MAGNETIZATION-TRANSFER AND T-2 RELAXATION COMPONENTS IN TISSUE

T-2 relaxation makes an important contribution to tissue contrast in magnetic resonance (MR) imaging. Many tissues are known to exhibit multicomponent T-2 relaxation that suggests some compartmental segregation of mobile protons on a T-2 timescale. Magnetization transfer (MT) is another relaxation mechanism that can be used to produce tissue contrast in MR imaging. The MT process depends strongly on water-macromolecular interactions. To investigate the relationship between multicomponent T-2 relaxation and the MT process, multiecho T-2 measurements have been combined with MT measurements for freshly excised samples of cardiac muscle, striated muscle, and white matter. For muscle, short T-2 components show greater MT than long T-2 components, consistent with the belief that they represent distinct water environments. For white matter, quantitative MT measurements were identical for the two major T-2 components, apparently because of exchange between the T-2 compartments on a timescale characteristic of the MT experiment. Implications for accurate modeling of MT in tissue and the use of MT for MR image contrast are discussed.