Double wave-vector (DWV) or d-PFG experiments with two diffusion weighting periods applied successively in a single acquisition offer access to microscopic tissue properties. With a short mixing time τm between the two diffusion weightings, the experiment can be used to determine cell or compartment sizes, for a long τm diffusion anisotropy present on a microscopic scale can be investigated. For instance, even in a white matter (WM) region- of-interest (ROI) that appeared isotropic in a DTI experiment, i.e. has a fractional anisotropy (FA) equal to 0, anisotropic diffusion could be detected demonstrating the additional information that DWV can provide compared to DTI. Recent studies showed that a measure of the microscopic diffusion anisotropy, the MA index, ca n be determined in the living human brain, and normal values and their variation in a group of young (< 33 y), healthy volunteers have been reported. In this study, DWV and DTI measurements were performed in a group of old (> 60 y), healthy volunteers. Their MA and FA values were determined and compared to those reported for young volunteers in order to investigate age-related changes of the diffusion anisotropy.
Double wave-vector (DWV) or d-PFG experiments with two diffusion weighting periods applied successively in a single acquisition offer access to microscopic tissue properties. With a short mixing time τm between the two diffusion weightings, the experiment can be used to determine cell or compartment sizes, for a long τm diffusion anisotropy present on a microscopic scale can be investigated. For instance, even in a white matter (WM) region-of-interest (ROI) that appeared isotropic in a DTI experiment, i.e. has a fractional anisotropy (FA) equal to 0, anisotropic diffusion could be detected demonstrating the additional information that DWV can provide compared to DTI. Recent studies showed that a measure of the microscopic diffusion anisotropy, the MA index, can be determined in the living human brain, and normal values and their variation in a group of young (< 33 y), healthy volunteers have been reported. In this study, DWV and DTI measurements were performed in a group of old (> 60 y), healthy volunteers. Their MA and FA values were determined and compared to those reported for young volunteers in order to investigate age-related changes of the diffusion anisotropy.