Characterizing white matter with magnetization transfer and T2

Abstract

A magnetization-transfer (MT) CPMG hybrid experiment was performed to analyze T2 relaxation and MT characteristics in bovine optic nerve. Two exchanging liquid pools with their own, independent MT characteristics were necessary to model both the T2 relaxation and the MT data. The model agrees well with the experimental data and yields physically realistic parameters. The MT effect for myelin water is approximately nine time larger than that for intra/intercellular water, indicating that the MT characteristics observed for white matter are mainly related to myelin. The model can be used to probe parameters that would be difficult to achieve experimentally. The exchange process between the two tissue compartments does not drastically afflict the amplitudes and relaxation rates of the T2 components, but is fast enough to significantly influence their MT characteristics. Although, both the MT and T2 experiments described in this paper are too time consuming to be applied in routine clinical work, presented results can be useful in interpreting clinical pulse sequences that are sensitive to myelin.