Real-time diffuse correlation spectroscopy with on-chip correlators for measuring human cerebral blood flow and brain function

Diffuse correlation spectroscopy (DCS) is a noninvasive optical technique that probes microvascular blood flow in deep tissues. Here, we present and validate a new onchip hardware correlator for highspeed DCS measurements. The correlator is embedded in a custombuilt 512 × 512 singlephoton avalanche diode (SPAD) array named ATLAS, which computes intensity autocorrelation functions directly onchip at a sampling rate of 116 Hz - the fastest DCS acquisition reported to date. Unlike conventional DCS systems that suffer from low light throughput and therefore cannot resolve cardiac pulsations at sourcedetector separations (𝜌) beyond 30 mm, our massively parallel onchip architecture computes autocorrelations within each macropixel, eliminating the datathroughput bottleneck. This enables highSNR, realtime detection of pulsatile blood flow even at 𝜌 = 50 mm on the human forehead. In phantom experiments at 𝜌 = 25 mm, ATLASDCS achieves a 12fold improvement in signaltonoise ratio over a conventional singlechannel DCS instrument while operating at 116 Hz. In human subjects, we resolve functional hyperemia during a mental arithmetic task at 𝜌 = 30 mm. Furthermore, we integrate ATLASDCS with a frequencydomain nearinfrared spectroscopy (FDNIRS) module, enabling simultaneous monitoring of blood flow and tissue oxygenation. With this combined system, we can concurrently resolve core hemodynamic parameters. The onchip parallelized DCS design substantially improves detection speed, depth sensitivity, and realtime capability, paving the way for wearable, highspeed cerebral blood flow monitoring in both clinical and research settings.