Dynamic physiological temperature and pressure sensing with phase-resolved low-coherence interferometry

Abstract

We report the development and characterisation of highly miniaturised fibre-optic sensors for simultaneous pressure and temperature measurement, and a compact interrogation system with a high sampling rate. The sensors, which have a maximum diameter of 250 µm, are based on multiple low-finesse optical cavities formed from polydimethylsiloxane (PDMS), positioned at the distal ends of optical fibres, and interrogated using phase-resolved low-coherence interferometry. At acquisition rates of 250 Hz, temperature and pressure changes of 0.0021 °C and 0.22 mmHg are detectable. An in vivo experiment demonstrated that the sensors had sufficient speed and sensitivity for monitoring dynamic physiological pressure waveforms. These sensors are ideally suited to various applications in minimally invasive surgery, where diminutive lateral dimensions, high sensitivity and low manufacturing complexities are particularly valuable.

Optical interferometric temperature sensors for intravascular blood flow measurements

“…Fourier transforms were performed on interferograms acquired by the spectrometer, and the complex components corresponding to the length of the etalon were selected. Changes in the optical path length of the dome were linearly related to the change in the unwrapped argument of the complex phase 10,12 . A secondary optical fibre delivered light for pulsed upstream thermal tagging (pulse duration 0.4 s; power: 1 W).…”

“…When the dome experiences an external temperature change, its optical path length increases. This change in optical path length can then be related to a change in temperature 10 . Temperature measurements were performed using phase-resolved spectral-domain low coherence interferometry (SD-LCI) 11 , a method which continuously interrogates the changes in the length of the dome with nanometre-scale resolution.…”

“…The SD-LCI system, shown in Figure 1, includes a broadband single-mode laser source centred at 1550 nm. A commonpath interferometer was formed from the etalon comprising the distal end of the fibre and the outer surface of the PDMS dome, as previously described by Coote et al 10 . Fourier transforms were performed on interferograms acquired by the spectrometer, and the complex components corresponding to the length of the etalon were selected.…”

Dynamic Characterisation of Fibre-Optic Temperature Sensors for Physiological Monitoring

“…Many of the aforementioned techniques are performed as minimally invasive interventional procedures, in which highly miniaturised and flexible sensors are needed for integration into catheters, needles and guidewires. Fibre-optics can readily meet these requirements, and fibre-optic temperature sensing approaches include fibre Bragg gratings (FBG) and long period fibre gratings (LPFG) [ 32 , 33 , 34 , 35 , 36 , 37 ]; polymer-based [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ], inorganic [ 48 , 49 , 50 ] and microbubble-based [ 51 ] Fabry–Pérot (FP) cavities; multimode interference (MMI) segments [ 52 , 53 , 54 , 55 , 56 , 57 , 58 ]; infiltrated photonic crystal fibre and hollow-core fibre [ 59 , 60 ]; fluorescence-based methods [ 22 , 23 , 24 ]; and sensors based on polymer optical fibres [ 61 , 62 , 63 , 64 ]. The wide variety of geometries and materials employed in these sensors can lead to very different response times, from sub-millisecond for a silicon FP cavity [ 50 ] to hundreds of milliseconds for packaged FBGs [ 18 , 36 ].…”

“…Although polymer FP cavity-based fibre-optic temperature sensors have been investigated [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ], many of these studies have not considered the response of the sensors to rapid, dynamic temperature changes. Characterising the dynamic response can be challenging: a common method is to rapidly immerse the sensor into water at a different temperature to the ambient room temperature, providing temperature step input [ 17 , 18 , 35 , 36 , 50 ].…”