Techniques for Chest Radiography, Fluoroscopy, Tomography (including CT and MR) and Ultrasound
Fred W Wright in Radiology of the Chest and Related Conditions, 2022
Absorption coefficients - Ambrose (1973) wrote 'The values of the absorption coefficients are calculated on a standard scale, adopting zero as the value for water.... Since the absorption coefficients are measured to an accuracy of 0.5 %, the method is able to detect and register small differences in tissue density.' Originally a scale from minus 500 for air to plus 500 for compact bone was used by Hounsfield (1973). He found that at 120 KV, fat had an absorption coefficient which was 10% less than water, whilst tissues on average gave a value approximately 3% greater than water. The 'print out scale' was doubled to extend from minus 1,000 (air density) to plus 1,000, the figures commonly being referred to as Hounsfield units. Water is 0, fat being about -80 to -100, CSF +2, blood +50, white and grey matter in brain +24 and + 36, kidneys +40, muscle +55, liver + 60 and haematomas and extravasated blood +80 to +90 (when blood clots, haemoconcentration recurs due to retraction of fibrin and this results in increased density on CT - this can last for 7 to 30 days, until liquefaction occurs). CT machines can detect iodine in contrast agents at a concentration of 1 in 1,000. Both air collections and surgical clips or other metal collections (e.g. prostheses or amalgam tooth fillings) may cause considerable artefact formation.
EM behavior when the wavelength is much smaller than the object
James R. Nagel, Cynthia M. Furse, Douglas A. Christensen, Carl H. Durney in Basic Introduction to Bioelectromagnetics, 2018
The magnitude of the scattering from a Rayleigh particle depends strongly—in fact, to the fourth power—on the size of the particle compared to the wavelength. If the effective particle size is s, the power scattering efficiency of the particle is proportional to (s/λ)4. Over the visible wavelengths, there is a dramatic change in the scattering power for a particle of a given size when going from the short-wavelength end of the spectrum to the long-wavelength end. Figure 4.21 shows that the relative scattering efficiency is more than nine times larger for blue light than for red light. This helps explain the blue color of the sky. We see scattered sunlight when we look up through the atmosphere, and this scattering (from the molecules in the air) is much more effective for the blue portion of sunlight than for red. Even though the scattering from each air molecule is very small, the huge number of molecules makes the total scattered power visible. Random fluctuations in the air density also cause scattering with the same behavior.
History of high altitude medicine and physiology
Andrew M. Luks, Philip N. Ainslie, Justin S. Lawley, Robert C. Roach, Tatum S. Simonson in Ward, Milledge and West's High Altitude Medicine and Physiology, 2021
In 1968, the Olympics were held for the first time at high altitude in Mexico City (2240 m). This occasioned a significant burst of research into the impact of high altitude on physical performance (Balke et al. 1965; Buskirk et al. 1967; Faulkner et al. 1967; Pugh 1967; Williams 1966). In sports where lower air density lent itself to better performance, world records were set. In contrast, oxygen demanding endurance events were performed at a much slower pace than in previous Olympics at lower altitudes. However, this Olympics was a preview of the coming dominance of East African (Kenyan and Ethiopian) runners, with winners in the 1500, 5000, and 10,000 m races, all from these countries. How East Africans do so well in endurance running events remains a mystery today in the early 21st century. The research undertaken to support athletes for the 1968 Olympics also was the foundation for current research on training at high altitude. In the late 1990s, this idea experienced a revival based on the work of Levine and colleagues using a model of living at high altitude and training at lower altitude (Levine and Stray-Gundersen 1997), which has since come into question (Siebenmann et al. 2011). Further information on this topic can be found in Chapter 18.
Intraocular pressure changes in eyes with small incision lenticules and laser in situ keratomileusis
Published in Clinical and Experimental Optometry, 2019
Kuo‐jen Wang, Wai W Wang, Che‐liang Tsai, I‐jong Wang
The numerical tools used for simulating IOP were from OpenFoam (version 2.3.0) from OpenCFD Ltd. (OpenFOAM is an open source C++ computational continuum mechanics software and is a registered trademark of OpenCFD Ltd., Reading, UK; http://www.openfoam.com, and Scilab [version 5.5.1] from Scilab Enterprise, Rungis, France; http://www.scilab.org/). The OpenFoam program is a fluid dynamics simulator used to simulate the air‐puff pressure impinging on the corneal surface. The airflow parameters used for this modelling were incompressible airflow with an air density of 1.1855-kg/m3, an air viscosity of 15.68 × 10−6 m2/s, and a peak pressure profile of 30-mmHg with a duration of 28-ms. The geometric parameters of the air chamber were an internal diameter of the nozzle of 2.4-mm and a working distance from the tip of the air nozzle to the cornea of 11-mm. The airflow solver used was incompressible pisoFoam (PISO = pressure implicit split operator) of the Reynolds‐averaged stress turbulence model.1992 The temporal variation and spatial distribution profile of the flow pressure on the corneal surface was calculated. This pressure profile was then provided to shape the boundary conditions for simulating corneal deformation, which was also performed with a solver solid displacement foam in OpenFoam.
Analysis and forecasting of air quality index based on satellite data
Published in Inhalation Toxicology, 2023
Tinku Singh, Nikhil Sharma, Manish Kumar
Pollutant levels have also been studied over the seasons. The seasons were classified into Winter (December to January), Spring (February to March), Summer (April to June), Monsoon (July to Mid-September), and Autumn (September end to November). The level of air pollutants over the different seasons has been summarized in Table 4. The outcome shows that SO2, NO2, CO, and AQI levels during Winter and Spring were higher than those during the rest of the year. The cold air becomes denser and flows more slowly than warm air during the winter. Because of this density, cold air holds pollutants but does not blow them away. The levels of NO2, SO2, CO, and AQI were minimum during the Monson. As the rain falls, the contaminants are delivered to the ground and deposited there which leads to a better AQI (Tian et al. 2021). Additionally, Figure 11 shows the simple moving average plots of different pollutants throughout the study period, which helps in determining the pollutant’s level during the different months.
The impact of arm-crank position on the drag of a paralympic hand-cyclist
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
Paul Mannion, Yasin Toparlar, Eoghan Clifford, Magdalena Hajdukiewicz, Thomas Andrianne, Bert Blocken
A single force transducer was positioned in vertical alignment with the hand-cycle model’s centre of gravity for force measurements (Figure 4a). A rectangular baseplate (0.56 × 0.16 m) below the hand-cycle geometry acted as the connecting geometry to which the force transducer was attached. The location of the vertical axis of the transducer with respect to the baseplate was 0.285 m from its leading edge and centred laterally. The force transducer used was a six-axis Delta model (ATI Industrial Automation 2018). The force transducer was calibrated prior to testing and had a linear response. In addition, the transducer was certified as compliant with the ISO 9001 standard to ensure performance within stated specifications. The transducer was zeroed in the wind-tunnel setup prior to imparting any wind load, and a settling time of 30 s was also provided at full wind load before force measurements were recorded (at 10 Hz for 180 s). The manufacturers of the force transducers reported a conservative maximum error estimate of 1.24 N at a 95% confidence interval, including both random and systematic errors. Additional corrections (via temperature measurements and accounting for atmospheric pressure) were made to the drag measurements to account for the difference in air density between the wind-tunnel experiments and the air density (1.225 kg/m3) used in the CFD simulations. The turbulence intensity of the flow in the wind-tunnel was below 0.2% (Blocken, Toparlar, and Andrianne 2016).
Related Knowledge Centers
- Carbon Dioxide
- Density
- Partial Pressure
- Gravimetric Analysis
- Standard Temperature & Pressure
- Lifting Gas