Flow-controlled air-jet for in vivo quasi steady-state and dynamic elastography with MHz optical coherence tomography

Objective: Optical coherence elastography (OCE) has been introduced for several medical applications to determine tissue mechanical parameters. However, in order to measure sensitive healthy tissue like brain in vivo, the excitation force needs to be carefully controlled and as low as possible (under 100 μN). Preferably, the excitation should be applied in a non-contact manner. Methods: In this work, an air-jet excitation source for this specific purpose has been developed and characterized. The design focus was set on the exact measurement and control of the generated excitation force to better comply with in vivo medical safety requirements during surgery. Results: Therefore, an excitation force control and measurement system based on the applied gas flow was developed. Conclusion: This system can generate short, high dynamic air-puffs lasting fewer than 5 ms, as well as quasi-static excitation forces lasting 700 ms. The force range covers 1μN to 40 mN with a force error margin between 0.1% and 16% in the relevant range. The excitation source, in conjunction with a 3.2 MHz optical coherence system, enables phase-based, dynamic, and quasi steady-state elastography, as well as robust non-contact classical indentation measurements. Significance: The presented system is a preliminary prototype intended for further development into a clinical version to be used in situ during brain tumor surgery.