Combined assessment of vascular territories and haemodynamic parameter maps

Introduction: Defining watershed (WS) areas – the border zone regions supplied by the most distal branches of the cerebral arteries – is critical as these regions are most susceptible to haemodynamic ischaemia, and may even play a role in thrombo-embolic stroke due to reduced wash-out of capacity. Territorial arterial spin labelling (TASL) has been shown to provide a method of selectively labelling individual cerebral arteries to spatially map the perfusion territory of the internal carotid arteries (RICA and LICA) and basilar artery (BA) [1]. Multiphase ASL data provides a method to estimate of haemodynamic parameters of perfusion rate (f), arterial blood volume (CBVa) and arterial (Δ) and tissue (δ) transit times [2]. It has been suggested that transit time maps can provide a method to distinguish the cerebral watershed areas from main territory regions, due to the increased transit time of blood to the distal branches of the cerebral arteries. Here we assess the correspondence between these methods, additionally mapping the anterior cerebral artery (ACA) territory. Probabilistic TASL maps and mean haemodynamic parameter maps are formed, with the aim of generating an MNI atlas of these haemodynamic parameter estimates and territories as a reference for comparison with disease, such as stenoocclusive carotid disease, where cerebral haemodynamics are altered [3].