Balanced SSFP profile asymmetries are sensitive to white matter tract structure

INTRODUCTION. Balanced SSFP has the unusual property that the signal is sensitive to resonance frequency. Considering only T1, T2 and diffusion effects, this dependence is predicted to be symmetric with respect to the experimental center frequency (Fig. 3a, “theory”). However, we recently demonstrated that the signal measured in vivo is asymmetric (Fig. 3a, points) [1]. For a region-of-interest analysis in the brain, we noted strongest asymmetry in white matter and hypothesized that this effect may relate to tissue microstructure. Theory predicts that asymmetries can result from multiple tissue compartments or non-exchanging water pools that are frequency shifted relative to each other [2]. Here, we present the first maps of SSFP asymmetry, demonstrate excellent consistency of the effect across subjects, and describe several observations that may help elucidate its source.