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Dual-Energy X-ray Computed Tomography
Published in Paolo Russo, Handbook of X-ray Imaging, 2017
This approach is based on fast tube voltage switching between low and high kilovoltage as the tube-detector array pair rotates, as illustrated in Figure 39.9. Projection data is collected twice for approximately the same X-ray source position along the 360° arc of rotation (i.e., one for low- and one for high-tube voltage). This approach may be implemented only if advanced high-frequency low-capacitance generator and very fast detectors with low afterglow are available. Introduced by General Electric, an innovative scintillator material (Gemstone detector; GE Healthcare) has been reported to be 100-times faster than the standard ceramic (Gadolinium OxySulfide: GOS) scintillators This detector enabled increased speed of data sampling, allowing the collection of low- and high-energy projection data from a single X-ray source, which switches less than every 0.25 milliseconds as the X-ray tube-detector array pair rotates. Thus, low- and high-energy projection data are acquired essentially simultaneously (the temporal mismatch is <0.5 ms), without limitations in the scan FOV employed.
Detector construction
Published in Ross I. Berbeco, Beam’s Eye View Imaging in Radiation Oncology, 2017
The primary function of the scintillator is to convert the photons and the secondary electrons to light. The Compton interactions occur not only in the build-up plate but also in the scintillator. Indirect flat-panel imagers use a phosphor as scintillation material. These phosphors are typically doped with an element that creates an activation state (luminescence centers) in the forbidden band. Most scintillators for high-energy flat panels use gadolinium oxysulfide (Gd2O2S) as a scintillation material. It is deliberately doped with terbium (Tb), which determines the wavelength of the emitted light photons. In a Gd2O2S:Tb scintillator, the peak wavelength is around 545 nm (green light). Figure 2.9 shows a simplified illustration of the scintillation process. When the secondary particle (Compton electron) deposits part of its energy, it excites electrons of the atom with which it interacts. These electrons are excited into the conduction band; from there they fall back through the activation states to the valence band. When moving from the excited activator state to the activator ground state, the energy difference is released as a light photon. In materials doped with terbium, the energy difference of the two activator states is such that it equals the energy of a green light photon. Thus, the released photon has a wavelength of 545 nm or about 2.3 eV. However, some electrons return to the valence band without going through the activator center and do not generate light.
Neutron and Proton Imaging
Published in Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull, X-Ray Imaging, 2016
Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull
Electronic imaging of thermal neutrons usually employs a scintillator. Gadolinium oxysulfide screens have been highly developed for medical imaging with x-rays. This same screen is a useful detector of thermal neutrons via capture of neutrons by 157Gd and subsequent electron emission. The emitted electron excites the scintillating gadolinium oxysulfide. 157Gd is 16% of natural Gd. Other scintillators used with thermal neutrons combine an isotope that undergoes (n,α) reactions (6Li or 10B) in combination with a scintillator, such as ZnS(Ag). The emitted α-particle lights the scintillator. Light from the scintillator is imaged using lens and mirror coupling to a charge-coupled device (CCD) or direct contact with a photodiode array. Electronic detection enables CT and radiographic studies requiring reference images (for example, an empty container). At least one turning mirror is necessary when employing a CCD in order to remove it from the radiation field (Toops et al. 2013).
X-ray-acquired imaging and detection radiography system using digital radiography with a DSLR digital camera: preliminary results of a pilot study
Published in Radiation Effects and Defects in Solids, 2023
Jae Yul Lee, Kyum Cha Lee, Dae Cheol Kweon
Gadolinium oxysulfide (GOS) was used as the scintillator to acquire images using an image-processing method (7). The GOS-based scintillator screens were manufactured to the required dimensions by Toshiba (Toshiba Corporation, Japan). In the X-ray imaging system, the X-ray irradiation device projects X-rays toward the object to be photographed. X-rays penetrating the subject are projected onto a dark box. X-rays irradiated from the X-ray irradiation device pass through the object located between the X-ray irradiation device and the dark box, and generate an image on the fluorescence plate on one side of the dark box, where the X-rays are converted into visible light, and the digital camera placed inside the digital camera protection box takes a picture and finally obtains an X-ray image. As shown in Table 1, the X-ray imaging system using a DSLR camera comprises a digital camera equipped with a CMOS image sensor (Canon EOS 6D, Japan).
Performance Testing of Dysprosium-Based Scintillation Screens and Demonstration of Digital Transfer Method Neutron Radiography of Highly Radioactive Samples
Published in Nuclear Technology, 2022
William Chuirazzi, Aaron Craft, Burkhard Schillinger, Nicholas Boulton, Glen Papaioannou, Amanda Smolinski, Kyrone Riley, Andrew Smolinski, Michael Ruddell
The scintillator screen parameters are displayed in Table I. Screens 1 through 7 were the top performers from the initial testing campaign, while screens 8 through 16 were fabricated specifically for this experiment. Screens 8 through 16 were fabricated to test the performance of different scintillator materials and thicknesses. Similarly to the previous seven screens, three of the nine new screens use a ZnS:Cu scintillator, which allows for direct comparison between the previous and new sets of scintillator screens. Additionally, new scintillators include three screens each with gadolinium oxysulfide (GOS:Tb) and ZnS:Ag. Scintillator thicknesses of 100, 200, and 300 μm were coated directly on the 100-µm-thick dysprosium substrates for each of the three scintillator materials. The 100- and 200-μm thicknesses allow screens of similar compositions but with different manufacturers to be compared. Previous results showed that a thicker scintillator produced a higher light output because there was more ZnS to interact with the decay radiation, though a thicker scintillator would also degrade resolution due to light diffusion. The 300-μm thickness was included to determine if a higher light output was possible with an even thicker layer of scintillator material.
Performance improvement of the filter-type ‘transXend’ energy-resolving detector by considering noise sensitivity
Published in Journal of Nuclear Science and Technology, 2018
Tien-Hsiu Tsai, Takumi Hamaguchi, Ikuo Kanno
For a filter-type transXend detector like that shown in Figure 2 of Ref. [8], the response function of each channel is the response function of the base detector multiplied by the photon transmittance of the applied filter. Considering a scintillator-coupled FPD as the base detector, its response function can be approximately given as the energy absorption of the scintillator. Because the base detector of each channel is the same FPD, the response function difference between each channel mainly depends on the photon transmittances of the filters used, which are determined by their material and thickness and can be calculated using the mass attenuation coefficients of the filter materials [12]. For example, the four-channel system with Cu and Sn filters described above has the response functions shown in Figure 1. Figure 1(a) is the energy absorption of a 0.15-mm-thick gadolinium oxysulfide (GOS) scintillator determined by a Geant4 simulation [13,14]. Figure 1(b) displays the photon transmittances of the filter(s) of each channel: (1) none, (2) 0.1-mm-thick Cu only, (3) 0.1-mm-thick Sn only, and (4) both 0.1-mm-thick Cu and 0.1-mm-thick Sn. The final response functions are depicted in Figure 1(c). In this case, channel (1) without a filter is the lowest-energy channel, and channel (4) is the highest-energy channel.