Attenuation Profiles Research Articles

Invertibility of multi-energy X-ray transform.

PurposeThe goal is to provide a sufficient condition for the invertibility of a multi‐energy (ME) X‐ray transform. The energy‐dependent X‐ray attenuation profiles can be represented by a set of coefficients using the Alvarez–Macovski (AM) method. An ME X‐ray transform is a mapping from N AM coefficients to N noise‐free energy‐weighted measurements, where N≥2.MethodsWe apply a general invertibility theorem to prove the equivalence of global and local invertibility for an ME X‐ray transform. We explore the global invertibility through testing whether the Jacobian of the mapping J(A) has zero values over the support of the mapping. The Jacobian of an arbitrary ME X‐ray transform is an integration over all spectral measurements. A sufficient condition for J(A)≠0 for all A is that the integrand of J(A) is ≥0 (or ≤0) everywhere. Note that the trivial case of the integrand equals 0 everywhere is ignored. Using symmetry, we simplified the integrand of the Jacobian to three factors that are determined by the total attenuation, the basis functions, and the energy‐weighting functions, respectively. The factor related to the total attenuation is always positive; hence, the invertibility of the X‐ray transform can be determined by testing the signs of the other two factors. Furthermore, we use the Cramér–Rao lower bound (CRLB) to characterize the noise‐induced estimation uncertainty and provide a maximum‐likelihood (ML) estimator.ResultsThe factor related to the basis functions is always negative when the photoelectric/Compton/Rayleigh basis functions are used and K‐edge materials are not considered. The sign of the energy‐weighting factor depends on the system source spectra and the detector response functions. For four special types of X‐ray detectors, the sign of this factor stays the same over the integration range. Therefore, when these four types of detectors are used for imaging non‐K‐edge materials, the ME X‐ray transform is globally invertible. The same framework can be used to study an arbitrary ME X‐ray imaging system, for example, when K‐edge materials are present. Furthermore, the ML estimator we presented is an unbiased, efficient estimator and can be used for a wide range of scenes.ConclusionsWe have provided a framework to study the invertibility of an arbitrary ME X‐ray transform and proved the global invertibility for four types of systems.

MEASUREMENT OF HALF-VALUE LAYER IN COMPUTED TOMOGRAPHY SCANNERS USING LUMINESCENCE OF POLYETHERSULFONE RESIN BY X-RAY IRRADIATION.

In this study, a method for estimating the half-value layer (HVL) and effective energy (Eeff) by imaging the luminescence from a polyethersulfone (PES) resin with rotating irradiation of X-rays in a computed tomography scanner was developed. The luminescence of the PES resin was imaged using a charge-coupled device camera. The PES-HVL was determined from the luminance attenuation profile corresponding to the X-ray attenuation within the resin. The PES-HVLs for tube potentials of 80-135 kVp were converted into Eeff values and were compared to those of a conventional lead-covered case method. The Eeff obtained using the proposed luminescence imaging method agreed within ~3.9% of that obtained using the conventional method. Moreover, dose simulations based on the X-ray spectrum calculated from the HVLs were performed using a poly(methyl methacrylate) phantom with a diameter of 16 cm. The simulated doses based on the luminescence imaging method agreed with the in-phantom dosimetry within ~9%.

A novel strategy to develop deep learning for imagesuper-resolution using original ultra-high-resolution computed tomography images of lung as training dataset.

PurposeTo improve the image quality of inflated fixed cadaveric human lungs by utilizing ultra-high-resolution computed tomography (U-HRCT) as a training dataset for super-resolution processing using deep learning (SR-DL).Materials and methodsImage data of nine cadaveric human lungs were acquired using U-HRCT. Three different matrix images of U-HRCT images were obtained with two acquisition modes: normal mode (512-matrix image) and super-high-resolution mode (1024- and 2048-matrix image). SR-DL used 512- and 1024-matrix images as training data for deep learning. The virtual 2048-matrix images were acquired by applying SR-DL to the 1024-matrix images. Three independent observers scored normal anatomical structures and abnormal computed tomography (CT) findings of both types of 2048-matrix images on a 3-point scale compared to 1024-matrix images. The image noise values were quantitatively calculated. Moreover, the edge rise distance (ERD) and edge rise slope (ERS) were also calculated using the CT attenuation profile to evaluate margin sharpness.ResultsThe virtual 2048-matrix images significantly improved visualization of normal anatomical structures and abnormal CT findings, except for consolidation and nodules, compared with the conventional 2048-matrix images (p < 0.01). Quantitative noise values were significantly lower in the virtual 2048-matrix images than in the conventional 2048-matrix images (p < 0.001). ERD was significantly shorter in the virtual 2048-matrix images than in the conventional 2048-matrix images (p < 0.01). ERS was significantly higher in the virtual 2048-matrix images than in the conventional 2048-matrix images (p < 0.01).ConclusionSR-DL using original U-HRCT images as a training dataset might be a promising tool for image enhancement in terms of margin sharpness and image noise reduction. By applying trained SR-DL to U-HRCT SHR mode images, virtual ultra-high-resolution images were obtained which surpassed the image quality of unmodified SHR mode images.

Mantle temperature and density anomalies: The influence of thermodynamic formulation, melt, and anelasticity

Deriving a quantitative geodynamical interpretation from tomography models is a difficult task. It is also a timely task, particularly given the many high-resolution tomography models published in recent years. It is important to assess mantle structure in terms of density and temperature anomalies. Here, we provide a new estimation of the conversion factors between seismic velocity anomalies and density anomalies, Rρ/v, and between seismic velocity anomalies and temperature anomalies, RT/v. These conversion factors are found by considering the constraints provided by thermodynamics, the influence of melt, and anelasticity. To determine the elastic component, we performed thermodynamic simulations by considering several compositions representative of normal or plume-enriched mantle. We also explore the effects of the presence of melt on seismic velocity and consider a radial attenuation profile to account for anelasticity. We provide an envelope of acceptable models, by combining the range of possible solutions combining the elastic, anelastic, and melt relationships used in deriving the conversion factors. Several of the frequently used velocity-density scaling relationships are encompassed in this envelope. We assess the validity of our result by calculating temperature anomalies from the tomographic models using our scaling relationships—these anomalies lie within the range constrained by melting temperatures registered in volcanic rocks (±300 K). Further, we show that the geoid model computed through our velocity-density scaling from the S40RTS tomography provides a good fit to the observed geoid.

Optimized Bolus Threshold for Dual-Energy CT Angiography with Monoenergetic Images: A Randomized Clinical Trial.

Background The bolus-tracking technique from single-energy CT has been applied to dual-energy CT (DECT) without optimization or validation. Further optimization is imperative because of a paucity of literature and differences in the attenuation profile of virtual monoenergetic images (VMIs). Purpose To determine the optimal trigger threshold with bolus-tracking technique for DECT angiography (DECTA) in a phantom study and assess the feasibility of an optimized threshold for bolus-tracking technique in DECTA at 40 keV with a 50% reduced iodine dose in human participants. Materials and Methods A phantom study with rapid kilovoltage-switching DECT was performed to determine the optimal threshold for each kiloelectron-volt VMI. In a prospective study, consecutive participants who underwent whole-body CT angiography (CTA) from August 2018 to July 2019 were randomized into three groups: single-energy CTA (SECTA) with standard iodine dose (600 mg of iodine per kilogram), DECTA with 50% reduced iodine dose (300 mg of iodine per kilogram) by using a conventional threshold, and DECTA with 300 mg of iodine per kilogram by using an optimized threshold. A trigger threshold of 100 HU at 120 kVp was used as a reference for comparison. Injected iodine doses and aortic CT numbers were compared among the three groups using Kruskal-Wallis test. Results Ninety-six participants (mean age ± standard deviation, 72 years ± 9; 80 men) were evaluated (32 participants in each group). The optimized threshold for VMIs at 40 keV was 30 HU. The median iodine dose was lower in the optimized DECTA group (13 g) compared with conventional DECTA (19 g) and SECTA (26 g) groups (P < .017 for each comparison). The median aortic CT numbers were higher in the order corresponding to conventional DECTA (655-769 HU), optimized DECTA (543-610 HU), and SECTA (343-359 HU) groups (P < .001). Conclusion The optimized trigger threshold of 30 HU for bolus-tracking technique during dual-energy CT angiography at 40 keV achieved lower iodine load while maintaining aortic enhancement. ©RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Malayeri in this issue.

Dispersion and attenuation of shear wave in couple stress stratum due to point source

This study discusses the propagation of a horizontally polarised shear wave in a layered composite structure consisting of couple stress stratum over a functionally graded orthotropic viscoelastic substrate due to point source existing at an imperfect interface of the stratum and substrate. Because of the CS effect in the stratum, the existence of the second kind of dispersive (shear) wave is established along with conventional first kind of a shear wave. The closed-form dispersion equations and damping equations of the first and second kind of a dispersive wave are derived by adopting non-traditional boundary conditions and Green’s function technique. The effect of characteristic length of microstructure, imperfect bonding parameter and functional gradient parameters on velocity profiles and attenuation profiles of the first and second kind of dispersive wave has been computed numerically and delineated graphically. For validation, established results are matched with the classical one.

Energy spectra of neutrons penetrating concrete and steel shielding blocks from 24 GeV/c protons incident on thick copper target

In this study, experimental measurements were performed on the spectra of neutrons which penetrate concrete and steel of various thicknesses values when a proton beam of 24 GeV/c was incident on a copper target at the CHARM facility in the East Hall of the CERN Proton Synchrotron (PS) The thicknesses of concrete and steel ranged up to 360 cm and 80 cm, respectively. To measure the neutron spectra, an NE213 scintillator was positioned on the top roof of the shielding structure as the neutron detector. The light output distributions of the detector were converted into the neutron energy spectra using the unfolding method with a calculated response matrix after removing the γ-ray and charged particle events by pulse-shape discrimination and veto counter signals, respectively. The neutron spectra were in agreement with the results obtained using the Monte Carlo simulation code, PHITS, within a factor of 1.4 except for the case of steel 80 cm. The attenuation profiles for concrete and steel were consistent with previous foil activation results within the respective uncertainties.

Next generation live-attenuated yellow fever vaccine candidate: Safety and immuno-efficacy in small animal models

Yellow fever (YF) remains a threat to human health in tropical regions of Africa and South America. Live-attenuated YF-17D vaccines have proven to be safe and effective in protecting travellers and populations in endemic regions against YF, despite very rare severe reactions following vaccination — YF vaccine-associated viscerotropic disease (YEL-AVD) and neurological disease (YEL-AND). We describe the generation and selection of a live-attenuated YF-17D vaccine candidate and present its preclinical profile. Initially, 24 YF-17D vaccine candidate sub-strains from the Stamaril® and YF-VAX® lineage were created through transfection of viral genomic RNA into Vero cells cultured in serum-free media to produce seed lots. The clone with the ‘optimal’ preclinical profile, i.e. the lowest neurovirulence, neurotropism and viscerotropism, and immunogenicity at least comparable with Stamaril and YF-VAX in relevant animal models, was selected as the vaccine candidate and taken forward for assessment at various production stages. The ‘optimal’ vaccine candidate was obtained from the YF-VAX lineage (hence named vYF-247) and had five nucleotide differences relative to its parent, with only two changes that resulted in amino acid changes at position 480 of the envelope protein (E) (valine to leucine), and position 65 of the non-structural protein 2A (NS2A) (methionine to valine). vYF-247 was less neurovirulent in mice than Stamaril and YF-VAX irrespective of production stage. Its attenuation profile in terms of neurotropism and viscerotropism was similar to YF-VAX in A129 mice, a ‘worst case’ animal model lacking type-I IFN receptors required to initiate viral clearance. Thus, vYF-247 would not be expected to have higher rates of YEL-AVD or YEL-AND than Stamaril and YF-VAX. In hamsters, vYF-247 was immunogenic and protected against high viremia and death induced by a lethal challenge with the hamster-adapted Jimenez P10 YF virus strain. Our data suggests that vYF-247 would provide robust protection against YF disease in humans, similar to currently marketed YF vaccines.

Measurements and Monte Carlo simulations of high-energy neutron streaming through the access maze using activation detectors at 24 GeV/c proton beam facility of CERN/CHARM

ABSTRACT A measurement of high-energy neutron streaming was performed through a maze at the CERN (Conseil Européen pour la Recherche Nucléaire) High-energy AcceleRator Mixed-field (CHARM) facility. The protons of 24 GeV/c were injected onto a 50-cm-thick copper target and the released neutrons were streamed through a maze with several corridor-legs horizontally designed with the shield walls in the facility. Streaming neutrons were measured by using aluminum activation detectors placed at 10 locations in the maze. From the radionuclide production rate in the activation detectors, the attenuation profile along the maze was obtained for the reaction of 27Al(n,α)24Na. Monte Carlo simulations performed with two codes, the Particle and Heavy Ion Transport System (PHITS) and CERN FLUktuierende KAskade (FLUKA), gave good agreements with the measurements within a factor of 1.7 for the production rates ranging over more than 3 orders of magnitude.

Modelling on Impact of Building Obstruction for V2I Communication Link in Micro Cellular Environment

In vehicular communication, signal transmission in vehicle-to-infrastructure (V2I) mode typically takes place on highways, urban, suburban and rural environments. The presence of buildings in these environments poses a challenge to model path loss (PL) due to multiple propagation mechanisms such as diffractions and reflections. However, very little attention has been made to address building effects on the performance of V2I communication links in microcell environment. This paper investigates signal propagation characteristics caused by the impact of building under micro-cellular environment whereby the base station or road-side-unit (RSU) is usually located under the rooftop of building to allow communication between RSU and mobile station or on-board-unit (OBU) on the road. The goal of this paper is to validate and discuss available path loss models based on effect of building obstruction towards RSU-OBU links specifically in residential housing area. The channel measurements are conducted based on static line-of-sight (LOS) settings of a real-world environment at 2.4 GHz frequency band using IEEE 802.15.4 XBee S2C compliant device to measure its receive power. The results are demonstrated based on received signal strength indicator (RSSI) and root mean square error (RMSE). The attenuation profile is validated and compared with suitable path loss models to evaluate best fit and most compatible model based on our measurements data and environment. The analysis shows that several V2I path loss models and V2V channel models are applicable to be used as a reference to model in LOS microcell environment with building obstruction. The finding shows that PL Urban yields the best fit V2I path loss model in terms of RMSE when compared to our measurement campaign at 2.4 GHz.

Effects of dietary supplementation of Chlorella vulgaris on oxidative stress attenuation and serum biochemical profile of pregnant New Zealand White rabbits

Oxidative stress negatively affects animals during gestation period and this condition is almost inevitable in the Tropics because of temperature elevation; therefore, objective of this study was evaluation of antioxidant effects of Chlorella vulgaris supplementation in pregnant rabbits. New Zealand white rabbits (40) were randomly distributed into five groups (n = 8) on day 0 of their gestation and were supplemented with 0, 200, 300, 400 and 500 mg Chlorella vulgaris biomass per kg body weight respectively throughout the gestation period. Blood was collected from the animals in the last week of gestation for serum oxidative stress and biochemical profile assessments. There was significant difference in serum malondialdehyde concentration, total antioxidant capacity but protein carbonyl content was not significantly different. There was also significant difference in superoxide dismutase activity, catalase activity and glutathione concentration. Furthermore, the results showed that serum biochemical profiles of the rabbits were within the normal ranges for healthy rabbits. The study therefore concluded that supplementation of Chlorella vulgaris significantly protects the rabbits against oxidative stress damage and has no deleterious effects on their organs function; hence, the microalga was recommended as an antioxidant supplement for pregnant rabbits.

SERUM EXPRESSION OF MICRORNA-142 IN A COHORT OF BULGARIAN PATIENTS WITH INFLAMMATORY BOWEL DISEASES

The focus of the research was to investigate the anatomical location of the rabbit liver. Thus, we applied a topographic algorithm, using dorsal frozen cuts and CT algorithm with coronary slices. The used animals were 13 matured, healthy clinically white New Zealand rabbits. We measured the metric CT parameters – transverse and craniocaudal sizes. At the level of the dorsal plane, located 15 mm ventrally from the spine, dorsal part of lobus hepatis sinister was found, and on the right and laterally - lobus hepatis dexter. At the level of the dorsal plane, located 30 mm ventrally from the spine, lobus hepatis dexter was located cranially relative to lobus hepatis sinister medialis and reached caudally to pars pylorica. Lobus hepatis sinister lateralis remained caudal to lobus hepatis sinister medialis and touched corpus ventriculi. Lobus hepatis sinister lateralis was found cranially to corpus ventriculi and pars pylorica. Lobus caudatus caudally touched the right kidney. At the level of the dorsal plane, located 45 mm ventrally from the spine, lobus hepatis dexter was found to be in the same dorsal plane with the left lobe of the liver. CT normodense heterogeneous anatomical image of lobus hepatis dexter was parallel to that of lobus hepatis sinister, which determined the transverse location of the organ. The obtained imaging analysis of the liver’s anatomical parts and their proximity to other organ structures were interpreted depending on their attenuation profile. The transverse size of the organ at 15 mm ventrally from the spine showed a value of 76.16 mm, and at 30 mm ventrally, this parameter reached a value of 81.48 mm. The highest values were obtained at 45 mm ventrally - 85.21 mm. CT anatomical study added and confirmed the results of the topographic investigation.

GPM搭載2周波レーダによる降水減衰特性高度プロファイルの推定

GPM搭載2周波レーダによる降水減衰特性高度プロファイルの推定

Iron oxides in novel skin care formulations attenuate blue light for enhanced protection against skin damage.

BackgroundUltraviolet (UV) radiation is a main cause of aging of sun‐exposed skin, but greater attention is being focused on the damaging effects of high‐energy visible (HEV) light (400 and 500 nm). HEV light exposure has increased with expanding use of consumer electronics, such as smartphones, which have a peak emission in the 400‐490 nm range. Sunscreens containing titanium dioxide and zinc oxide protect against UVA and UVB radiation but provide limited protection against HEV light.AimIron oxides including red iron oxide (Fe2O3), yellow iron oxide (Fe(OH)3/FeOOH), and black iron oxide (Fe3O4) effectively block HEV light, each with a different attenuation profile. Zinc oxide, titanium dioxide, and iron oxides with patented skin care ingredients have been incorporated into several formulations to provide enhanced skin protection (Colorescience, Inc).MethodsThe percent of HEV light attenuation from 400 nm to 490 nm light was measured in vitro using a technique known as diffuse transmittance spectroscopy using a Perkin Elmer Lambda™ 750 UV/Vis/NIR Spectrophotometer equipped with a 100‐mm integrating Labsphere® and PbS detector.ResultsProducts formulated with zinc oxide, titanium dioxide, and iron oxides demonstrated 71.9%‐85.6% attenuation across the tested wavelengths of 415‐465 nm.ConclusionSunscreens formulated with iron oxides provide enhanced protection against blue light, especially when combined with zinc oxide. To our knowledge, similar studies with iron oxides have not been performed.

Contour Mapping for Rain Rate and Rain Attenuation in Microwave and Millimetre Wave Earth-Satellite Link Design in Tropical Tanzania

Rain rate and rain attenuation predictions are vital in the analysis of the performance of earth-satellite link at higher frequencies beyond 10 GHz for satellite system planning. This study intended to address lack of rain attenuation profile based on local rainfall data collected from various parts of the country. A one-minute integration time rainfall rate used to estimate the rain-induced attenuation was obtained by converting the annual rainfall data collected for 40 years from 22 locations in Tanzania using a combination of Chebil and refined Moupfouma-Martin methods. The International Telecommunication Union (ITU) standard was used to predict attenuation caused by one-minute rain rate. Contour maps for rain rate and rain attenuation were then generated over different percentages of times of 0.1% and 0.01% for both Ku and Ka-bands using the Kriging interpolation method in ArcGIS software. The maps show higher predicted rain rate values compared to the values given by the ITU in zones K, M and N. The developed maps can be used for rapid and precise estimation of link budget for satellite system design in Tanzania.&#x0D; Keywords: contour maps; one-minute; rain attenuation; integration time; Ku-band and Ka-bands

New Emphasis on Water Transparency as Socio-Ecological Indicator for Urban Water: Bridging Ecosystem Service Supply and Sustainable Ecosystem Health

The perspective on water transparency changed since the early days of limnology from being a physical parameter of optical water property to an ecological indicator tracking algal turbidity due to eutrophication or an overall success of sustained lake restoration in the late 60ies to 80ies. In modern cities, where ecosystems are commonly deteriorated by man-made modifications, water transparency offers a great opportunity to the public to raise socio-ecological consciousness concerning urban green-blue spaces. We thus re-emphasise water transparency as a key indicator of multi-functional value when assessing an oxbow lake of the riverine floodplain in Vienna, the Alte Donau. Our study covers the eutrophication from 1987-1994 due to the inclusion of the riverine landscape in the urban area, the following lake restoration with an ecosystem shift from a nutrient-rich, algal-turbid water body to a nutrient-poor, clear-water macrophyte controlled system and the impact of global warming in recent decades. We used light attenuation profiles to identify depth layers of specific ambient light requirements for photosynthetic domains (phytoplankton and submerged macrophytes), and to interpret Secchi measurements. Here we calculated the depth at 1% (minimum light requirements for phytoplankton growth as euphotic depth), 3% (minimum light requirements for macrophytes as maximum macrophyte colonization depth) and 12% (preferred light requirements for phytoplankton development) of surface ambient light. A Secchi disk water transparency of 1.5m (“lake bottom view”), judged as good water quality by human perception, refers to mesotrophic conditions with a maximum colonization depth for macrophytes exceeding the mean lake depth in Alte Donau. Water clarity required for sustained macrophyte growth, in particular for favouring bottom-dwelling Chara meadows instead of tall-growing Myriophyllum spicatum, is 3.5m Secchi depth and thus exceeds by far water clarity requested due to bathing aesthetics. Global warming, mirrored by an advanced warming in spring seems to favor significantly a higher yield of macrophytes mainly built up by Myriophyllum at the expense of the yield of algae. The prolongation of the summer period above 21°C, however, coincides with lowered Secchi transparency. Water visibility during the hot season thus seems to be slightly hampered against lake restoration efforts by global warming.

Optimum Power Allocation Based on Channel Conditions in Optical Satellite Downlinks

The integration of optical satellite links in the next-generation networks and in the fifth generation cellular systems has been proposed in order to guarantee the handling of the extreme data traffic growth and the high-pitched demand for networks’ resources. The optical satellite communication downlink is studied and more specifically, a geostationary satellite with multiple transmitters and an optical ground station with multiple receiving terminals are considered. In this contribution a novel power allocation methodology is proposed for the downlink. The allocation methodology takes into account the scintillation effects due to atmospheric turbulence and maximizes the ergodic network capacity under total expected power and peak power constraints. The analytical optimizing schemes are based on convex optimization methods and have been inspired by waterfilling algorithm. We present emulated power allocation results using real experimental downlink data from ARTEMIS optical satellite campaign and then we investigate the performance of the proposed algorithm with extended numerical results and comparison with other allocation policies. In particular, the new power allocation strategy achieves the highest spectral efficiency, according to the power constraints, for various channel conditions and attenuation profiles and also surpasses two simple baseband allocation methods by intelligently taking advantage of the number of channels and the total expected power.

Progress in modelling fast-ion D-alpha spectra and neutral particle analyzer fluxes using FIDASIM

FIDASIM is a code that models signals produced by charge-exchange reactions between neutrals and ions (both fast and thermal) in magnetically confined plasmas. With the ion distribution function as input, the code predicts the efflux to a neutral particle analyzer diagnostic and the photon radiance of Balmer-alpha light to a fast-ion D diagnostic, in addition to many other related quantities. A new, parallelized version of the Monte Carlo code FIDASIM has been developed in Fortran90 that is substantially faster than the original interactive data language version. Modified algorithms include more accurate treatments of the time dependent collisional-radiative equations that describe neutral energy levels, of the cloud of ‘halo’ neutrals that surround the injected neutral beam, and of finite Larmor radius effects. Enhanced physics capabilities include modelling ‘passive’ signals from cold edge neutrals, the ability to treat general three-dimensional magnetic confinement configurations, and calculations of diagnostic-specific weight functions that enable tomographic reconstructions of the fast-ion distribution function. Neutral beam attenuation, beam emission, and fast-ion birth profiles are also modelled. The new algorithms have been successfully validated against experimental data and new features have been tested through benchmarks between two independently developed versions of the code.

Performance evaluation of near-real time angular tube current modulation in X-ray computed tomography using real-time dosimeter: a phantom study

In X-ray computed tomography (CT), angular tube current modulation (TCM) minimizes the unnecessary travel of X-rays in the anteroposterior direction. This study aimed to evaluate the performance of near-real time angular TCM in a CT scanner using a real-time dosimeter when different-sized elliptical phantoms were scanned. Air kerma and air kerma rate profiles of small and large elliptical phantoms were measured using a solid-state detector with a fixed tube current (FTC) and TCM with the same volume CT dose index (6.20 mGy for the small phantom and 12.32 mGy for the large phantom) displayed on the CT console. Image noises were evaluated by measuring the standard deviation of CT numbers in specific regions in the phantoms. The air kerma at the central and upper and lower peripheral holes were decreased with TCM, whereas air kerma at left and right peripheral holes were increased. With both phantom sizes, the air kerma rate profiles stabilized when TCM was used after the first two cycles. The standard deviations of CT numbers in images of the small phantom were 10.7 ± 1.3 and 10.3 ± 1.2 Hounsfield units (HU) with the FTC and TCM, respectively, and those of the large phantom were 20.6 ± 2.0 and 19.6 ± 1.7 HU, respectively. Therefore, angular TCM can adjust the tube current during each tube rotation according to the phantom’s angular attenuation profile and can decrease the image noises. It can also decrease the variance of air kerma within the in-plane direction.

Wave speed and attenuation profiles in a stratified marine sediment: Geo-acoustic modeling of seabed layering using the viscous grain shearing theory.

In the viscous grain shearing (VGS) theory of wave propagation in an unconsolidated sediment, the dispersion formulas for the phase speed and attenuation of the compressional and shear wave involve two parameters, the compressional modulus, γp, and the shear modulus, γs, which depend on the radius of the circle of contact between contiguous grains in the granular medium. The radius of contact itself depends on the overburden pressure, and hence depth, in the sediment. Based on these observations, the VGS theory is extended to create a geo-acoustic model of a horizontally stratified sediment in which each layer has a uniform porosity, bulk density, and mean grain size, all of which are assumed known from geological survey data. In a given layer, the overburden pressure consists of the contributions from all the higher layers. From the overburden pressure, the compressional and shear moduli are expressed as functions of depth throughout the layer, thereby allowing the frequency dependent phase speed and attenuation profiles of both types of wave to be computed from the VGS dispersion formulas. To illustrate the VGS geo-acoustic modeling technique, two examples are discussed, one of which represents the mud overlying sand sediment at the New England Mud Patch.