Physics
Gamma Camera
A gamma camera is a medical imaging device that detects gamma rays emitted by radioactive substances injected into the body. It is commonly used in nuclear medicine to create images of internal organs and tissues. The camera consists of a scintillation crystal, photomultiplier tubes, and electronic components to capture and process the gamma ray signals.
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12 Key excerpts on "Gamma Camera"
eBook - ePubFarr's Physics for Medical Imaging , E-Book
Farr's Physics for Medical Imaging , E-Book
- Alim Yucel-Finn, Fergus Mckiddie, Sarah Prescott, Rachel Griffiths(Authors)
- 2023(Publication Date)
- Elsevier(Publisher)
5: Nuclear Imaging
- The Gamma Camera
- Real-Time Signal Corrections
- Gamma Camera Performance Parameters and Quality Control
- Practical Gamma Camera Imaging
- Image Quality
- Tomographic Imaging
- Radiation Protection and Dosimetry
- References
The Gamma Camera
The goal of radionuclide imaging, or nuclear medicine, is to image the distribution of the radiopharmaceutical within the patient using the gamma radiation that it emits. The imaging device used to achieve this is known as a Gamma Camera.The main components of a Gamma Camera are:- • A collimator
- • A large-area radiation detector
- • Electronics for radiation detection
- • Electronics for signal processing
- • A computer for image display and data storage
The first four components are generally grouped in the detector head, as shown in Fig. 5.1 . The original basic design for the Gamma Camera detector head was formulated in the mid-1950s and has undergone little change since then, although there have considerable improvements in individual components. The early Gamma Cameras were analogue devices, but modern cameras are digital devices, and there will be a further generational step forward in this respect in the next few years.Collimator
After a patient has been injected with the radiopharmaceutical, they are emitting gamma rays in all directions. To obtain an interpretable image, some correlation must be achieved between the origin of the emission within the patient and its position within the image. The collimator establishes a linear relationship between the origin and the point of contact on the surface of the radiation detector (i.e., only photons travelling directly perpendicular to the surface are allowed through the collimator).The most common type is the parallel-hole collimator, in which hole shapes may be round, square, triangular, or more typically, hexagonal. Collimators are generally made of lead because of its high linear attenuation coefficient; the lead between two adjacent holes is called the septum. A collimator for imaging technetium-99m (99 Tcm ) will have tens of thousands of holes each of about 1–2 mm in diameter. The thickness of the septa is determined by the energy of the gamma photons emitted by the radiopharmaceutical. The septa must be thick enough to absorb most of the photons incident upon them. Thus, collimators designed for 131 I (364 keV) have thicker septa than those designed for 99 Tcm
- Dimitrios Ventzas(Author)
- 2012(Publication Date)
- IntechOpen(Publisher)
The photodetector is used to detect and measure the number of photons emitted by an interaction in the scintillator crystal. The number of photons due to scintillation (or intensity) is generally proportional to the energy deposited within the crystal. Due to the high atomic number, and therefore high density, scintillator detectors give high braking efficiency for photons of about 500 keV. 3. The mini Gamma Camera The mini Gamma Camera is an imaging device commonly used in nuclear medicine as a diagnostic tool. The radiation comes from the patient who is previously injected, usually intravenously, with a radioactive tracer. The mode of conducting the clinical diagnosis is called scintigraphy. The radioisotope tracer can be monitored inside the patient's body by the mini Gamma Camera and making easier to establish a medical diagnosis. The analysis offered by the gammagrams is especially functional rather than anatomical such as x-rays. They serve to assess whether a patient's metabolism is working properly adhering tracers, for example in platelets, red blood cells or other cells where a correct operation is checked. It is possible to mark the glucose molecules to assess which areas of the brain are activated (consume more glucose) at certain times. Without loss of generality it can be say that a Gamma Camera consists of three components: a head or radiation detector, a data acquisition system and image reconstruction algorithms, as shown in Fig. 6. Fig. 6. Schematic of the Gamma Camera parts. The three components are: a head or radiation detector, an electronic data acquisition system and image reconstruction algorithms The photon detector is responsible for converting the radiation-matter interaction into analog electrical pulses; it is usually composed of a collimator, a scintillator crystal and a photomultiplier tube (PMT). The collimator allows the passage only of radiation emitted perpendicular to the head and is usually constructed of lead or tungsten.
No longer available |Learn moreNuclear Medicine
Radioactivity for diagnosis and therapy
- Richard Zimmermann(Author)
- 2007(Publication Date)
- EDP Sciences(Publisher)
II. Imaging Tools The images produced in nuclear medicine are essentially obtained using a camera that detects gamma rays. This specific gamma imaging tool is equipped with a detection head that analyses an area up to 40 x 60 cm in a single pass. The rays, which are emitted in every direction within the area, are selected by a collimator as they pass through, and only those which are perpendicular to the detector are taken into consideration. This detector composed of a crystal that is sensitive to radiation (sodium iodide for example) is coupled to a photomultiplier which transforms the impact of the radiation into an electronic impulse. The impacts are analysed point 64 NUCLEAR MEDICINE GAMMA RAY IMAGING 65 by point in a planar image. The quality of a Gamma Camera depends on the the detection crystal’s sensitivity and the collimator’s resolu- tion. Moving the detection head along the length of the body gives a static planar scintigraphy image of the whole body within minutes. This technique is used in almost all types of nuclear medi- cine indications, with the exception of those concerning the heart and the brain. The same type of equipment, used over a specific region, gives a dynamic image with which the evolution of the radiopharmaceu- tical’s distribution through the organs can be monitored over a precise length of time. The processes of blood irrigation can also be monitored. Finally, observing the functioning of the liver or kidneys is no longer a problem when plates are taken sequentially, over a predetermined period and with defined and regular spacing between each acquisition. The SPECT method (Single Photon Emission Computed Tomography) applies the Gamma Camera principles to a scanner, a tool that is equivalent to the devices used in radiography. The photon source is by contrast located in the patient himself since the radioisotope has been injected. This method does not, of course, require any additional irradiation.
eBook - ePubPhysics in Nuclear Medicine E-Book
Physics in Nuclear Medicine E-Book
- Simon R. Cherry, James A. Sorenson, Michael E. Phelps(Authors)
- 2012(Publication Date)
- Saunders(Publisher)
Chapter 18 ), has matched the Gamma Camera for a balance of image quality, detection efficiency, and ease of use in a hospital environment. The Gamma Camera has thus become the most widely used nuclear-imaging instrument for clinical applications.B Basic Principles of the Gamma Camera
1. System Components
Figure 13-1 illustrates the basic principles of image formation with the Gamma Camera. The major components are a collimator, a large-area NaI(Tl) scintillation crystal, a light guide, and an array of PM tubes. Two features that differ from the conventional NaI(Tl) counting detectors described in Chapter 12 are crucial to image formation. The first is that an imaging collimator is used to define the direction of the detected γ rays. The collimator most commonly consists of a lead plate containing a large number of holes. By controlling which γ rays are accepted, the collimator forms a projected image of the γ-ray distribution on the surface of the NaI(Tl) crystal (see Section B.3). The second is that the NaI(Tl) crystal is viewed by an array of PM tubes, rather than a single PM tube. Signals from the PM tubes are fed to electronic or digital position logic circuits, which determine the X-Y location of each scintillation event, as it occurs, by using the weighted average of the PM tube signals (see Section B.2).FIGURE 13-1Basic principles and components of a modern Gamma Camera. The outputs of each photomultiplier (PM) tube are amplified and digitized using an analog-to-digital converter (ADC). The X-Y locations for each gamma ray that interacts in the NaI(Tl) crystal are computed from the digitized signals. The energy deposited by the gamma ray, E , which is proportional to the total measured pulse amplitude, also is computed by summing the individual PM tube signals. If E
eBook - PDF- M Flower(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
336 169 Radioisotope Imaging position of each X-ray is known, only the γ -ray detection position is determined for a radio-isotope source within the body. To produce an image it is, hence, necessary to provide some form of collimation, which defines the photon direction. This takes the form of mechanical (i.e. lead) collimation in the Gamma Camera or electronic collimation in the positron camera. In this chapter, we will explain the function and development of the modern Gamma Camera and positron camera, including the most recent improvements brought about by the use of improved scintillation crystals, faster electronics and advanced microprocessor technology. Different modes of radioisotope imaging are possible with planar static imaging with a Gamma Camera (planar scintigraphy) being the most common form. These single-view images consist of two-dimensional (2D) projections of the three-dimensional (3D) activity distributions in the detector’s field of view (FOV). Temporal changes in the spatial distri-bution of radiopharmaceuticals can be studied by taking multiple planar gamma-camera images over periods of time that may vary from milliseconds to hundreds of seconds. This form of imaging (dynamic scintigraphy) is fundamental to the use of radioisotopes in showing the temporal function of the organ/system being examined as compared to the ‘snap-shot’ of function obtained in planar scintigraphy. Computer Gamma Camera Radiopharmaceutical injection FIGURE 5.1 Illustration of the radioisotope imaging process carried out using a single-photon-emitting radionuclide. The direction of the incident photon is determined by a collimator mounted on the Gamma Camera. γ 1 γ 2 FIGURE 5.2 Illustration of radioisotope imaging using a positron-emitting radionuclide. The two annihilation photons are detected by a pair of the many detectors surrounding the patient defining the line of response (LOR) through the point of radionuclide decay.
eBook - PDF- Anthony B. Wolbarst, Robert G. Zamenhof, and William R. Hendee(Authors)
- 2006(Publication Date)
- Medical Physics Publishing(Publisher)
The Gamma Camera is now a mature product, and many in the field do not expect significant future technical advances. Indeed, camera performance is about as good today as it can be using a single-crystal design. Advances will come from segmented crystals or matrices of individual scintillation crystals. This has already happened for niche gamma-camera applications. 4.1.4 Single Photon Emission Computed Tomography (SPECT) An important consequence of the development of fully digital gamma-camera systems was the invention of Single Photon Emission Computed Tomography (SPECT)—the nuclear medi- cine counterpart to x-ray computed tomography (CT). By rotat- ing typically two or three gamma-camera heads together around the patient, it is possible to acquire time-dependent, CT- like images and to display them in either two or three dimen- sions. SPECT has become ubiquitous in cardiac clinics for studies of myocardial perfusion and other cardiac functions; it is common, when performing SPECT imaging of the heart, to gate the acquisition of projection images so that 8 or 16 phases of the heart are acquired. Reconstruction of each of the phases and subsequent organization of the data allows a beating-heart ciné-like display. While more than half of SPECT studies in the United States are for coronary artery disease, another quarter are for bone, and the rest for brain, prostate, thyroid, etc. 4.1.5 Positron Emission Tomography (PET) Nuclear medicine imaging mostly utilizes radionuclides that decay by single gamma-ray emission, preferably with no or little associated beta-minus particle emission, as is the case with metastable Tc-99m (Figure 4–4a). Some radionuclides such as fluorine-18 (F-18), however, undergo beta-plus decay, in which a positron is emitted (Figure 4–4b).
eBook - PDF- Philip Palin Dendy, Brian Heaton(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
337 10 Diagnostic Imaging with Radioactive Materials F I McKiddie SUMMARY This chapter covers the following aspects of imaging with radioactive materials: • Requirements of imaging systems and techniques for obtaining accurate data • Principles of operation of the Gamma Camera • Additional features of modern Gamma Camera systems • Parameters influencing image quality • Gamma Camera performance • Data display and storage • Methods of data acquisition • Quality control of the Gamma Camera and other aspects of nuclear medicine CONTENTS 10.1 Introduction ........................................................................................................................ 338 10.2 Principles of Imaging ........................................................................................................ 339 10.2.1 The Gamma Camera ............................................................................................. 340 10.2.1.1 The Detector System ............................................................................... 341 10.2.1.2 The Collimator ......................................................................................... 342 10.2.1.3 Pulse Processing ...................................................................................... 345 10.2.1.4 Correction Circuits .................................................................................. 346 10.2.1.5 Image Display .......................................................................................... 347 10.2.2 Additional Features on the Modern Gamma Camera ..................................... 347 10.2.2.1 Dual Headed Camera ............................................................................. 347 10.2.2.2 Whole Body Scanning ............................................................................ 347 10.2.2.3 Tomographic Camera .............................................................................
eBook - PDF- Luca Saba, Warren M. Rozen, Alberto Alonso-Burgos, Diego Ribuffo, Luca Saba, Warren M. Rozen, Alberto Alonso-Burgos, Diego Ribuffo(Authors)
- 2018(Publication Date)
- CRC Press(Publisher)
The mechanism of localisation of a radiopharmaceutical in a particular target organ depends on different processes as antigen–antibody reactions, physicochem-ical adsorption or chemisorption, receptor site binding, and transport of a chemical species across a cell membrane and into the cell. The biological functions can be displayed as images, numerical data, or time–activity curves. The different uptake of the radiopharmaceutical can reveal the normal or altered state of tissue metabolism or specific function of an organ system. Another important use is to predict the effects of surgery and assess changes since treatment. 4.2.2 N UCLEAR M EDICINE I NSTRUMENTATION 4.2.2.1 Gamma Camera Detector 4.2.2.1.1 Introduction The purpose of nuclear medicine imaging is to obtain a picture of the distribution of a radiophar-maceutical within the body after the administration and its metabolism in the patient. In order to get images, it is necessary to detect the radiation emitted by the radionuclide. Alpha particles and electrons ( β± particles, auger and conversion electrons) are not used for imaging because they can-not penetrate more than a few millimetres of tissue. Gamma ( γ ) radiation is non-particulate and penetrating, making it useful for diagnostic imaging purposes. Gamma ray in the approximate energy range of 60–600 keV (or annihilation photons, 511 keV in PET) is sufficiently penetrating in body tissues to be detected by an external radiation detector used in diagnostic nuclear medicine. There are two types of nuclear imaging methods: single-photon imaging and PET. The distinc-tion between these two imaging modalities is based on the physical properties of the radioisotopes used for imaging. Radioisotopes emitting single γ -ray are used to obtaine single-photon imaging (Table 4.2). The most widely used single-photon emitters include 99m Tc, 201 Tl, and 123 I.
eBook - PDF- Joseph D. Bronzino, Donald R. Peterson, Joseph D. Bronzino, Donald R. Peterson(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
The more detector that TABLE 11.1 Gamma Ray Detection Type of Sample Activity (μCi) Energy (keV) Type of Instrument Patient samples, for example, blood, urine 0.001 0–5000 Gamma counter with annular NaI(TI) detector, 1 or 2 PMTs, external Pb shielding Small organ function < 30 cm field of view at 60 cm distance 5–200 20–1500 2–4-in. NaI(TI) detector with flared Pb collimator Static image of body part, for example, liver, lung 0.2–30 50–650 Rectilinear scanner with focused Pb collimator Dynamic image of body part, for example, xenon in airways 2–30 80–300 Anger camera and parallel-hole Pb collimator Static tomographic image of body part See Section 11.1 11 -3 Nuclear Medicine surrounds the patient, the more sensitive the system will be. Table 11.2 lists in order from least sensitive to most sensitive some of the geometries used for imaging in nuclear medicine. This generally is also a listing from the older methods to the more recent. For the purposes of this section, we shall consider that the problems of counting patient and other samples and of detecting the time course of activity changes in extended areas with probes are not our topic and confine ourselves to the attempts made to image distributions of gamma-emitting radionu-clides in patients and research subjects. The previous section treats the three-dimensional imaging of these distributions; this section will treat detection of the distribution in a planar fashion or the image of the projection of the distribution onto a planar detector. 11.1.2 Detection of Photon Radiation Gamma rays are detected when atoms in a detector are ionized and the ions are collected either directly as in gaseous or semiconductor systems or by first conversion of the ionized electrons to light and subsequent conversion of the light to electrons in a photomultiplier tube (P-M tube or PMT). In all cases there is a voltage applied across some distance that causes a pulse to be created when a photon is absorbed.
eBook - PDF- Paul Suetens(Author)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
Chapter 5 Nuclear Medicine Imaging 5.1 Introduction The use of radioactive isotopes for medical purposes has been investigated since 1920, and since 1940 attempts have been undertaken to image radionu- clide concentration in the human body. In the early 1950s, Ben Cassen introduced the rectilinear scanner, a “zero-dimensional” scanner, which (very) slowly scanned in two dimensions to produce a projection image, like a radiograph, but this time of the radionu- clide concentration in the body. In the late 1950s, Hal Anger developed the first “true” Gamma Camera, introducing an approach that is still being used in the design of all modern cameras: the Anger scintil- lation camera, 32 a 2D planar detector to produce a 2D projection image without scanning. The Anger camera can also be used for tomogra- phy. The projection images can then be used to com- pute the original spatial distribution of the radionu- clide within a slice or a volume, in a process similar to reconstruction in X-ray computed tomography. Already in 1917, Radon published the mathemati- cal method for reconstruction from projections, but only in the 1970s was the method applied in med- ical applications – first to CT, and then to nuclear medicine imaging. At the same time, iterative recon- struction methods were being investigated, but the application of those methods had to wait until the 1980s for sufficient computer power. The preceding tomographic system is called a SPECT scanner. SPECT stands for single photon emission computed tomography. Anger also showed that two scintillation cameras could be combined to detect photon pairs originating after positron emis- sion. This principle is the basis of PET (i.e., positron emission tomography), which detects photon pairs. Ter-Pogossian et al. built the first dedicated PET 32 S. R. Cherry, J. Sorenson, and M. Phelps. Physics in Nuclear Medicine. W.B. Saunders Company, Philadel- phia, third edition, 2003.
eBook - PDF- Simon R. Cherry, Ramsey D. Badawi, Jinyi Qi, Simon R. Cherry, Ramsey D. Badawi, Jinyi Qi(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
Res. , 177, 2012; Humm, J.L. et al., Eur. J. Nucl. Med. Mol. Imaging , 30, 2003; Zanzonico, P., Semin. Nucl. Med. , 34, 2004; With kind permission from Springer Science+Business Media: Clinical Nuclear Medicine , Physics, Instrumentation, and Radiation Protection, 2007, 1–33, Zanzonico, P., and S. Heller. a The intrinsic efficiency of 2-cm-thick coincidence detectors for 511 keV annihilation γ-rays. 6.3 Basic Principles of Radiation Detection 175 times and a threefold greater light output than BGO. However, lutetium-based scintilla-tors are relatively expensive. NaI(Tl) is the material of choice for most Gamma Cameras and SPECT scanners, as it is relatively inexpensive, can be fabricated with large areas, and has adequate stopping power for the 80–300 keV gamma rays typically imaged with these systems. 6.3.2 S EMICONDUCTOR -B ASED I ONIZATION D ETECTORS Semiconductor radiation detectors represent the main alternative to scintillator detector– based imaging systems. Such detectors are so-called direct-conversion devices, a major advantage of which is that they avoid the random effects associated with scintillation production and propagation and conversion of the optical signal to an electronic signal. When an x- or γ -ray interacts in a semiconductor detector, one or more energetic electrons are created and subsequently lose energy through ionization, among other processes. The ionization creates electron-hole (e-h) pairs, where a hole is the positively charged electron vacancy in the valence band left when the electron has been raised into the conduction (i.e., mobile-electron) band. Application of a bias voltage creates an electric field that causes the two types of charge carriers to migrate in opposite directions. These moving charges induce transient currents in the detector electrodes, thereby allowing measurement of the detec-tor’s response to an incident x- or γ -ray. Semiconductor detectors offer several potential advantages over scintillator detectors [8].
eBook - ePub- Yi-Hwa Liu, Albert J. Sinusas(Authors)
- 2017(Publication Date)
- CRC Press(Publisher)
1 Principles and instrumentation of SPECT/CT R. Glenn Wells1.1 Introduction1.2 Radioisotopes used in spect1.3 The Gamma Camera1.3.1 NaI(Tl) scintillation detector1.3.2 Photomultiplier tubes1.3.3 Positioning electronics1.3.4 Energy and spatial resolution1.3.5 Collimators1.3.5.1 Parallel-hole collimators1.3.5.2 Pinhole collimators1.3.6 Cadmium-zinc-telluride detectors1.4 3-D image reconstruction1.4.1 Sampling requirements1.4.2 Filtered backprojection1.4.3 Iterative reconstruction1.5 Factors that influence SPECT image quality1.5.1 Attenuation1.5.2 Scatter1.5.3 Distance-dependent collimator resolution1.5.4 Patient motion1.6 Computed tomography1.6.1 Basics of CT1.6.2 CT-based correction of nuclear medicine images1.6.3 Hybrid SPECT/CT camera designs1.6.3.1 Slow-rotation CT1.6.3.2 Fast-rotation CT1.6.4 Advantages and disadvantages of SPECT/CT1.6.5 Synergy of SPECT and CT1.7 ConclusionReferences1.1 IntroductionSingle-photon emission computed tomography (SPECT) is technology for creating three-dimensional (3-D) images of the distribution of radioactively labeled substances within a subject. The energy of the radiation emitted is high enough to penetrate the patient tissues, allowing visualization of structures at all depths inside the patient. The energy is too high to be seen directly with the human eye and so a specially designed high-density detector is used to measure the emitted signals. The detector provides a 2-D picture of the radiation. By rotating the detector around the patients, a collection of pictures is obtained that can be converted into a 3-D image of the radioactivity distribution. Because the radioactive label is attached to a substance, the images track where that substance goes after being injected into the body. Thus, images of the radioactivity distribution can provide information on the function of different organs and physiologic systems with respect to the injected substance. For example, images of the distribution of 99m
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