The impact of sex and vascular risk factors on brain tissue changes with aging: magnetization transfer imaging results of the Austrian stroke prevention study.

BACKGROUND AND PURPOSE: Quantitative MR imaging techniques allow detection of subtle tissue changes that occur with brain aging beyond the accumulation of WMH and brain atrophy. To what extent sex and cerebrovascular risk factors impact these changes is largely unknown. We attempted to study these risk factors in the context of the community-based ASPS. MATERIAL AND METHODS: We performed MTI in 328 neurologically asymptomatic ASPS participants (age range, 52-87 years). FLAIR was used to delineate WMH and to define NABT. The MTR was measured globally in NABT by using a histogram analysis technique and focally in WMH. Associations of MTR metrics with sex and a large battery of different cerebrovascular risk factors (age, arterial hypertension, diabetes mellitus, smoking, body mass index, cholesterol and triglyceride levels, glycated hemoglobin, and the presence of cardiac disease) were assessed with univariate and multiple regression analysis. RESULTS: Age was seen to affect all MTR histogram metrics of NABT, and a faster decrease of the MTR peak height occurred in men. Independent associations with MTR metrics were found for arterial hypertension and diabetes mellitus. Besides lesion grade, arterial hypertension was also significantly associated with a lower MTR in WMH. CONCLUSIONS: Microstructural tissue changes of NABT increase with aging and may be more extensive in men. Diabetes mellitus and hypertension appear to add to tissue destruction. The exact mechanisms involved await further clarification.

Spin-galvanic effect.

There is much recent interest in exploiting the spin of conduction electrons in semiconductor heterostructures together with their charge to realize new device concepts. Electrical currents are usually generated by electric or magnetic fields, or by gradients of, for example, carrier concentration or temperature. The electron spin in a spin-polarized electron gas can, in principle, also drive an electrical current, even at room temperature, if some general symmetry requirements are met. Here we demonstrate such a 'spin-galvanic' effect in semiconductor heterostructures, induced by a non-equilibrium, but uniform population of electron spins. The microscopic origin for this effect is that the two electronic sub-bands for spin-up and spin-down electrons are shifted in momentum space and, although the electron distribution in each sub-band is symmetric, there is an inherent asymmetry in the spin-flip scattering events between the two sub-bands. The resulting current flow has been detected by applying a magnetic field to rotate an optically oriented non-equilibrium spin polarization in the direction of the sample plane. In contrast to previous experiments, where spin-polarized currents were driven by electric fields in semiconductor, we have here the complementary situation where electron spins drive a current without the need of an external electric field.