A model for the dynamics of spins 3/2 in biological media: Signal loss during radiofrequency excitation in triple-quantum-filtered sodium MRI

We have derived the differential equations that describe the dynamics of sp in-3/2 nuclei in the presence of radiofrequency (RF) fields and both static and fluctuating quadrupolar interactions. The formalism presented was used to predict the sodium triple-quantum-filtered (TQ-filtered) signal loss in a whole-body scanner, where the widths of the hard 90 degrees RF pulses ar e on the same order of magnitude as the transverse relaxation times. A smal l piece of bovine nasal cartilage, known for exhibiting residual quadrupola r splittings, was used to test the theory. The sample was modeled as consis ting of small domains, each characterized by a static quadrupolar interacti on constant, with an overall Gaussian distribution across the sample. An in crease of about 15% in the TQ-filtered signal strength, as the 90 degrees R F pulse width was decreased from 500 to 100 mus, was predicted and demonstr ated experimentally for this particular sample. (C) 2000 Academic Press.