High-Resolution Maps of Magnetization Transfer with Inherent Correction for RF Inhomogeneity and T1 Relaxation Obtained from 3D FLASH MRI

empirical equation for the magnetization transfer (MT) FLASH signal is derived by analogy to dual-excitation FLASH introducing a novel semiquantitative parameter for MT, the per centage saturation imposed by one MT pulse during TR. This parameter is obtained by a linear transformation of the inverse signal, using two reference experiments of proton density and T, weighting. The influence of sequence parameters on the MT saturation was studied. An 8.5-min protocol for brain imaging a 3 T was based on nonselective sagittal 3D-FLASH at 1.25 mm isotropic resolution using partial acquisition techniques (TRITE alpha = 25ms/4.9ms/5 degrees or 11 ms/4.9ms/15 degrees for the T-1 reference). 12.8 ms Gaussian MT pulse was applied 2.2 kHz off-resonance with 540 degrees flip angle. The MT saturation maps showed an excel lent contrast in the brain due to clearly separated distributiom for white and gray matter and cerebrospinal fluid. Within the limits of the approximation (excitation <15 degrees, TR/T-1 << 1) the MT term depends mainly on TR, the energy and offset of the MT pulse, but hardly on excitation and T, relaxation. It is inherently compensated for inhomogeneities of receive and transmit RF fields. The MT saturation appeared to be a sensitive parameter to depict MS lesions and alterations of normal-appearing white matter. Magn Reson Med 60:1396-1407, 2008. (C) 2008 Wiley Liss, Inc.