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Scintillation Detectors
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
For low energy X-ray detectors scintillator density and atomic number are less important; the mean free path of low-energy photons in, for instance, yttrium-based YAP or YAG-detectors (see below) are similar to heavy bismuth-based BGO-detectors as long as the photon energy is below the K-edge of Bi (90 keV).
Photon Counting Detectors Viewed as Nonlinear, Shift-Variant Systems
Published in Katsuyuki Taguchi, Ira Blevis, Krzysztof Iniewski, Spectral, Photon Counting Computed Tomography, 2020
X-ray detectors are tools used in x-ray imaging. As such, photon counting detectors must not only be compared to and benchmarked against each other. Instead, all competing technologies must be considered in a fair and unbiased comparison to assess whether photon counting brings a true benefit. Energy integrating detectors, in fact, comprise a wide range of technologies and commercial designs. While those flat panel detectors that employ thin film transistors on amorphous silicon have been the hallmark of modern cone beam x-ray imaging, this technology is now being replaced by one relying on CMOS electronics more and more. CMOS technology is also the basis of photon counting detectors and enables integrating complex and low-noise signal amplification electronics into each individual pixel. Consequently, the x-ray images produced by CMOS-based energy integrating detectors are known to show very little readout noise or dark current. Unlike photon counting detectors, energy integrating detection concepts based on CMOS technology do not suffer from the multiple counting of events, or their complete loss. In addition, they are a lot cheaper to fabricate in comparison to photon counting detectors (at the time of writing). It will therefore be very interesting to see which concept will prevail, and it may well be that different applications will require different kinds of detectors even in the distant future. Either way, there will be an abundance of questions to study and comparisons to make, and the science of x-ray detection is very likely to remain an exciting field for many years to come.
Design and Assessment Principles of Semiconductor Flat-Panel Detector-Based X-Ray Micro-CT Systems for Small-Animal Imaging
Published in Iniewski Krzysztof, Integrated Microsystems, 2017
Alejandro Sisniega, J. J. Vaquero, M. Desco
Since x-ray detectors can be simply modeled using cascaded devices [29–32], for the sake of clarity the following explanation divides signal generation into two different stages, namely, x-ray conversion and data readout. Information on the position, where the x-ray photon is detected, and on its deposited energy, is generated at the beginning of the first stage where the x-ray photons (primary quanta) are stopped. Subsequent steps do not add new information to form the image. Thus, it is important to have a low noise level and adequate amplification in the stages following x-ray capture to ensure that no information is lost after the x-ray photons are detected. The stage with the poorest quanta detection capability, the quantum sink, limits system performance in terms of SNR. Since the information lost in the quantum sink cannot be recovered, a well-designed detector should have its quantum sink at the very first stage of image formation, namely, when x-ray photons are stopped [20].
An outlook on using serial femtosecond crystallography in drug discovery
Published in Expert Opinion on Drug Discovery, 2019
Alexey Mishin, Anastasiia Gusach, Aleksandra Luginina, Egor Marin, Valentin Borshchevskiy, Vadim Cherezov
In this section, we will describe major developments and state-of-the-art related to sample preparation, data collection, and data processing for an SFX experiment. The layout of a typical SFX beamline includes beam focusing and conditioning modules, a sample chamber with an integrated sample delivery system, and an X-ray detector (Figure 2). To reduce background scattering due to a strong XFEL beam, the sample chamber is kept under vacuum or filled with helium at atmospheric pressure. Helium chambers offer simplicity and flexibility in exchange for a moderately increased background. They also can accommodate a broader variety of sample delivery methods along with optical laser systems for time-resolved pump-probe experiments, as well as allow for diverse sample environments such as pressure, temperature, humidity, etc. X-ray detectors for SFX have special requirements due to an extremely large number of photons arriving at the detector within a few femtosecond pulse duration and a high pulse repetition rates at modern XFELs. Finally, SFX data processing requires the development of special software for assembling a dataset using static diffraction snapshots captured from thousands of crystals in random orientations.
Distribution of the C statistic with applications to the sample mean of Poisson data
Published in Journal of Applied Statistics, 2020
PG 1116+215 is a quasar located at a distance from Earth of approximately 2.5 billion light years and it has been observed by the Chandra X-ray satellite several times [6,7]. The X-ray detectors used by Chandra collect individual photons from the source and neighboring areas in the sky, and measure each photon's wavelength. The photons are distributed in data points according to their wavelengths, and this distribution is usually referred to as the source's spectrum.
Shields and garb for decreasing radiation exposure in the cath lab
Published in Expert Review of Medical Devices, 2018
Aris Karatasakis, Emmanouil S. Brilakis
The main source of operator radiation dose is scatter from the patient, hence minimizing patient radiation dose (by thoughtful use of fluoroscopy, using low frame per second angiography, use of collimation, and optimal patient and X-ray detector positioning) will also lead to lower operator dose. Moreover, operator dose can be decreased by shielding through (1) personal protective equipment; and (2) shielding [2,3].