Radioactive isotopes provide physicians the unique ability to “look” inside the living body and observe soft tissues and organs in a manner similar to the way X-rays provide an image of a patient’s bones. Nuclear technicians often inject certain radioisotopes into the bloodstream so that physicians can detect clogged arteries and monitor the overall performance of a patient’s circulatory system. For example, physicians often use the medical radioisotope thallium-201 (half-life, 73.5 hours), to identify regions of a patient’s heart that are not receiving enough blood. The medical profession calls this important procedure the exercise thallium heart scan—because they use a radioisotope tracer in conjunction with an exercise test to examine a person’s heart muscle. During the procedure, a nuclear medicine technician injects a small quantity of radioactive thallium-201 into the patient’s vein while he or she walks on a treadmill. The thallium attaches itself to the patient’s red blood cells and then circulates throughout the body. Of special interest here is the fact that the gamma ray–emitting thallium tracer eventually enters the heart muscle through the coronary arteries and then collects in the cells of the heart muscle that come in contact with the flowing blood. A gamma camera carefully records the locations in the patient’s body of the gamma rays that are emitted as the thallium-201 decays. Because thallium-201 travels along with the blood, those regions of the heart muscle that have normal circulatory functions have easily detectable gamma ray signals.
Regions of the heart muscle that have an insufficient supply of blood due to blocked or clogged arteries will have lower or even negligible gamma ray signals. The medical radioisotopes (radiopharmaceuticals) commonly used in nuclear medicine emit characteristic gamma rays that are easily detected outside the body by gamma cameras. These special cameras are sensitive radiation detection devices that work in conjunction with computers to form images containing important diagnostic information about the area of the body under investigation. The presence or absence of telltale gamma radiation from the particular medical tracer provides the physician with a great deal of diagnostic data about the organ under study. Physicians sometimes use two sets of gamma camera images taken at different times—for example, while a patient is exercising and, then, is at rest. A differential comparison of the gamma ray patterns in these images reveals to the cardiologist which regions of the patient’s heart have experienced a temporary reduction in blood flow and which regions are permanently blocked or damaged—possibly due to a previous, silent (undetected) heart attack. Radioactive isotopes like thallium-201 play a very important role in the practice of nuclear cardiology. The amount of ionizing radiation dose a patient receives from a typical nuclear medicine procedure is comparable to the dose a patient would receive from a diagnostic X-ray.
Iran Medical Progress amid the Pressures of West and US Unilateral Sanctions
