Estimation of magnetization transfer rates from PACE experiments with pulsed RF saturation

A new imaging method has been developed for estimating the magnetization tr ansfer rate (MTR) in a biologic two-pool system such as the brain tissue. T he transfer rate is calculated from the ratio of the MTR to T-1sat, where T -1sat is the apparent longitudinal relaxation time under complete saturatio n of the macromolecular pool. MTR and T-1sat maps were obtained with a phas e acquisition of composite echo (PACE) technique combined with pulsed radio frequency (RF) saturation. The influences of RF saturation power and freque ncy offset on quantitative results were investigated with phantom and in vi vo measurements. In white matter of seven healthy volunteers we found a mea n transfer rate of 1.5 sec(-1), where the highest transfer rate was found i n the genu of the corpus callosum, (k(f) = 1.9 sec(-1)). It could be shown that conditions near to complete saturation can also be reached under commo n restrictions by the specific absorption rate. (C) 2000 Wiley-Liss, Inc.