부산대학교 도서관

By definition, radiofrequency (RF) pulses are the pivotal elements of NMR pulse sequences. Vice versa, the effect of a particular pulse on the evolution of magnetization will depend on the context of the sequence. While the product operator formalism provides a general framework to describe the effect of hard pulses on weakly coupled spin systems, there is no consistent framework describing the effect of selective pulses in the context of MRI sequence. The excitation profile is the result of frequency dependent trajectories describing the complex interaction of nutation and precession. In spin-echo sequences, the refocusing pulse acts on a spatial distribution of transverse magnetization that may by spatially dispersed by the magnetic field gradient applied during the RF pulse. This situation is further complicated in the STEAM sequence, as the stimulated echo is created from a spatial distribution of transverse and longitudinal components. Aim of the thesis was a qualified choice of selective RF pulses for an improved voxel definition of the STEAM localization and a critical appraisal of optimised RF pulse shapes. The problem was addressed by theory, by numerical simulations and with experimental methods.