Abstract
Bioimpedance spectroscopy measurements can be used for tissue characterization. These measurements can be performed in soft tissues by direct contact of a non-invasive probe consisting of two or four electrodes. The amount of force applied by users can be quite different, and the measurements can vary as a result. To compensate for this, we have built an electrical impedance probe (diameter 3.2 mm) with fibre optic contact-force and temperature sensors built in it. The different sensors of the probe were tested individually. The errors in magnitude and phase angle of the probe are <0.9% and <4°, respectively, for a 0.9% NaCl solution. The linear dynamic range of the force sensor was from 0 to 100 grams. An ex-vivo experiment on a section of proximal colon from a guinea-pig was performed. Twenty bioimpedance measurements were taken in a frequency range of 5 kHz to 1 MHz, while simultaneously recording the force applied. For an increase in contact pressure applied to tissue from 0 to 15.4 kPa, the maximum change in resistivity was 33% at 5 kHz and the minimum was 6.6% at 142 kHz. The probe is small enough to be introduced via the instrument port of an endoscope.
Highlights
The variability of readings of a small probe due to the force applied has been demonstrated to be significant in in-vitro studies[8,9]
Fibre optic techniques are suitable for biomedical applications due to the small size, high flexibility and immunity to electromagnetic interference[13,14,15,16]
This paper describes the design, implementation and validation of what appears to be the first probe for bioimpedance measurement with an integrated fibre optic contact-force sensor
Summary
The variability of readings of a small probe (diameter 3.2 mm) due to the force applied has been demonstrated to be significant in in-vitro studies[8,9]. A further issue for electrical sensors for these sort of applications is that the long leads are susceptible to electrical noise and they impose additional hurdles regarding electrical safety. For these reasons, we have explored an alternative option based on fibre optics sensing technology. Fiber Bragg gratings (FBGs) have the advantage of high sensitivity and stability and have been used to measure pressure, strain and temperature[13,17,18,19,20] making them highly suited for this application
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