The Investigation Of The Signal Properties Of Intermolecular Multiple-Quantum Coherences And Corresponding MRI Applications

Intermolecular multiple-quantum coherence (iMQC) phenomenon is a hot topic in the NMR field. In this thesis, the properties of iMQC signals and their applications are investigated. The results extend the previous iMQC theory and its applications, and are summarized as follows:1. The apparent longitudinal relaxation behavior of iMQC in the slow chemical exchange system was investigated. Analytical expressions were derived from a combination of the dipolar field theory and product operator formalism. The results show that the signal intensity is a multi-exponential function of the relaxation recovery time. The combination of the iMQC technique and the chemical exchange dependent saturation transfer (CEST) will enhance the MRI contrast.2. Intermolecular double-quantum coherence (iDQC) was utilized to enhance the CEST MRI contrast. Both theoretical and experimental results demonstrate that compared to the conventional single-quantum coherence signal, iMQC signal is more sensitive to the change of the magnetization magnitude, thus it is easier to obtain a better contrast in the CEST-like experiments. However, although the iMQC technique can be used to improve the MRI contrast, its intrinsic low signal-to-noise ratio (SNR) limits its applications. Therefore, how to improve the SNR of iMQC signal is still an important topic in iMQC field.3. The factors influencing the iMQC signal intensity were analyzed, and the possible ways to enhance the SNR of iMQC signal were discussed. In addition, the properties of the signals from the CRAZED-like sequences were investigated with the strength of the coherence selection gradients (CSGs) ranging from zero to a large value. The results demonstrate that the intensity of the signal obtained without CSGs is much stronger than the intensity of the signal obtained with CSGs.