共查询到8条相似文献,搜索用时 15 毫秒
1.
Bortolotti V Camaiti M Casieri C De Luca F Fantazzini P Terenzi C 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,181(2):287-295
NMR relaxation time distributions of water (1)H obtained by a portable single-sided surface device have been compared with MRI internal images obtained with a laboratory imaging apparatus on the same biocalcarenite (Lecce Stone) samples during capillary water uptake. The aim of this work was to check the ability of NMR methods to quantitatively follow the absorption phenomenon under different wettability conditions of the internal pore surfaces. Stone wettability changes were obtained by capillary absorption of a chloroform solution of Paraloid PB72, a hydrophobic acrylic resin frequently used to protect monuments and buildings, through one face of each sample. Both relaxation and imaging data have been found in good quantitative agreement each other and with masses of water determined by weighing the samples. In particular the Washburn model of water capillary rise applied to the imaging data allowed us to quantify the sorptivity in both treated and untreated samples. Combining relaxation and imaging data, a synergetic improvement of our understanding of the water absorption kinetics at both pore and sample scales is obtained. Since relaxation data have been taken over the course of time without interrupting the absorption process, simply by keeping the portable device on the surface opposite to the absorption, the results show that the single-sided NMR technique is a powerful tool for in situ evaluation of water-repellent treatments frequently used for consolidation and/or protection of stone artifacts. 相似文献
2.
Li L Marica F Chen Q MacMillan B Balcom BJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,186(2):282-292
MRI has considerable potential as a non-destructive probe of porous media, offering the possibility of rapid quantification of local oil and water content. This potential has not yet, however, been completely realized. In this paper, we explore a general magnetization preparation approach to the discrimination of water and oil in a model, representative, porous medium. These measurements have, as a common element, a centric scan pure phase encode readout based on the SPRITE methodology. Magnetization preparation permits facile T1, T2 and diffusion coefficient mapping as the basis for oil and water discrimination. Diffusion coefficient mapping proved to be the most robust approach to discrimination of oil and water. These methods are illustrated through static experiments and a dynamic immiscible fluid displacement experiment. 相似文献
3.
An analytical expression for a single-pulse nuclear echo signal in magnetically ordered materials has been obtained taking
into account inhomogeneous broadening of the spectroscopic transition and non-uniform distribution of the enhancement factor.
The signal has been shown to result from superimposing the nuclear magnetic moment oscillations of the same amplitude and
phase that arise upon termination of a radio-frequency pulse. The cause for the effective suppression of oscillations of nuclear
magnetic moments in the initial phase of the free precession signal has been determined analytically. The single-pulse echo
signal amplitude has been found as a function of the external variable magnetic field strength, the exciting pulse duration,
the inhomogeneous NMR line broadening, and the distribution width of the enhancement factor. The results have been compared
with experimental data observed in a Co2MnSi ferromagnetic polycrystalline sample.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 387–394, May–June, 2009. 相似文献
4.
Proietti N Capitani D Rossi E Cozzolino S Segre AL 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,186(2):311-318
Wall paintings in the XVI century Serra Chapel in the "Chiesa di Nostra Signora del Sacro Cuore" Rome, have been studied using unilateral NMR. In order to map the distribution of moisture content in the wall painted, a large number of Hahn echo measurements, covering large areas of the wall painting were performed. Because the intensity of the Hahn echo is proportional to the amount of moisture in the area under study, the experimental data were transformed into 2D gradient colour maps which allowed an easy visualization of the moisture content of the wall. The state of conservation of the wall painting was monitored using T2 measurements specially with regards to outcropping salt. 相似文献
5.
R.I. Chelcea R. Fechete E. Culea D.E. Demco B. Blümich 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,196(2):178-190
The single-sided NMR-MOUSE sensor that operates in highly inhomogeneous magnetic fields is used to record a CPMG 1H transverse relaxation decay by CPMG echo trains for a series of cross-linked natural rubber samples. Effective transverse relaxation rates 1/T2,short and 1/T2,long were determined by a bi-exponential fit. A linear dependence of transverse relaxation rates on cross-link density is observed for medium to large values of cross-link density. As an alternative to multi-exponential fits the possibility to analyze the dynamics of soft polymer network in terms of multi-exponential decays via the inverse Laplace transformation was studied. The transient regime and the effect of the T1/T2 ratio in inhomogeneous static and radiofrequency magnetic fields on the CPMG decays were studied numerically using a dedicated C++ program to simulate the temporal and spatial dependence of the CPMG response. A correction factor T2/T2,eff is derived as a function of the T1/T2 ratio from numerical simulations and compared with earlier results from two different well logging devices. High-resolution T1–T2 correlations maps are obtained by two-dimensional Laplace inversion of CPMG detected saturation recovery curves. The T1–T2 experimental correlations maps were corrected for the T1/T2 effect using the derived T2/T2,eff correction factor. 相似文献
6.
Feasibility of similarity coefficient map in improving morphological evaluation of T2* weighted MRI for renal cancer
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wang Hao-Yu Hu Jiani Xie Yao-Qin Chen Jie Yu Amy Wei Xin-Hua Dai Yong-Ming Li Meng Bao Shang-Lian E. M. Haacke 《中国物理 B》2013,22(3):38702-038702
The purpose of this paper is to investigate the feasibility of similarity coefficient map (SCM) in improving morphological evaluation of T2* weighted (T2*W) magnatic resonance imaging (MRI) for renal cancer. Simulation studies and in vivo 12-echo T2*W experiments for renal cancers were performed for this purpose. The results of the first simulation study suggest that SCM can reveal small structures which are hard to be distinguished from the background tissue in T2*W images and the corresponding T2* map. The capability of improving morphological evaluation is likely due to the improvement in signal to noise ratio (SNR) and carrier to noise ratio (CNR) by SCM technique. Compared with T2*W images, SCM can improve SNR by a factor ranging from 1.87 to 2.47. Compared with T2* maps, SCM can improve SNR by a factor ranging from 3.85 to 33.31. Compared with T2*W images, SCM can improve CNR by a factor raging from 2.09 to 2.43. Compared with T2* maps SCM can improve CNR by a factor raging from 1.94 to 8.14. For a given noise level, the improvements of SNR and CNR depend mainly on the original SNRs and CNRs in T2*W images, respectively. In vivo experiments confirmed the results of the first simulation study. The results of the second simulation study suggest that more echoes are used to generate SCM, and higher SNR and CNR can be achieved in SCM. In conclusion, SCM can provide improved morphological evaluation of T2*W MR images for renal cancer by unveiling fine structures which are ambiguous or invisible in the corresponding T2*W MR images and T2* maps. What is more, in practical application, for a fixed total sampling time, one should increase the number of echoes as much as possible to achieve SCMs with better SNR and CNR. 相似文献
7.
Hans Adriaensen Maja Musse Stéphane Quellec Alexandre Vignaud Mireille Cambert François Mariette 《Magnetic resonance imaging》2013
The transverse relaxation signal from vegetal cells can be described by multi-exponential behaviour, reflecting different water compartments. This multi-exponential relaxation is rarely measured by conventional MRI imaging protocols; mono-exponential relaxation times are measured instead, thus limiting information about of the microstructure and water status in vegetal cells. In this study, an optimised multiple spin echo (MSE) MRI sequence was evaluated for assessment of multi-exponential transverse relaxation in fruit tissues. The sequence was designed for the acquisition of a maximum of 512 echoes. Non-selective refocusing RF pulses were used in combination with balanced crusher gradients for elimination of spurious echoes. The study was performed on a bi-compartmental phantom with known T2 values and on apple and tomato fruit. T2 decays measured in the phantom and fruit were analysed using bi- and tri-exponential fits, respectively. The MRI results were compared with low field non-spatially resolved NMR measurements performed on the same samples. 相似文献