MULTICOMPONENT T-1 RELAXATION AND MAGNETIZATION-TRANSFER IN PERIPHERAL-NERVE

We report here a study of longitudinal relaxation (T-1) and magnetisat ion transfer (MT) in peripheral nerve. Amphibian sciatic nerve was mai ntained in vitro and studied at a magnetic field strength of 3 T, A CP MG pulse sequence was modified to include either a saturation pulse to measure T-1 relaxation or an off-resonance RF irradiation pulse to me asure MT. The resulting transverse relaxation (T-2) spectra yielded fo ur components corresponding to three nerve compartments, taken to resu lt from myelinic, axonal, and inter-axonal water, and a fourth corresp onding to the buffer solution water in which the nerve sample was bath ed. Each nerve component was analysed for T-1 relaxation and MT. All t hree nerve T,components exhibited unique T-1 relaxation and MT charact eristics, providing further support for the assignment of the componen ts to unique physical compartments of water. Numerical investigation o f T-1sat measurements of each of the three nerve T-2 components indica tes that while the two shorter-lived exhibit similar steady-state magn etisation transfer ratios (MTRs), their respective MT properties are q uite different, Simulations demonstrate that mobile water exchange bet ween these two components is not necessary to explain their similar st eady-state MTR. In the context of the assignment of these two componen ts to signal from myelinic and axonal water, this is to say that these two microanatomical regions of nerve may exhibit similar steady-state MTR characteristics despite possessing widely different MT exchange r ates. Therefore, interpreting changes in MTR solely to reflect a chang e in degree of myelination could lead to erroneous conclusions. (C) 19 98 Elsevier Science Inc.