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, T_1Ds in those tissues. Measurement of T_1D by modeling the frequency and power dependence of steady state ihMT has yielded T_1D 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 T_1D that was largely independent of other MT parameters. A T_1D 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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