Safety Issues
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Many of the techniques used in medical imaging involve the use of ionising radiation i.e. X-rays and gamma rays. These include general X-ray examinations, fluoroscopic screening, CT, digital angiography, mammography,OPG and nuclear medicine. X-rays and gamma rays are examples of electromagnetic radiation. The electromagnetic spectrum encompasses many familiar forms of radiation including visible light, ultraviolet light, infrared radiation (heat) and radio waves. Ionising radiation is at the higher energy end of the spectrum. A unique property of ionising radiation is the ability to displace electrons from their orbits. A chemical substance that has had an electron displaced from its orbit can react with other chemicals. The ability to change chemical structure constitutes the main safety concern with exposure to ionising radiation. In medical imaging, the total dose of radiation used is small and is therefore not significant when balanced against the potential benefit of the examination.
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In fact we are all exposed throughout our lives to natural sources of radiation including ionising radiation. Natural extraterrestrial sources (cosmic rays) and naturally occurring radioactive elements on earth contribute around 75% of the average Australian person's exposure with medical X-rays and nuclear medicine accounting for around 10 to 15% combined.
Even though the risks are so small, precautions are used to minimise radiation exposure to patients, escorts and staff. The staff are exposed to radiation on a daily basis and as the risks accumulate, lead shielding and lead gowns are used as required by legislation. All radiographers are monitored for radiation exposure with radiation sensitive badges. Escorts are allowed in the examination rooms only if essential e.g. in the case of a distressed child. Lead gowns are provided to escorts to minimise unnecessary radiation exposure. The examination is tailored to the minimum number of images consistent with an accurate diagnosis again to reduce the total radiation dose. Modern equipment also can assist in reducing the radiation load e.g. with automatic exposure control in general X-ray examinations and efficient X-ray detectors in CT scanners. X-ray tests are not ordered or performed unless they are considered to be of benefit to the patient. When all is considered, there is no justification for undue concern in respect of the radiation exposure.
Another safety issue relates to the use of X-ray contrast media. QDI only uses non-ionic contrast media (currently Omnipaque) which is the safest available. During an injection, a sensation of heat, an unusual taste or smell or a sensation in the bladder may be experienced for less than a minute. After this short period, there is no noticeable side effect of the contrast agent. The contrast is filtered by the kidneys and passes unaltered into the urine with most of the dose eliminated within four hours. Occasionally minor allergic reactions such as hives can occur. More rarely a major allergic reaction can occur with a more widespread rash, swelling in the larynx, asthma or a drop in blood pressure. All QDI sites that administer contrast are stocked with drugs, emergency equipment and oxygen to deal with these rare reactions. Patients with a history of allergic reactions, asthma, diabetes or myeloma with kidney failure require special precautions. |
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