While a non-invasive capacitive sensing technique to detect carotid artery stenosis is a promising research area, there is currently no evidence of it being used as a clinically validated diagnostic tool. The current gold standard for non-invasive screening remains duplex ultrasound.

The theoretical foundation for using capacitive sensing is based on the idea that stenosis-induced changes in blood flow and arterial wall stiffness could be detected as measurable differences in electrical capacitance.

Potential of capacitive sensing for carotid stenosis detection

• Sensing principle: Capacitive sensors measure changes in capacitance, which could correspond to subtle variations in blood volume and vessel wall movement during each heartbeat.
• Pulse waveform analysis: Researchers have developed capacitive patches to monitor the carotid pulse conveniently. These sensors provide detailed pulse waveforms, and studies are exploring whether distinct waveform characteristics can serve as a predictive tool for cardiovascular diseases.
• Arterial wall stiffness: Capacitive sensors are also being developed to assess arterial stiffness, a risk marker for cardiovascular disease. By measuring changes in arterial wall strain, these sensors could potentially identify the loss of elasticity associated with atherosclerosis and stenosis.
• Implantable devices: While not non-invasive, implantable capacitive sensors have been developed and tested to measure strain directly from arteries in vivo. These studies show a direct link between capacitive changes and arterial properties, demonstrating the underlying potential of the technology.

Challenges for clinical adoption

Several significant challenges must be overcome for non-invasive capacitive sensing to be a reliable method for diagnosing carotid stenosis:

• Signal accuracy: The technique must be able to accurately isolate the signal from the carotid artery itself, differentiating it from surrounding tissues and organs.
• Motion artifacts: The sensitivity of capacitive sensors also makes them vulnerable to motion artifacts from head and neck movements, which can interfere with the signal and produce unreliable readings.
• Sensitivity and specificity: For a diagnostic technique to be clinically viable, it must demonstrate a high degree of sensitivity (correctly identifying those with the condition) and specificity (correctly excluding those without it). Published studies on related waveform analysis techniques have shown mixed results regarding these metrics.
• Quantifying stenosis: Current devices like duplex ultrasound and magnetic resonance angiography (MRA) provide quantitative measurements of the degree of stenosis, which is critical for treatment decisions. A non-invasive capacitive technique would need to correlate its readings with the actual degree of narrowing.

Summary of current diagnostic methods

For an effective and accurate non-invasive diagnosis, healthcare providers currently rely on these methods:

• Duplex ultrasound: The most common and important non-invasive test for diagnosing carotid artery disease. It provides images of the vessels and measures blood flow and velocity.
• Computed tomography angiography (CTA) and MRA: These are used to confirm the degree of stenosis and plan surgical intervention, especially when ultrasound is limited.
• Video-based motion analysis (VMA): A new, non-contact technique that uses a video of the neck to analyze skin-surface pulses. It has shown promise as a screening tool but is not a definitive diagnostic test.