Gamma Camera & Basic Principles Mustafa Özasil 20140420 Nicosia 2017

Contents Introduction Main Components of Gamma Camera Working Principle of Gamma Camera Procedure & Preparation of Patient Pros & cons of Gamma Camera Future Aspect & State of Art Conclusion

Introduction Gamma camera is a device that uses gamma rays to carry out functional scans on patients body and produces an image to examine the area of interest. Gamma rays are a form of electromagnetic radiation. Gamma rays have the highest frequency and lowest wavelength in the electromagnatic spectrum.

Gamma Camera & Basic Principles Components

Components of Gamma Camera There are 5 main components found in a gamma camera system. Collimator Scintilator Photomultiplier Tubes Computer Monitor

Components of Gamma Camera Collimator Collimator is a device that limits the passage of gamma rays. The rays that are parallel to the holes on the collimator can pass through it. Unparallel rays are blocked by the collimator. There are severel different collimator designs: Parallel Hole Collimators Slanthole Collimators Converging & Diverging Collimators Fan Beam Collimators Pinhole Collimators

Components of Gamma Camera Parallel Hole Collimators All holes parallel to each other. Simplest collimator design.

Components of Gamma Camera Slanthole Collimators Slanthole design is a variation of parallel hole collimator where all tunnels are slanthed at a specific angle. Slanthole design generates an oblique view. This collimator can be positioned close to body for the maximum gain in resolution.

Components of Gamma Camera Converging & Diverging Collimators In converging design the holes are focused on organ. Organs appear larger at the face of scintillator with a converging collimator. The diverging collimator is obtained when a converging collimator is flipped over , this collimator used to enlarge the field of view

Components of Gamma Camera Fan Beam Collimators Fan beam collimators are specially designed for regtangular camera head to image the smaller organs like brain and heart.

Components of Gamma Camera Pinhole Collimators Pinhole collimators are cone-shaped collimators. They have a single hole with interchangeable inserts. They can regenerate magnified images of small organs like thyroid and joint.

Components of Gamma Camera Scintillator Scintillator is made up of sodium iodide(NaI) crystal. Scintillator produces multi-photon flashes of light when incoming gamma rays hits to the surface of crystal.

Components of Gamma Camera Photomultiplier Tube (PMT) PMT is used to convert light signals of a few hundred photons into a useable current pulse without significantly increasing the noise. PMT is an evacuated glass envelope with 2 main parts. Photo Cathode Electron Multiplier

Components of Gamma Camera Computer The computer processes the current pulse that has been produced and turns it into an useable image.

Components of Gamma Camera Monitor The image of produced is displayed on the monitor.

Gamma Camera & Basic Principles Working Principle

Working Principle of Gamma Camera A radioactive tracer is injected to the patients body. The most commonly used tracer is ‘Techtenium-99m’. It is a metastable nuclear isomer. It has a relatively long half life of 6 hours. It has ability to be incorporated into a variety of molecules in order to target different systems within the body.

Working Principle of Gamma Camera The tracer emmits radiation in all directions as it travels through the patients body. The gamma camera gets hit by the gamma rays that emmited. Gamma rays passes through the collimator. Then the gamma rays hits to the scintillator. The scintillator absorbs the gamma energy and turn it into multi-photon flashes of light.

Working Principle of Gamma Camera Then light photons are delivered to the PMT. At the PMT, the photocathode comprises a photosensitive coating. The light photons that penetrates the PMT liberates low-energy (1 eV or less) electrons from the cathode.

Working Principle of Gamma Camera The number of photoelectrons produced will be about the same as the number of light photons. Thus the photoelectrons total charge will be too small to provide a detectable electrical signal so we use an electron multiplier.

Working Principle of Gamma Camera The electron multiplier consists of an arrengment of dynodes. Each photoelectron is accelerated towards and strikes the first dynode. And there , its energy is absorbed and results in emmission of several secondary electrons. This process of electron multiplication continues down the dynode chain and eventually a large sinal is collected at the anode.

Working Principle of Gamma Camera The collected signal is proccessed in the computer to produce the image. The produced image is displayed on the screen.

Gamma Camera & Basic Principles Procedure and Preparation of Patient

Procedure and Preparation of Patient 3 phase of procedure and preparation of patient. Pre Scan During Scan Post Scan

Procedure and Preparation of Patient Pre Scan Patients should take off all the metallic stuff and jewellery. Female patients should inform the technologist if they are preagnant or breastfeeding. All patients should state the list of the medications they are using.

Procedure and Preparation of Patient During Scan The tracer is injected intravenously to the patient. Patient might be asked to lie and stay still for 15 minutes or more before the scan while their body absorbs the tracer.

Procedure and Preparation of Patient Post Scan Most of the radioactive tracer leaves the body through the urine within a few hours.

Gamma Camera & Basic Principles Pros & Cons

Pros of Gamma Camera Gamma camera can be used to create images of specific parts of the body. E.g. Breast-Specific Gamma Imaging(BSGI) is used when mamogram is inconclusive. Gamma rays has the highest energy in radiation spectrum which supplies high resolution, and high sensitivity. Gamma cameras have high positive predictive value and high accuracy. Some modern gamma cameras have more than one crystal, allowing 3-D imaging of organs.

Cons of Gamma Camera Usage of harmful radiation. Gamma cameras have high cost. Discomfort of patient due to long scan time and the need for patient to stay still. Tracer may cause allergic reactions on patients. Pregnants should not go under gamma rays.

Gamma Camera & Basic Principles State of Art & Future Aspect

State of Art Most modern gamma cameras are completely digital. The output of PMT is directly digitilized by an analog-to-digital converter (ADC). Thus errors in energy and positioning caused by noise and pulse distortions due to analog positioning circuitry are eleminated.

Future Aspect The scan time should be reduced to improve patient confort. Cost of the device and so the cost of the procedure could be reduced.

Gamma Camera & Basic Principles Conclusion

Conclusion Gamma cameras offer an unique service with its : High accuracy High specifity High resolution High sensitivity High positive predictive value 3-D option Harmful radiation and high cost are the reasons why gamma camera is not very common.

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