表面活性剂CTAB水溶液中的T2弛豫分散研究

用CPMG脉冲序列测定了表面活性剂十六烷基三甲基溴化铵（CTAB）分子中的氮甲基(N-CH₃)质子的横向弛豫时间（T₂表观）,并发现测得的T₂表观\}与序列中的重聚脉冲间隔时间的一半τ _cp有关,说明存在横向弛豫分散现象. 当在τ_cp≤1 ms时,T₂表观与τ²_cp}呈线性关系;而当τ_cp≥4.6 ms时,T₂表观变得与τ_cp无关. 利用Luz-Meiboom两体化学交换模型计算了不同浓度的CTAB溶液中的N-CH₃质子的本征横向弛豫时间（T₂本征）和化学交换速率k_ex,发现k_ex与T₂本征和自扩散系数D一样,在临界胶束浓度（CMC）附近发生突变. 这个突变反映了CTAB分子在从单体到胶束的转变过程中其动力学特性发生了改变.      

癸基萘磺酸钠胶束中分子动态的质子核磁共振研究

在298、303和313 K下对浓度为0.82 和2.59 mmol/L的癸基萘磺酸钠的重水溶液中质子的自旋-自旋弛豫（T₂）时间进行了测量. 浓度为0.82 mmol/L 的溶液(临界胶束浓度CMC以下)中的所有质子的T₂值均随温度上升而增长，说明整个分子运动变的更自由. 然而，浓度在CMC以上(2.59 mmol/L)时，分子中一部分参与形成栅栏层的质子的T₂值却表现出相反的效应，它们的运动随温度上升而变慢，说明在高温下为防止水分子进入疏水胶束壳内，这些栅栏层的质子堆积的更紧密. 同时分子中其他质子的T₂值随温度上升而增长，表现出正常的分子运动的温度效应.     

基于改进非线性拟合的核磁共振T2谱多指数反演

核磁共振T₂谱多指数反演算法是开展复杂体系样品核磁共振(NMR)弛豫研究最重要的数学工具. 常用的T₂谱多指数反演算法一般都是事先给出弛豫时间T₂分布的布点, 然后转化为线性拟合问题进行求解. 在求解的T₂谱较为分散的时候, 反演得到的T₂谱精确度不高, 分辨率较低. 非线性拟合是解决这个问题的有效办法. 本文针对分散T₂谱反演利用非线性拟合时遇到的初值依赖及运算复杂问题, 利用线性回归最小二乘方法, 改进了其中的带非负约束非线性优化模型, 将搜索的反演参数从T₂, f 减少为T₂, 加快了收敛速度, 减少了对初值的依赖, 提高了反演精度, 使算法更加稳健. 通过用改进的Levenberg-Marquardt算法和差分进化算法进行计算机模拟反演及实验数据反演, 验证了改进方法在核磁共振T₂ 谱反演中的有效性.     

分子间多量子相干横向弛豫时间(和自扩散系数)测量的参数优化和数据处理方法

针对测量横向弛豫时间T₂的CPMG脉冲序列和我们所设计的可同时测量高极化单组份单 峰核自旋体系n阶分子间多量子相干横向弛豫时间T_2,n和自扩散系数D_n的改进的CRAZED脉冲序列,分析了影响测量T₂、T_2,n（或D_n）的各种因素,并着重从技术方面讨论了准确测量T_2,n和D_n的实验参数优化和实验数据处理方法.     

油井样品NMR T2谱的影响因素及T2截止值的确定方法

T₂ 谱是核磁共振（NMR）测、录井技术应用与解释、评价的基础. 岩样T₂ 谱受仪器测量参数、样品性质（岩性、颗粒大小、样品粒度、样品干湿状态、孔隙流体含量及性质、磁化率、润湿性）及地层水矿化度等因素的影响. T₂ 截止值是T₂ 谱中最重要的参数之一,选取的科学性与准确性直接影响到核磁共振测量结果. 通过文献查询,对T2 谱的影响因素及T₂ 截止值的确定方法进行了分析.     

双色噪声驱动非对称双稳系统平均第一穿越时间研究

利用统一色噪声近似理论,研究乘性色噪声和加性色噪声驱动的非对称双稳系统中,势阱的非对称性和噪声对系统两个方向的平均第一穿越时间T₊（x_s1→x_s2）和T_-（x_s2→x_s1）的影响（x_s1和x_s2是双稳系统的两个稳定点）.数值结果表明：T₊（x_s1→x_s2）随乘性噪声的自关联时间τ₁以及加性噪声的自关联时间τ₂的增大而减小.T_-（x_s2→x_s1）随乘性噪声的自关联时间τ₁以及加性噪声的自关联时间τ₂的增大而增大.在曲线（T₊（x_s1→x_s2）,λ）和（T_-（x_s2→x_s1）,λ）上都存在单峰.T₊（x_s1→x_s2）随非对称系数r的增大而增大,T_-（x_s2→x_s1）随非对称系数r的增大而减小. 关键词： 统一色噪声近似 平均第一穿越时间 加性色噪声 乘性色噪声     

丙烯腈γ辐射聚合的NMR研究

用¹H NMR、¹³C NMR谱、自旋-晶格弛豫时间（T₁）和自旋-自旋弛豫时间（T₂）研究了丙烯腈在⁶⁰Co γ射线辐射聚合后的大分子结构变化与大分子链的运动. 结果表明随着辐射剂量增大，在单体形成聚合物的过程中，聚合物主链上出现了少量的-OH基团，继续增大辐射剂量， -OH部分被氧化. 对聚合物溶液的变温氢谱的研究表明，溶剂中的残余水与上述-OH形成氢键，且随着温度升高氢键被破坏，同时H₂O与-OH之间还存在着质子交换. 利用¹³C NMR谱对丙烯腈辐射聚合的产物进行了序列结构分析. 对T₁和T₂的研究表明，辐射剂量的增大并未影响到聚丙烯腈的链运动，证明了在丙烯腈的辐射聚合过程交联反应未发生.     

不同能量的氦原子与同位素分子H2(D2，T2)碰撞分波截面的理论计算

用Tang-Toennies势模型和密耦近似方法计算了不同能量下惰性气体原子He与H₂及其同位素D₂,T₂替代碰撞体系的振转激发碰撞截面. 通过分析He-H₂(D₂,T₂)各碰撞体系分波截面的差异,总结出在H₂分子的对称同位素替代情形下He-H₂(D₂,T₂)碰撞体系分波截面随量子数和体系 关键词： 散射截面 密耦方法 同位素     

嵌段共聚物溶致液晶相中水的2H-NMR动力学分析

采用D₂O 的²H-NMR线型和弛豫分析了PEO-PPO-PEO/D₂O/对二甲苯体系的层状和六角液晶相的动力学行为. 通过实验测得了两个不同体系的自旋 晶格弛豫时间T₁、自旋-自旋弛豫时间T₂和²H-NMR 谱. ²H-NMR 谱均为具有四极劈裂的粉末谱线型，且在谱图的中心，β_LD=54.7°时存在一个倒峰. 倒峰的出现直接表明引起体系中弛豫的主要动力学过程处于极窄化区域. 采用NMR弛豫模型，通过调节动力学参数，使理论模拟的²H-NMR谱、弛豫时间、倒峰的大小与实验的对应量相吻合，求得了体系的动力学参数.     

两个非离子表面活性剂复配体系的NMR研究

通过核磁共振（NMR）技术对NP-10/Tween40和NP-10/C₁₀E₆两个复配体系在不同比例下混合胶束的排列方式、相互作用点及其不同分子间与相同分子间的作用变化进行了研究和比较.二维NOESY实验结果证明了：（1）这两种复配体系的相互作用是随混合比例的不同而变化的;（2）两个复配体系的不同分子间相互作用点有相同之处,但NP-10/Tween40分子间相互作用大于NP-10/C₁₀E₆.横向弛豫时间（T₂）表明,当NP-10/Tween40和NP-10/C₁₀E₆体系的混合比分别为1：2和1：4后,其不同分子间的相互作用开始减小,相同分子间作用开始起主导作用,暗示了复配体系中的理想混合配比和协同效应的变化.横向弛豫时间与纵向弛豫时间之比（T_R=T₂/T₁）反映了与NP-10/C₁₀E₆相比,NP-10/Tween40混合胶束分子链的运动受限更加严重.空间距离计算结果也佐证了NP-10/Tween40和NP-10/C₁₀E₆复配体系的较为理想的配比分别为1：2和1：4;NP-10/Tween40不同分子间距离小于NP-10/C₁₀E₆.     

The oral administration of MnCl2: A potential alternative to IV injection for tissue contrast enhancement in magnetic resonance imaging

Mn⁺² (as MnCl₂) was administered to rabbits intravenously and orally (a route of administration which based upon our previous experiments in rats⁷ promises to give selective hepatobiliary enhancement with less systemic toxicity). Nuclear magnetic relaxation dispersion or T₁ (NMRD) was performed on selected tissues (heart, liver, kidney, serum, and bile) in both animal groups to examine possible qualitative and semiquantitative differences in T₁ relaxation at equivalent sacrifice times. One animal was given an oral dose of MnCl₂ (620 micromoles/kg) and imaged sequentially (T₁ weighted sequence, .12T) for 30 minutes. The NMRD curves for organ tissues show an increase in relaxation efficacy in the 10–20MHz range characteristic of Mn-macromolecular complexes and are similar irrespective of the route of administration. The lack of increased relaxation enhancement for bile in this frequency range reflects cleavage of this complex upon excretion. Decreased overall relaxation in the liver is observed when oral Mn⁺² is compared to IV Mn⁺² due to the small fraction of administered dose that is absorbed. However, the images document a significant increase in the intensity of liver signal after the oral dose. We suspect this dose may ultimately be adjusted downward to give selective hepatobiliary effects.     

Control of the interparticle spacing in superparamagnetic iron oxide nanoparticle clusters by surface ligand engineering

Polymer-mediated self-assembly of superparamagnetic iron oxide(SPIO) nanoparticles allows modulation of the structure of SPIO nanocrystal cluster and their magnetic properties. In this study, dopamine-functionalized polyesters(DApolyester) were used to directly control the magnetic nanoparticle spacing and its effect on magnetic resonance relaxation properties of these clusters was investigated. Monodisperse SPIO nanocrystals with different surface coating materials(poly(ε-caprolactone), poly(lactic acid)) of different molecular weights containing dopamine(DA) structure(DA-PCL2k,DA-PCL1k, DA-PLA1k)) were prepared via ligand exchange reaction, and these nanocrystals were encapsulated inside amphiphilic polymer micelles to modulate the SPIO nanocrystal interparticle spacing. Small-angle x-ray scattering(SAXS)was applied to quantify the interparticle spacing of SPIO clusters. The results demonstrated that the tailored magnetic nanoparticle clusters featured controllable interparticle spacing providing directly by the different surface coating of SPIO nanocrystals. Systematic modulation of SPIO nanocrystal interparticle spacing can regulate the saturation magnetization(Ms) and T_2 relaxation of the aggregation, and lead to increased magnetic resonance(MR) relaxation properties with decreased interparticle spacing.     

Quantitative NumART2* mapping in functional MRI studies at 1.5 T

Quantitative mapping of the effective transverse relaxation time, T₂* and proton density was performed in a motor activation functional MRI (fMRI) study using multi-echo, echo planar imaging (EPI) and NumART₂* (Numerical Algorithm for Real time T₂*). Comparisons between NumART₂* and conventional single echo EPI with an echo time of 64 ms were performed for five healthy participants examined twice. Simulations were also performed to address specific issues associated with the two techniques, such as echo time-dependent signal variation. While the single echo contrast varied with the baseline T₂* value, relative changes in T₂* remained unaffected. Statistical analysis of the T₂* maps yielded fMRI activation patterns with an improved statistical detection relative to conventional EPI but with less activated voxels, suggesting that NumART₂* has superior spatial specificity. Two effects, inflow and dephasing, that may explain this finding were investigated. Particularly, a statistically significant increase in proton density was found in a brain area that was detected as activated by conventional EPI but not by NumART₂* while no such changes were observed in brain areas that showed stimulus correlated signal changes on T₂* maps.     

T2 relaxation time histograms in multiple sclerosis

An accurate measurement of the transverse relaxation time T₂, and the histogram of T₂ in the brain parenchyma can be accomplished in vivo using a multi-echo magnetic resonance imaging sequence. An estimate of the error in the T₂ measurement is derived using copper sulfate doped water phantoms. Correction factors are calculated and applied to the signal intensity of each voxel prior to the in vivo T₂ evaluation. These corrected T₂ are in good agreement with the theoretical values calculated from copper sulfate concentrations. This technique is then applied to calculate T₂ histograms of the brain. The population studied was composed of normal volunteers and multiple sclerosis patients. The corrected T₂ histogram method discriminates the normal control population from the MS population, and also discriminates between relapsing-remitting patients and primary progressive or secondary progressive patients. Moreover using this approach we are able to detect in MS patients a global shift of the T₂ of the white mater toward higher values. The results of this study showed that the method is easy to implement and may be used to characterize MS pathology.     

测量电子自旋——晶格弛豫时间T1的技术问题

本文讨论应用连续波方法测量电子自旋——晶格弛豫时间T₁的实验技术问题。分析液氮翻滚使T₁测量结果很不一致的原因,提出用吹冷气冷冻样品方法,可以解决液氮翻滚对测量T₁所产生的影响.用改进的方法测量ZnS:Mn、Cu粉末样品的T₁,获得重复性较好的实验结果。     

氟哌酸1HNMR的测定及过渡金属离子对其影响

氟哌酸^*[即1-乙基-6-氟-4-氧-7-(1-哌嗪)-3-(1,4-二氢化喹啉甲酸]是一种广谱、安全、有效、可供口服的抗感染药。我们测定了它的¹H自旋-晶格弛豫时间T₁及其在Cr³⁺、Mn²⁺、和Fe³⁺等过渡金属离子存在下的T₁值。实验结果表明,在加入过渡金属离子前后,氟哌酸不同位¹H的T₁值发生了一定的变化。据此可揭示过渡金属离子和氟哌酸形成配合物的配位点,从而可确定所形成配合物的结构。     

Identification of patients with hereditary haemochromatosis by magnetic resonance imaging and spectroscopic relaxation time measurements

A total of 4302 healthy blood donors were screened for elevated serum ferritin and transferrin saturation. Fifteen had increased serum ferritin at a follow-up examination. Five relatives of these donors also entered the study. Eleven patients had elevated liver iron concentrations, while five had normal liver iron concentrations. The R₂ relaxation rate in the liver was first measured with a conventional multi-spin-echo imaging sequence, and then by a volume-selective spectroscopic multi-spin-echo sequence, in order to achieve a minimum echo time of 4 msec. No correlation was found between the relaxation rate R₂ and the liver iron concentration, when R₂ was calculated from the imaging data. Multi-exponential transverse relaxation could be resolved when the spectroscopic sequence was used. A strong correlation between the initial slope of the relaxation curve and the liver iron concentration was found (r = 0.90, p < 0.001). Signal intensity ratios between liver and muscle were calculated from the first three echoes in the multi-echo imaging sequence, and from a gradient echo sequence. A strong correlation between the logarithm of the signal intensity ratios and the liver iron concentration was found. Although both spectroscopic T₂ relaxation time measurements and signal intensity ratios could be used to quantify liver iron concentration, the gradient echo imaging seemed to be the best choice. Gradient echo imaging could be performed during a single breath hold, so motion artifacts could be avoided. The accuracy of liver iron concentration estimates from signal intensity ratios in the gradient echo images was about 35%.     

小白鼠肌肉组织的NMR质子自旋交换分析

本文在Zimmerman-Brittin两相质子交换核磁共振弛豫模型基础上,分析了NMR弛豫实验中检测信号与各相表现和本征弛豫多数的关系,编写了自动化处理实验数据的计算机程序,这一技术可用于复相系统中不同成分的NMR表现和本征弛豫特性研究中,本文中的样品是选用健康新鲜的小白鼠肌肉,没加任何处理,用h-h,s-h,s-s脉冲序列,反转恢复法(π-τ-π/2)在强场下(0.92T)做T₁、T₂测定实验,分析结果表明本征弛豫参数T₁=1050ms,T₂=4500μs的成分是由肌肉中的"自由水"引起的,其质子相对含量为69%;本征弛豫参数T₁=530ms,T₂=26μs的成分是由肌肉中的"束附水"引起的,其质子相对含量为9%,本征弛豫多数T₁=530ms,T₂=1250μs的成分是由肌肉中的各种大分子和有机物引起的,其质子相对含量为9%,本征弛豫参数T₁=470ms,T₂=1250μs的成分由样品中的脂肪引起的,其质子相对含量为13%,在肌肉组织中的质子与水中质子之间有强烈的交换作用,其交换率k=1000s^-1.在脂肪中的质子与其它成分之间没有交换作用。     

Multicomponent water proton transverse relaxation and T2-discriminated water diffusion in myelinated and nonmyelinated nerve

The influence of compartmental boundaries on water proton transverse relaxation and diffusion measurements was investigated in three distinct excised nerves, namely, the non-myelinated olfactory nerve, the Schwann cell myelinated trigeminal nerve, and the oligodendrocyte myelinated optic nerve of the garfish. The transverse relaxation decay curves were multiexponential and their decomposition yielded three primary components with T₂ values 30–50, 150, and 500 ms, which were subsequently assigned to water protons in the myelin, axoplasm, and interaxonal compartments. The short T₂ component was absent in the non-myelinated olfactory nerve, but present in both myelinated nerves and thus provides supporting evidence for the use of quantitative T₂ measurements to measure the degree of myelination. The signal contribution of each T₂ component to the apparent diffusion coefficient measurements was varied by incrementing the spin-echo time with a preparatory CPMG train of radiofrequency pulses. The apparent diffusion coefficient and its anisotropy were shown to be independent of the spin-echo time over the range of 70 to 450 ms.