MRI of cerebral micro-vascular flow patterns: A multi-direction diffusion-weighted ASL approach

Abstract

The study and clinical assessment of brain disease is currently hindered by a lack of non-invasive methods for the detailed and accurate evaluation of cerebral vascular pathology. Angiography can detect aberrant flow in larger feeding arteries/arterioles but cannot resolve the micro-vascular network. Small vessels are a key site of vascular pathology that can lead to haemorrhage and infarction, which may in turn trigger or exacerbate neurodegenerative processes. In this study, we describe a method to investigate microvascular flow anisotropy using a hybrid arterial spin labelling and multi-direction diffusion-weighted MRI sequence. We present evidence that the technique is sensitive to the mean/predominant direction of microvascular flow in localised regions of the rat cortex. The data provide proof of principle for a novel and non-invasive imaging tool to investigate cerebral micro-vascular flow patterns in healthy and disease states.

Non‐contrast MR imaging of blood‐brain barrier permeability to water

“…23,[57][58][59] However, the T 2 difference can also be because of oxygenation changes as the spin flows from artery to capillary, to veins. A more advanced technique is to use diffusion or intra-vascular-incoherent-motion (IVIM) weighted ASL to separate microvascular and extravascular signals by applying magnetic field gradients, [60][61][62] which can then give water exchange rate between the 2 compartments by fitting the signal to a tracer kinetic model. 19,20,63 A confounding factor of this method is that it relies on the assumption that diffusion gradients can fully remove vascular signal while having no effect on the tissue signal.…”

Comparison of perfusion signal acquired by arterial spin labeling–prepared intravoxel incoherent motion (IVIM) MRI and conventional IVIM MRI to unravel the origin of the IVIM signal

“…To further distinguish the intravascular and extravascular contributions to the ASL signal, an alternative two‐compartment, biexponential model was implemented following the work of Silva et al and Wells et al : …”

Pattern recognition analysis of directional intravoxel incoherent motion MRI in ischemic rodent brains

“…However, conventional methods such as dynamic susceptibility contrast MRI (DSC‐MRI) or arterial spin labeling MRI (ASL‐MRI) are limited in their detection of directional blood flow. Recent multidirection ASL approaches provide anisotropic cerebral blood perfusion but only for arteries …”