The purpose of this study was to develop a CT simulation platform that is 1) compatible with voxel-based computational phantoms, 2) capable of modeling the geometry and physics of commercial CT scanners, and 3) computationally efficient. Such a simulation platform is designed to enable the virtual evaluation and optimization of CT protocols and parameters for achieving a targeted image quality while reducing radiation dose. Given a voxelized computational phantom and a parameter file describing the desired scanner and protocol, the developed platform DukeSim calculates projection images using a combination of ray-tracing and Monte Carlo techniques. DukeSim includes detailed models for the detector quantum efficiency, quantum and electronic noise, detector crosstalk, subsampling of the detector and focal spot areas, focal spot wobbling, and the bowtie filter. DukeSim was accelerated using GPU computing. The platform was validated using physical and computational versions of a phantom (Mercury phantom). Clinical and simulated CT scans of the phantom were acquired at multiple dose levels using a commercial CT

Chain length of substituted n-alkyl groups is proposed to be a convenient design element for the generation of noncentrosymmetric crystal lattices of interest in optical second harmonic generation (SHG). Powder studies on 7,7-Bis(n-alkylamino)-8,8-dicyanoquinodimethanes indicate that moderate solid-state optical SHG is obtained when the alkyl chains are of length 4, 5, and 6, and no detectable SHG occurs when the chains are of length 0, 3, 7, 8, and 12. The significant role of the intermediate alkyl chain length in generating noncentric crystal lattices is examined using the crystal structures of the propyl, butyl, and octyl derivatives presented in this paper.

The increasing awareness of the adverse effects associated with radiation exposure in computed tomography (CT) has necessesitated the quantification of dose delivered to patients for better risk assessment in the clinic. The current methods for dose quantification used in the clinic are approximations, lacking realistic models for the irradiation conditions utilized in the scan and the anatomy of the patient being imaged, which limits their relevance for a particular patient. The established gold-standard technique for individualized dose quantification uses Monte Carlo (MC) simulations to obtain patient-specific estimates of organ dose in anatomically realistic computational phantoms to provide patient-specific estimates of organ dose. Although accurate, MC simulations are computationally expensive, which limits their utility for time-constrained applications in the clinic. To overcome these shortcomings, a real-time GPU-based MC tool based on FDA's MC-GPU framework was developed for patient and scanner-specific dosimetry in the clinic. The tool was validated against (1) AAPM's TG-195 reference datasets and (2) physical measurements of dose acquired using TLD chips in adult and pediatric anthropomorphic phantoms. To demonstrate its utility towards providing individualized dose estimates, it was integrated with an automatic segmentation method for generating patient-specific models, which were then used to estimate patient-and scanner-specific organ doses for a select population of 50 adult patients using a clinically relevant CT protocol. The organ dose estimates were compared to corresponding dose estimates from a previously validated MC method based on Penelope. The dose estimates from our MC tool agreed within 5% for all organs (except thyroid) tabulated by TG-195 and within 10% for all TLD locations in the adult and pediactric phantoms, across all validation cases. Compared against Penelope, the organ dose estimates agreed within 3% on average for all organs in the patient population study. The average run duration for each patient 6

Radiation chemical reactions of • OH, O •-, and SO 4 •-with benzaldehyde, acetophenone, and benzophenone have been studied using both pulse and steady-state radiolysis techniques. The observed rates for the • OH addition (k ) (2.6-8.8) × 10 9 M -1 s -1 ) are higher than those found for the SO 4 •-reaction (k ) (0.7-4.0) × 10 9 M -1 s -1 ). The rate for the reaction of O •-with benzaldehyde is higher than that found for • OH, while a reverse trend is observed in the case of the two ketones. Optical absorption spectra of the intermediate transients formed in the reactions of • OH and SO 4 •-with all three compounds are similar with a peak around 370-380 nm. The absorption spectra from the O •-reaction have shown a major peak at 310 nm and are somewhat different from those obtained in the reaction of • OH. The yields of the phenolic products formed in the reaction of • OH with benzaldehyde and acetophenone in the presence of 0.1 mM ferricyanide corresponded to only 30% and 50% • OH yields, respectively. Benzoic acid is a major product formed with benzaldehyde in the reaction of • OH as well as SO 4 •-with G values of 2.1 and 1.3 per 100 eV, respectively. The formation of the exocyclic OH adduct is a major pathway in the reactions of • OH (by addition) and of SO 4 •-from hydrolysis of the initially formed radical cation (k ) 2.4 × 10 4 s -1 ) with benzaldehyde. The exocyclic OH adduct undergoes disproportionation to give benzoic acid. The formation of the exocyclic OH adduct of acetophenone is possibly hindered owing to the bulky -COCH 3 group.

Intermolecular interactions across the air−water interface are the basis for a variety of investigations on monolayers and adsorption phenomena at the interface. We present a systematic study of the influence of different anions in the aqueous subphase on the formation and stabilization of a monolayer of the cationic amphiphile N-octadecyl-4-dimethylaminopyridinium. Some polyanions such as polystyrenesulfonate in the subphase are shown to impart strong stability to the monolayer. The monolayer stabilization through ionic complex formation at the air−water interface is modeled using semiempirical quantum chemical computations. The significance of including solvation effects in the computations is highlighted.

Although tube current modulation (TCM) is routinely implemented in modern computed tomography (CT) scans, no existing CT simulator is capable of generating realistic images with TCM. The goal of this study was to develop such a framework to (1) facilitate patient-specific optimization of TCM parameters and (2) enable future virtual imaging trials (VITs) with more clinically realistic image quality and x-ray flux distributions. The framework was created by developing a TCM module and integrating it with an existing CT simulator (DukeSim). The developed module utilizes scanner-calibrated TCM parameters and two localizer radiographs to compute the mAs for each simulated CT projection. This simulation pipeline was validated in two parts. First, DukeSim was validated in the context of a commercial scanner with TCM (SOMATOM Force, Siemens Healthineers) by imaging a physical CT phantom (Mercury, Sun Nuclear) and its computational analogue. Second, the TCM module was validated by imaging a computational anthropomorphic phantom (ATOM, CIRS) using DukeSim with real and module generated TCM profiles. The validation demonstrated DukeSim's realism in terms of noise magnitude, noise texture, spatial resolution, and image contrast (with average differences of 0.38%, 6.31%, 0.43%, and −9 HU, respectively). It also demonstrated the TCM module's realism in terms of projection-level mAs and resulting noise magnitude (2.86% and −2.60%, respectively). Finally, the framework was applied to a pilot VIT simulating images of three computational anthropomorphic phantoms (XCAT, with body mass indices (BMIs) of 24.3, 28.2, and 33.0) under five different TCM settings. The optimal TCM for each phantom was characterized based on various criteria, such as minimizing mAs or maximizing image quality. 'Very Weak' TCM minimized noise for the 24.3 BMI phantom, while 'Very Strong' TCM minimized noise for the

The aim of this study was to develop and validate a simulation platform that generates photon-counting CT images of voxelized phantoms with detailed modeling of manufacturer-specific components including the geometry and physics of the x-ray source, source filtrations, anti-scatter grids, and photon-counting detectors. The simulator generates projection images accounting for both primary and scattered photons using a computational phantom, scanner configuration, and imaging settings. Beam hardening artifacts are corrected using a spectrum and threshold dependent water correction algorithm. Physical and computational versions of a clinical phantom (ACR) were used for validation purposes. The physical phantom was imaged using a research prototype photon-counting CT (Siemens Healthcare) with standard (macro) mode, at four dose levels and with two energy thresholds. The computational phantom was imaged with the developed simulator with the same parameters and settings used in the actual acquisition. Images from both the real and simulated acquisitions were reconstructed using a reconstruction software (FreeCT). Primary image quality metrics such as noise magnitude, noise ratio, noise correlation coefficients, noise power spectrum, CT number, in-plane modulation transfer function, and slice sensitivity profiles were extracted from both real and simulated data and compared. The simulator was further evaluated for imaging contrast materials (bismuth, iodine, and gadolinium) at three concentration levels and six energy thresholds. Qualitatively, the simulated images showed similar appearance to the real ones. Quantitatively, the average relative error in image quality measurements were all less than 4% across all the measurements. The developed simulator will enable systematic optimization and evaluation of the emerging photon-counting computed tomography technology.

Background: Anaemia is a global public health problem affecting around 800 million children and women worldwide. Anaemia, defined as a reduced haemoglobin concentration, is associated with increased peri-natal mortality, increased child morbidity and mortality, impaired mental development, impaired immune competence, increased susceptibility to lead poisoning, and decreased performance at work.Methods: This paper attempts to understand the determinants underlying iron intake in select countries in Asia using multivariate regression analyses of recent data from the Demographic and Health Surveys of eight countries of Afghanistan, Cambodia, India, Indonesia, Myanmar, Nepal, Pakistan, and the Philippines. The individual level data was analysed, using Predictive Analytics Software for Windows (PASW) 18.0 release.Results: After adjusting for standard co-variates, exposure to newspaper was found to be associated with increased adherence to iron tablets or syrup, in five of the eight countries (India, Indonesia, Nepal, Pakistan, and the Philippines). Exposure to television was significantly associated with coverage and adherence to iron tablets or syrup in Afghanistan, India, Indonesia and Myanmar. Those who received at least three antenatal care visits were much more likely to adhere to at least 90 days of iron tablet or syrup or iron and folic acid tablets supplementation.Conclusions: Based on insights from eight demographic and health surveys, mass media (including print and TV), as well as antenatal care-seeking visits seem to be a particularly effective ways of reaching women and in increasing the likelihood of uptake of iron only or iron and folic acid supplements.