An Optical Neuro-monitor of Cerebral Oxygen Metabolism and Blood Flow for Neonatology

Overview

Feasibility trial on the use of a hybrid optical device integrating time-resolved near-infrared spectroscopy (TRS) and diffuse correlation spectroscopy (DCS) for measurement of cerebral oxygen metabolism and blood flow in neonates. The device wil be tested in four settings measuring: 1. Changes in cerebral oxygenation and haemodynamics after birth 2. precision and repeatability 3. The cerebral vaso-reactivity to arterial carbon dioxide 4. Assessment of the user-friendliness and loss of signal in routine care

The BabyLux project aims to provide a precise, accurate, and robust device to continuously monitor cerebral oxygen metabolism and blood flow in critically ill newborn infants. This will be achieved by combining time resolved near-infrared spectroscopy (TRS) with newly developed diffuse correlation spectroscopy (DCS) in a single device. The innovative aspects of the project are related to the use of advanced solutions, based on state-of-the-art photonic components, which have already been tested in laboratory and clinical tests on adults. Time Resolved Near-infrared spectroscopy and Diffuse Correlation Spectroscopy The proposed solution will integrate two advanced photonic techniques, TRS and DCS. Both techniques rely on the use of an optical fibre probe (sensor) to illuminate with very low power near-infrared light the scalp and to collect the diffusively reflected optical signal that has propagated through the scalp and skull, and therefore carries information on the deeper cortical region. The different absorption spectra of oxygenated and deoxygenated haemoglobin in the near-infrared range allows for the non-invasive monitoring of the two species in the cortical tissue. TRS and DCS prototypes are available and have been technically tested in laboratory settings and successfully validated during preclinical trials on adult volunteers and patients. Measured TRS/DCS parameters TRS measures the attenuation and the temporal broadening of relatively short light pulses (pulse duration \~100 ps) through a diffusive medium (e.g. a neonate's head). TRS has the ability to resolve path-lengths (or equivalently time-of-flights) of photons that have propagated through the tissues. This enables TRS to separate the absorption and scattering coefficients allowing for absolute measurements, and to utilize time-gating of path-lengths to emphasize signals from deeper tissues. This is particularly important for separating intra- and extra-cerebral signals for brain monitoring. DCS relies on the fact that temporal correlation of light fields in turbid media also obeys a diffusion equation, albeit a slightly different one than is used for TRS. Thus DCS shares the light penetration advantages of TRS, but, since DCS explicitly measures red blood cell movement, it provides a direct measure of quantities such as cerebral blood flow (CBF). The specific combination of DCS and TRS allows for the assessment of cerebral oxygen metabolism and CBF in a complete (i.e. CBF and oxygenation are simultaneously and independently provided), accurate (i.e. based on absolute measurements of optical parameters) and robust (i.e. potentially less affected by artefacts related to superficial systemic activity or sensor/head movements) way. The aim of this study is to perform clinical measurements using the BabyLux instrument in different clinical real-life settings to validate this new technology in terms of feasibility, repeatability of measurements, and user friendliness in neonatal medicine. The BabyLux system is tested in four different real-life settings to measure: 1. The increase in oxygenation and change in blood flow during the minutes after birth to specify the expected range of measurement; 2. The precision and repeatability of measurements by reapplying the NIRS sensor several times on slightly different sites of the head in a relatively steady condition; 3. The cerebral vaso-reactivity to arterial carbon dioxide tension in mechanically ventilated newborns to monitor induced changes in cerebral blood flow; 4. The user-friendliness and loss of signal in routine care situations (e.g. during 24-hour monitoring of neonates undergoing intensive care).

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