Near-Infrared Transillumination Back Scattering Sounding—New Method to Assess Brain Microcirculation in Patients with Chronic Carotid Artery Stenosis

PURPOSE The purpose of the study was to assess the responses of pial artery pulsation (cc-TQ) and subarachnoid width (sas-TQ) to acetazolamide challenge in patients with chronic carotid artery stenosis and relate these responses to changes in peak systolic velocity (PSV), cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT) and time to peak response (TTP). METHODS Fifteen patients with carotid artery stenosis ≥ 90% on the ipsilateral side and <50% on the contralateral side were enrolled into the study. PSV was assessed using colour-coded duplex sonography, CBF, CBV, MTT and TTP with perfusion computed tomography, cc-TQ and sas-TQ with near-infrared transillumination/backscattering sounding (NIR-T/BSS). RESULTS Based on the ipsilateral/contralateral cc-TQ ratio after acetazolamide challenge two groups of patients were distinguished: the first group with a ratio ≥ 1 and the second with a ratio <1. In the second group increases in CBF and CBV after the acetazolamide test were significantly higher in both hemispheres (ipsilateral: +33.0% ± 8.1% vs. +15.3% ± 4.4% and +26.3% ± 6.6% vs. +14.3% ± 5.1%; contralateral: +26.8% ± 7.0% vs. +17.6% ± 5.6% and +20.0% ± 7.3% vs. +10.0% ± 3.7%, respectively), cc-TQ was significantly higher only on the ipsilateral side (+37.3% ± 9.3% vs. +26.6% ± 8.6%) and the decrease in sas-TQ was less pronounced on the ipsilateral side (-0.7% ± 1.5% vs. -10.2% ± 1.5%), in comparison with the first group. The changes in sas-TQ following the acetazolamide test were consistent with the changes in TTP. CONCLUSIONS The ipsilateral/contralateral cc-TQ ratio following acetazolamide challenge may be used to distinguish patient groups characterized by different haemodynamic parameters. Further research on a larger group of patients is warranted.