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Radionuclide Imaging in Oral and Maxillofacial Diagnosis Introduction Henri Bequerel (1896) Marie Curie (1898 ) Introduction Nuclear radiology is a sub-specialty of radiology in which radioisotopes are introduced into the body for the purpose of imaging, evaluating organ function, or localizing disease or tumors. Introduction Radionuclide imaging is the technique of producing diagnostic images by analyzing the radiation emitted from a patient who has previously been given radioactive medications Introduction Nuclear medicine differs from most other imaging modalities in that the tests primarily show the physiological function. Nuclear Imaging Basic Principle In diagnosis, radioactive substances are administered to patients and the radiation emitted is measured. The majority of these diagnostic tests involve the formation of an image using a gamma camera. After the radioactive tracer material is administered. The patient lies very still on a table while a special camera detects gamma radiation. Which is transmitted to computer . The physician studies the computerized images to assess how well an organ is functioning. Essential Requirements The radiopharmaceutical The radiation detection system The analyzing system The display and recording system Radiopharmaceuticals They are radioactive compounds. when these agents are injected I.V. into the patients, they are up taken by the target tissues, accumulate in them, then detected and imaged by external detectors. And imaging systems. Radiopharmaceuticals Radiopharmaceuticals Natural Artificial Radionuclide Production They are produced by : Generators Cyclotrons Nuclear reactors Radionuclide (label) All radiopharmaceuticals include in their molecule structure a radionuclide (label) which: Enables their movement within the body to be traced Physiological function to be assessed. Choice of radionuclide Able to combine to form a wide range of chemical compounds Have a specific activity Give suitable type of emission Have a suitable radioactive decay rate Today, technetium 99mTc is the most widely used imaging isotope in nuclear medicine!! Technetium Chemically versatile Conveniently available Emits only gamma photons ( 140 ke V) Decay rate T1/2= 6 hours Obtaining Technetium Mo-99 is obtained from the nuclear reactor as a fission by-product or produced from Mo-98, a naturally occurring metal, by neutron flux exposure. Tc-99m is generated at the site of its use from its parent radionuclide (Mo-99) by a chemical process called solvent extraction method. The basic Tc-99m compound obtained from this method is sodium pertechnetate (NaTcO). Technetium Generator Essential Requirements The radiopharmaceutical The radiation detection system The analyzing system The display and recording system Gamma Camera Gamma Camera A gamma camera is an imaging device, most commonly used as a medical imaging device in nuclear medicine. It produces images of the distribution of gamma ray emitting radionuclides. The gamma camera Detector Collimator Photomultiplier tubes (PMT) Preamplifier Amplifiers Pulsed-height analyzer (PHA) An X-Y positioning circuit Display or recoding device Prevents scattered radiation discards they determine the scatter photons location of each scintillation as it the crystal protects occurs in the crystal. and prevents the detection of radiation detects the from outside the fluorescent flashes collimator field of and converts Sodium iodide with view. scintillations into weak thallium doping in a signals light-sealed housing. It converts photon energy into light amplify signals from the PMT The analyzing system The purpose of the analyzing system is twofold: Position analysis: The precise position in the scintillation crystal is computed Signal strength analysis: detected with (PHA) Single Photon Emission Computed Tomography (SPECT) Single Photon Emission Computed Tomography (SPECT) SPECT studies entail: acquiring rotating delayed static images, generally sixty-four projections over 360º followed by computer reconstruction to provide three dimensional multiplanar slices in the axial, coronal, and sagittal planes, relative to the patient’s body. Single Photon Emission Computed Tomography (SPECT) Use of a gamma camera with the capacity to rotate 360 degrees about the patient multiple detectors single moving detector Single Photon Emission Computed Tomography (SPECT) Because of the complex threedimensional anatomy with extensive overlap of bony structures, It may be difficult to evaluate with planar bone scan images. Single Photon Emission Computed Tomography (SPECT) SPECT bone scanning offers both enhanced: image contrast resolution more accurate localization of active disease as it provides 3D information allowing the interpreters to visualize in transaxial, coronal, and sagittal slices, structures that would overlap on planar views. Single Photon Emission Computed Tomography (SPECT) The SPECT technique: easier to perform better reproducibility Gives better localization of the condyles Better sensitivity More time and cost efficient Salivary gland scan Salivary gland scan Definition A salivary gland scan is a nuclear medicine test that examines the uptake and secretion in the salivary glands of a radioactively labeled marker substance. The pattern of uptake and secretion shows if these glands are functioning normally. Scintigraphy (radioisotope imaging) It provides a functional study of the salivary glands, taking advantage of the selective concentration of specific radiopharmaceuticals in the gland. Scintigraphy (radioisotope imaging) It depends on the selective conc. Of 99mTc in the gland and then its excretion (the dye appears after injection and reaches max. conc. Within 30 mints). Salivary gland scan Purpose Evaluation of functional status of salivary glands Vasculatrity Duct function Patency of larger ducts Detection and evaluation of mass lesions Proprative localization of tumors Scintigraphy (cont.) Advantages: Disadvantages: Allow bilateral Lacks specificity comparison.of the 4 radiation dose glands in one image. Demonstrates little Can be performed in morphology acute infection or gland which can not be cannulated. Computer analysis of the results are possible. Salivary gland scan The patient is positioned under a gamma scintillation camera that detects radiation. The patient then is injected with a low-level radioactive marker, usually technetium-99m or technetium pertechnetate. Salivary gland scan Immediately after the injection, imaging begins. After several images, the patient is given lemon drop candies to suck on, which stimulate the salivary glands. Another set of images is made for comparison purposes. Normal results Normally functioning salivary glands take up the radiopharmaceutical then secrete it when stimulated by the lemon drops. Abnormal results Abnormally functioning salivary glands fail to exhibit a normal uptake and secretion pattern. Scintigraphy (radioisotope imaging) Saliva excreated in the mouth Parotid Subman. Thyroid 0-5 min 6-15 min * 16-20 min 21-25 min *=Acid stimulation at 15 min. Subman. Parotid * * Scintigraphy (radioisotope imaging) Bone Scanning Bone Scanning Definition A bone scan is a diagnostic procedure used to evaluate abnormalities involving bones and joints. A radioactive substance is injected intravenously, and the image of its distribution in the skeletal system is analyzed to detect certain diseases or conditions. Bone Scanning Bone is an extraordinarily dynamic tissue. Constant turnover in response to metabolic or mechanical demands results in a steady state between new bone formation and resorption. Bone-imaging techniques there are a number of ways to perform a bone scan study. The method chosen is typically influenced by the clinical diagnosis to be evaluated. Bone-imaging techniques Bone-imaging techniques include, basically: standard bone scan three-phase bone scan single photon emission computed tomography (SPECT) Standard bone scans involve the acquisition of static images three hours after tracer administration. Delayed static images may be useful in the evaluation of benign conditions, such as condylar hyperplasia. Three-phase study Three-phase study comprises flow assessment, blood pool image, delayed static views acquisition. Three-phase study Three-phase study comprises flow assessment, blood pool image, delayed static views acquisition. Three-phase study The dynamic flow study requires rapid sequential images for sixty seconds during the intravenous administration of the radiotracer. This is followed by a blood pool image reflecting tissue hyperemia and is acquired immediately after the flow study. Three hours after radiotracer administration, the bony uptake of technetium-99m labeled diphosphonates is maximal, and a significant proportion of the unbound tracer will have been excreted by the kidneys. Therefore, the final delayed staticimages are acquired at this time. Three-phase study Three-phase examinations are frequently performed to evaluate: trauma inflammatory disease, primary bone tumors. Normal results The normal appearance of the scan will vary according to the patient's age. In general, a uniform concentration of radionuclide uptake is present in all bones in a normal scan. Abnormal results Bone scanning Hot spots uptake Cold spots uptake Bone Scanning Scintigraphically, areas of increased bone metabolism are evidenced and appear as areas of increased radiotracer uptake, namely “hot spots.” Bone Scanning Decreased uptake is associated with metabolically inactive bone, lack of osteogenesis, or an absent vascular supply.where there is diminished or absent uptake, are called “cold spots.” Advantages of bone scan In many clinical conditions, bone scintigraphy will demonstrate abnormalities long before the radiographs. Conventional radiologic techniques demonstrate bony changes when there has been an alteration of 30 to 50 % of the bone mineral content Dependes on differential absorption Bone scans Has the ability to show reactive modifications in osteoblastic activity that would not appear on radiographic images, but do not show morphologic changes positive if there is, approximately, a 10 % increase in the osteoblastic activity above normal Bone Scanning Bone scintigraphy has the potential to provide valuable information concerning the diagnosis and follow-up of several oral conditions such as: primary or metastatic malignancies, benignneoplasms, cystic lesions, inflammatory and infectious processes, metabolic diseases, fibro-osseous dysplasias, hyperplasias, bone graft viability Primary and Metastatic Malignancies The superior sensitivity of bone scintigraphy in providing valuable information for preoperative assessment of the malignant lesions’ extent has been reported by many authors. The most frequently encountered scintigraphic pattern in malignant bone lesions is that of one or multiple randomly distributed foci of intensely increased radiotracer uptake, the so-called “hot spots” Inflammatory and Infectious Processes Inflammation represents a dynamic process that takes place in the connective tissue as a reaction to intrinsic and/or extrinsic agents. Accordingly, some oral conditions such as osteomyelitis, traumatic injuries osteoarthritis, periapical lesions, periodontal disease play an important role in bone metabolism and result in a positive bone scan image. Inflammatory and Infectious Processes The usefulness of the bone scan as a diagnostic aid for inflammatory responses of the temporomandibular joints (TMJ) is somewhat controversial. However, attempts have been made to improve the evaluation of the metabolic and physiological status of TMJ bony structures. In fact, bone scans may demonstrate inflammatory reactions that take place in TMJ bony structures, Inflammatory and Infectious Processes Inflammatory and Infectious Processes Fibro-Osseous Dysplasias Fibrous dysplasias of the jaw are believed to be benign, self-limiting, but nonencapsulated, lesions occurring mainly in young subjects. Histologically, they are characterized by the replacement of normal bone by a cellular fibro-osseous tissue containing islands or trabeculae of metaplastic bone. Fibro-Osseous Dysplasias Radiographs are usually adequate for the diagnosis however, bone scintigraphy is often useful to establish the extent and activity of maxillofacial lesions. Fibro-Osseous Dysplasias Bone Graft Viability Bone scintigraphy provides a means of predicting graft failure before radiographic or clinical changes become apparent and, thus, helping to avoid a loss of surrounding bone from graft necrosis or infection. useful in reconstruction of the jaw that usuallyinvolves a vascularized bone autograft, becauseclinical monitoring of the transplanted bone is difficult In Conclusion Conclusion Radionuclide imaging has its advantages and disadvantages Morphologic and physiologic imaging modalities,in combination, should support each other in offering valuable information diagnosis Thank You