SUBMITTED BY: Rupal Patle BDS IV YearPeoples Dental Academy
INTRODUCTION DEFINITION: Nuclear imaging is a method of producing images by detecting radiation from different parts of the body after a radioactive tracer material is administered. The images are recorded on computer and on film. The nuclear imaging physician interprets the images to make a diagnosis. Radioactive tracers used in nuclear medicine are, in most cases, injected into a vein.
DIFFERENCE FROM OTHER RADIOLOGIC TECHNIQUES Nuclear imaging assesses how organs function (FUNCTIONAL IMAGING). Whereas other imaging methods Eg. Film radiography, CT, MRI, Diagnostic ultrasonography assess anatomy, or how the organs look (MORPHOLOGIC IMAGING). In some human diseases (bone disorders eg. Condylar hyperplasia) abnormal biochemical process occur prior to the anatomic change. In such diseases, such abnormal biochemical changes can be assessed with the help of nuclear imaging technique. It would not be wrong to call Nuclear Medicine as "Radiology” done inside out" or "Internal Radiology" because it records radiation emitting from within the body rather than radiation that is generated by external sources like Xrays. This technique allows measurement of tissue function and provides an early marker of disease through measurement of biochemical change.
PRINCIPLE OF NUCLEAR IMAGING TECHNIQUE THE STEPWISE PROCEDURE OF NUCLEAR IMAGING:Radionuclides are administered via vein or mouth They distribute in the body according to their affinity for particular tissues so called target tissues. Radionuclides emit gamma radiations. Detected by γ-scintillation cameraWhich forms images showing location of radionuclides in the body.
MAIN INDICATIONS OF NUCLEAR IMAGING Nuclear imaging technique is used for assessing function of:- Salivary gland as salivary scans- Brain- Thyroids- Heart- Lungs- Gastro-intestinal system It is also used for diagnosis of:- Metastatic diseases- Bone tumors as bone scans
RADIOISOTOPES AND RADIOACTIVITY RADIOACTIVITY: Spontaneous emission of radiation, from unstable atomic nuclei. OrIt is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles (ionizing radiation). RADIOISOTOPES: Radioisotopes are isotopes with unstable nuclei which undergo radioactive disintegration. This disintegration is often accompanied by emission of radioactive particles or radiation. The important emissions include: - Alpha particles - Beta- (electron) particles - Beta+ (positron) particles - Gamma radiation.
The main properties & characteristics of these emissions are summarized in table given below: PROPERTY ALPHA BETA- PARTICLES GAMMA RAYS BETA+ PARTICLES PARTICLESNATURE Particulate – two Particulate – Electromagnetic Particulate – protons and two electrons radiation – positron interacts neutrons identical to X-rays very rapidly with aSIZE Large Small Nil negative electronCHARGE Positive Negative Nil to produce 2SPEED Slow Fast Very fast gamma rays –RANGE IN TISSUE 1 – 2 mm 1 – 2 cm As with X-rays annihilation radiation –ENERGY RANGE 4 – 8 MeV 100 keV – 6 MeV 1.24 keV – 12.4 properties asCARRIED MeV shown in adjacentDAMAGE CAUSED Extensive Ionization Ionization – similar column ionization damage to X-raysUSE IN NUCLEAR Banned Very limited Main emission PETMEDICINE used
RADIOISOTOPES USED INCONVENTIONAL NUCLEAR MEDICINE An ideal radionuclide has following properties: - A short half life. - Emits γ-rays. - Capable of binding to a variety of biomolecules. Examples of radionuclides together with their target tissues or target diseases: - Technetium (99mTc) – Salivary glands, thyroid, bone, blood, liver, lung & heart. - Iodine (131I ) – Thyroid - Gallium ( 67Ga) – Tumors & inflammation - Krypton (81K) – Lung
For imaging Technetium is used extensively, as it has following properties:A. Technetium is a gamma emitter. This is important as the rays need to penetrate the body so the camera can detect them.B. It has a short half life of 6 1/2 hours. Thus the amount of radioactive exposure is limited.C. It is readily attached to a variety of different substances that are concentrated in different organs, eg: Tc + MPD (methylene disphosphonate) in bone Tc + sulphur colloid in the liver and spleen.D. It is easily produced, as and when required, on site. Technetium-99m generator or technetium cow or moly cow, is a device used to extract the isotope 99mTc from a source of decaying molybdenum-99.
γ – SCINTILLATION CAMERA A gamma camera, also called a scintillation camera or Anger camera, is a device used to image gamma emitting radioisotopes, a technique known as scintigraphy. These cameras capture photons and convert them to light and then to a voltage signal. This signal is reconstructed to an image that shows distribution of radionuclide in the patient.
Parts of γ – scintillation camera:A. Collimator: First part of the camera that absorbs γ-rays that do not travel parallel to its plates. The figure illustrates a magnified view of a parallel-hole collimator attached to a crystal. The collimator simply consists of a large number of small holes drilled in a lead plate. Gamma- rays entering at an angle to the crystal get absorbed by the lead and that only those entering along the direction of the holes get through to cause scintillations in the crystal. If the collimator was not in place these obliquely incident gamma-rays would blur the images produced by the gamma camera. In other words the images would not be very clear.
B. Scintillation crystal: The γ-rays that pass through the collimator then strike scintillation crystal. Made up of sodium iodide with trace amount of thallium. This crystal shows florescence when it absorbs γ-rays. These flashes of light are detected by photomultiplier tubes coupled to the crystal.
C. Photomultiplier tubes: These tubes detects the flashes of light and convert the light into electronic signal & amplify the signal. Size of signal is directly proportional to energy of absorbed photon.
D. Analog to digital converter: The signals from photomultiplier tubes go through an analog to digital converter (ADC) This component is used to convert the analogue information produced by the imaging system so that it is coded in the form of binary numbers. In this way the analog signal is digitalized & used to produce image by computer.
BONE SCANS Bone scan can detect 10 – 15 % mineral lossIndications:1. Metabolic bone diseases such as fibrous dysplasia2. Pagets disease3. Osteoarthritis4. Osteomyelitis5. Metastasis to bone
Bone scan phases: PHASE TIME IMPORTANCE FIRST PHASE: First 30 sec Differences in vascularity to Radionuclide angiography region. phase/ dynamic vascular flow phase SECOND PHASE: At 5 min Difference in blood flow Blood pool phase and vascular permeability in bone THIRD PHASE: 2 – 4 hours later Distribution of radioisotope Bone scintigraphy phase/ in bone and metabolic osseous delayed static image activity of bone
SALIVARY SCANS Principle:The ability of the salivary glands intercalated duct epithelial cells to transport large monovalent anions, including iodide and pertechnetate, from the surrounding capillaries and secrete them into the saliva provides the principle for imaging the salivary glands with Tc-99m pertechnetate. The functional capabilities, structural integrity and location of the glands can be assessed.
Indications for salivary gland imaging include: Evaluation of functional status of salivary glands presentation of xerostomia presentation of pain Detection and evaluation of duct patency pain upon salivation presentation of xerostomia Detection and evaluation of mass lesions Preoperative localization of tumors Detecting aplasia of agenesis of gland Obstructive disorders Traumatic lesions and fistulas Function of gland after surgery
Salivary scan phases PHASE TIME IMPORTANCEFIRST PHASE: Initial At 5 min Distribution of radioisotopephase in glandSECOND PHASE: At 10 min (saliva stimulated Retention of radioisotope inWashout phase by sour drink / candy) gland
Fig 3- Salivary glands scan Region of interest on scintigraphic image: area 7, oral cavity areas 1 and 2, parotid glands areas 4 and 5, submandibular glands area 3, background for parotid glands area 6, background for submandibular glands and oral cavity.
ADVANTAGES OF NUCLEARMEDICINE OVER CONVENTIONAL RADIOGRAPHY Target tissue function is investigated. All similar target tissues can be examined during one investigation, e.g. the whole skeleton can be imaged during one bone scan. Computer analysis and enhancement of results are available.
DISADVANTAGES Poor image resolution – only minimal information of target tissue is obtained. The radiation dose to the whole body can be relatively high. Images are not usually disease-specific. Difficult to localize exact anatomical site of source of emission. Fascilities are not widely available.
Further developments in radioisotope imaging techniques include: SPECT (single photon emission computed tomography) PET (Positron emission tomography)
SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY (SPECT) SPECT is a method of acquiring tomographic slices through a patient. Most gamma cameras have SPECT capability. In this technique either a single or multiple gamma cameras is rotated 360 degrees about the patient. Image acquisition takes about 30 – 45 min.
Recent SPECT images have been fused with CT images to improve identifying of the location of the radionuclide. Distribution of radioactivity is displayed as a cross- sectional image or SPECT scan. This image gives the exact anatomical site of the source of the emissions to be determined.
ADVANTAGES OF SPECT1. Better detailed resolution2. Enhanced contrast3. Localization of defects is more precise and more clearlyseen.4. Extend and size of defects is better defined.
APPLICATIONS OF SPECT 1. Heart Imaging 2. Brain Imaging 4. Tumor detection SPECT can be used to detect tumors in cancer patients in the early stages. 5. Bone Scans In maxillofacial region, the most common use of nuclear medicine is to investigate abnormal metabolite bone activity, for instance, in assessing growth activity in cases of condylar hyperplasia. Traditionally a combination of 99mTc MDP and gallium citrate is used to assess bone activity.+
POSITRON EMISSION TOMOGRAPHY (PET) PET is more advanced imaging modality in nuclear medicine. The distribution of radioactivity in slices of organs can be obtained in a more accurate way using PET. In the PET camera two cameras called Anger cameras are place on opposite sides of the patient. This increases the collection angle and reduces the collection times which are the limitations of SPECT. PET, radiopharmaceuticals are labeled with positron emitting isotopes. A positron combines rather quickly with an electron. As a result the two gamma quanta are emitted almost in opposite directions .
The mass of the two particles is annihilated (the destruction of a particle and its antiparticle when they collide) with the emission of 2 gamma rays of high energy (511 keV) at 180 degree to each other. These emissions, known as annihilation radiation, can then be detected simultaneously (in coincidence) by opposite radiation detectors which are arranged in a ring around the patient. The exact site of origin of each signal is recorded and a cross-sectional slice is displayed as a PET scan.
REFERENCESEssentials of dental radiography & radiology ERIC WHAITES EDITION 4 YEAR OF PUBLICATION -2008, Publishers – Elsevier Page 15Oral radiology – principles and interpretation STUART WHITE & MICHAEL. J. PHAROAH EDITION 6 YEAR OF PUBLICATION- 2009 Publishers – Elsevier Page 2Textbook of Dental & maxillofacial radiology FRENY R KARJODKAR SECOND EDITION YEAR OF PUBLICATION- 2009 Publishers – JAYPEE Page 17Internet