Simultaneous 3D quantitative magnetization transfer imaging and susceptibility mapping

Abstract

Purpose: Introduce a unified acquisition and modeling strategy to simul-taneously quantify magnetization transfer (MT), tissue susceptibility (𝜒)and T∗2 . Theory and Methods: Magnetization transfer is induced through the appli-cation of off-resonance irradiation between excitation and acquisition of anRF-spoiled gradient-echo scheme, where free pool spin–lattice relaxation (TF1 ),macromolecular proton fraction (f ) and magnetization exchange rate (kF ) werecalculated by modeling the magnitude of the MR signal using a binary spin-bathMT model with B+1 inhomogeneity correction via Bloch-Siegert shift. Simultane-ously, a multi-echo acquisition is incorporated into this framework to measurethe time evolution of both signal magnitude and phase, which was further mod-eled for estimating T∗2 and tissue susceptibility. In this work, we demonstratethe feasibility of this new acquisition and modeling strategy in vivo on the braintissue. Results: In vivo brain experiments were conducted on five healthy subjects tovalidate our method. Utilizing an analytically derived signal model, we simul-taneously obtained 3D TF1 , f , kF , 𝜒 and T∗2 maps of the whole brain. Our resultsfrom the brain regional analysis show good agreement with those previouslyreported in the literature, which used separate MT and QSM methods.Conclusion: A unified acquisition and modeling strategy based on an analyticalsignal model that fully leverages both the magnitude and phase of the acquiredsignals was demonstrated and validated for simultaneous MT, susceptibility andT∗2 quantification that are free from B+1 bias.