Quantum chemical insight into the effects of the local electron environment on T₂*-based MRI

T₂* relaxation is an intrinsic magnetic resonance imaging (MRI) parameter that is sensitive to local magnetic field inhomogeneities created by the deposition of endogenous paramagnetic material (e.g. iron). Recent studies suggest that T₂* mapping is sensitive to iron oxidation state. In this study, we evaluate the spin state-dependence of T₂* relaxation using T₂* mapping. We experimentally tested this physical principle using a series of phantom experiments showing that T₂* relaxation times are directly proportional to the spin magnetic moment of different transition metals along with their associated magnetic susceptibility. We previously showed that T₂* relaxation time can detect the oxidation of Fe²⁺. In this paper, we demonstrate that T₂* relaxation times are significantly longer for the diamagnetic, d¹⁰ metal Ga³⁺, compared to the paramagnetic, d⁵ metal Fe³⁺. We also show in a cell culture model that cells supplemented with Ga³⁺ (S = 0) have a significantly longer relaxation time compared to cells supplemented with Fe³⁺ (S = 5/2). These data support the hypothesis that dipole-dipole interactions between protons and electrons are driven by the strength of the electron spin magnetic moment in the surrounding environment giving rise to T₂* relaxation.