Compromise in cognitive function in patients with carotid bifurcation disease is well documented. This might result from hypoperfusion of the affected hemisphere. However, not every patient with asymptomatic high-grade carotid stenosis will have compromised blood flow because collateral blood flow, via the circle of Willis, might provide adequate compensation. In their previous reports, Lal et al 1 and Gray et al 2 showed a clear correlation between carotid stenosis and impaired cognitive function but did not provide a mechanism. In their current report, Khan et al 3 have taken several further steps. They have developed a novel method for the measurement of cerebral hemisphere blood flow using perfusion-weighted magnetic resonance imaging to measure the time to peak flow transit time and mean transit time delay to measure cerebral perfusion. In addition, they were able to correlate these magnetic resonance imaging findings with the duplex scan parameters, which will now provide a simpler method for assessing brain hypoperfusion in patients with carotid stenosis.

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