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Exposure Indicators
Published in Christopher M. Hayre, William A. S. Cox, General Radiography, 2020
Conventional film screen radiography was largely used in the decades preceding the advent of digital X-ray imaging systems and is still in limited use today in developing countries (Bansal, 2006: 426; Thomas and Banerjee, 2013: 139–142). A general rule in conventional film screen radiography is that the product of milliampere and the exposure time (mAs) is responsible for the film blackening or density. The peak kilovoltage (kVp), also known as the quality of the X-ray beam, controls the image contrast (Curry, Dowdey and Murry, 1990: 148; Trapnell, 1967: 5). The radiographer’s choice of kVp and mAs is responsible for the quantity and quality of the X-ray beam that is generated. Radiographers’ knowledge of the effect of mAs and kVp on the film is therefore essential to produce optimal diagnostic films in conventional film screen radiography (Curry, Dowdey and Murry, 1990: 148; Whitley et al., 2016: 41).
X-ray Vision: Diagnostic X-rays and CT Scans
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
The peak-kilovoltage, milliamperage, and the exposure time are referred to as tube ratings. Longer exposure times TE naturally result in more x-rays contributing to the production of a radiograph, and, for fixed kVp, the total number of x-rays produced per second is proportional to the mA as follows from Equation 5.2. Recall that peak-kilovoltage, kVp (see Section 5.3.1 above) determines the maximum kinetic energy of an electron entering the anode, which in turn puts an upper limit on the energy of an x-ray photon generated in the bremsstrahlung process. This determines not only how many x-rays strike the image receptor, but the overall patient dose as well. (The patient dose is the amount of energy transferred from the x-rays to the body, and an important measure of the procedure's level of risk.) The milliamperage and exposure time must be chosen carefully to optimize the conditions for image formation, taking into account time constraints such as relevant body motions, which could blur the image if too long an exposure were used.
X-Ray-Based Imaging
Published in John G Webster, Minimally Invasive Medical Technology, 2016
In mammography, as compared to conventional radiography in which contrast between bone, soft tissue and lung is desired, tissue contrast between soft tissues is required. Lower peak kilovoltage is used, typically 20–35 kVp, in order to maximize soft-tissue contrast. This reduces the X-ray beam, so in order to compensate, the filament current is increased, which increases patient exposure.
Advanced X-ray shielding and antibacterial smart multipurpose fabric impregnated with polygonal shaped bismuth oxide nanoparticles in carbon nanotubes via green synthesis
Published in Green Chemistry Letters and Reviews, 2021
Sarika Verma, Medha Mili, Charu Sharma, Harsh Bajpai, Kunal Pal, Dilshad Qureshi, S. A. R. Hashmi, A. K. Srivastava
The adverse radiation effects may be minimized by attenuating the X-ray radiation energy to ∼60–100 kVp (peak kilovoltage) before they reach the human body (2). Hence, attempts are made to develop shielding materials or equipment that can attenuate X-ray radiation energy. Nanostructured materials are appropriate for radiation shielding purposes because they provide a wide surface area distribution, which causes X-ray radiation to dissipate at a faster rate. Some of the nanostructures include nanofibers, nanoribbons, quantum dots and nanotubes. Among the above, nanotubes have gained much attention in the last decade. Carbon nanotubes (CNT) are of extensive interest in X-ray shielding applications in recent years (3–5). CNT are categorized into two types, namely, single-walled CNT (SWCNT) and multiple-walled CNT (MWCNT). The SWCNT exhibits a monolayered structure, while the MWCNT exhibits multiple layers of nanotubes. Since SWCNT have only a single wall, they are inefficient to dissipate the X-ray radiation energy compared to MWCNT. The presence of numerous layers enhances the interaction between the radiation and MWCNT, thereby increasing the radiation's scattering, which leads to faster energy attenuation. Secondly, being lighter in weight, the MWCNT accelerates the quicker dissipation of X-rays. Further, these carbon nanostructures’ shielding performance can be enhanced when incorporated with the salts of heavy metals like zinc, bismuth, iron, cerium, thallium, americium, gadolinium etc. (6,7). These metals have several free electrons in their outer shells, which increases the probability of Compton scattering of X-ray photons from the surface of the shielding materials (8). Since carbon atoms are present in a sp2 hybridized state in a planar form in the nanotubes, they make weak Van der Waals interaction with their neighboring nanotube structures current in the same plane. However,π orbitals form stronger bonds with metals through a perpendicular plane to the CNT axis (9,10). Aghaz et al. (11) have reported that the nanoparticle-based composites exhibited better shielding as compared to the micro particle-based composites at higher energy levels (>80 keV) (11). In a recent study, Mahmoudian et al. (12) have reported that the cerium-oxide and CNT-based composites exhibited synergistic effects against X-ray radiations in diagnostic applications (12).