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Study On Transverse Relaxation Time And Self-Diffusion Coefficient Of Intermolecular Multiple Quantum Coherences

Posted on:2002-10-01Degree:DoctorType:Dissertation
Country:ChinaCandidate:S K ZhengFull Text:PDF
GTID:1101360062975580Subject:Physical chemistry
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Intermolecular multiple quantum coherence (iMQC) is a physical phenomenon that possesses some very intriguing properties. iMQC is potentially useful for medical imaging. Recently there has been great interest in the potential use of iMQC mechanisms for magnetic resonance imaging (MH) contrast Because the parameters such as proton density, longitudinal relaxation time 7\, transverse relaxation time T2, self-diffusion coefficient DT, are related to MRI contrast mechanisms, it is worth studying their iMQC properties.The purpose of this dissertation is mainly concerned with the properties of T2 and DT ofiMQC in highly polarized spin systems, and relevant methods, which improve the signal to noise ratio of nuclear magnetic resonance (NMR) signal. Main results are summarized as follows.1. Direct measurement of iMQC transverse relaxation time and self-diffusion coefficientWe proposed a new pulse sequence for measuring the transverse relaxation time, T^,, and self-diffusion coefficient, Dn , of n order iMQC simultaneously in梐梙ighly polarized single-component spin system. The pulse sequence effectively suppresses the effects of radiation damping, inhomogeneity of magnetic field and variation of dipolar correlation distance, all of which may affect quantitation of T2 ?and Dn. Experimental results of T2 measured by the pulsesequence are accordance with those measured by CPMG pulse sequence. We also measured the T^n and Dn of n order iMQC, the experimental results reveal that the quantitative relationship between T2^ (n :> 1) and T^ is T^ f"T2l/n and the quantitative relationship between Dn (nal) and DT is Dn**nDT, where T2l and DT is the transverse relaxation time andself-diffusion coefficient of single quantum coherence (SQC). All experimental results are agree with our theoretical predictions. These results will be helpful for understanding the fundamental properties and mechanisms of the transverse relaxation time and self-diffusion coefficient of iMQCs. Because the properties of iMQCs are different from those of intramolecular MQCs, they may provide a new contrast mechanism in MRI.2. Optimization of experimental parameter and processing method of experimental data for measuring transverse relaxation time and self-diffusion coefficient of iMQCsSeveral experimental parameters, which may affect the measuring results of T2ll and Dn,have been analysis. The processing methods of experimental data and optimization of experimental parameters for these measurements were d/scussed in detail. Filling-zero technique was used to improve the fitting results. The principle of selecting the strength of GltG2,G3 and G4 is that the decay caused by the corresponding effect of detected parameter occupied most of the overall decay. The principle of selecting the strength of G5 and G6 is that the area of G5 is kept to be constant in arrayed experiment in the condition of fulfilling the selection of the coherence transfer pathway. In order to improve signal-to-noise-ratio, the optimal-flip angles /? of different coherence orders were obtained analytically.3. Selective excitation technique in combination with PFG and its application to the measurement of iMQC transverse relaxation time in two-component spin systemsa. Study OB phase properties of selective pulses in combination with PFGPhase properties of selective pulses in combination with PFG have been studied theoretically and experimentally. The results show that: for symmetric and antisymmetric shaped pulses, by using selective single PFG spin-echoes (SPFGSE) and selective double PFG spin-echoes (DPFGSE), pure in-phase magnetizations can be obtained in their whole excitation bandwidth. However, for other shaped pulses, the magnetization without phase distortions can only be obtained by using DPFGSE. Moreover, using doubly-selective SPFGSE, neither symmetric (or antisymmetric) nor non-symmetric shaped pulses can provide pure in-phase magnetization.b. Solvent suppression by selective excitation technique in combination with PFGThe...
Keywords/Search Tags:Nuclear magnetic resonance (NMR), Intermolecular multiple quantum coherence (iMQC), Transverse relaxation time (T2), Self-diffusion coefficient (D_T), Selective pulse, Pulse field gradient (PFG), Data processing
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