COMPETITION BETWEEN RADIATION DAMPING AND TRANSVERSE RELAXATION EFFECTS ON NMR SIGNAL INTENSITIES

It has been found in experiments that the NMR signal intensity of the proton in water increases linearly with the pulse flip angle theta(O) (theta(O)<7 pi) even when the concentration of H2O is as low as 4%. This results from the competition between radiation damping and transverse relaxation effects, which can be interpreted by the solution of the Bloch equations in the presence of the radiation damping terms but with the longitudinal relaxation term neglected. A saw-tooth-like peak height as a function of the pulse flip angle is predicted as long as T-1 >> T-2(*) greater than or equal to Tr (where Tr is the radiation damping time). Thus for a fairly strong magnetization,the maximum peak height cannot be obtained with a pi/2 pulse, but with a pulse very close to pi instead.