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Abstract #0802

In-vivo measurement of a new source of tissue contrast, the dipolar relaxation time,T1D, using a modified ihMT sequence

Gopal Varma1, Valentin H Prevost2, Olivier M Girard2, Guillaume Duhamel2, and David C Alsop1

1Radiology, Division of MR Research, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States, 2CRMBM-CEMEREM UMR 7339, CNRS-AMU, Aix Marseille Université, Marseille, France

The enhanced inhomogeneous magnetization transfer (ihMT) in certain tissues, especially white matter, has recently been explained as a result of longer dipolar relaxation times, T1Ds in those tissues. Measurement of T1D by modeling the frequency and power dependence of steady state ihMT has yielded T1D estimates but with great uncertainty. Here we introduce a dynamic ihMT experiment that switches between positive and negative frequency irradiation at varying times. Fits to the ihMT signal decay curve as a function of switching time at one (absolute) offset frequency and power enabled highly precise mapping of T1D that was largely independent of other MT parameters. A T1D of 6.4±0.5ms for white matter was in good agreement with reported ex-vivo measurements using Jeener-Broekaert echoes.

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