BACKGROUND: Transcranial Doppler (TCD) CO2-reactivity and oxygen-15 positron 
emission tomography (PET) have both been used to measure the cerebral 
haemodynamic state in patients who may have a compromised blood flow. Our 
purpose was to investigate whether PET and TCD identify the same patients with 
an impaired flow state of the brain in patients with internal carotid artery 
(ICA) occlusion.
METHODS: Patients with recent transient ischaemic attack or minor ischaemic 
stroke associated with ICA occlusion underwent TCD with measurement of 
CO2-reactivity and oxygen-15 PET within a median time interval of 6 days.
RESULTS: We included 24 patients (mean age 64 ± 10 years). Seventeen (71%) 
patients had impaired CO2-reactivity (≤20%), of whom six had absent reactivity 
(0%) or steal (<0%) in the hemisphere ipsilateral to the ICA occlusion. PET of 
the perfusion state of the hemisphere ipsilateral to the ICA occlusion 
demonstrated stage 1 haemodynamic compromise (decreased cerebral blood flow 
(CBF) or increased cerebral blood volume (CBV) without increased oxygen 
extraction fraction (OEF)) in 13 patients and stage 2 (increased OEF) in 2 
patients. In 12 patients (50%), there was agreement between TCD and PET, 
indicating haemodynamic compromise in 10 and a normal flow state of the brain in 
2 patients. There was no significant correlation between CO2-reactivity and CBF 
ipsilateral/contralateral hemispheric ratio (r = 0.168, p value = 0.432), OEF 
ratio (r = -0.242, p value = 0.255), or CBV/CBF ratio (r = -0.368, p 
value = 0.077).
CONCLUSIONS: In patients with symptomatic ICA occlusion, identification of an 
impaired flow state of the brain by PET and TCD CO2-reactivity shows concordance 
in only half of the patients.