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61.
Bydder M Yokoo T Hamilton G Middleton MS Chavez AD Schwimmer JB Lavine JE Sirlin CB 《Magnetic resonance imaging》2008,26(3):347-359
Quantification of fat has been investigated using images acquired from multiple gradient echoes. The evolution of the signal with echo time and flip angle was measured in phantoms of known fat and water composition and in 21 research subjects with fatty liver. Data were compared to different models of the signal equation, in which each model makes different assumptions about the T1 and/or T2* relaxation effects. A range of T1, T2*, fat fraction and number of echoes was investigated to cover situations of relevance to clinical imaging. Results indicate that quantification is most accurate at low flip angles (to minimize T1 effects) with a small number of echoes (to minimize spectral broadening effects). At short echo times, the spectral broadening effects manifest as a short apparent T2 for the fat component. 相似文献
62.
To assess the reproducibility of quantitative measurements of cartilage morphology and trabecular bone structure of the knee at 7 T, high-resolution sagittal spoiled gradient-echo images and high-resolution axial fully refocused steady-state free-precession (SSFP) images from six healthy volunteers were acquired with a 7-T scanner. The subjects were repositioned between repeated scans to test the reproducibility of the measurements. The reproducibility of each measurement was evaluated using the coefficient(s) of variation (CV). The computed CV were 1.13% and 1.55% for cartilage thickness and cartilage volume, respectively, and were 2.86%, 1.07%, 2.27% and 3.30% for apparent bone volume over total volume fraction (app.BV/TV), apparent trabecular number (app.Tb.N), apparent trabecular separation (app.Tb.Sp) and apparent trabecular thickness (app.Tb.Th), respectively. The results demonstrate that quantitative assessment of cartilage morphology and trabecular bone structure is reproducible at 7 T and motivates future musculoskeletal applications seeking the high-field strength's superior signal-to-noise ratio. 相似文献
63.
64.
本文利用原位低场核磁共振(LF-NMR)技术在真实固液反应环境中对光催化还原Cr(Ⅵ)反应进行了定量研究,并对Ag纳米颗粒负载量不同的Ag担载石墨相氮化碳复合光催化剂(Ag/g-C3N4)在可见光照射下催化Cr(Ⅵ)还原为Cr(Ⅲ)的性能进行了研究.研究发现,Ag纳米颗粒负载(负载量分别为1 wt.%、2 wt.%、5 wt.%和10 wt.%)可以有效提高g-C3N4的光催化性能;且负载量为5 wt.%时光催化性能最优,为无Ag负载的g-C3N4的4倍.此外,本文还通过横向弛豫时间(T2)定量分析了反应体系中顺磁性Cr(Ⅲ)离子的浓度,证实了采用LF-NMR弛豫法评价光催化Cr(Ⅵ)还原反应性能的可行性. 相似文献
65.
桂质廷(1895~1961),我国著名的地球物理学家.他是建国初期中国科学院地球物理组专门委员,第一个巡测了我国境内地磁常量的中国人.他最先和学生一道在国内进行了高空电离层的常规观测.他所创建的武汉大学游离层实验室,50年来未曾间断电离层的观测研究.本文着重介绍他的生平简历、教学态度、学术成就和爱国主义思想. 相似文献
66.
基于辣根过氧化物酶(HRP)催化 H2O2-Luminol系统,对一种新型酚类衍生物 4-(1,2,4-三氮唑-1-基)苯酚对化学发光的增强作用进行了研究。用HRP标记急性心肌梗死标志物心肌肌钙蛋白Ⅰ(cTnⅠ)单克隆抗体,通过cTnⅠ的双抗体夹心免疫反应,建立了简单、灵敏和快速检测人血清中的cTnⅠ含量的增强型酶发光免疫分析方法。实验结果表明,cTnⅠ在1.2 ~ 24 ng/mL浓度范围内与增强型发光强度具有良好的线性关系(R=0.99),变异系数(n= 8)为 4.7%。最后,使用该方法对人血清样品中的cTnⅠ含量进行测定,测试结果具有较好的稳定性和精度,能够满足临床检测要求。 相似文献
67.
By means of improved ligand-field theory, the "pure electronic" pressure-induced shifts (PS's) and the PS's due to electron-phonon interaction (EPI) of R1 line and R2 line of YAG:Cr3 have been calculated, respectively.The calculated results are in very good agreement with the experimental data. It is demonstrated that the admixture of |t22(3T1)e4T2> and |t322E> bases in the wavefunction of R1 level of YAG:Cr3 and its change with pressure play a key role for the PS of R1 line. The behaviors of the "pure electronic" PS of R1 line and the PS of R1 line due to EPI are different. It is the combined effect of them that gives rise to the total PS of R1 line, which has satisfactorily explained the experimental results. The systematic analyses and comparisons between the feature of R1-line PS of YAG:Cr3 and the ones of three laser crystals (GSGG:Cr3 , GGG:Cr3 and ruby) have been made, and the origin of the difference between them has been revealed. 相似文献
68.
Ultra-high-field clinical MRI scanners (e.g., 7 T and above) are becoming increasingly prevalent and can potentially enhance diagnostic ability through higher contrast, resolution and/or sensitivity. Diffusion-weighted MRI is a highly valued component in today's radiological exam and may benefit from the enhanced signal-to-noise ratio provided by high field with the appropriate imaging strategy. The most common diffusion pulse sequence readout (echo-planar imaging (EPI)) has been widely employed for in vivo human 7 T diffusion tensor imaging (DTI). In this article, we present results of brain DTI at 7 T with two diffusion-weighted imaging pulse sequence readouts: echo-planar imaging (EPI-DTI) and turbo spin echo (TSE-DTI). Results indicate that analogous coverage, quality and resolution typical of lower field (2 mm) can be obtained by properly processed EPI-DTI at 7 T, and, with some reduction in efficiency and sharpness, TSE-DTI at 7 T. Furthermore, 7 T TSE-DTI shows promise in obtaining higher-resolution results in targeted acquisitions of specific brain areas. 相似文献
69.
Mitchell J Graf von der Schulenburg DA Holland DJ Fordham EJ Johns ML Gladden LF 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,193(2):218-225
Flow propagators, used for the study of advective motion of brine solution in porous carbonate and sandstone rocks, have been obtained without the influence of Nuclear Magnetic Resonance (NMR) relaxation times, T1 and T2. These spin relaxation mechanisms normally result in a loss of signal that varies depending on the displacement ζ of the flowing spins, thereby preventing the acquisition of quantitative propagator data. The full relaxation behaviour of the system under flow needs to be characterised to enable the implementation of a true quantitative measurement. Two-dimensional NMR correlations of ζ − T2 and T1 − T2 are used in combination to provide the flow propagators without relaxation weighting. T1 − ζ correlations cannot be used due to the loss of T1 information during the displacement observation time Δ. Here the moments of the propagators are extracted by statistical analysis of the full propagator shape. The measured displacements (first moments) are seen to correlate with the expected mean displacements for long observation times Δ. The higher order moments of the propagators determined by this method indicate those obtained previously using a correction were overestimated. 相似文献
70.
Jia-Jia Geng Rui-Yun Guo Dong-Ze He Jing-Fei Zhang Xin Zhang 《Frontiers of Physics》2015,10(5):109501
We explore the impact of the Sandage−Loeb (SL) test on the precision of cosmological constraints for f(T) gravity theories. The SL test is an important supplement to current cosmological observations because it measures the redshift drift in the Lyman-α forest in the spectra of distant quasars, covering the “redshift desert” of 2 ≲ z ≲ 5 . To avoid data inconsistency, we use the best-fit models based on current combined observational data as fiducial models to simulate 30 mock SL test data. We quantify the impact of these SL test data on parameter estimation for f(T) gravity theories. Two typical f(T) models are considered, the power-law model f(T)PL and the exponential-form model f(T)EXP. The results show that the SL test can effectively break the existing strong degeneracy between the present-day matter density Ωm and the Hubble constant H0 in other cosmological observations. For the considered f(T) models, a 30-year observation of the SL test can improve the constraint precision of Ωm and H0 enormously but cannot effectively improve the constraint precision of the model parameters. 相似文献