Nuclear Medicine

Nuclear medicine is one of the important medical aspects that employs the radiation and emission of the radioisotopes to extract functional and morphological information about the specific organs for diagnosing or treating their possible diseases. The heart, thyroid, kidney, bones, brain, liver, and many other organs can be easily imaged by different imaging techniques in nuclear medicine, and also disorders in their functionality can be easily revealed by imaging techniques in nuclear medicine. Also, in some cases, the radioisotopes can be used to treat malfunctioned and diseased organs. Diagnosis and therapy are two major applications of nuclear medicine in the medical field.

Radioactive tracers and radiolabeled molecules are being widely used in diagnostic procedure in the field of nuclear medicine. Most of the radioactive tracers emit a few of the well-known particles such as gamma, beta, or alpha. Since the alpha and beta particles have a short range to pass the tissue and body organs, they can be easily absorbed inside the body and they also cannot be detected by most of the nuclear detectors which operate from outside of the body. On the contrary, gamma rays have a longer range and less chance of nuclear interaction with tissue. Therefore, gamma rays are good candidates for imaging techniques in nuclear medicine.

A radioisotope should be bounded to a pharmaceutical carrier and this combination is called radiopharmaceutical. Each radiopharmaceutical has an effective half-life with respect to its biological and radioactive half-lives. Radiopharmaceutical effective half-life is one of the important parameters for choosing an appropriate radioisotope for both imaging and therapeutic applications. Diagnostic techniques in nuclear medicine employ different imaging modalities and provide reliable and unique information compared to the other techniques. Absorption of radiotracer in an organ with malfunction (hot spots) and regular absorption of radiotracer in normal organs (cold spots) enable physicians to distinguish and diagnose the level of abnormality in an organ. Nowadays, brain and heart imaging with single photon emission computed topography (SPECT) technique routinely are being used and is a part of American Cardiac Association protocol in coronary artery disease diagnosis procedure.

Radioisotope and pharmaceutical technologies have been playing an important role in both diagnostic and therapeutic fields of nuclear medicine. These technologies have tied together and worked hand to hand to produce a variety set of radiopharmacies for different application of advanced imaging and therapeutic techniques. One of the most important and promising radioisotopes is beta+ (positron) particle. The positron's mass is the same as an electron and carries the same charge of an electron but positive. This particle has recently opened a new door to medical physicists and researchers in this field. This particle produces two identifiable gamma rays with specific energy of 0.512 (MeV) after annihilation event. Therefore, this radioisotope can be directed and be absorbed inside the target organ for producing a couple of gamma with the same energy, which can easily pass through the body and be detected by nuclear detectors. The outcome of this is the positron emission tomography (PET) technique, which is one of the state-of-the-art imaging technologies in nuclear medicine, and helps to provide both functional and morphological information from the target organ in diagnosis procedure using positron annihilation mechanism. In a new combined imaging technique, PET and a computed X-ray tomography (CT) scan the patient and, after co-registration of the two images (PET-CT), provide with almost 30 percent better diagnosis than with traditional gamma camera alone. Therefore, the PET-CT imaging system is a very powerful and significant tool, which provides unique information on a wide variety of diseases including dementia to cardiovascular disease, brain diseases such as Parkinson's and Alzheimer's, and cancer. A distinct advantage of nuclear medicine imaging techniques compare to traditional imaging techniques (X-ray) is that both bone and soft tissue [Page 1254]can be successfully imaged at the same time with a reasonable image contrast.

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