Spatio-temporal anomalous diffusion imaging: results in controlled phantoms and in excised human meningiomas

Recently, we measured two anomalous diffusion (AD) parameters: the spatial and the temporal AD indices, called gamma and alpha, respectively, by using spectroscopic pulse gradient field methods. We showed that y quantifies pseudo-superdiffusion processes, while a quantifies subdiffusion processes. Here, we propose gamma and alpha maps obtained in a controlled heterogeneous phantom, comprised of packed micro-beads in water and in excised human meningiomas. In few words, alpha maps represent the multi-scale spatial distribution of the disorder degree in the system, while y maps are influenced by local internal gradients, thus highlighting the interface between compartments characterized by different magnetic susceptibility. gamma maps were already obtained by means of AD stretched exponential imaging and alpha-type maps have been recently achieved for fixed rat brain with the aim of highlighting the fractal dimension of specific brain regions. However, to our knowledge, the maps representative of the spatial distribution of alpha and gamma obtained on the same controlled sample and in the same excised tissue have never been compared. Moreover, we show here, for the first time, that a maps are representative of the spatial distribution of the disorder degree of the system. In a first phase, gamma and alpha maps of controlled phantom characterized by an ordered and a disordered rearrangement of packed micro-beads of different sizes in water and by different magnetic susceptibility (Delta chi) between beads and water were obtained. In a second phase, we investigated excised human meningiomas of different consistency. Results reported here, obtained at 9.4T, show that alpha and gamma maps are characterized by a different image contrast. Indeed, unlike y maps, a maps are insensible to (Delta chi) and they are sensible to the disorder degree of the microstructural rearrangement. These observations strongly suggest that AD indices alpha and gamma reflect some additional microstructural information which cannot be obtained using conventional diffusion methods based on Gaussian diffusion. Moreover, alpha and gamma maps obtained in excised meningiomas seem to provide more microstructural details above those obtained with conventional DTI analysis, which could be used to improve the classification of meningiomas based on their consistency. (C) 2013 Elsevier Inc. All rights reserved.