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Unilateral Magnet for Magnetic Resonance Imaging
ZHANG Yan-li，XIE De-xin，BAI Bao-dong，ZENG Lin-suo
Chinese Journal of Magnetic Resonance, 2006, 23(3): 283-292.
Openness is a desired property for the magnets used in magnetic resonance imaging (MRI). For this reason, the design and making of unilateral magnets, which give a homogenous region, usable for imaging, that is external or “remote” from the magnet, has been attracting more and more attention and research interests. In this paper, the feasibility of designing a unilateral MRI magnet with a sliceshaped imaging region is discussed on the basis of the theory of saddle point. The properties of magnetic fields generated by different types of unilateral magnets were derived by simulation, and the results showed that it is possible to have a unilateral magnet that can generate remote saddle points in the field profile while having sources on one side. The configuration of a unilateral permanent magnet specially designed for MRI is presented, which can produce a sliceshaped imaging region with high field homogeneity. The results obtained in this study will build a strong basis for future scientific researches on fully opened MRI system with homogeneous magnetic field.
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Quantum Chemical Calculation on 13 C NMR Shifts of Small Drug Molecules
SU Yong-chao，ZHENG An-min，LI Shen-hui，CHEN Lei，DENG Feng
Chinese Journal of Magnetic Resonance, 2006, 23(3): 293-301.
Prediction of chemical shifts using quantum chemical calculation is helpful for assigning NMR spectra, and of great importance in structure determination. In this paper, we evaluated the performance of different quantum chemical methods for calculating 13C chemical shifts of acetylsalicylic acid and its derivatives. When Hartree-Fock (HF) and density functional theories (DFT) were used to compute phenyl 13C chemical shifts, both the CSGT method and the GIAO method yielded results that agreed reasonably well with the experimental values, while the former method often showed better performance than the latter. Calculated phenyl 13 C chemical shifts showed excellent agreement with the experimental results when B3PW91//CSGT at 6-311G(d, p) level was used. When the B3LYP//GIAO method was used for calculation, the difference between the results obtained by applying 6-31G(d, p) and 6-311++G(3df, 3pd), respectively, was only δ 0.01~2.04. The MP2 method was often more time-consuming, but the results it gave show only marginal improvement in terms of calculation accuracy. It was found that the greater effect of electronic correlation, the more the electronic atmosphere of C atoms affects the accuracy of chemical shift calculation. For the reason, the HF method performed not so well because the calculation did not take electronic correlation into account. It was also found that the length of C chain also has effects on the calculated results.
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Comparison of Gridding Algorithms Used in Spiral Magnetic Resonance Imaging
HUANG Min，GUAN Jin-an，HUANG Li，LU Song-tao
Chinese Journal of Magnetic Resonance, 2006, 23(3): 303-311.
Spiral magnetic resonance imaging (MRI) data are sampled in the k -space with non-uniform spiral trajectory so that gridding must first be performed to transform the raw data into uniform space before fast Fourier transform (FFT reconstruction) can be used to reconstruct images. In this paper, we compared two classes of gridding algorithms, the large matrix resampling algorithm proposed by Claudia et al and the double-sized gridding algorithm proposed by Jackson et al, with respect to the speed of computation and the quality of resultant images. First, it was shown that, while capable of getting images with similar quality relative to those obtained by the latter, the former algorithm is faster and easier to implement. Secondly, our results showed that data-driven interpolation is more efficient than grid-driven interpolation when the doublesized gridding algorithm is used. Lastly, in the large matrix resampling algorithm, when the efficient-versus-redundancy data ratio surpasses 310∶1, it is more efficient not to average the values of gridding points of the large matrix. The conclusions are helpful to improve the gridding and reconstruction techniques used in spiral MRI.
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Structure Determination of A Novel Natural Product Isolated from the Leaves of Panax Ginseng CA Meyer
WANG Li-bo, GAO Hui-yuan, WU Bin, SONG Xiao-mei, TANG Zhi-shu, WANG Wei, WU Li-jun
Chinese Journal of Magnetic Resonance, 2006, 23(3): 321-326.
A novel natural product was isolated from the leaves of Panax ginseng CA Meyer by column chromatography. Using mass spectrometry, NMR spectroscopy and conventional chemical methods, the chemical structure of the compound was determined to be dammar-20(22), 24-diene-3β, 6α, 12βtriol. Complete assignment of 1 H and 13 C chemical shifts of this compound was obtained, and the results pointed out an error existed in the previous assignment.
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An NMR Study on A Derivative of Dichromium Ene
JIANG Hong, TU Shu-jiang, LIU Xin-you, YANG Jun-shan, FENG You-jian
Chinese Journal of Magnetic Resonance, 2006, 23(3): 333-339.
The structure of a derivative of dichromium ene was determined by NMR (1 H NMR, 13 C NMR, DEPT, 1 H-1 H COSY, HSQC and HMBC) methods to be 7-(4-bromophenyl)-7H-pyrano[3,2-c:5,6-c′] dichromium ene 6,8-dione. The 1 H and 13 C chemical shifts of the compound were assigned.
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Spectral Data Deduced Structure of New Drug Lomerizine Dihydrochloride
CHEN Yue, LI Jian-feng, WEI Ya-bing, SHEN Jing-shan
Chinese Journal of Magnetic Resonance, 2006, 23(3): 341-348.
The ultraviolet spectrum, infrared spectrum, 1D and 2D nuclear magnetic resonance (1 H NMR, 13 C NMR, 1 H-1 H COSY, HMQC and HMBC) spectra and mass spectra of new drug lomerizine dihydrochloride were reported and interpreted. All the NMR signals were assigned. Based on the mass spectral data, the possible fragmentation pathways were discussed. The infrared spectrum was analyzed to derive the types of vibration of the functional groups of this compound. The structure of the compound was determined.
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An ESR Study on CdGd2 (WO2 )4 Single Crystal
SUN Gui-fang, HOU Bi-hui, RUAN Shu-ren, XIAO Xiao-guang
Chinese Journal of Magnetic Resonance, 2006, 23(3): 373-378.
The structure and magnetic properties of CdGd2 (WO2 )4 single crystal were studied by X-ray diffraction, magnetic measurement and electron spin resonance (ESR) experiments. The results showed that the crystal structure is tetragonal with lattice parameters a =b =0.5204 nm and c =1.136 0 nm. σ -T and ESR experiments showed that the crystal is paramagnetic and anisotropic. The magnetic properties of the crystal reflected its structure characteristics well. Landé factor g 2 tensor was calculated, and found to be consistent with the result obtained by theoretical calculation.
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NMR Relaxation of the Fluid in Rock Porous Media
GONG Guo-bo, SUN Bo-qin, LIU Mai-li, YE Chao-hui, GAO Bing-jun
Chinese Journal of Magnetic Resonance, 2006, 23(3): 379-395.
Spin relaxation time measurement is one of the most important applications of NMR technology. Relaxation parameters derived from NMR measurements provide structural and dynamic information of molecules. Applications in porous media further show that the distribution of relaxation time can be use to determine pore size, irreducible water saturation, and formation permeability etc. In this paper we described three relaxation mechanisms and how they can be used to obtain information about rock porous media. Bulk relaxation time of free-fluid is used to differentiate the type of fluids and the quality of oil, surface relaxation distribution provides information of pore size and capillary bonding, and diffusion coefficient improves the capability of fluid typing and pore geometry determination. We also summarized various methods for measuring relaxation times and selfdiffusion coefficient, as well as their distributions.
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Quantitative Measurement of γ -Aminobutyric Acid Concentration in vivo by Magnetic Resonance Spectroscopy: A Review
CHEN Yao-wen, SHEN Zhi-wei, SU Ji-wei, Liang Bing, WU Ren-hua
Chinese Journal of Magnetic Resonance, 2006, 23(3): 409-417.
γ -Aminobutyric acid (GABA) is an important metabolite in the brain. Magnetic Resonance Spectroscopy (MRS) has proven to be a valuable technique for measuring cerebral metabolite concentrations non-invasively in vivo . However, reliable detection of GABA in vivo using MRS is difficult and faces various challenges. With the developments of spectral editing techniques and specialized software packages for processing MRS data, many methods have been proposed to measure GABA in vivo . In this article, the background knowledge of GABA was briefly reviewed, and the MRS techniques currently used to do quantitative measurement of GABA in vivo were reviewed. At the end, proposals of further studies were briefly mentioned.
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