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Introduction to the Physics and Applications of Laser Produced Plasmas
Published in M.B. Hooper, Laser-Plasma Interactions 4, 2020
Dense, relatively cool plasmas are generally opaque to their own emissions and can therefore be studied only by absorption spectroscopy. Two approaches have been particularly useful. The first is observation of the shift of the K-edge, which is closely related to the behaviour of the plasma electrons in the non ideal plasma(11). The second is concerned with the X-ray absorption fine structure above the K-edge. These small oscillations in the absorption coefficient originate in resonance between the De Broglie wavelength of the ejected photoelectron and the distance to nearest neighbour ions. The separation and the degree of correlation in positions of ions in the non classical plasma can be studied from the form of the EXAFS spectrum. Interesting new work in this area has been reported recently, as illustrated by Figure 3(12).
Clinical Applications of Photon-Counting Detector Computed Tomography
Published in Katsuyuki Taguchi, Ira Blevis, Krzysztof Iniewski, Spectral, Photon Counting Computed Tomography, 2020
Shuai Leng, Shengzhen Tao, Kishore Rajendran, Cynthia H. McCollough
The ability of PCD-CT to simultaneously discriminate multiple tissue types or contrast materials using their spectral signatures provides an opportunity for the development of new contrast agents and imaging techniques. Nanoparticle-based contrast agents have demonstrated longer blood pool retention (45), and have been successfully used as blood pool contrast agents to image leaky blood vessels in an animal tumor model (46). Several reports using heavy-metal based nanoparticles (gold (10), ytterbium (47), and gadolinium (48)) as potential CT contrast agents have also been published. Individualized nanoparticles that are functionalized and antibody-conjugated to target a specific tissue type or region of interest (e.g., cancerous cells, fibrotic collagenous tissue, macrophages) have been used in combination with PCD-CT to facilitate molecular imaging. This relies on the ability of PCD-CT to measure the K-edges of those high-Z materials that fall within the diagnostic CT energy range. The user-defined energy thresholds in PCD-CT can be placed close to the K-edge energy of high-Z contrast materials in order to capture the discontinuity in attenuation profile, as shown in Figure 5.10. This helps distinguish the K-edge of one material from other materials (e.g., bone, soft tissue, second contrast agent) and more importantly, quantify the concentration of the contrast materials in a given target site using material decomposition techniques. This approach has been mainly tested on rodents imaged using small-animal PCD-CT scanners.
Imaging modalities and challenges
Published in Rolf Behling, Modern Diagnostic X-Ray Sources, 2021
Attempts have been made to quantitatively measure the concentration of “K-edge material” such as iodine and in particular gadolinium or bismuth, whose k-edges are close to the mean energy used in CT (see Roessl & Proksa, 2007). This so-called K-edge imaging would require measurements at more than two energies, e.g., employing photon-counting detectors with at least three energy bins or dual-layer detectors illuminated with X-rays with alternating tube voltage. This technology is still in the research phase (see, e.g., Dunning et al., 2020).
Relation Between the Characteristic X-Ray Intensity and Incident Electron Energy Using the Monte Carlo Method and Measurements
Published in Nuclear Technology, 2022
Runqiu Gu, Jianfeng Cheng, Wanchang Lai, Xianli Liao, Guangxi Wang, Juan Zhai, Chenhao Zeng, Jinfei Wu, Xiaochuan Sun
The intensities of the K-series characteristic X-rays of molybdenum, rhodium, and silver and the L-series characteristic X-rays of W and Pt have maximum values at 500, 600, 650, 250, and 300 keV. The peak of the bremsstrahlung spectrum produced by the interaction between the incident electron beam and the target substance varies with increasing incident electron energy. The characteristic X-ray of the target material will have multiple absorption edges, such as the K-edge, L-edge, and M-edge, as the atomic number increases. The greater the atomic number is, the higher the fluorescence yield of the absorption edge is at a lower energy, so the intensity of the characteristic X-ray energy is stronger, and the transition near the absorption edge is more pronounced. Thus, the bremsstrahlung spectrum will exhibit multiple peaks. This probably occurs for the reasons described previously. The efficiency of direct excitation of characteristic X-rays by electrons will gradually decrease with increasing incident electron energy, and the indirect excitation of the bremsstrahlung peak will dominate in a particular energy range. Thus, the characteristic X-rays of several target materials will decrease slowly in this energy range. The various trends of the K-series characteristic X-rays of W and Pt occur for the same reasons.