Embedded Soft Inductive Sensors to Measure Arterial Expansion of Tubular Diameters in Vascular Phantoms

Measuring diameter change in flexible tubular structures embedded in opaque material is challenging. In this article, we present a soft braided coil embedded in an elastomer tube as a method to continuously measure such a change in diameter. By measuring the inductance change in the braided coil, we estimate the instantaneous diameter with a simple inductance model. In applying this method, we demonstrate that diameter waves in a vascular phantom, a model of a radial artery embedded in a viscoelastic wrist structure, can be recorded continuously. Four sensors were made, and their ability to measure physiologically relevant simulated pulse waves was assessed. Several pressure pulse profiles were generated using a precision digital pump. Inductance of the coil was measured simultaneously as the change in diameter was recorded using an optical laser/mirror deflection measurement. One sensor was then embedded in a vascular phantom model of the human wrist. The diameter of the simulated radial artery was recorded via ultrasound and estimated from coil inductance measurements. The diameter estimates from the inductance model corresponded well with the comparator in both experimental setups. We demonstrate that our method is a viable alternative to ultrasound in recording diameter waves in artery models. This opens opportunities in empirical investigations of physiologically interesting fluid-structure interaction. This method can provide new ability to measure diameter changes in tubular systems where access is obstructed.