Soto Astorga, RDP; (2015) Haemoglobin sensing with optical spectroscopy during minimally invasive procedures. Doctoral thesis , UCL (University College London).

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Abstract

Many clinical procedures involve the use of minimally invasive devices such as needles and catheters. Providing increased information about tissues that are adjacent to the device tips could reduce the probability of complications in these procedures. Optical fibres are well suited for integration into medical devices and they can be used to provide information relevant to tissue characterisation. This dissertation is centred on the integration of optical fibres into needles and catheters to obtain information about haemoglobin. In two studies, reflectance spectroscopy was performed. Two optical fibre geometries were tested, and for each, Monte Carlo simulations were used to estimate the reflectance values and the pho- ton penetration depths. In the first study, reflectance spectroscopy was performed with a double clad fibre. Experiments using expired human red blood cells were performed to determine the sensitivity of the measurements to oxygen saturation variation at physiological levels. Distinction between normal oxygen saturation values in veins and arteries was possible, making this fibre potentially useful to verify needle placement during a venous catheterisation or during a transseptal puncture. In the second study, two polymer optical light fibres were directly integrated into an epidural catheter. This optical catheter was tested during an ex-vivo swine laminectomy in the lumbar region. Another ex-vivo experiment was performed on chicken wings to discern blood vessels from other tissues. This information could be used during anaesthesic procedures to reduce the risk of toxicity from an intravascular injection. With reflectance spectroscopy, the depth in tissue from which signal is obtained is limited by the inter-fibre distance. This limitation motivated a third study, in which photoacoustic imaging was used to obtain image contrast for haemoglobin. The results of the three studies suggest that the integration of optical fibres into medical devices during minimally invasive procedures can allow for clinically relevant measurements of tissue properties in real-time.

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