Modeling quantum noise of phosphors used in medical X-ray imaging detectors

The noise properties of the granular phosphor screens, which are utilized in X-ray imaging detectors, are studied in terms of the quantum noise transfer function (QNTF). An analytical model, taking into account the effect of K-characteristic X-rays reabsorption within the phosphor material and the optical properties of the phosphor, was developed. The optical properties of the phosphor material required by the model were obtained from literature, except for the optical diffusion length (σ) that was determined by data fitting and was found to be 26 cm²/g. The deviation between theoretical and experimental data is σ depended. Specifically for σ=26 cm²/g and σ=25 cm²/g the respective deviations between experimental and predicted results were 0.698% and −1.597%. However for relative differences in σ more than 15% from the value 26 cm²/g, the corresponding deviations exceed by 6 times the value of 0.698%. The model was tested via comparison to experimental results obtained by a set of Y₂O₃:Eu³⁺ phosphor screens prepared by sedimentation. The model may be used to evaluate the effect of screen thickness and irradiation geometry on quantum noise of phosphor materials for transmission and reflection mode.     

Modeling quantum and structure noise of phosphors used in medical X-ray imaging detectors

The noise properties of granular phosphors used in X-ray imaging detectors are studied in terms of a noise transfer function, NTF. This study is performed in high-exposure conditions where the contribution of structure noise to total screen noise is considerable. An analytical model, based on the cascaded linear systems methodology presented in the literature, is developed. This model takes into account the quantum noise and structure noise. Furthermore, it considers the effect of the K X-rays reabsorption on the phosphor material and the effect of screen thickness on the NTF. The model was validated against experimental results obtained by a set of Zn₂SiO₄:Mn phosphor screens prepared by sedimentation. The model may be used to evaluate the effect of screen thickness and the effect of the characteristic X-rays on NTF in high-exposure conditions where structure noise is considerable.     

Evaluation of the GSO:Ce scintillator in the X-ray energy range from 40 to 140 kV for possible applications in medical X-ray imaging

The purpose of the present study was to evaluate, under X-ray medical imaging conditions, the X-ray luminescence efficiency (XLE) and the optical quantum gain (OQG) of the Gd₂SiO₅:Ce scintillator in single crystal form, suitable for tomographic applications. Intrinsic physical properties and light emission characteristics of the Gd₂SiO₅:Ce scintillator, were also studied. Both experimental and Monte Carlo techniques were used. Various X-ray tube voltages (40–140 kV), currently employed in X-ray imaging applications, were used. XLE was found to vary slowly with X-ray tube voltage from (0.021±0.003) to (0.017±0.003). OQG varied from (317±18) to (466±23) light photons per incident X-ray. These values were adequately high for imaging applications using the particular energy range. Additionally, it was found by Monte Carlo simulations that for crystal thicknesses higher than 0.5 cm both XLE and OQG reached saturation levels, indicating that higher thickness crystals are of no practical use in X-ray medical imaging.     

医学影像新技术在脑血管病诊断中的应用

本文综述了第四届全国脑血管病学术会议有关影像学检查,包括MRI、CT、SPECT、TCD等在脑血管病诊断方面的有关内容,MRI在发现早期脑梗塞方面较CT优越,CT依然是诊断脑梗塞及脑出血的主要检查手段,SPECT及TCD对缺血性脑血管病的诊断有很大帮助,合理选择以上检查方法对脑血管病的早期诊断、指导治疗、判断预后及随访有重要意义。     

Features of the attenuation and single-sided imaging potential of near-infrared laser radiation in tissue-like liquid turbid media

Tissue-like phantoms are important tools in studying light propagation and scattering in biological tissues and in the development, testing and calibration of novel optical diagnostic and therapeutic methods and instruments. This motivates the interest in characterizing the optical properties of tissue-simulating turbid media. In the present work, using an original approach, the specific features have been revealed experimentally and interpreted physically (as owing to the polydispersity of the ensemble of scatterers) of the generally non-linear behaviour of the extinction (total attenuation) coefficient of Intralipid-20% dilutions in distilled water, depending on the Intralipid concentration, for near-infrared laser radiation of different wavelengths. At relatively low incremental concentrations, the values obtained of the extinction coefficient are shown to increase linearly being in agreement at each wavelength of concern with results for the integral scattering coefficient predicted by empiric formulae found by other authors. Comparative estimation has been performed as well, depending on the radiation wavelength, of the potentialities of single-sided optical sensing of tissue-like media. The estimates obtained outline the advantage of the wavelengths around the upper limit of the tissue optical window.     

关于医用X线胶片感光测定时辐射能的标准和计算

本文扼要地介绍了医用X线胶片感光测定时,用于使胶片曝光的几种辐射能标准,阐述了其技术背景、特点及曝光能量计量单位和有关计算。     

Investigations on the physicochemical properties of thiocyanate and allylthiourea complex crystals for blue-violet laser light generation

Recent experiments strongly suggest that the complexes of bimetallic thiocyanates, and allylthiourea and their Lewis base adducts can generate blue-violet light by using direct frequency doubling laser diodes. The organometallic complexes of Allylthiourea (AT) and thiocyanate (SCN) are interesting category of SHG materials. In the present study, novel organometallic complex crystals such as ATCC, MMTC, and MMTD are synthesized and their growth conditions are investigated. The physicochemical properties of the grown crystals are studied by various characterization techniques. Preliminary studies confirm that the SHG efficiencies of these crystals are greater than that of urea.     

袖套式挠性接管性能及管路减振效果的试验研究

本文对袖套式挠性接管的平衡性能、静刚度参数及阻抗特性进行了试验研究 ,并在试验室用船用往复式舱底泵对袖套式挠性接管进行了不同压力状态下的管路减振效果的试验 ,试验结果表明袖套式挠性接管具有良好的减振效果和实船运用前景。     

考虑异质材料的线接触性能建模与分析

提出了一种考虑材料非均匀特性的线接触弹性场数值建模方法。该方法基于数值化等效夹杂方法（NEIM）,以矩形异质材料作为基本单元,并在此基础上,结合镜像法,可求解得到线接触载荷作用下的材料弹性场。利用对比验证、参数化分析及算例验证的方法,将本文方法计算结果与有限元法（FEM）和传统等效夹杂方法（EIM）计算结果进行对比,并分析研究了异质材料分布参数对材料线接触性能的影响。结果表明:本文方法相较FEM和传统EIM具有优越性,可处理和简化涂层问题及任意分布的异质材料线接触问题。不同位置异质材料将引起基体最大von Mises应力的增大或减小;异质材料的尺寸以及异质材料和基体之间的材料差异将影响基体应力集中程度。      

Modeling of the effect of the temperature field configuration in a fluid on the refraction of laser radiation

The effect of the temperature field configuration in a fluid on the refraction of laser radiation is modeled. Calculations of the refraction of geometrical-optics rays in the boundary layer in the case of spherically and elliptically stratified temperature fields are presented. Translated from Metrologiya, No. 7, pp. 33–40, July, 2008.     

Modeling of the rough-interface effect on a converging light beam propagating in a skin tissue phantom

Light distribution in a strong turbid medium such as skin tissue depends on both the bulk optical properties and the profiles of the interfaces where mismatch in the refractive index occurs. We present recent results of a numerical investigation on the light distribution inside a human skin tissue phantom for a converging laser beam with a wavelength near 1 mum and its dependence on the roughness of the interfaces and index mismatch. The skin tissue is modeled by a two-layer structure, and within each layer the tissue is considered macroscopically homogeneous. The two interfaces that separate the epidermis from the ambient medium and the dermis are considered randomly rough. With a recently developed method of Monte Carlo simulation capable of treating inhomogeneous boundary conditions, light distributions in various cases of interface roughness and index mismatch are obtained, and their relevance to the measurements of optical parameters of the skin tissue and laser surgery under the skin surface are discussed.     

Study of optical properties and light induced effects on Inq3 thin film used in organic light emitting devices

In this report, the optical properties of tris-(8-hydroxyquinoline) metal complex Inq₃; used as light-emitting layer in electroluminescent (EL) devices are shown. The material has been synthesized and the thin films have been deposited by thermal evaporation on quartz and silicon substrates. The optical constants (n and k) of Inq₃ thin films have been determined using spectroscopic ellipsometry. Light induced effects on optical properties of films have been studied using ellipsometry, photoluminescence and UV–visible transmission measurements. Enhanced photoluminescence intensity with shift in peak position as well as modification in optical constants on light exposure in vacuum indicates phase transformation in Inq₃ films.     

Modeling the combined effect of static and varying phase distortions on the performance of adaptive optical systems

The end-to-end performance achieved by an adaptive optical (AO) imaging system is determined by a combination of the residual time-varying phase distortions associated with atmospheric turbulence and the quasi-static unsensed and uncorrectable aberrations in the optical system itself. Although the effects of these two errors on the time-averaged Strehl ratio and the time-averaged optical transfer function (OTF) of the AO system are not formally separable, such an approximation is found to be accurate to within a few percent for a range of representative residual wave-front errors. In these calculations, we combined static optical system aberrations and time-varying residual phase distortion characteristics of a deformable mirror fitting error, wave-front sensor noise, and anisoplanatism. The static aberrations consist of focus errors of varying magnitudes as well as a combination of unsensed and uncorrectable mirror figure errors derived from modeling by the Gemini 8-Meter Telescopes Project. The overall Strehl ratios and OTF's that are due to the combined effect of these error sources are well approximated as products of separate factors for the static and time-varying aberrations, as long as the overall Strehl ratio that is due to both errors is greater than approximately 0.1. For lower Strehl ratios, the products provide lower bounds on the actual values of the Strehl ratio and the OTF. The speckle transfer function is also well approximated by a product of two functions, but only where AO compensation is sufficiently good that speckle imaging techniques are usually not required.     

Characterization of adsorbed silane on fillers used in dental composite restoratives and its effect on composite properties

The purpose was to study the effect of silane treatment of fillers on viscosity, flexural strength, and hydrolytic degradation of experimental dental composite resins fabricated with these fillers. The fillers consisted of a mixture of barium glass and amorphous silica. The resin was mainly based on ethoxylated bisphenol A dimethacrylate and polycarbonate dimethacrylate. The adsorption of silane on the filler surface was characterized by FTIR. There was significant correlation between the adsorbed silane on filler surface and the silane concentration in silane/methanol solution used for filler treatment. The silane concentration varied from 0.75 to 14% by weight. An increase in silane concentration led to a decrease in viscosities of the corresponding composite resins. The flexural strengths of composites with silanated fillers were greater than that of composites with unsilanated fillers: however, no significant difference was found between the flexural strengths of various silanated groups. The resistance to hydrolytic degradation of different composites increased when the fillers were treated with silane and was the highest at 1.1% silane.     

太阳日辐照量对太阳能热水系统热性能检测影响研究

针对太阳能热水系统热性能评价规范中对太阳辐照量要求差异较大,影响实际操作的问题,开展太阳辐照量对太阳能热水系统热性能测试的影响规律研究.该文进行86d太阳日辐照量监测和27 d对不同日辐照量下平板太阳能热水系统热性能的短期测试研究.结果显示:南京市满足测试规范要求的日辐照量天气较少,在5～10月约占总天数的28％;随着日辐照量的升高,水箱的温升增加,当日辐照量较大时,贮水箱温升与日辐照量的线性关系不明显;平板太阳能热水系统热性能评定指标系统温升性能At17与太阳日辐照量无关,由太阳能热水系统本身性能决定.对太阳能热水系统热性能检测的日辐照量要求可适当放宽,其标准需开展系统研究;太阳能热水器热水系统的日平均热效率,可作为评定指标之一.     

Influence of forward and multiple light scatter on the measurement of beam attenuation in highly scattering marine environments

Using three-dimensional Monte Carlo radiative transfer simulations, we examine the effect of beam transmissometer geometry on the relative error in the measurement of the beam-attenuation coefficient in an aquatic environment characterized by intense light scattering, especially within submerged bubble clouds entrained by surface-wave breaking. We discuss the forward-scattering error associated with the detection of photons scattered at small angles (< 1 degrees) and the multiple-scattering error associated with the detection of photons scattered more than once along the path length of the instrument. Several scattering phase functions describing bubble clouds at different bubble void fractions in the water are considered. Owing to forward-scattering error, a beam-attenuation meter (beam transmissometer) with a half-angle of receiver acceptance of 1.0 degrees and a path length of 0.1 m can underestimate the true beam attenuation within the bubble cloud by more than 50%. For bubble clouds with a beam attenuation of as much as 100 m(-1), the multiple-scattering error is no more than a few percent. These results are compared with simulations for some example phase functions that are representative of other scattering regimes found in natural waters. The forward-scattering error for the Petzold phase function of turbid waters is 16% for a typical instrument geometry, whereas for the Henyey-Greenstein phase function with the asymmetry parameter of 0.7 and 0.9 the error range is 8-28%.     

The effect of salinity and temperature on electromagnetic wave attenuation in brine

Ice slurries are typically formed from an aqueous solution of water and salt (NaCl) at 5% salinity. Ice pigs, used in many industry areas, are taken from a bulk ice slurry and used to clear waste or recover product from pipes. Ice fraction is a key property of an ice slurry, since it determines it's ‘thickness’ and therefore cleaning capacity. Electromagnetic wave interrogation has been shown to accurately predict an ice fraction to within an error of ±1.2%. The largest remaining process error comes from inherent salinity variation, which affects the electromagnetic wave attenuation significantly. Increasing electromagnetic wave attenuation with increasing salinity and the effect of temperature, shown to also increase attenuation, is quantified. Calibration methods are proposed, aiming to eliminate the unwanted effect of varying salinity. Analysis on multiple samples showed a 16% reduction in average error, and 9% reduction in maximum error when the calibration method was applied.