Abstract
Small form-factor sensors are widely used in minimally invasive intravascular diagnostic procedures. Manufacturing complexities associated with miniaturizing current fiber-optic probes, particularly for multi-parameter sensing, severely constrain their adoption outside of niche fields. It is especially challenging to rapidly prototype and iterate upon sensor designs to optimize performance for medical devices. In this work, a novel technique to construct a microscale extrinsic fiber-optic sensor with a confined air cavity and sub-micron geometric resolution is presented. The confined air cavity is enclosed between a 3 μm thick pressure-sensitive distal diaphragm and a proximal temperature-sensitive plano-convex microlens segment unresponsive to changes in external pressure. Simultaneous pressure and temperature measurements are possible through optical interrogation via phase-resolved low-coherence interferometry (LCI). Upon characterization in a simulated intravascular environment, we find these sensors capable of detecting pressure changes down to 0.11 mmHg (in the range of 760 to 1060 mmHg) and temperature changes of 0.036 °C (in the range 34 to 50 °C). By virtue of these sensitivity values suited to intravascular physiological monitoring, and the scope of design flexibility enabled by the precision-fabricated photoresist microstructure, it is envisaged that this technique will enable construction of a wide range of fiber-optic sensors for guiding minimally invasive medical procedures.
Highlights
M INIATURE minimally-invasive sensors allow for fine spatial resolution and targeted point measurements at critical sites, for biomedical diagnostics [1], [2]
This multi-cavity design was further modified with the aim of improving detection sensitivity and reducing the superluminescent diode (SLD) illumination power required for low-coherence interferometry (LCI) interrogation (see Fig. 1(d) and MATERIALS AND METHODS section)
It was observed in raytracing simulations that the beam spot at the outer surface of the deformable diaphragm was found to diverge significantly more in Sref compared to Slensed., yielding an almost 4-fold larger beam spot irradiance area with Sref
Summary
M INIATURE minimally-invasive sensors allow for fine spatial resolution and targeted point measurements at critical sites, for biomedical diagnostics [1], [2]. Fiber-optic pressure and temperature sensors comprise one or more responsive optical cavities that are interferometrically interrogated to measure corresponding deflections Such probes can be formed by affixing an optical cavity structure consisting of a deformable diaphragm extrinsic to a waveguiding optical fiber. The presence of low-reflectance deformable polymer interfaces forming lowfinesse cavities presents a challenge in obtaining adequate signal to noise ratio (SNR) at low optical illumination in interferometric sensing probes We have overcome these challenges through a combination of freeform 3D multi-cavity sensor design, optical path raytracing, TPP and single-step microstructure bonding to an SM optical fiber. Optical path length changes of the low-finesse cavities in these sensors were interrogated by phase-resolved lowcoherence interferometry (LCI) We characterized these devices to evaluate their structural design fidelity and application potential for sensing pressure and temperature changes in the range of minimally invasive interventions in a simulated intravascular environment
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