Pathological characterization of T2*-weighted MRI contrast in the striatum of Huntington's disease patients

Previous MRI studies consistently reported iron accumulation within the striatum of patients with Huntington's disease (HD). However, the pattern and origin of iron accumulation is poorly understood. This study aimed to characterize the histopathological correlates of iron-sensitive ex vivo MRI contrast change in HD brains. To this end, T2*-weighted 7T MRI was performed on postmortem tissue of the striatum of three control subjects and 10 HD patients followed by histological examination. In addition, formalin-fixed paraffin-embedded material of three control subjects and 14 HD patients was selected for only histology to identify the cellular localization of iron using stainings for iron, myelin, microglia and astrocytes. As expected HD striata showed prominent atrophy. Compared to controls, the striatum of HD patients was in general more hypointense on T2*-weighted highfield MRI and showed a more intense histopathological staining for iron. In addition, T2*-weighted MRI identified large focal hypointensities within the striatum of HD patients. Upon histological examination, these large focal hypointensities frequently colocalized with enlarged perivascular spaces and iron was found within the vessel wall and reactive astrocytes. In conclusion, we show that the striatum of HD patients has a distinctive phenotype on T2*-weighted MRI compared to control subjects. On ex vivo MRI, these contrast changes are heavily biased by enlarged perivascular spaces from which it is currently unknown whether this is a fixation artefact or a disease specific observation. Clinically, the observation of iron within reactive astrocytes is of importance for the interpretation and understanding of the potential underlying mechanisms of T2*-weighted MRI results in HD patients.Neuro Imaging Researc

Water balance versus land surface model to simulate Rhine river discharges

Accurate streamflow simulations in large river basins are crucial to predict timing and magnitude of floods and droughts and to assess the hydrological impacts of climate change. Water balance models have been used frequently for these purposes. Compared to water balance models, however, land surface models carry the potential to more accurately estimate hydrological partitioning and thus streamflow, because they solve the coupled water and energy balance and are able to exploit a larger part of the information provided by regional climate model output than water balance models. Owing to increased model complexity, however, they are also more difficult to parameterize. The purpose of this study is to investigate and compare the accuracy of streamflow simulations of a water balance approach (Spatial Tools for River basins and Environment and Analysis of Management (STREAM)) and a land surface model (Variable Infiltration Capacity (VIC)) approach. Both models are applied to the Rhine river basin using regional climate model output as atmospheric forcing, and are evaluated using observed streamflow and lysimeter data. We find that VIC is more robust and less dependent on model calibration. Although STREAM performs better during the calibration period (Nash-Sutcliffe efficiency (E) of 0.47 versus E = 0.29 for VIC), VIC more accurately simulates discharge during the validation period, including peak flows (E = 0.31 versus E = 0.21 for STREAM). This is the case for most locations throughout the basin, except for the Alpine part where both models have difficulties due to the complex terrain and surface reservoirs. In addition, the annual evaporation cycle at the lysimeters is more realistically simulated by VIC