What is a radiopharmaceutical?
A radiopharmaceutical is a medication used in nuclear medicine that has a radioactive part and a pharmaceutical part. The radioactive part is sometimes referred to as a radioactive label or a radioactive tracer. The radioactive part is an unstable element (radioisotope) that gives off energy as it decays (disintegrates or breaks down) and changes to a different element or energy state. The actual amount of the radioactive substance given for most imaging tests is usually very small; approximately millionths of a gram. The dose of ionising radiation received by a patient having a nuclear medicine test can be very low or moderate - the dose varies between different types of studies. The ionising radiation is in a similar range to that received from computed tomography (CT) imaging. The radioactive part is most commonly Technetium 99m, but other radioisotopes such as iodine 123, indium 111 and gallium 67 are also used. Fluorine 18 is a radioisotope used in positron emission tomography (PET) imaging.
The body does not feel the ionising radiation, and it does not make you 'warmer' or 'glow in the dark'. The number of times the nuclear medicine camera takes images does not determine the dose of ionising radiation received during a nuclear medicine test. It is determined by the type and amount of radiopharmaceutical injected, the half-life of the radioisotope and how quickly this is eliminated from the body in urine, stools or breath. The half-life is the time taken for half of the radioactive atoms to decay or change their energy state. For most radioisotopes used in nuclear medicine, this half-life is measured in hours, so after a day or so there is very little radioactivity remaining.
The pharmaceutical part can be a few atoms or a complex molecule that helps take the radioactive part to the area of the body being studied. It is mostly the choice of the pharmaceutical part that determines where the radiopharmaceutical will go in the body and what organ system will be shown. Technetium 99m MDP is used for a nuclear bone scan, whereas technetium 99m MAG3 is used for a nuclear renal scan.
What is a gamma camera?
A gamma camera is a machine that is able to detect and make images from the very small amounts of ionising radiation emitted from patients having a nuclear medicine study. The gamma camera usually has a table, often narrow, on which the patient lies. The images are taken using the camera 'head'.
A camera might have one, two or occasionally three heads, with one or more being used to obtain the images. Each camera head has a flat surface that has to be very close to the patient. The camera heads might be supported in a number of different ways using strong metal arms or a gantry. There are no unusual sensations associated with having images taken with a gamma camera and the machine makes no noise.
How is nuclear medicine different from normal x-ray and CT examinations?
During a normal x-ray or CT examination, an image is formed from the 'shadow' created by the body as it is positioned between the x-ray machine (source of the x-ray beam) and the x-ray detector. The body stops some, but not all, of the X-rays and the patient is not made radioactive by the X-rays.
In nuclear medicine studies, the radiopharmaceutical given to the patient makes them, and the organ system or body part being studied, radioactive for a short time. This ionising radiation (usually a gamma ray) is emitted or released from the body, and can be detected and measured using a nuclear medicine gamma camera. All living things contain some radioisotopes (such as carbon 14 and potassium 40); a nuclear medicine study will make them 'more radioactive than normal' for a short time – hours or days.
An x-ray or CT image is formed from ionising radiation (x-rays) that passes through the body, but does not arise from the body; whereas a nuclear medicine image is formed from the ionising radiation (usually gamma rays) emitted from within the body. A gamma ray has similar properties to an x-ray, but it arises from the nucleus of an atom, whereas an x-ray arises from the electron shell of an atom.
Another way that nuclear medicine is different from x-ray and CT examinations is that an x-ray study shows what something looks like. This gives indirect information about how it is working: normally, abnormally, diseased, injured and so on. In nuclear medicine studies, the radiopharmaceutical usually only goes to the part of the body or organ system if it has some function and so shows how it is working. The images can also give information about what the body part or organ system looks like.
Nuclear medicine and x-ray tests are often complementary, providing different information that together make a diagnosis more certain.
What are the benefits of a Nuclear Medicine Study?
A nuclear medicine study helps your doctor evaluate how a particular area of your body or organ system is working. It can give information about how an injury, disease or infection might be affecting your body. It can also be used to show improvement or deterioration of a known abnormality after any treatment you might have had. Nuclear medicine studies are very good at showing how an organ system is working, and often complement other investigations and imaging studies.
