Imaging photoplethysmography reveals changes in cerebral blood supply caused by temporary arterial occlusion

During temporary arterial occlusion (TAO), which is often used in neurosurgery, particularly when clipping aneurysms, it is critically important to intraoperatively assess changes in blood supply to the brain. This study aimed to demonstrate the feasibility of using imaging photoplethysmography (IPPG) to quantify spatiotemporal changes in cerebral perfusion during TAO. The reaction of the cerebral blood supply to unilateral or bilateral occlusion of the common carotid arteries (CCAs) was studied in anesthetized rats by video-recording the cortex through a thinned parietal bone with synchronous electrocardiogram registration and simultaneous blood flow monitoring in the middle cerebral artery using transcranial ultrasound. We show that (i) unilateral occlusion of the right CCA leads to a significant decrease in the amplitude of the pulsatile component (APC) of the IPPG waveform ipsilaterally, whereas APC changes in the contralateral hemisphere are statistically insignificant; (ii) subsequent occlusion of both CCAs leads to a dramatic bilateral drop in APC; and (iii) occlusion cessation causes a significant increase in APC, exceeding the baseline value. APC reflects the pulsatile dynamics of the light returned from the cortex, which may correspond to changes in cerebral hemodynamics due to sequential violation and restoration of blood supply to the brain. The data obtained provides an experimental justification for the future implementation of the IPPG technique in neurosurgery.