Echo time‐dependent quantitative susceptibility mapping contains information on tissue properties

Abstract

Decomposition of voxel constituents into meaningful parameters may lead to informative measures that reflect changes in tissue microstructure. Magn Reson Med 77:1946-1958, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Exploring the origins of echo-time-dependent quantitative susceptibility mapping (QSM) measurements in healthy tissue and cerebral microbleeds

“…Non-linear phase evolution has also been demonstrated in vivo in some white matter fiber tracts [39, 40] and, as expected, has been shown to cause TE-dependent QSM measurements in healthy brain tissue [41]. These observations have been attributed to sub-voxel level compartmentalization of the MRI signal [39–41]. In the white matter, two and three compartment hollow cylinder models have been used to simulate microstructural compartmentalization [39, 40, 46–48]; and multi-component fitting has been used to test for compartmentalization of real data acquired in vivo [40, 49–57].…”

“…Multi-exponential signal decay and non-linear frequency and phase evolution in the MRI signal from biological tissues has been noted in numerous studies [39–41, 49, 53–56, 67], with such effects generally being attributed to the compartmentalization of the signal due to microstructure within imaging voxels. In the white matter, these effects are increasingly explained using multi-compartment tissue models, with the magnetic susceptibility anisotropy in the myelin sheath playing a key role [39–41].…”

“…In the white matter, these effects are increasingly explained using multi-compartment tissue models, with the magnetic susceptibility anisotropy in the myelin sheath playing a key role [39–41]. Recently published work by Sood et al has reported that susceptibility values calculated using QSM are also TE-dependent and the profile of this variation varies by brain region as expected based on the TE-dependence of the apparent frequency shift [41]. …”

“…Orientation-dependent susceptibility effects have been demonstrated in vivo , particularly in tissues with highly ordered microstructure [43, 45–47]. Non-linear phase evolution has also been demonstrated in vivo in some white matter fiber tracts [39, 40] and, as expected, has been shown to cause TE-dependent QSM measurements in healthy brain tissue [41]. These observations have been attributed to sub-voxel level compartmentalization of the MRI signal [39–41].…”

“…These qualitative and quantitative observations are increasingly used as an adjunct to conventional MRI in the study of aging and a range of disease pathologies [11, 14–38]. It has recently been reported that frequency shift [39, 40] and QSM [41] values calculated in various brain regions vary with echo time when calculated from individual echoes from a multi-echo GRE acquisition. These observations are inconsistent with the assumption inherent in QSM that frequency shift is a time-independent function of the local magnetic field; and proper analysis and understanding of this effect is essential both for the interpretation of susceptibility measurements made using QSM and potential exploitation of new information that may be derived from multi-echo GRE data.…”