AN MRI METHOD FOR MEASURING T-2 IN THE PRESENCE OF STATIC AND RF MAGNETIC-FIELD INHOMOGENEITIES

A magnetic resonance imaging method for measuring the T-2 relaxation t ime constant is proposed. It is based on the assumption that, under ve ry general conditions, the MR signal near a spin echo has a special sy mmetry arising from the refocusing nature of the 180 degrees RF pulse. A gradient echo sampling of the spin echo (GESSE) sequence is impleme nted to evaluate T-2 by collecting multiple gradient echoes before and after the spin echo. This approach is a modification of the GESFIDE s equence proposed by Ma and Wehrli. However, our approach compares imag es that are not separated by any RF pulses and, as a result, is insens itive to slice profile imperfections. In addition, the calculated T-2 value does not rely on any special assumptions about the MRI signal be havior in the presence of an inhomogeneous static magnetic field and, hence, is insensitive to the presence of static magnetic field inhomog eneities.