bulky equipment needed for its use.
The risks of radiation exposure posed by such 'nuclear screenings' are negligible when compared to their potential benefits. As in all situations where radioactivity is involved, however, precautions are at a maximum and so the number of examinations is kept to a minimum. Though the doses absorbed can vary considerably between tests, they are generally comparable to those absorbed in the course of the more common X-ray scans.
The X-ray radiographies or scans mentioned above all involve radiation whose sources are external to the body, whereas exposure resulting from a tracer located inside the body is referred to as internal. The radioisotopes which are administered usually have very short biological half-lives and as a result leave the body in the space of a few hours. The relevant effective doses (Medical Internal Radiation Doses) are measured by dosimeters and then modulated according to the patient's age and sex.