Cheap Camera Sensor Achieves 20x Boost in Brain Blood Flow Monitoring

Published in IEEE Journal of Selected Topics in Quantum Electronics. DOI: 10.1109/JSTQE.2025.3537642. Lead author Mingjun Zhao, NYU Langone Health.

How do you measure blood flowing through a brain that sits behind a centimeter or two of skull and scalp? You can shine coherent light on the head and watch the speckle pattern dance -- the rate of dancing correlates with blood flow. The technique, called diffuse correlation spectroscopy (DCS), has been known for decades. The problem is that by the time light travels through all that tissue and back out, the signal is vanishingly weak.

Boosting that signal has typically meant using expensive single-photon avalanche diode (SPAD) arrays -- detectors sensitive enough to count individual photons but costing roughly two orders of magnitude more than standard camera sensors. That cost barrier has kept noninvasive brain blood flow monitoring confined to research settings.

A team led by Mingjun Zhao at NYU Langone Health has found a way around this constraint. Their approach, called interferometric diffusing wave spectroscopy (iDWS), uses a standard CMOS camera sensor -- the kind found in consumer electronics -- and boosts the weak brain signal through coherent amplification with a stronger reference beam. The results, published in the IEEE Journal of Selected Topics in Quantum Electronics, show a 20-fold improvement in signal-to-noise ratio over previous iDWS implementations.

Amplifying the whisper from the brain

The core idea is interferometry. Instead of trying to detect the faint light returning from the brain directly, the system mixes it with a much stronger reference beam from the same laser source. The two beams interfere with each other, and the interference pattern amplifies the brain signal enough for a conventional camera sensor to detect it.

Zhao's team optimized multiple aspects of the system: the number of independent measurement channels, camera duty cycle and full well capacity, laser power, noise mitigation strategies, and data processing algorithms. The cumulative result was an overall 20x improvement in signal quality.

At 852 nanometers wavelength, the system demonstrated pulsatile cerebral blood flow monitoring -- tracking the beat-by-beat fluctuations in brain blood flow -- at source-to-collector separations of 4 to 4.5 centimeters. That distance matters because longer separations sample deeper tissue, and 4+ centimeters is sufficient to reach the brain in most adults.

The team has since optimized a 1,064 nanometer version that achieves pulsatile measurements at over 5 centimeters separation, pushing even deeper into brain tissue.

Cost and clinical practicality

The financial implications are significant. The CMOS sensor used in iDWS costs roughly 100 times less than a comparable SPAD array. For a technology aimed at bedside monitoring in intensive care units -- where cerebral blood flow measurement could guide treatment of stroke, traumatic brain injury, and other neurological emergencies -- cost is a major barrier to adoption.

Beyond cost, iDWS offers a technical advantage over another competing approach called speckle contrast optical spectroscopy (SCOS). Because iDWS uses short camera exposures that capture the rapid speckle fluctuations generated by high cerebral blood flow, it achieves better brain sensitivity than SCOS, which relies on longer exposures that blur out the fastest fluctuations.

From optical table to hospital cart

One of the study's most practical achievements is engineering. Interferometers are notoriously sensitive to vibration -- they typically require pneumatically isolated optical tables, the kind of heavy, expensive equipment found in physics laboratories but not in hospital rooms.

Zhao's team built the entire iDWS system on a mobile cart and defined the conditions under which stable operation is possible. Zhao described this as a milestone in the clinical translation of interferometric diffuse optical methods, noting the challenge of stabilizing an interferometer without isolation tables in space-starved clinical settings.

Using the cart-based system, the team performed preliminary measurements of cerebral blood flow in a patient in the Neuro Intensive Care Unit -- the first report of iDWS CBFi monitoring in a clinical setting. The results, while preliminary, demonstrate that the technology can operate in real hospital conditions.

The road from demonstration to deployment

Several hurdles remain before iDWS could become a routine clinical tool. The preliminary Neuro ICU measurements involved a single patient and were not designed to validate the technology against established methods like transcranial Doppler or perfusion MRI. Such validation studies will be essential.

The system was demonstrated on adults with moderate skin pigmentation (Fitzpatrick scale 4). Performance across the full range of skin tones -- particularly in individuals with high melanin content, where light absorption is greater -- needs systematic evaluation. Darker skin absorbs more near-infrared light, which could reduce signal quality at the separations needed for brain sensitivity.

Long-term operational stability in a clinical environment, with its vibrations from foot traffic, equipment, and HVAC systems, has not been established. The team has defined conditions for stable operation but acknowledges that ongoing optimization will be needed for robust clinical use.

The researchers plan to test long-term operability in the Neuro ICU, implement time-of-flight filtering to further improve brain specificity, and validate iDWS for diagnosing and monitoring treatment of neurological disorders including ischemic stroke and traumatic brain injury.

If successful, the technology could fill a genuine clinical gap: continuous, noninvasive, bedside monitoring of brain blood flow at a price point that makes widespread adoption feasible. For the estimated 795,000 Americans who experience a stroke each year, and the many more with traumatic brain injuries, that capability could meaningfully improve care.