<I>In vivo</I> vascular mapping of the human hippocampus using MICRO imaging

BACKGROUND: There is an urgent need for better detection and understanding of vascular abnormalities at the micro-level, where critical nourishment cellular metabolic changes occur. This especially case structures such as midbrain hippocampus, both feeding draining vessels are quite small. The hippocampus a complex grey matter structure that plays important role in spatial episodic memory. It can be affected by wide range pathologies including abnormalities. Being able to monitor normal aging various hippocampal subfields will allow us understand vulnerability across hippocampus.
 METHODS: We recently introduced concept microvascular in-vivo contrast revealed origins (MICRO) protocol image micro-cerebral vessels.1-3 MICRO uses ferumoxytol, ultra-small superparamagnetic iron oxides (USPIO) agent, induce susceptibility arteries veins; imaging with high resolution (0.22×0.44×1 mm3) weighted sequence (SWI) 3 T. Although increased enhances visibility small sub-voxel vessels, accompanying strong signal loss large deteriorates local tissue contrast. Hence, data collected different time points during gradual administration (final concentration = 4 mg/kg) ferumoxytol. Dynamically acquired SWI were co-registered combined (phase gradient-based adaptive combination or SWIPGAC) reduce blooming artifacts from preserving small-vessel contrast.
 RESULTS: presence ferumoxytol helped enhance microvasculature, something has previously only been demonstrated cadaver brain studies. Figure 1 shows difference between pre-contrast SWIPGAC visualizing micro-vasculature four healthy subjects. intra-hippocampal superficial major (obtained through non-linear subtraction method) veins averaging T1-shortening map, quantitative mapping (QSM) R2* maps) used overlay third column visualize penetrating hippocampus. fissure, along fimbria, granular cell layer dentate gyrus cornu ammonis layers (except CA1), showed higher micro-vascular density than other parts CA1 region exhibited significant correlation age (R=−0.37, p<0.05, n=37). demonstrating overall vascularity process. Moreover, reduction was more prominent volume (R=−0.1, p>0.05, n=37) subfield.
 CONCLUSIONS: With this USPIO-induced increase comes potential study cerebral using high-resolution SWI. negative functional vessel (FVD) (especially CA1) age. FVD vs age, suggesting atrophy may precede reductions volume. Mapping vasculature immediate implications effects etiology many neurovascular diseases. brings into decade microvasculature entire human body.