image: Researchers demonstrated that speckle contrast optical spectroscopy (SCOS) can be used for cuff-less blood pressure monitoring. The new system can acquire measurements from the wrist or finger.
Credit: Gwyneth Moe
WASHINGTON — Researchers have shown, for the first time, that speckle contrast optical spectroscopy (SCOS) can be used for cuff-less blood pressure monitoring. The new technology could improve early detection and management of hypertension.
“Hypertension affects nearly half of all adults in the US and is the leading cause of cardiovascular disease,” said Ariane Garrett, a doctoral student in Darren Roblyer’s lab at Boston University. “This research is a step towards a wearable device that would let people monitor their blood pressure any time, without a cuff.”
SCOS is a noninvasive imaging technique that measures blood flow by analyzing speckle patterns formed by coherent light scattering from cells and tissue. While it has been used for other applications such as brain and tissue monitoring, this is one of the first studies to explore how SCOS signals relate to blood pressure.
In the Optica Publishing Group journal Biomedical Optics Express, the researchers showed that blood flow and volume information simultaneously acquired by placing their SCOS device on the finger and wrist of 30 volunteers was up to 31% more accurate at estimating blood pressure than using blood volume information alone. Blood volume information, known as photoplethysmography, is the basis of several commercialized optical blood pressure monitors.
“Studies show that tracking blood pressure throughout the day, and especially at night, provides a better picture of someone’s health,” said Roblyer. “A wearable version of our device would be easier and more comfortable for patients and could help doctors catch conditions like masked hypertension, where clinic readings don’t reflect the true blood pressure.”
Boosting blood pressure accuracy
The work began as a collaboration between Roblyer and David Boas’ research teams at Boston University and Meta Platforms’ Reality Labs. The investigators hypothesized that the blood flow and volume waveforms — visual representations of how the light signal changes over time — measured by SCOS would contain valuable information related to cardiovascular health and could potentially be used to estimate blood pressure.
In 2023, they showed that features extracted from the blood flow waveforms were strongly correlated with blood pressure. In the new work, they demonstrate that blood flow and volume waveforms from SCOS can be used to predict blood pressure.
“The SCOS device enables us to measure blood pressure much more frequently than a cuff-based device,” said Roblyer. “This is important because there has been a lot of research indicating that single time point measurements of blood pressure using a cuff in a clinician’s office are not a good reflection of a person's true blood pressure in their daily life. However, it is difficult to take frequent cuff measurements due to the cumbersome nature of the cuff.”
To apply SCOS to blood pressure monitoring, the researchers developed a device that uses two laser wavelengths (532 nm and 808 nm), which allows them to obtain SCOS waveforms from different tissue volumes. Their device acquires speckle images at a higher frame rate than systems developed by other groups, which makes it possible to extract fine time scale features from the waveforms and explore their relationship to blood pressure.
Illuminating vital signs
To test the device, the researchers used it to acquire measurements from 30 volunteers while also acquiring measurements with a continuous blood pressure monitor. The measurements were taken while at rest and during a leg press exercise designed to induce blood pressure changes. They then extracted features from the blood flow and volume waveforms and used a machine learning model to estimate the blood pressure.
They trained one model using both blood flow and volume information, and one using just blood volume (photoplethysmography) information. The model combining blood flow and volume information improved accuracy by up to 31% and predicted systolic blood pressure with low average absolute errors of 2.26 mmHg. Measurements acquired from 20 volunteers several weeks later showed that the improvement was sustained.
“Our results showed that SCOS improves blood pressure estimation by enabling simultaneous measurements of blood flow and volume changes using the wrist or finger,” said Garrett. “This opens a new way to track cardiovascular health with optical tools.”
Next, the researchers plan to develop a wearable version of the SCOS device. To do this, they will make the device smaller and develop ways to handle data on the device, rather than externally. They will then test how well it works when people move around or wear it for long periods.
Paper: A. Garrett, B. Kim, N. Z. Gurel, E. J. Sie, B. K. Wilson, F. Marsili, J. P. Forman, N. M. Hamburg, D. A. Boas, D. Roblyer, “Speckle contrast optical spectroscopy for cuffless blood pressure estimation based on microvascular blood flow and volume oscillations,” Biomed. Opt. Express, 16, 3004-3016 (2025).
DOI: 10.1364/BOE.560022
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About Biomedical Optics Express
Biomedical Optics Express serves the biomedical optics community with rapid, open-access, peer-reviewed papers related to optics, photonics and imaging in biomedicine. The journal scope encompasses fundamental research, technology development, biomedical studies and clinical applications. It is published monthly by Optica Publishing Group and edited by Christoph Hitzenberger, Medical University of Vienna, Austria. For more information, visit Biomedical Optics Express.
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Biomedical Optics Express
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Speckle contrast optical spectroscopy for cuffless blood pressure estimation based on microvascular blood flow and volume oscillations