小脑星形细胞瘤的MRI诊断

目的探讨小脑星形细胞瘤的MRI表现,提高对本病的诊断水平.方法回顾性分析经手术及病理证实的31例小脑星形细胞瘤的MRI资料. 结果实质瘤体型7例,瘤在囊内型10例,囊在瘤内型13例,1例表现为完全囊性,31例均表现不同程度的梗阻性脑积水表现. 结论小脑星形细胞瘤具有特征性,增强扫描有助于病灶检出和定性诊断.术前诊断是可能的,但需与血管母细胞瘤、髓母细胞瘤、室管膜瘤、转移瘤相鉴别.     

Fully Nonlinear Simulations of Wave Resonance by An Array of Cylinders in Vertical Motions

The finite element method (FEM) is employed to analyze the resonant oscillations of the liquid confined within multiple or an array of floating bodies with fully nonlinear boundary conditions on the free surface and the body surface in two dimensions. The velocity potentials at each time step are obtained through the FEM with 8-node quadratic shape functions. The finite element linear system is solved by the conjugate gradient (CG) method with a symmetric successive overelaxlation (SSOR) preconditioner. The waves at the open boundary are absorbed by the combination of the damping zone method and the Sommerfeld-Orlanski equation. Numerical examples are given by an array of floating wedge- shaped cylinders and rectangular cylinders. Results are provided for heave motions including wave elevations, profiles and hydrodynamic forces. Comparisons are made in several cases with the results obtained from the second order solution in the time domain. It is found that the wave amplitude in the middle region of the array is larger than those in other places, and the hydrodynamic force on a cylinder increases with the cylinder closing to the middle of the array.     

Temporal variations in free core nutation period

Based on the nearly diurnal resonance in the tidal gravity observations,the temporal variations in period of the Earth's free core nutation (FCN) are investigated by using the tidal gravity observations of 18-year duration recorded continu-ously with a superconducting gravimeter (SG) at Brussels. The effects of the global oceanic tide loading and local barometric pressure on the SG observations have been removed by using eleven high-precision global digital models of oceanic tides and barometric pressure me...     

睾丸精原细胞瘤的CT和MRI表现

目的：探讨睾丸精原细胞瘤的CT、MRI特点,以提高对本病的认识。方法：回顾性分析有完整CT或MRI平扫及增强资料、经手术及病理证实的13例睾丸精原细胞瘤的影像表现。3例患者行CT检查,10例行MRI检查。结果：13例中有3例为未降睾丸并发精原细胞瘤。睾丸精原细胞瘤CT主要表现为中等均匀密度,增强扫描轻度到中度强化;MRI主要表现为结节状,信号较均匀,T2WI呈稍低信号,可见低信号线状纤维血管分隔,增强时分隔强化,肿瘤实质轻度强化。未降睾丸并精原细胞瘤位于正常睾丸下降路径,可发生于腹膜后、盆腔等部位,病灶体积较大,密度或信号不均,增强扫描明显强化。结论：睾丸精原细胞瘤的CT、MRI表现具有一定的特征性,具有较高的诊断和鉴别价值。     

磁共振弥散加权成像在直肠癌淋巴结转移评估中的价值综述

随着生活水平的提高,直肠癌在我国的发病率明显提高[1],随之而来的是对诊疗水平要求的提升。据国内外多项研究表明,直肠癌患者是否伴淋巴结转移,是否进行术前辅助放化疗、手术方式及范围的选择,是否进行术后放疗,局部复发率以及远端转移率等密切相关,是一项重要的影响预后的因素[2]。而常规的成像方式对淋巴结状态的评估差强人意[3]。目前磁共振成像在直肠癌的淋巴结状态判断方面日益受到重视。本文就其在直肠癌淋巴结转移中应用及展望进行综述。     

Electron paramagnetic resonance studies on clinochlore from Longitudinal Valley area,northeastern Taiwan

A natural sample of clinochlore from the Longitudinal Valley area of northeastern Taiwan has been characterized by using the powder X-ray diffraction (XRD), differential thermal analysis and electron paramagnetic resonance (EPR) spectroscopic techniques. The lattice parameters of the monoclinic (IIb) clinochlore with the composition (Mg_2.988 Al_1.196 Fe_1.6845 Mn_0.026)_5.8945 (Si_2.559 Al_1.441)₄ O₁₀ (OH)₈ have been calculated from the powder XRD data and are found to be a = 5.347 Å, b = 9.223 Å, c = 14.250 Å, β = 97.2° and Z = 2. The thermal behaviour of the sample showed the typical behaviour of clinochlore with a hydroxyl content of 12.5 wt%. The EPR spectrum at room temperature exhibits two resonance signals centred at g ≈ 2.0 and g ≈ 8.0. The signal at g ≈ 2.0 shows a six-line hyperfine structure which is a characteristic of Mn²⁺ ions in octahedral symmetry. The resonance signal at g ≈ 8.0 is a characteristic of Fe³⁺ ions. The EPR spectra have also been recorded at different temperatures (123–295 K). The population of spin levels (N) has been calculated for g ≈ 2.0 and g ≈ 8.0 resonance signals. It is observed that N increases with decreasing temperature. From EPR spectra, the spin-Hamiltonian parameters have been evaluated. The zero-field splitting parameter (D) is found to be temperature dependent. The peak-to-peak width of the g ≈ 8.0 resonance signal is found to increase with decrease in temperature.     

Using magnetic resonance imaging for experimental analysis of fine‐sediment infiltration into gravel beds

Sedimentologists recognize that development of a fine‐resolution, truly three‐dimensional analytical tool is essential if the internal structure of an opaque material is to be examined. This paper therefore seeks to: (i) test the viability of magnetic resonance imaging for sedimentological research; and (ii) investigate fine‐sediment infiltration into gravel beds. The results of six experiments are analysed quantitatively using Image J post‐processing software. Data indicate that magnetic resonance imaging‐based measurements of particle axes and volumes are comparable with standard laboratory techniques. Furthermore, the technique permits visualization and analysis of differences in the pattern of fine‐sediment infiltration (median particle diameter, d) into a framework of gravel (median particle diameter, D). Data clearly illustrate a siltation process for samples of D/d = 34 and a sealing process for samples of D/d = 7 where the seal is restricted to a depth equal to 2D. This pore‐scale visualization is valuable to the understanding of hydraulic–sediment–habitat interactions.     

低渗透储集层T2截止值实验研究

由于一个地区甚至一口井很难有一个统一的截止值,无法用单一的截止值方法区分束缚水和自由流体,因而核磁共振测井解释束缚水饱和度存在着实用上的困难．为此,本文借鉴已发表的实验方法对塔中地区低渗透储层岩心进行核磁共振实验．实验结果分析时充分考虑岩石孔隙结构的变化,发现T2截止值与孔隙结构综合指数(√κ/φ)密切相关,提出了一种应用于测井解释的变T2截止值方法,并在实际测井解释中获得了良好的应用效果。     

土-水特征曲线与核磁共振曲线的关系

土-水特征曲线在非饱和土的研究中扮演着重要的角色,其预测方法的研究具有重要的科学意义。以武汉黏性土为研究对象,在土-水特征曲线试验和核磁共振（NMR）试验的基础上,利用Fredlund-Xing模型对试验数据进行拟合分析。结合KST模型和Young-Laplace理论,建立了基质吸力与土体中孔隙水的弛豫时间（T2）之间的理论关系式,试验结果表明该理论关系式并不能简单有效的描述基质吸力与T2值之间的实际关系。基于土-水特征曲线和NMR试验结果,建议了基质吸力与T2值之间的经验关系式,在此基础之上,给出了基于NMR曲线的不同初始干密度非饱和黏性土土-水特征曲线的预测方法。     

高煤级煤储层含水性特征及其对吸附能力的影响

为了研究高煤级煤储层含水性对吸附能力的影响,对阳泉-寿阳区块8件代表性煤样开展了镜质体反射率、显微组分、孔隙度、压汞、核磁共振和甲烷等温吸附等实验,分析了煤储层孔径分布、核磁共振T2谱响应特征、核磁孔隙度以及煤岩吸附能力,同时对煤储层含水性和煤储层吸附能力的相互关系进行了分析。研究结果表明：高煤级煤储层孔隙以微孔发育为主,孔隙含水性以微小孔中的束缚水赋存状态为主,且其含水量随最大镜质体反射率(Ro,m)的增大而增加。在影响高煤级煤储层吸附能力的多种因素中,煤储层含水性对煤岩吸附能力起着决定性的作用,尤其体现在微小孔中的束缚水对吸附能力的影响,束缚水含量越高,煤岩吸附能力越差。