NUCLEAR IMAGING Prepared By: Muhammad Yaseen Trainee Med. Physicist Radiology Department Mail: firstname.lastname@example.org
Contents Introduction Advantages Of Nuclear Imaging Radiography Vs Nuclear Imaging Radioisotopes used in NM Radiopharmaceuticals Gamma Camera SPECT Safety Summary
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.
Advantages Of Nuclear Medicine 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.
Radiographic Vs Nuclear ImagingRadiographic Imaging Nuclear ImagingTransmission Type Image Emission Type Of ImageMorphologic Imaging Functional ImagingHigh Resolution Low ResolutionUse X-rays Use Gamma RaysShort Time Long Time
Radioisotopes Used In Conventional 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
For Imaging Technetium Is Used Extensively, As It Has Following PropertiesA. 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, e.g. - Tc + MDP (methylene disphosphonate) in bone - Tc + sulphur colloid in the liver and spleen.D. It is easily produced, as and when required, on site.
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
Principle Of Nuclear Imaging Technique THE STEPWISE PROCEDURE OF NUCLEAR IMAGING:Radionuclides are administered via vein or mouthThey distribute in the body according to their strength 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.
GAMMA 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. These signals are reconstructed to an image that shows distribution of radionuclide in the patient.
Gamma Camera Components Collimator Crystal PM Tubes Analog To Digital Convertor X And Y Positioning Circuits A Visual Display With Display Electronics
Collimator The collimator can be made from lead foil. The collimator stops about 99.9% of the available photons. The walls of each channel in the collimator are called septa, and if a photon manages to penetrate the wall, it is called septal penetration.
Parallel Hole Collimator LEGP (low energy general purpose) or LEAP (low energy all purpose). To increase the resolution, smaller diameter holes are needed. To increase sensitivity, the holes need to be wider.
Parallel Hole Collimator To image higher energy isotopes such as Ga-67 or I-131, the collimator needs to have thicker septa in order to stop penetration. This produces a heavier collimator with lower sensitivity.
Crystal (NaI) 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.
Photo Multiplier Tube Extremely sensitive detector of light in the ultraviolet, visible and near infrared Multiplies the signal produced by incident light by as much as 108 • single photons can be resolved High gain, low noise, high frequency response, and large area of collection A tiny and normally undetectable current becomes a much larger and easily measurable current
Components Of PMT Made of a glass vacuum tube Photocathode Several dynodes One anode
Analog To Digital Convertor 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
Further Developments in Radioisotope Imaging Techniques Include SPECT (single photon emission computed tomography) And PET (Positron emission tomography)
Single Photon Emission Computed Tomography 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.
Applications of SPECT Heart Imaging Brain Imaging Tumor detection SPECT can be used to detect tumors in cancer patients in the early stages. Bone Scans
Advantages of SPECT Better detailed resolution Enhanced contrast Localization of defects is more precise and more clearly seen. Extend and size of defects is better defined.
Limitation Of Nuclear Medicine 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. Facilities are not widely available.
Safety Precautions Injected patient should avoid to keep away from everyone but specially from children and pregnant women Only authorized users are allowed to handle the source. Do not look directly into bore hole of the source holder or cover it with any part of your body. Use Lead Apron, lead goggles and lead thyroid shield