Hybrid interferometric near infrared spectroscopy (hybrid iNIRS) enables time-of-flight–resolved non-invasive blood flow monitoring in humans in vivo 

Hybrid interferometric near infrared spectroscopy (hybrid iNIRS) enables time-of-flight–resolved non-invasive blood flow monitoring in humans in vivo | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Hybrid interferometric near infrared spectroscopy (hybrid iNIRS) enables time-of-flight–resolved non-invasive blood flow monitoring in humans in vivo Marcin Marzejon, Dawid Borycki This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8492157/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract Interferometric near-infrared spectroscopy (iNIRS) uniquely offers time-of-flight (TOF) resolution for depth-resolved optical property and blood-flow assessment in tissue, but single-mode collection constrains photon throughput and single-channel implementations impose stringent analog bandwidth and digitization rates to resolve both TOF and speckle dynamics. Conversely, continuous-wave parallel interferometric NIRS (CW-πNIRS) boosts photon detection via spatial multiplexing on camera sensors, yet sacrifices TOF information and remains limited by camera readout. Here we reconcile these trade-offs with a hybrid swept-source, hybrid iNIRS platform that combines TOF encoding with multi-speckle, heterodyne detection. Liquid-phantom experiments map the trade-space among sweep speed, and speckle decorrelation, indicating that sweep rates ≥10 kHz are required to outpace decorrelation while preserving TOF contrast. In vivo forearm and forehead measurements demonstrate depth-resolved blood flow measurements during cuff occlusion. By simultaneously overcoming photon-starvation and electronic-bandwidth ceilings, this approach establishes a new operating regime for diffuse optical monitoring and provides a scalable hardware foundation for haemodynamic sensing in vivo . Physical sciences/Optics and photonics Physical sciences/Physics Full Text Additional Declarations No competing interests reported. Supplementary Files SupplementaryInformation.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 01 Mar, 2026 Reviews received at journal 13 Feb, 2026 Reviews received at journal 17 Jan, 2026 Reviewers agreed at journal 08 Jan, 2026 Reviewers agreed at journal 06 Jan, 2026 Reviewers invited by journal 06 Jan, 2026 Editor invited by journal 06 Jan, 2026 Editor assigned by journal 04 Jan, 2026 Submission checks completed at journal 04 Jan, 2026 First submitted to journal 31 Dec, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8492157","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":570419514,"identity":"d58b004c-d583-46a8-aa52-60841b6d33e9","order_by":0,"name":"Marcin Marzejon","email":"","orcid":"","institution":"Institute of Physical Chemistry, Polish Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Marcin","middleName":"","lastName":"Marzejon","suffix":""},{"id":570419515,"identity":"dee2e4b7-2adf-4b6b-b98e-133bc997965c","order_by":1,"name":"Dawid 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Conversely, continuous-wave parallel interferometric NIRS (CW-πNIRS) boosts photon detection via spatial multiplexing on camera sensors, yet sacrifices TOF information and remains limited by camera readout. Here we reconcile these trade-offs with a hybrid swept-source, hybrid iNIRS platform that combines TOF encoding with multi-speckle, heterodyne detection. Liquid-phantom experiments map the trade-space among sweep speed, and speckle decorrelation, indicating that sweep rates ≥10 kHz are required to outpace decorrelation while preserving TOF contrast. \u003cem\u003eIn vivo \u003c/em\u003eforearm and forehead measurements demonstrate depth-resolved blood flow measurements during cuff occlusion. 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