In vivo quantitative 1H MRS of cerebellum and evaluation of quantitation reproducibility by simulation of different levels of noise and spectral resolution

A quantitative analysis of cerebellar metabolites in normal subjects has been performed by proton MR spectroscopy (MRS) with relaxation time correction. Quantitation was carried out in seven healthy human subjects with the well-established LCModel program. The prior knowledge utilized for quantitation was obtained from solutions containing the major brain metabolites and MRS investigated under the same experimental conditions. The tissue water signal was used as an internal standard for the in vivo studies. Both in vitro (for the prior knowledge template) and in vivo data were acquired separately at 1.5 T by PRESS sequence (TR, 1500 ms; TE, 30 ms). The absolute concentration of main cerebellar metabolites was corrected for relaxation time effects. Different noise and line broadening conditions were considered and simulated in the spectral processing in order to evaluate the effect of spectral quality on the concentration estimates.     

Alzheimer''s disease histologically proven studied by MRI and MRS: Two cases

Two patients affected by severe Alzheimer's disease (AD) were investigated by MRI and image-guided ³¹P MRS. In one case, ¹H MRS was additionally performed. In both cases the diagnosis of AD was confirmed, post mortem, by the pathologist. The spectral parameters of the ³¹P MR spectra were estimated by fitting the ³¹P MR signals in the time domain. Our ³¹P MRS results suggest that it is possible to detect the membrane catabolism, as indexed with the level of PDE resonances visible in in vivo ³¹P MRS, at least in severe AD cases. The ¹H spectrum from AD brain showed a marked decrease of NAA signal respect to choline.     

Correlation software algorithm for portable laser spectral analysis of heavy metal dopants

A novel correlation algorithm for laser spectral analyser (LSA) has been created for simultaneous determination of heavy metals' content in condensed matters, particularly in soils. This work is devoted to the design of a portable laser spectroscopy device for material contamination analysis using software with an original correlation algorithm. Detection sensitivity that can be achieved using this technique varies within 10–100 ppm. It has been demonstrated that acceptable results may be achieved during in-situ measurements. For a huge number of heavy metals, the limits of detection, which were determined experimentally with respect to unpolluted soil sample are lower. This system may provide fast in-situ analysis of heavy metal content and it uses optical fibre sensors.     

An implicit high-order spectral difference approach for large eddy simulation

The filtered fluid dynamic equations are discretized in space by a high-order spectral difference (SD) method coupled with large eddy simulation (LES) approach. The subgrid-scale stress tensor is modelled by the wall-adapting local eddy-viscosity model (WALE). We solve the unsteady equations by advancing in time using a second-order backward difference formulae (BDF2) scheme. The nonlinear algebraic system arising from the time discretization is solved with the nonlinear lower–upper symmetric Gauss–Seidel (LU-SGS) algorithm. In order to study the sensitivity of the method, first, the implicit solver is used to compute the two-dimensional (2D) laminar flow around a NACA0012 airfoil at Re = 5 × 10⁵ with zero angle of attack. Afterwards, the accuracy and the reliability of the solver are tested by solving the 2D “turbulent” flow around a square cylinder at Re = 10⁴ and Re =  2.2 × 10⁴. The results show a good agreement with the experimental data and the reference solutions.     

New fast spectral analysis method for solid materials

We propose a new fast method for direct spectral analysis of solid materials based on laser ablation of the sample in deionized water and real-time transport of the aqueous suspension of nanoparticles into the inductively coupled plasma of an emission spectrometer. As a result, we have all the instrumental and methodological advantages of standard equipment, along with calibration of the spectrometer using standard aqueous solutions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 281–282, May–June, 2007.     

可见光液晶光谱成像系统研究

利用向列相液晶材料的电控双折射效应,研制了用于可见光波段光谱调谐的大口径液晶可调滤光片,透过光谱测试表明,该滤光片在可见光波段(420~700 nm)以20 nm光谱分辨率可实现连续调谐和任意波长选择。利用该滤光片搭建了一种小型光谱成像系统,并在实验室内对若干样品进行了测试,结果表明,该系统可同时实现高图像分辨率和高光谱分辨率光谱成像,具备高、超光谱分辨率光谱成像的应用潜力,在生物医学、环境保护和资源探测等领域具有较好的应用前景。     

Cerebellar metabolite alterations detected in vivo by proton MR spectroscopy

The aim of our work was to evaluate the feasibility of in vivo single-voxel quantitative proton MR spectroscopy in order to identify possible alterations in the main metabolite concentrations due to some metabolic dysfunctions in the cerebellum of patients suffering from a particular form of migraine called “with aura.” Measurements of metabolite levels in the cerebellum disclosed reduced choline values (normalized both to N-acetyl-aspartate and creatine) in the patient group with respect to the age-matched control group. Our interest in this pathology is motivated by the fact that there are no available specific biochemical markers for migraine characterization, and the current diagnostic only takes advantage of the medical history and the clinical examination.     

A new spectral calibration method for Fourier domain optical coherence tomography

Spectral calibration is important for a Fourier domain optical coherence tomography (FD-OCT) system. A new spectral calibration method for FD-OCT is presented. Through the iterated mapping of spectral interferograms detected by an optical spectrum analyzer and the CCD grating spectrometer, multiple groups of calibration coefficients are obtained. By comparing the effects of these coefficients on improving the amplitude of the axial point spread function (PSF), optimum coefficients are obtained. In this method, no additional calibration laser source is needed, reducing the complexity of the system. The cross-sectional images of a glass plate in milk are acquired, and the experimental results indicate that the axial resolution and signal-to-noise ratio (SNR) are effectively improved with the proposed spectral calibration method.     

Bias sensitive spectral sensitivity in double -SiC:H pin structures

In this work we discuss the use of multilayer stacked structures (p(SiC:H)/i(SiC:H)/n(SiC:H)/p(SiC:H)/i(Si:H)/n(Si:H)) sandwiched between two transparent conductive contacts as colour sensing devices. The thickness and the absorption coefficient of both front and back p–i–n cells were specifically designed in order to achieve simultaneously high blue collection and red transmittance in the front cell and full green absorption and high red collection in the back cell. Electric and optical sensing methods were used for measuring the current–voltage characteristics and the spectral sensitivity, under different experimental conditions. Results show that the spectral sensitivity of the device is strongly modulated by the applied voltage, which allows colour selectivity. The results were supported by a physical model.     

On the voxel size and magnetic field strength dependence of spectral resolution in magnetic resonance spectroscopy

While the inherent low sensitivity of in vivo MR spectroscopy motivated a trend towards higher magnetic fields, B(0), it has since become apparent that this increase does not seem to translate into the anticipated improvement in spectral resolution. This is attributed to the decrease of the transverse relaxation time, T(2)*, in vivo due to macro- and mesoscopic tissue susceptibility. Using spectral contrast-to-noise ratio (SCNR) arguments, we show that if in biological systems the linewidth (on the frequency scale) increases linearly with the field, the spectral resolution (in parts per million) improves approximately as the fifth-root of B(0) for chemically shifted lines and decreases as about B(0)(4/5) (in hertz) for a structure of J-coupled multiplets. It is also shown that for any given B(0) there is a unique voxel size that is optimal in spectral resolution, linking the spectral and spatial resolutions. Since in practical applications the spatial resolution may be dictated by the target anatomy, nomograms to determine the B(0) required to achieve the desired spectral resolution at that voxel size are presented. More generally, the scaling of the nomograms to determine the achievable spectral and spatial resolutions at any given field is described.     

时间-频率联合分析消除太赫兹光谱干涉

基于Fourier变换的传统太赫兹时域光谱分析技术从不同长度的太赫兹信号中产生了不一致的光谱结果,增加太赫兹时域采样长度又会造成光谱的干涉,不利于太赫兹光谱测量的研究和应用。应用小波变换方法对太赫兹波谱作时间—频率联合分析,将不同时刻的太赫兹波谱展开到二维的时间-频率平面,消除了光谱分析的不一致性和光谱干涉的影响。     

基于影像光谱库的遥感波段模拟方法研究

针对常规的影像-影像多光谱影像波段模拟模型对研究区参考影像的依赖和随机性采样带来的模型不稳定问题以及光谱库-影像波段模拟模型中光谱库在类别、时间和空间上的不完善导致模型缺乏适用性问题,本文提出了基于影像光谱库的波段模拟方法。首先对与待模拟影像具有相似类别组成的参考影像进行光谱聚类,然后对各个光谱类别进行采样,形成影像光谱库,接着提取光谱库中的等量类别样本训练BP神经网络(BPN)回归模型,最后利用BPN模拟目标影像的波段。实验结果表明:该方法能够更为精确的模拟出TM蓝波段,其模拟均方根误差(RMSE)较光谱库-影像模型提高了1.3,较影像-影像模型提高了0.6,与影像-影像和光谱库-影像模型相比,该方法更加稳定可靠;该方法能够成功的应用到SPOT和MSS的蓝波段的模拟中并取到较好的效果。     

啁啾脉冲频域相移的模拟与实验研究

在超快光学瞬态相移的测量中,结合线性啁啾脉冲与频谱干涉技术,可以获得啁啾脉冲相移随频谱的变化规律。光脉冲经过光栅色散和透镜聚焦后,不同的频率成分以空间上的不同坐标展开。当两束脉冲频谱同时在空间上展开时,相同的频谱成分会产生干涉。基于傅里叶变换频谱干涉技术,从频谱干涉图中提取相移,并对其进行了数值模拟和实验研究。结果表明,通过对不同类型频域相移进行重构所得到的结果反映出了相移随脉冲频谱变化的特性。实验结果表明了这种重构算法是有效的,与模拟结果具有较好的一致性。     

Monte Carlo uncertainty simulation of surface emissivity at ambient temperature obtained by dual spectral infrared radiometry

The Monte Carlo statistical method was used to estimate the uncertainty of the emissivity, obtained by dual spectral infrared radiometry, of gray surfaces at ambient temperature. A large number of simulations were carried out, by selecting a wide range of values from parameters that directly affect the resulting emissivity: the emissivity of the target surface, the background temperature of the surrounding surfaces, the maximum error of the detectors, and the width and spectral location of the bands of the detectors.In summary, the level of uncertainty grows very quickly as the background temperature approximates the target surface. In terms of the spectral characteristics of the detectors, it was found that narrow bands, far apart from each other, and short wavelength bands provide the lowest uncertainty from all simulated emissivity values.     

S2O‾自由基光电子能谱的Franck-Condon分析

本文考虑多振动模混合和热带效应,凭借谐振子模型,推得计算两维-四振动模Franck-Condon重叠积分的解析表示,且应用于S2O‾ 自由基光电子能谱的理论研究。对于S2O( 1A′) – S2O‾( 2A″) 光脱附过程,结合分子轨道从头算和密度泛函理论,计算Franck-Condon因子,从而得到电子跃迁振动谱线的相对强度,理论上得到的光电子能谱与实验上观测到的能谱达到较好的一致;进一步在光谱模拟过程中,拟合实验能谱得到可靠的负离子自由基S2O‾电子态（ 2A″）的几何结构参数：键长R(SS) = 2.008 +/-0.005Å 和 R(SO) = 1.519+/-0.005Å.     

Optimization of conditions for spectral determination of chlorine content in cement-based materials

A combination laser/electrospark method is used for fast determination of chlorine in cement-based materials. Excitation of the spectra is carried out both directly in an ablation plume and when a pulsed electric discharge is applied to it. In both cases, we obtain calibration curves that are linear for the major concentration range of practical importance for the analyte element, up to 1.5%. The chlorine detection limit for the combination discharge approach is 0.05%. We consider the basic steps and characteristic features of the proposed experimental procedures. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 289–295, May–June, 2007.     

光谱成像技术无损鉴别西洋参饮片的研究

应用电可控液晶光谱成像装置,测定不同市售来源的西洋参饮片,以期为其质量控制提供新的方法。系统光谱分辨率5nm,光谱覆盖范围为405～680nm,空间分辨率50lp·mm-1。从成像光谱立方体中提取特征光谱曲线,构建饮片指纹图谱;采用主成分等聚类分析方法解析其指纹图谱,用于饮片真伪鉴别与质量判定。结果与性状,显微及理化鉴定结果相吻合。表明光谱成像分析技术可用于中药指纹图谱的构建和质量评价,操作方法简便、快速、无损。     

Theoretical and experimental treatment of the spectral interferences in atomic absorption spectroscopy

Spectral line interference may occur in atomic absorption spectroscopy, when there is a significant overlap of the emission line profile with the absorption line profiles of any interfering species in the flame. The presence of the spectral interference can cause errors in the measurements of the net absorbance, and in the background correction.Both theoretical calculations and experimental observations reported in this paper provide a remark of this interference effect. It can be concluded from the experimental results, that the spectral interference is located close to the resonance wavelength of the analyte.Two different examples representing various types and degrees of spectral interference are discussed.     

In vivo 31P MRS of human brain at high/ultrahigh fields: a quantitative comparison of NMR detection sensitivity and spectral resolution between 4 T and 7 T

The primary goal of this study was to establish a rigorous approach for determining and comparing the NMR detection sensitivity of in vivo ³¹P MRS at different field strengths (B₀). This was done by calculating the signal-to-noise ratio (SNR) achieved within a unit sampling time at a given field strength. In vivo ³¹P spectra of human occipital lobe were acquired at 4 and 7 T under similar experimental conditions. They were used to measure the improvement of the human brain ³¹P MRS when the field strength increases from 4 to 7 T. The relaxation times and line widths of the phosphocreatine (PCr) resonance peak and the RF coil quality factors (Q) were also measured at these two field strengths. Their relative contributions to SNR at a given field strength were analyzed and discussed. The results show that in vivo ³¹P sensitivity was significantly improved at 7 T as compared with 4 T. Moreover, the line-width of the PCr resonance peak showed less than a linear increase with increased B₀, which leads to a significant improvement in ³¹P spectral resolution. These findings indicate the advantage of high-field strength to improve in vivo ³¹P MRS quality in both sensitivity and spectral resolution. This advantage should improve the reliability and applicability of in vivo ³¹P MRS in studying high-energy phosphate metabolism, phospholipid metabolism and cerebral biogenetics in the human at both normal and diseased states noninvasively. Finally, the approach used in this study for calculating in vivo ³¹P MRS sensitivity provides a general tool in estimating the relative NMR detection sensitivity for any nuclear spin at a given field strength.