The amount of radiation exposure from an imaging test depends on the type of imaging test used and the part of the body being tested. This is about the same amount of radiation that people are naturally exposed to over the course of 10 days. For one year, our natural background radiation dose is approximately 3 mSv. Medical procedures account for almost all (96%) of human exposure to artificial radiation.
For example, a chest x-ray generally gives a dose of approximately 0.01 rem (10 millirem) and a full body CT scan gives a dose of 1 rem (1000 mrem), as shown in the table to the left. Are Nuclear Medicine Tests Safe? Yes, nuclear medicine procedures are very safe. We carefully select the radiotracer and radiation dose to ensure minimum radiation exposure and maximum accuracy. You are exposed to almost the same amount of radiation in a nuclear medicine test as in a diagnostic x-ray. A number of interesting observations can be made on the basis of the data provided in the Table.
Computed tomography and some nuclear medicine studies are associated with much higher radiation doses than x-rays. In particular, radiation doses from some CT and nuclear medicine studies fall within the range that, according to direct epidemiological evidence, are associated with an increased risk of cancer. It should also be noted that recent evidence suggests that CT radiation doses can vary widely between institutions. Radiography doses are within the range for which there is no epidemiological evidence of increased cancer risk (but there may be a very small increase in cancer risk if threshold hypothesis is correct). Spinal and abdominal x-ray has substantially higher radiation doses than chest and limb x-ray.
The effective dose of a PET is modest and depends on the activity of the injected FDG (18F-fluoro deoxyglucose) and is normally 8 mSv for adults using 400 MBq and is the same whether imaging of one part of the body or the whole body. The effects of radiation are known to be cumulative in nature. However, the repair mechanisms in the body are quite active and spacing out procedures with appropriate time intervals helps reduce the effects of radiation, as is done in radiation therapy. At this time, there is no formal mechanism to record and track a patient's cumulative radiation exposure, as is the case with staff. Patients are advised, in their own interest, to inform all physicians about their previous radiological examinations. Although a small amount of radioactive glucose is injected for the PET exam, this will not affect diabetes.
However, it is important for the PET imaging team to know the patient's diabetes. This ensures that the best results of the scan can be achieved and unnecessary doses of radiation are avoided. Positron emission tomography will not affect the conduct of these investigations. However, if other imaging tests are also planned, it is important to avoid any unnecessary duplication of testing by ensuring that all physicians involved in patient care are aware of the imaging tests being performed on the patient. If your doctor recommends a CT scan or a nuclear medicine scan, ask if another technique would work, such as a lower-dose x-ray or a test that does not use radiation, such as an ultrasound (which uses high-frequency sound waves) or an MRI (which depends on magnetic energy).The radiation you receive from x-rays, CT scans, and nuclear images is ionizing radiation, high-energy wavelengths, or particles that penetrate tissue to reveal internal organs and structures in the body. However, many experts are concerned about an explosion in the use of higher radiation dose tests, such as computed tomography and nuclear imaging.
Below 10 mSv, which is a relevant dose range for radiography and some nuclear medicine and CT studies, there is no direct epidemiological data to support an increased risk of cancer. If you need a CT scan or nuclear scan to treat or diagnose a medical condition, the benefits often outweigh the risks. In addition, it is widely accepted that epidemiological data directly suggest an increased risk of cancer in the range of 10 mSv to 100 mSv, which is relevant for nuclear, cardiac and many CT studies. It is important to ask if the center is accredited for CT by the American College of Radiology since accredited centers must undergo regular radiation dose evaluations and are more likely to have considered protocol modifications to reduce the dose.
The benefits of these tests, when appropriate, far outweigh any radiation-associated cancer risk, and the risk of a single CT scan or nuclear imaging test is quite small. Because the radiation weighting factor for x-rays and gamma rays is 1.0, 1 Gy equals 1 Sv in medical imaging. Some researchers suggest that direct epidemiological data from atomic bomb survivors and workers in the nuclear industry indicate an increased risk of cancer in this dose range while others argue that there is no data to support an increase in cancer risk below 100 mSv and that neutron irradiation and other confounding factors may explain the putative low-dose carcinogenic effect seen in atomic bomb survivors.
