An impurity known as activator sodium or thallium is added to these materials for detecting gamma rays. The thickness of the thalliumactivated sodium iodide naltl crystal determines how efficient it is in absorbing photons of a given energy. Gamma camera gamma camera gamma cameras are made of a crystal. The key differences between a czt gamma camera and csi really lie with the conversion technology. Lead grid collimator only allows gamma cameras aligned. What is the relationship between the energy of an absorbed gamma ray and the amount of light produced by a gamma camera crystal. Sodium iodide is hygroscopic so cannot be left exposed to the air. To absorb gamma rays and convert them into visiblelight photons. Fluorescent materials thalliumactivated sodium iodide, naitl is a crystalline material which is widely used for the detection of gamma rays in scintillation detectors. Apr, 2015 thalliumdoped sodium iodide, typically written naitl, is a scintillator that converts the energy from the incident gamma radiation into light in the visible spectrum that is then detected with a photomultiplier tube. The detection element at the heart of a gamma camera is a large rectangular crystal of sodium iodide doped with thallium. Quality assurance testing of gamma camera and spect systems. The basic components of gamma camera are collimator, sodium iodide nai crystal, photomultiplier tubes pmt and position logic circuit.
Light is picked up by detectors photomultiplier tubes located behind the crystal. The iodide has a charge of 1 and is sold as the sodium iodide salt nai. Thalliumdoped sodium iodide produces one of the highest signals in a pmt per amount of radiation absorbed. In the case of digirads technology, each solidstate gamma camera detector contains an array of. Saintgobain crystals is considered to be the leader in scintillation technology and is the largest producer of sodium iodide crystals in the world. The results of this study indicate that the revised correction method can be employed to considerably improve the performance of a small gamma camera using a naitl platetype crystal. Conventional gamma cameras two detectors heads most common, although single head and triple head cameras are used each head has single large nai sodium iodide crystal, up to 40 cm x 60 cm. Moreover, inorganic scintillators are used during spacebased missions for observing cosmic gamma rays. An array of these tubes is situated behind the sodium iodide crystal and may be placed directly on the crystal, connected to the crystal by light pipes, or optically coupled to the crystal with a siliconelike material. The anger camera uses one large, thin sodium iodide crystal for absorbing gamma.
Gamma cameras or scintillation cameras are pieces of apparatus which allow radiologists to carry out scintigraphy scans, tests which provide detailed diagnoses about the functioning of the thyroid, the heart, the lungs and many other parts of the body. In the gamma camera the detector is still a sodium iodide crystal, but of larger diameter now up to. However, pure nal crystals do not scintillate at normal room temperatures. Sep 10, 2015 when a gamma ray interacts with the nai crystal it deposits energy this energy is what causes the photons to be given off. Sometimes, the excited state is metastable, so the relaxation back down. A photomultiplier tube pmt converts a light pulse into an electrical signal of measurable magnitude. Figure 143 shows photopeak detection efficiency versus. Slides to iaea nuclear medicine physics handbook iaea human.
The photomultiplier tube pmt is an instrument that converts light to electrical signals. The scintillation spectrometer1 using a sodium iodide crystal thalliumactivated identifies the incident gamma ray energy with the response to the photoelectric, compton and when energetically. The gamma camera employs a sodium iodide crystal that is relatively thin in comparison with most other sodium iodide detectors used in nuclear medicine. How a gamma camera works a sodium iodide crystal gives a tiny flash when a gamma photon hits it. I sodium iodide is also used for the treatment of hyperthyroidism and thyroid cancer. Quality assurance testing of gamma camera and spect. The most common inorganic crystal used as a gamma ray detector is the sodium iodide nal crystal 3, which exhibits many desirable characteristics, such as high density, high light output, transparency, and a suitable index of refraction. A gamma camera with a pinhole or parallel collimator may be substituted for an uptake probe 15. Localizes the position where the gamma ray interacts in the crystal sodium iodide crystal. This in turn affects the sensitivity of the camera system. Typical small fieldofview cameras used a 250310 mm diameter crystal. Pdf quality control of gamma camera with spect systems.
Apr 14, 2006 the anger camera uses one large, thin sodium iodide crystal for absorbing gamma. The applications of scintigraphy include early drug development and nuclear medical imaging to view and analyse images of the human body or the distribution of medically injected, inhaled, or. The main function of crystal is convert gamma ray to photons of visible light. Forms a projection image by allowing only gamma rays traveling. Why is sodium iodide doped with thallium in the crystal which. As a general rule, the thinner the crystal, the better the resolution, but again, just as in collimation, the tradeoff is sensitivity. Inorganic materials like cesium iodide csi or sodium iodide nai make the scintillators used for gammaray detection.
Inorganic materials like cesium iodide csi or sodium iodide nai make the scintillators used for gamma ray detection. Tcpertechnetate forms the main isotopes used for thyroid. The gamma camera is made up of many parts, each part performs as a specific function in converting gamma rays into light images and finally we get app ropriate viewing image. Analog gamma cameras use photomultiplier tubes pmts and hygroscopic sodium iodide nai crystals which require a signi. When a gamma ray is absorbed by the sodium iodide crystal, a visible light flash known as a scintillation is cre ated. Sep 18, 2009 gamma camera developed by hal anger at berkeley in 1957 therefore also called anger camera an electronic device that detects gamma rays emitted by radio pharmaceautical e. Since many small field of view systems were purchased primarily for thallium imaging of the heart, most small field systems used to include a 14 in. Scintigraphy scans get their name from the ability of some crystals such as sodium iodide. Basic physics of nuclear medicinescintillation detectors. A gamma photon interacts with the crystal to produce many photons of visible light.
Sodium iodide is a type of detector among the scintillation detectors. This flash is picked up by photomultipliers which convert the flash into into an electrical signal. Electrical output from detectors is fed to computer to produce image. Many of the products incorporate scintillation materials, both inorganic crystals and organic solids and liquids, where absorption of ionizing radiation. Pdf quality control of gamma camera with spect system is highly valuable for assurance performance characteristic. Tcpertechnetate is another isotope emitting gamma rays with a short half life and similar uptake mechanism based on sodium iodide symporter pump. Performance improvement of small gamma camera using naitl. Gamma camera operation g g array of photomultiplier tubes pmts. The information is recorded onto film as an analogue image or onto a computer, coupled to the camera, in digital form.
This brochure presents the basic properties of our radiation detection products and the mechanical features of various standard and specialty designs. This radiopharmaceutical is used far more frequently than the i1 sodium iodide b i1 sodium iodide. A gamma camera is a device, which is used as an imaging technique to produce functional scans of the brain, lungs, thyroid, liver, skeleton, gallbladder and kidneys. A small amount of tl is added in order to activate the crystal, so that the designation is usually naitl for the crystal. It is designed for investigators in nuclear medicine. Thyroid uptake measurement i123 or i1 as sodium iodide. In order to be able to detect the 511kev gamma rays produced in pet, the camera heads on this scanner contain thicker sodium iodide crystals than are normally used for gamma. When a signal from a detected event falls within a preselected energy.
Perchlorate washout test may be used to detect iodide organification defects 18,19. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate i. Horiba started manufacturing and development of the nai tl crystal shortly after nai tl was discovered. Gamma camera operation array of photomultiplier tubes pmts. The continuous sodium iodide scintillator crystal coupled to an array of. From the exterior to interior a camera is comprised of 1 head cover. As solid state imaging technologies, both produce high quality images that are a vast improvement over the old angerbased technology. A scintillator is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. Almost all modern gamma cameras use thalliumdoped sodium iodide nai as the scintillation crystal. The sodium iodide detector crystal in a gamma camera is hermetically sealed to prevent exposure. Gamma camera gamma camera gamma cameras are made of a.
This scintillation is sampled by an array of photomul tiplier tubes that create a set of electronic pulses. Anger camera after its inventor, has long been the dominant spect detector system. Not only that, but a predictable number of photons are emitted depending on the energy deposited in a sodium iodide crystal, depositing 1 mev of energy will cause about 42,000 scintillation photons to be emitted. Nai tl crystal scintillator has a very high luminescence scintillation efficiency and is available in a wide variety of sizes and geometries that makes it the most widely used scintillator. In the beginning, crystals with diameters of 1 inch to 3 inches were used as detectors for nuclear. The performance of regular naitlbased gamma cameras deteriorates when exposed to high. Scintillation detectors 19 when a gamma ray enters the crystal and undergoes an interaction, it produces one or more secondary electrons. The crystals used in gamma cameras based on photomultiplier tubes pmts are typically made of naitl. The crystal gives a tiny flash of visible light every time a gamma photon hits it. The emphasis in this previous investigation was the spread in the position of the centroid of light generated in multiple interactions, since the particular gamma ray camera of interest in that work records the centroid position whenever multiple events take place. It detects and amplifies the electrons that are produced by the photocathode. The energy of the photon, 159 kev, is ideal for the nai sodium iodide crystal detector of current gamma cameras and also for the pinhole collimators. Effects of temperature changes on nal crystals journal of nuclear.
Scintillation materials and assemblies saintgobain. Since the two gamma rays produced are emitted in opposite directions, the camera heads must be moved so that they are always opposite one another. The matched gamma cameraradionuclide compatibilities are enhanced by the cameras 0. The detection of gamma rays with crystal scintillators. A gamma camera having separate detectors respectively to determine the spatial location and energy of gamma radiation emanating from a patient is disclosed. The light signals are sampled by an array of photomultilier tubes that determine x and y locations and the energy of detected events. After 20 years, and many improvements, it remains the dominant imaging instrument in developed countries, but is still outnumbered by rectilinear scanners in most developing countries. In order to be able to detect the 511kev gamma rays produced in pet, the camera heads on this scanner contain thicker sodium iodide crystals than are normally used for gamma imaging. Sodium iodide scintillator article about sodium iodide. The preferred camera has two adjacent, mutually perpendicular arrays of parallel, coordinant signal producing scintillaters positioned on the face of a scintillating energy crystal. This radiopharmaceutical is used for specialized uptake studies. To detect the gamma photons we use a large crystal of sodium iodide.
In the beginning, crystals with diameters of 1 inch to 3 inches were used as detectors for nuclear physics experiments. The development of the nai tl plate for gamma cameras started in the 1970s. This method also provides high spatial resolution and linearity, like arraytype crystals do, while retaining the specific advantages of platetype crystals. Anger heads can weigh as much as 600 pounds while a solidstate head can range between 25 and 90 pounds. It gives approximately 20 times the counting rate of 1 i for the same administered dose. When a gamma ray interacts with the nai crystal it deposits energy this energy is what causes the photons to be given off. Thalliumactivated sodium iodide, naitl is a crystalline material which is widely used for the detection of gamma rays in scintillation detectors. A gamma ray from the patient interacts and produces visible light photons collimator. A twocrystal gammaray scintillation spectrometer nature. Basic principles of gamma camera imaging and quality control. Lead grid collimator only allows gamma cameras aligned with the holes to hit crystal allowing a.
Scintillation materials and assemblies saintgobain crystals. The crystal has the ability to stop incoming gamma rays and convert part of the deposited energy into scintillations. The applications of scintigraphy include early drug development and nuclear medical imaging to view and analyse images of the human body or the distribution of. While czt utilizes direct conversion, csi uses indirect conversion with the aid of photodiodes. Key differences between a czt gamma camera and a csi imager. Gamma and xray detection introduction canberra industries. Gamma rays penetrate into the nai crystal where they may experience interactions with the atoms inside the crystal. Thyroid uptake measurements may be determined using tc99mpertechnetate 17. Gamma camera gamma cameras are made of a crystal sodium iodide which produces a burst of light when gamma rays hit it. Another crystalline material sodium activated caesium iodide, csina is widely used for xray detection in devices such as the xray image intensifier.
Gamma cameras are made of a crystal sodium iodide which produces a burst of light when gamma rays hit it. Recently dual headed gamma cameras with pet capability have been produced, and one of these is in use here. The high z of iodine in nai gives good efficiency for gamma ray detection. Us3919556a us47004874a us3919556a us 3919556 a us3919556 a us 3919556a us 47004874 a us47004874 a us 47004874a us 3919556 a us3919556 a us 3919556a authority us united states prior art keywords photocathodes set forth scintillator tubes gamma camera prior art date 19740515 legal status the legal status is an assumption and is not a legal. The matched gamma camera radionuclide compatibilities are enhanced by the camera s 0. Jun 20, 2019 the key differences between a czt gamma camera and csi really lie with the conversion technology.
619 65 908 98 950 217 376 45 147 770 334 1501 907 912 281 23 1082 1065 475 591 1212 1312 958 1064 639 1097 1341 858 1166 263 638 1046