Laser speckle contrast imaging (LSCI) and imaging photoplethysmography (IPPG) are two simple, contact-free, camera-based ways to analyse cerebral blood flow non-invasively. Indeed, despite their long-standing reputation as rival modalities, they are underpinned by distinct physics. More specifically: LSCI reads tiny changes in scattered laser light, whereas IPPG reads heartbeat-driven absorption in green incoherent light. Therefore, these imaging modalities "see" different things within the brain. While LSCI maps are brightest over large surface veins and sinuses and show strong heartbeat-locked fluctuations there, the IPPG is minimal over big veins but clearly shows pulsations within brain tissue (parenchyma). The authors explain this by pressure waves from nearby arteries that move vessel walls and modulate speeds in ways LSCI detects, while IPPG responds to changes in red-blood-cell density in the capillary network. Ultimately, current study shows how to make LSCI and IPPG signals speak the same language, turning beat-by-beat changes into clear, real-time maps of perfusion without using any dye.
In heartbeat-synchronized animal experiments, the team reveals a consistent pattern: a drug administration first slows the heartrate, flow briefly dips, then rebounds to a stronger phase of blood delivery. Crucially, the authors introduce a simple index that converts LSCI's speckle "flicker" into a per-second perfusion measure, aligning it with IPPG. The result is a fuller, more robust picture: LSCI highlights large surface veins and vessel-wall motion; IPPG highlights pulsations in the brain tissue itself, resulting from arterial activity. Used together, these two views provide fast, robust, wide-field functional cerebral blood flows monitoring that could support safer neuro-surgery. As a significant step forward in translational biophotonics, this camera-based, dye-free approach is inherently portable and cost-effective, charting a practical path from pre-clinical studies to the operating theatre, and, ultimately, to bedside monitoring in Neurological Intensive Care Unit. The paper entitled " Advancing intraoperative cerebral blood flow monitoring: integrating imaging photoplethysmography and laser speckle contrast imaging in neurosurgery " was published in Frontiers of Optoelectronics (published on Sept. 26, 2025).
