InSiDe project applies laser vibrometry to cardiovascular disease

26 Mar 2025

Development of silicon photonics-based device moves on to clinical feasibility studies.

The InSiDe project, an EU-funded effort to improve diagnosis of early stage cardiovascular disease (CVD), has concluded its five-year research program.

Coordinated by imec via its associated Photonics Research Group at Ghent University, InSiDe aimed to create a hand-held device based around silicon photonics, capable of identifying different stages of CVDs.

At present CVDs account for 31 percent of all global deaths, according to imec, so early identification of individuals at risk and intervention to halt or reverse the pathological process would help meet a significant healthcare challenge.

"Arterial stiffness is an early marker for hypertension and can be used to guide treatment in individuals with elevated blood pressure and intermediate CV risk," commented the project.

"Early identification of arterial stenosis, valvular disease and heart desynchrony can improve CVD risk classification. However, no tools are available today to screen a large population under primary care for these indicators, and individuals that are considered to be at intermediate risk are too often undiagnosed."

As described at the project's launch in 2020, InSiDe builds on the work of Cardis, an earlier European project that demonstrated the concept of a mobile, low-cost laser vibrometry platform with integrated silicon photonics and validated the concept for the screening of arterial stiffness, detection of stenosis and heart failure.

Silicon photonics was a core technology for the project, allowing the implementation of advanced optical functionality in a chip produced in a CMOS fab environment, according to project partner Tyndall National Institute.

A clinical device accepted by all patients

The InSiDe device employs multi-beam laser Doppler vibrometry (LDV), measuring the phase and frequency change of laser light reflected from a target. If the target is moving, especially vibrating, the phase/frequency of the reflection beam will vary as a result of the Doppler effect.

This offers a route to detecting cardiac dysfunction via arterial stiffness. A low-power laser beam is directed towards the skin overlying an artery, and the skin's vibration amplitude and frequency arising from the heartbeat are extracted from the Doppler shift of the reflected beam. Algorithms can then automatically assess the stiffness parameters of interest.

No reflective patch on the skin is needed for the analysis in this method, a simplification described by the team as a gamechanger for clinicians and paving the way for a user-friendly device accepted by the medical community.

"The multi-beam interferometer, except from the laser source and focusing lens, will be realized in a silicon chip," commented the project. "Thanks to the CMOS-compatible fabrication process, we can implement a multi-beam LDV system in a compact device, enabling simultaneous measurements at multiple locations, eliminating the need for complex mechanical scanning."

The final evolution of the InSiDe platform includes a main and a secondary device, each having 4 sensing beams. This architecture can then be used for local stenosis and cardiac contraction measurements via only the main device, or for synchronized pulse wave measurements to derive carotid-femoral pulse wave velocity if both devices are employed.

The InSiDe instrument has now been employed in clinical feasibility studies in France and the Netherlands for assessing cardiac contraction, carotid artery stenosis, therapy adherence in patients with resistant hypertension, cardiac valve dysfunction, as well as the effect of COVID-19 infection.

"Feasibility of signal acquisition is good, the time to get useful signals was less than 10 minutes, and patients barely noticed that a measurement was performed," commented Frits Prinzen from Maastricht University.