Radiation detectors in nuclear medicine.

Department of Radiology, School of Medicine, State University of New York, Stony Brook 11794-8420, USA.
Radiographics (Impact Factor: 2.6). 01/1999; 19(2):481-502.
Source: PubMed


Single-photon-emitting or positron-emitting radionuclides employed in nuclear medicine are detected by using sophisticated imaging devices, whereas simpler detection devices are used to quantify activity for the following applications: measuring doses of radiopharmaceuticals, performing radiotracer bioassays, and monitoring and controlling radiation risk in the clinical environment. Detectors are categorized in terms of function, the physical state of the transducer, or the mode of operation. The performance of a detector is described by the parameters efficiency, energy resolution and discrimination, and dead time. A detector may be used to detect single events (pulse mode) or to measure the rate of energy deposition (current mode). Some detectors are operated as simple counting systems by using a single-channel pulse height analyzer to discriminate against background or other extraneous events. Other detectors are operated as spectrometers and use a multichannel analyzer to form an energy spectrum. The types of detectors encountered in nuclear medicine are gas-filled detectors, scintillation detectors, and semiconductor detectors. The ionization detector, Geiger-Müller detector, extremity and area monitor, dose calibrator, well counter, thyroid uptake probe, Anger scintillation camera, positron emission tomographic scanner, solid-state personnel dosimeter, and intraoperative probe are examples of detectors used in clinical nuclear medicine practice.

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    • "As the positron travels through the surrounding material, there is a continuous loss in its energy until it combines with an electron to- annihilate completely and emit a pair of 511 keV photons Figure 1). The emitted pair of 511 keV photons, the annihilation photons, have an energy equivalent to the combined rest mass of an electron and a positron [9], and they are emitted in opposite directions at approximately 180° from each other. The opposing PET detectors register the arrival of the annihilation photons as an event if they are detected within a narrow time frame [10], the timing window of the coincidence circuit, which is typically 3–15 nanoseconds in length. "
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    ABSTRACT: The recent introduction of high-resolution molecular imaging technology is considered by many experts as a major breakthrough that will potentially lead to a revolutionary paradigm shift in health care and revolutionize clinical practice. This paper explores the challenges and strengths of the current major imaging modalities, as well as the biophysics engineering their repertoire of capabilities. Advancements in the mechanical aspects of both PET and SPECT imaging will advance molecular imaging diagnostic capabilities and have a direct impact on clinical medicine and biomedical research practice. A better understanding of the strengths and limitations of functional imaging modalities in the context of their particular hardware and software mechanics will shed light onto how we can advance their diagnostic capabilities on a biological level. Herein, this paper demonstrates the fundamental biomechanical differences between PET and SPECT imaging, and how these fundamental differences translate into clinically relevant data acquisition for brain disorders.
    07/2013; 4:157. DOI:10.4172/2155-9619.1000157
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    • "Ionizing radiation is radiation composed of particles that individually carry enough energy to liberate an electron from an atom or molecule without raising the bulk material to ionization temperature. Ionizing radiation is generated through nuclear reactions, either artificial or natural, by very high temperature (e.g. the corona of the Sun), or via production of high energy particles in particle accelerators, or due to acceleration of charged particles by the electromagnetic fields produced by natural processes, from lightning to supernova explosions (Ranger, 1999). "
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    ABSTRACT: Design : Experiment was conducted to fifty five male Orycytolagus cuniculus rabbits subdivided into four groups. Control : animals received neither ionizing radiation nor radio protector. G1 : animals injected by 1 mCi of 99mTC with the legend Methoxy-Iso- Butyl-Isonitrile (MIBI) with no radio protection application. G2 : animals received a radio protective combination of vitamin E and selenium with no irradiation. G3 : animals received the ionizing radiation after prior protection with vitamin E and selenium combination. Vitamin E (α-tocopherol ) administered as 40 mg/kg body weight three times per week while Seleium was administered as 30 mg/day. This combination was administered for three weeks before irradiation. Whole blood methemoglobin reductase enzyme activity, different hemoglobin derivatives concentrations as well as antioxidants activity were measured to all animals. Results : outcome of this study showed minimum activity of methemoglobin reductase enzyme in animals irradiated with no prior protection application. The highest level of reductase activity was recorded in animals received prior protection with the combination before irradiation. Antioxidants activities and methemoglobin concentration approximately reach the normal levels after have been elevated in animals irradiated with ionizing radiation after administration of the combination.
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    • "Although for a point source detected by a simple cylindrical detector, the overall efficiency is commonly determined by two factors, the intrinsic ( int ) and geometric ( geom ) efficiencies (Ranger, 1999), the attenuation effect in the detector housing (absorption efficiency) should also be considered ( = int geom absp ). In this case, the geometric and theoretical absolute efficiencies of an HPGe detector at 1332 keV at 25 cm can be determined from detector parameters as specified by the manufacturer and the absorption efficiency from the mass attenuation coefficient of 1332 keV gamma rays in Al. "
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    ABSTRACT: A semi-empirical method to determine radionuclide concentrations in large environmental samples without the use of reference material and avoiding the typical complexity of Monte-Carlo codes is proposed. The calculation of full-energy peak efficiencies was carried out from a relative efficiency curve (obtained from the gamma spectra data), and the geometric (simulated by Monte-Carlo), absorption, sample and intrinsic efficiencies for energies between 130 and 3000 keV. The absorption and sample efficiencies were determined from the mass absorption coefficients, whereas the intrinsic efficiency was approximated by an empirical function. The deviations between calculated and experimental efficiencies for a reference material in most cases are less than 10%. Radionuclide activities in marine sediment samples calculated by the proposed method and by the experimental comparative method were not significantly different. This new method can be used for routine environmental monitoring when uncertainties up to 10% are acceptable.
    Radiation Measurements 01/2008; 43(1):77-84. DOI:10.1016/j.radmeas.2007.11.043 · 1.21 Impact Factor
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