Advancing intraoperative cerebral blood flow monitoring: integrating imaging photoplethysmography and laser speckle contrast imaging in neurosurgery

Intraoperative assessment of cerebral hemodynamics is crucial for the success of neurosurgical interventions. This study evaluates the potential of laser speckle contrast imaging (LSCI) and imaging photoplethysmography (IPPG) for contactless perfusion monitoring during neurosurgery. Despite similarities in their hardware requirements, these techniques rely on fundamentally different principles: light scattering for LSCI and light absorption for IPPG. Comparative experiments were conducted using animals (rats) when assessing the reaction of cerebral hemodynamics to adenosine triphosphate infusion. The results show different spatial and temporal characteristics of the techniques: LSCI predominantly visualizes blood flow in large venous vessels, especially in the sagittal and transverse sinuses, showing a pronounced modulation associated with the heart that cannot be explained by venous blood flow alone. In contrast, IPPG quantifies the dynamics of perfusion changes in the parenchyma, showing minimal signal in large venous vessels. We propose that LSCI signal modulation is significantly influenced by the movement of vessel walls in response to mechanical pressure waves propagating through the parenchyma from nearby arteries. A novel algorithm for LSCI data processing was developed based on this interpretation, producing perfusion indices that align well with IPPG measurements. This study demonstrates that the complementary nature of these techniques (LSCI is sensitive to blood cells displacements, while IPPG detects a change in their density) makes their combined application particularly valuable for comprehensive assessment of cerebral hemodynamics during neurosurgery.