The Basic Principles of Positron Emission Tomography - Essay Example

Introduction to PET Positron emission tomography (PET) is a nuclear medication imaging method that generates a three-dimensional representation or image of functional development in the body. The arrangement detects couple of gamma rays emitted circuitously by a positron-emitting radionuclide also known as tracer, which is then commenced into the body on an organically active molecule. Three-dimensional imagery of tracer absorption within the body is then assembled by computer analysis. In recent scanners, three dimensional imaging is often attained with the support of a CT X-ray scan performed on the patient for the duration of the same session, in the similar machine (H.Jadvar, 2004). Positron emission tomography (PET) is a diagnostic imaging modality that employs the use of radiopharmaceuticals to aid in analyzing a variety of health conditions. Simply put, it is a great tool that allows for clinicians to visualize a disease without having to perform invasive surgery on a patient. The technology of emission and transmission tomography began in the 1950’s by several scientists which led to the development of the first single place PET scanner by James Robertson and his associates at Brookhaven National Laboratory in 1961. However, it was only after the approval of fluorodeoxyglucose (FDG) by the Federal Drug Administrator, did the pace for PET pick up (Saha, 2005). The other Radionuclides used in PET are chemical substances that are used up by the body tissues during metabolism such as Oxygen, Carbon and Glucose. A radioactive substance is attached to the chemical entity and metabolism of the respective chemical in the targeted site is observed. PET Mechanism: The basic principle of a PET scanner lies within a radiopharmaceutical, such FDG that contains the positron fluorine-18. This positron combines with an electron, which is then converted into two gamma rays that travel into two opposite directions. The gamma rays are detected by scintillators on the scanner ring that produces light detected by a photomultiplier. Data from the numerous gamma ray detection events are converted into an image by utilizing a set of algorithms in the processing unit (Yu, 2006). Further explanation of PET scan can be elaborated by the synthesis of radioisotope, fluorine-18. In order to produce such a compound, a facility must be near or posses a cyclotron. This is because a radioisotope has short half life. For example, Fluorine-18 has a half-life of two hours. Hydrogen ions are created in the center of the cyclotron and accelerated between the two D shaped copper sheets inside a magnetic field. Once the hydrogen ions reach their peak velocity, they are averted on an aqueous solution enhanced with oxygen-18. Thus, the Flourine-18 is produced and now has to be tagged onto the glucose molecule. To remove the Flourine-18 from the aqueous solution, it is filtered through an ion-exchange column. Once separated from the solution, the Flourine-18 undergoes a substitution reaction in a solution of kryptofix, acetonitrile and potassium carbonate to complete the synthesis of FDG. Finally, the FDG has to be purified by passing it through ion-exchange column for a second time. Just as good practice with any procedure conducted in the laboratory, the FDG is quality controlled to ensure it is radionuclidic purity, bacterial endotoxin test, and sterility (Yu, 2006). Now the radiopharmaceutical can be administered to a patient or a subject, bearing in mind that FDG will require at least one hour for the metabolism, prior to the PET scan. The patient needs to be fasting prior to the administration. Patient must also avoid any type of strenuous exercise to evade any interference from muscular activity or unusual metabolism. Applications: There are many applications for PET. One of them being the utilization of PET is to detect tumors. Tumor cells generally consume much more glucose compared to normal cells due to the higher rate of replication. Their uptake of FDG will be greater than the surrounding area revealing a brighter color on the corresponding image produced on screen. One can also utilize PET to determine what stage the cancer is in, by having the ability to visualize if and where the tumor has metastasized. PET can also be used to determine if a patient has any tumor recurrences. In addition, PET it can be employed to determine the effectiveness of drug treatment. Usage of PET In observing speed with these milestones in the development of medical imaging, positron emission tomography (PET), and in recent times incorporated positron emission tomography-computed tomography (PET-CT), have now appeared not only as significant research tools but also as diagnostic imaging scheme in clinical medicine. There is slight doubt that in the near prospect PET and PET-CT will become even more imperative as clinical imaging tools for the assessment of many sickness processes. PET and PET-CT will also assist in the development from the current non-specific imaging methods on the way to patient-specific imaging valuation based on morphologic, molecular, physiologic and genetic markers of ailment. Eventually, the utilization of multi-modality imaging systems and “smart” specific imaging mediators will accomplish the key tasks of precise diagnosis, treatment valuation, observation, and prediction in individual patients. (radiologyinfo.org, 2012) Limitations of PET Limitations to the extensive use of PET occur from the elevated costs of cyclotrons required to generate the short-lived radionuclide’s for PET scanning. This requirement of PET for particularly personalized on-site chemical synthesis equipment to create the radiopharmaceuticals after radioisotope groundwork is very expensive and inconvenient. Few hospitals and universities are proficient of upholding such systems, and the majority clinical PET is supported by third-party suppliers of radiotracers that can provide many sites concurrently. The process utilizes FDG uptake to recognize physiological activity at the target site, but there are various sites in body where FDG uptake is variant, which can be misunderstood as malignant neoplasm. Thus, only a very experienced oncologist can avoid any false positive results (Shreve, Anzai, & Wahl, 1999). Patient compliance is also somewhat reduced, as patient needs to be fasting before the procedure and also require removing cloths, wallets, jewelry etc., for the imaging (Hamblen &Lowe, 2003). Advantages of PET Positron emission tomography (PET) is an extremely specific imaging technique using short-lived radio labeled materials to make authoritative images of the bodys biological function. PET is helpful in the perspective of cancer. Since, it can notice metastatic tumors that may not be imagined by other imaging techniques. It is also being progressively more used, not only as a cancer analytical tool, but also to assist physicians propose the most helpful therapies. For instance, it may be utilized to assess reply to chemotherapy. PET imaging is very precise in differentiating malignant from compassionate cell growths, and in evaluating the broadening of malignant tumors. PET is also used to identify recurring brain tumors and cancers of the lung, breast, colon, skin, lymph nodes and other organs. (webmd.com, 2011) PET is medicinal imaging modality that inspects all organ scheme of the body to explore for cancer in a single assessment. PET can notify where the tumor is, if it is benign or malignant and if the chemotherapy treatment is functioning. Prior to PET, CT scans would have been taken constantly until a tumor is big enough to be detected; with PET, a single scan of the whole body is sufficient to inform where the tumor is, and at a way prior stage. Disadvantages of PET Some of the disadvantages associated with PET are that the image is not revealed as clearly as it would in an MRI scan. Also, the radioactive isotope specified is only secure for the first couple of times it is used. PET scans can also be costly. Wider operation of PET MPI is delayed by a high cost of entrance, high on-going costs, and an undeveloped compensation structure. PET scanning is non-invasive, but it does entail revelation to ionizing radiation. (H.Jadvar, 2004) Conclusion Most PET scans are executed on instruments that are combined PET and CT scanners. The joint scans have been revealed to offer more precise diagnoses than the two scans performed discretely. References H.Jadvar, J. (2004). Clinical PET and PET/CT. London: Springer. radiologyinfo.org. (2012). Positron Emission Tomography. Retrieved June 16, 2012, from radiologyinfo.org: http://www.radiologyinfo.org/en/info.cfm?pg=pet webmd.com. (2011). Positron Emission Tomography (PET). Retrieved June 16, 2012, from webmd.com: http://www.webmd.com/a-to-z-guides/positron-emission-tomography Top of Form Shreve, P. D., Anzai, Y., & Wahl, R. L. (January 01, 1999). Pitfalls in oncologic diagnosis with FDG PET imaging: physiologic and benign variants.Radiographics : a Review Publication of the Radiological Society of North America, Inc, 19, 1.) Top of Form Yu, S. (October 01, 2006). Review of 18F-FDG synthesis and quality control. Biomedical Imaging and Intervention Journal, 2, 4.) Top of Form Hamblen, S. M., & Lowe, V. J. (January 01, 2003). Clinical 18F-FDG oncology patient preparation techniques.Journal of Nuclear Medicine Technology, 31, 1, 3-7. Top of Form Saha, G. B. (2005). Basics of PET imaging: Physics, chemistry, and regulations. New York, NY: Springer. Bottom of Form Bottom of Form Bottom of Form Bottom of Form Read More