Application of PET/CT in the Diagnosis of Oral Cancer

Nuclear medicine is one of the latest and cutting edge innovations in the diagnosis of Head and Neck Cancer. The extensive development of fusion imaging that can acquire both anatomic and functional images in a single scan has been a true evolution in medical imaging. Nuclear medicine aids in imaging the metabolism and other physiological process of specific organism human beings and thereby unveils the various functional and biochemical processes with accuracy which makes it a very dynamic and powerful tool in diagnosis and treatment of diseases. The purpose of this review is to discuss the application of nuclear medicine studies in the diagnosis of Head and Neck cancer. Introduction Nuclear medicine is a medical specialty in which radioactive materials are used for diagnosis by imaging and non-imaging techniques and for therapy in many disease processes. In nuclear medicine procedures, radionucleidesare combined with other elements to form chemical compounds, or else combined with existing pharmaceutical compounds, to form radiopharmaceutical. These radiopharmaceuticals, once administered to the patient, can localize to specific organs. This property of radiopharmaceuticals allows nuclear medicine to image disease process in the body, based on the cellular function and physiology, rather than physical changes in the tissue anatomy. 1 Nuclear medicine is "endo-radiology" because it records radiation emitting from within the body rather than radiation that is generated by external sources like X rays. Nuclear medicine imaging Studies are generally more organ or tissue specific (e.g.: lungs scan, heart scan, bone scan, brain Scan, etc.) than those in conventional radiology imaging, which focus on a particular section of the body (e.g.: chest X-ray, abdomen/pelvis CT scan, head CT scan, etc.). 1 PET/CT in Oral Cancer 2(2);2016 158 Journal Of Applied Dental and Medical Sciences 2(2);2016 Hybrid scanning techniques Nuclear medicine scans can be superimposed, using software on CT or MRI to highlight the part of the body in which the radiopharmaceutical is concentrated. This practice is often referred to as image fusion, for example SPECT/CT and PET/CT. The fusion imaging technique in nuclear medicine provides information about the anatomy and function, which would otherwise be unavailable, or would require a more invasive procedure or surgery. 2 Nuclear Imaging Radioisotope imaging is based upon making the tissues radioactive and the patient becoming the source of ionizing radiation. This is done by injecting certain radioactive compounds into the patient that have an affinity for particular tissues — so-called target tissues. The radioactive compounds become concentrated in the target tissue and their radiation emissions are then detected and imaged, using a gamma camera. 1 This investigation allows imaging the function of the target tissue to be examined under both static and dynamic conditions. Areas where uptake is goodimage demonstrates positive uptake or a ―hot spot‖and areas of non-uptake refereed as ―cold spot‖. Both cold and hot spots are significant for the presence of disease. Innuclear medicine procedures ionizing Xrays with energies of 20-510 Kev is used to generate an image. The patient, rather than machine, is the source of radiation.The sensitivities of nuclear medicine imaging are high. The specifity of nuclear medicine procedure is low. 1 Positron Emission Tomography PET is more advanced imaging modality , sensitivity 100 times than that of gamma camera, relies on positron-emitting radionuclides, was discovered by Dr. David Townsend & Dr. Ron Nutt Invented in 1970 Nuclear imaging lack accurate anatomic landmarks for precise localization and characterization of findings, despite the fact that specific radiopharmaceuticals are used for assessment and diagnosis of specific disease processes. These considerations explain why morphologic (CT) and functional imaging modalities (SPECT and PET) are complementary and not competing techniques. Diagnosis and characterization of disease by both CT and MRI imaging is based on morphologic criteria such as size, texture and tissue attenuation. CT and MRI provide information regarding changes in organ size and tissue density, as well as their precise spatial localization and topographic landmarks. PET imaging, on the other hand, is based on the bio-distribution of a radioactive agent over time and space, enabling visualization of dynamic physiological and pathophysiological processes that define the functional characteristics of disease. To overcome this limitation so these hybrid modalities allow in a single diagnostic procedure a combined evaluation of function and structure, while obtaining the most from each modality. 3 PET/CT PET produces a three-dimensional picture of functioning processes in the human body, allowing for the evaluation of tissue metabolic activity. In PET a positron emission radionuclide or tracer are able to track a specific biologic process at molecular level which is injected into the patient. As these radioactive tracers decay, they emit positrons, which are then PET/CT in Oral Cancer 2(2);2016 159 Journal Of Applied Dental and Medical Sciences 2(2);2016 detected using a PET scanner. The resulting images will help distinguish between normal and abnormal cellular/molecular activity. Positron emitters are radionuclides like fluorine-18, carbon-11, oxygen-15 and nitrogen-13, which in their non-radioactive state are normal constituents of all biologically active molecules. 4