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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