Positron Emission Tomography

positron emission tomography

Positron emission tomography (PET for short) is one of the most informative methods used in nuclear medicine. This medical imaging technique involves the application of a special camera and a radioactive chemical (tracer) for looking at organs in the body. The basis of this method is the possibility of using special detecting equipment, namely the PET scanner, in the body to monitor the distribution of biologically active compounds labeled with positron-emitting radioisotopes. The effectiveness of PET is largely determined by the available range of chemical compounds: radiopharmaceuticals. Namely, the choice of a suitable tracer allows us to study different processes like metabolism, transport of substances, the ligand-receptor interaction, gene expression, and other with the help of PET. In modern medicine, this type of tomography is considered a versatile device, since it allows using the radiopharmaceuticals that belong to different classes of biologically active compounds. Therefore, the development of new radioactive chemicals and efficient synthesis of already-established drugs are now becoming a key step in the improvement of PET scan approaches.

Everybody knows about the other methods of body scanning, such as computed tomography (CT) or magnetic resonance imaging (MRI). They help in viewing the anatomical structures of a body. Owing to CT or MRI, the specialists are able to provide us with the details about bony structures and soft issues. These techniques have to find the answer on how the body parts or abnormalities look like. However, the researchers looked for more useful scan methods for clinical purposes. The new medical technique was considered to answer how the body works and how all the inside processes flow. Thus, in 1961, James Robertson and his associates at Brookhaven National Laboratory built the first single-plane PET scan, nicknamed the “head-shrinker” (Vaughan editor, 2010, p.25-26). In 1976, the images of the brain and a whole body were acquired successfully while using the initial type of the PET scanner. With the passage of time the PET scans properties enhanced owing to the invention of labeled 2-fluorodeoxy-D-glucose (FDG). It is worthy of note, “the compound was first administered to two normal human volunteers by professor of radiology Abass Alavi in August 1976 at the University of Pennsylvania” (CT Scan vs. PET Scan, n.d.). Having put such a tracer liquid into a vein, it is possible to get the camera records of positively charged particles (positrons), which in their turn detect biochemical changes in an organ or tissue. It happens because “gamma rays are created during the emission of positrons, and the scanner then detects the gamma rays” (Johns Hopkins Medicine Health, n.d.). Creating an image map of an inspected organ or tissue occurs with the help of a computer, which analyzes those gamma rays.

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It is known that the first devices were equipped with a small number of detectors. But even the lack of detailed anatomical structures provided by PET, could not hold an extensive use of this technique in clinics. Thus, PET scanning is the most developing medical method in the USA nowadays. However, providing this technique remains a complicated process, since it is limited by the availability of the radiopharmaceuticals required for imaging. The physical life of radiotracer fluorodeoxyglucose (FDG) is very short (about only 2 hours). Therefore, each PET scanner must be in close proximity to PET radiopharmaceutical manufacturing facilities. The construction of such a center costs about $2 to $4 million. For this reason, clinical PET is mostly accessible in large cities. Smaller cities are served with mobile scanners a few days per week as well, herewith extending the PET scanning to the markets. However, the extension rate is not enough to be taken as a sufficient radiopharmaceutical supply throughout the country. The solution of this problem supposes creation of locally owned PET radiopharmaceutical manufacturing centers that produce quality products for a limited market.

Initially, it was assumed that the main use of PET would be cardiology. In the 1980s this method was used to determine alterations in the brain function caused with neuropsychiatric disorders (Kim, 2013, p.129). Nowadays, the positron emission tomography combined with the computed tomography, has become one of the most innovative clinical imaging facilities for cancer recognition and checking the blood flow. The statistic shows that oncology scans with FDG usage make up over 90% of all PET made images in a current practice. Thus, namely this type of tomography can detect metastatic tumors that might not be visualized by other imaging techniques. Hodgkin’s lymphoma, non-Hodgkin lymphoma, and lung cancer can be detected and diagnosed through the PET technique. In addition, the facility can be used to assess response to chemotherapy. As mentioned before, PET scans are effectively used in cardiology and neurology along with oncology. In cardiology, PET provides information on myocardial perfusion, metabolic rate, and also detects signs of coronary artery disease. The diagnosis of such neurological disorders as stroke, epilepsy, Parkinson’s disease and Alzheimer’s disease is possible owing to PET scanning as well. Various psychiatric diseases, including depression, Tourette syndrome, schizophrenia and others are investigated with the PET technique. Moreover, this tool assists designing the most appropriate and beneficial therapies in major areas of medicine.

It is obvious that the PET scan facilities have some disadvantages since the radiation is involved in the process. However, the risks are well worth it because PET systems help in saving lives through timely recognition of the tumors or other diseases. As it was mentioned, the machine exposes the patient to radiation during a scan process. In high doses, it might be very harmful to human bodies. Despite small amounts of radiation emitted by a PET scan, the patients can face great risks if they are under exposure of x-rays at their works or in their everyday lives. Another evident disadvantage of PET application is the cost. As the Internet site on diseases research indicates, “a PET scan costs can reach, on average, eleven hundred dollars” (PET Scan,2003-2010). Therefore, a situation remains problematic for people who would considerably benefit from a PET scan.

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Having overviewed such modern medical scan facility as PET, we can make the following conclusion on the above. Positron emission tomography is a diagnostic study of the physiological processes that are based on the detection of positron radiation being injected into a body. PET provides a unique opportunity to conduct an early diagnosis of cancer, neurological, and cardiovascular diseases, which are the most common causes of death. A survey of patients at a level of metabolism and vital processes in the body became accessible due to the refinement of the first types of positron emission tomography devices.

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