Clinical Neuroimaging Using 7 T MRI: Challenges and Prospects.

The aim of this article is to illustrate the principal challenges, from the medical and technical point of view, associated with the use of ultrahigh field (UHF) scanners in the clinical setting and to present available solutions to circumvent these limitations. We would like to show the differences between UHF scanners and those used routinely in clinical practice, the principal advantages, and disadvantages, the different UHFs that are ready be applied to routine clinical practice such as susceptibility-weighted imaging, fluid-attenuated inversion recovery, 3-dimensional time of flight, magnetization-prepared rapid acquisition gradient echo, magnetization-prepared 2 rapid acquisition gradient echo, and diffusion-weighted imaging, the technical principles of these sequences, and the particularities of advanced techniques such as diffusion tensor imaging, spectroscopy, and functional imaging at 7TMR. Finally, the main clinical applications in the field of the neuroradiology are discussed and the side effects are reported.

Rotational motion in LiBH4/LiI solid solutions.

We investigated the localized rotational diffusion of the (BH(4))(-) anions in LiBH(4)/LiI solid solutions by means of quasielastic and inelastic neutron scattering. The (BH(4))(-) motions are thermally activated and characterized by activation energies in the order of 40 meV. Typical dwell times between jumps are in the picosecond range at temperatures of about 200 K. The motion is dominated by 90° reorientations around the 4-fold symmetry axis of the tetrahedraly shaped (BH(4))(-) ions. As compared to the pure system, the presence of iodide markedly reduces activation energies and increases the rotational frequencies by more than a factor of 100. The addition of iodide lowers the transition temperature, stabilizing the disordered high temperature phase well below room temperature.

BH4− self-diffusion in liquid LiBH4.

The hydrogen dynamics in solid and in liquid LiBH4 was studied by means of incoherent quasielastic neutron scattering. Rotational jump diffusion of the BH4- subunits on the picosecond scale was observed in solid LiBH4. The characteristic time constant is significantly shortened when the system transforms from the low-temperature phase to the high-temperature phase at 383 K. In the molten phase of LiBH4 above 553 K, translational diffusion of the BH4- units is found. The measured diffusion coefficients are in the 10(-5)cm2/s range at temperatures around 700 K, which is in the same order of magnitude as the self-diffusion of liquid lithium or the diffusion of ions in molten alkali halides. The temperature dependence of the diffusion coefficient shows an Arrhenius behavior, with an activation energy of Ea = 88 meV and a prefactor of D0 = 3.1 × 10(-4)cm2/s.

Complex hydrides with (BH(4))(-) and (NH(2))(-) anions as new lithium fast-ion conductors.

Some of the authors have reported that a complex hydride, Li(BH(4)), with the (BH(4))(-) anion exhibits lithium fast-ion conduction (more than 1 x 10(-3) S/cm) accompanied by the structural transition at approximately 390 K for the first time in 30 years since the conduction in Li(2)(NH) was reported in 1979. Here we report another conceptual study and remarkable results of Li(2)(BH(4))(NH(2)) and Li(4)(BH(4))(NH(2))(3) combined with the (BH(4))(-) and (NH(2))(-) anions showing ion conductivities 4 orders of magnitude higher than that for Li(BH(4)) at RT, due to being provided with new occupation sites for Li(+) ions. Both Li(2)(BH(4))(NH(2)) and Li(4)(BH(4))(NH(2))(3) exhibit a lithium fast-ion conductivity of 2 x 10(-4) S/cm at RT, and the activation energy for conduction in Li(4)(BH(4))(NH(2))(3) is evaluated to be 0.26 eV, less than half those in Li(2)(BH(4))(NH(2)) and Li(BH(4)). This study not only demonstrates an important direction in which to search for higher ion conductivity in complex hydrides but also greatly increases the material variations of solid electrolytes.