Accurate monitoring of x, y, and z magnetization for analysis of hardware and pulse sequence performance in NMR spectroscopy
"A new nuclear magnetic resonance (NMR) imaging protocol has been developed to independently record the x, y, and z components of the nuclear net magnetization at any point in a pulse sequence while eliminating the observation of the other components. This protocol provides an experimental method of tracking magnetization which then can be used in conjunction with theoretical models to scrutinize the predicted outcome of each step in an NMR pulse sequence and potentially find further improvements to their effectiveness and efficiency. The protocol utilizes a rapid rotating-frame imaging pulse-train technique to obtain RF-field (B1) and resonance-offset (ΔB0) dependent profiles for each Cartesian component in the rotating magnetic coordinate system. The proposed protocol was used to analyze the distribution of the sample as a function of the B1 field strength in a selective, single-channel 1H probe as well as a standard, dual-channel broadband probe. Data from both probes show that the magnetization within a sample is exposed to a wide range of B1 field strength. Hard pulses of varying angles were examined showing that an expected pulse nutation angle, such as a 90° pulse, is only achieved for a very small portion of the sample. The protocol was also used to assess the performance of the widely used inversion-recovery sequence (180° - τ - 90°) for spin-lattice relaxation measurements and to find improvements for the newly developed solvent-suppression sequence EXCEPT. Independently monitoring the magnetization components helped to identify that the remaining solvent-signal intensity after the EXCEPT sequence is linked to portions of the sample located in areas of very low and very high B1 fields, leading to a targeted approach for improving the EXCEPT sequence"--Abstract, page iii.
Imaging, Magnetization monitoring, NMR spectroscopy, Nuclear magnetic resonance, Nuclear magnetization, Pulse sequence, Physical Chemistry
Missouri University of Science and Technology
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