  In ischemic stroke, leptomeningeal collaterals can provide compensatory blood
flow to tissue at risk despite an occlusion, and impact treatment response and
infarct growth. The purpose of this work is to test the hypothesis that local
perfusion with an appropriate Local Arterial Input Function (AIF) is needed to
quantify the degree of collateral blood supply in tissue distal to an
occlusion. Seven experiments were conducted in a pre-clinical middle cerebral
artery occlusion model. Magnetic resonance dynamic susceptibility contrast
(DSC) was imaged and post-processed as cerebral blood flow maps with both a
traditionally chosen single arterial input function (AIF) applied globally to
the whole brain (i.e. "Global-AIF") and a novel automatic delay and dispersion
corrected AIF (i.e. "Local AIF") that is sensitive to retrograde flow. Pial
collateral recruitment was assessed from x-ray angiograms and infarct growth
via serially acquired diffusion weighted MRI scans both blinded to DSC. The
degree of collateralization at x-ray correlated strongly with quantitative
perfusion determined using the Local AIF in the ischemic penumbra (R2=0.81)
compared to a traditionally chosen Global-AIF (R2=0.05). Quantitative perfusion
calculated using a Local-AIF was negatively correlated (less infarct
progression as local perfusion increased) with infarct growth (R2 = 0.79)
compared to Global-AIF (R2=0.02). Local DSC perfusion with a Local-AIF is more
accurate for assessing tissue status and degree of leptomeningeal
collateralization than traditionally chosen AIFs. These findings support use of
a Local-AIF in determining quantitative tissue perfusion with collateral supply
in occlusive disease.
