In vivo measurement of a new source of contrast, the dipolar relaxation time, T1D, using a modified inhomogeneous magnetization transfer (ihMT) sequence

PurposeThis paper describes a technique that can be used in vivo to measure the dipolar relaxation time, T-1D, of macromolecular protons contributing to magnetization transfer (MT) in tissues and to produce quantitative T-1D maps. Theory and MethodsThe technique builds upon the inhomogeneous MT (ihMT) technique that is particularly sensitive to tissue components with long T-1D. A standard ihMT experiment was altered to introduce a variable time for switching between positive and negative offset frequencies for RF saturation. A model for the dependence of ihMT was developed and used to fit data acquired in vivo. ResultsApplication of the method to images from brains of healthy volunteers produced values of T-1D=(5.91.2) ms in gray matter and T-1D=(6.2 +/- 0.4) ms in white matter regions and provided maps of the T-1D parameter. ConclusionThe model and experiments described provide access to a new relaxation characteristic of tissue with potentially unique diagnostic information. Magn Reson Med 78:1362-1372, 2017. (c) 2016 International Society for Magnetic Resonance in Medicine.