Abstract
Tissue oximetry with near-infrared spectroscopy (NIRS) is a technique for the measurement of absolute tissue oxygen saturation (StO2). Offering a real-time and non-invasive assessment of brain oxygenation and haemodynamics, StO2 has potential to be used for the assessment of newborn brain injury. Multiple algorithms have been developed to measure StO2, however, issues with low measurement accuracy or extracranial tissue signal contamination remain. In this work, we present a novel algorithm to recover StO2 in the neonate, broadband multidistance oximetry (BRUNO), based on a measurement of the gradient of attenuation against distance measured with broadband NIRS. The performance of the algorithm was compared to two other published algorithms, broadband fitting (BF) and spatially resolved spectroscopy (SRS). The median error when recovering StO2 in light transport simulations on a neonatal head mesh was 0.4% with BRUNO, 4.2% with BF and 9.5% with SRS. BRUNO was more sensitive to brain tissue oxygenation changes, shown in layered head model simulations. Comparison of algorithm performance during full oxygenation-deoxygenation cycles in a homogeneous dynamic blood phantom showed significant differences in the dynamic range of the algorithms; BRUNO recovered StO2 over 0–100%, BF over 0–90% and SRS over 39–80%. Recovering StO2 from data collected in a neonate treated at the neonatal intensive care showed different baseline values; mean StO2 was 64.9% with BRUNO, 67.2% with BF and 73.2% with SRS. These findings highlight the effect of StO2 algorithm selection on oxygenation recovery; applying BRUNO in the clinical care setting could reveal further insight into complex haemodynamic processes occurring during neonatal brain injury.
Highlights
Tissue oximetry with near-infrared spectroscopy (NIRS) is a non-invasive technique for assessing tissue oxygenation and haemodynamics through the measurement of tissue oxygen saturation StO2
Model 1 was homogeneous; the true oxygenation was equal to grey matter (GM); models 2 and 3 were heterogeneous and the truth was expected to be an average of GM and white matter (WM) oxygenation
The algorithm was applied to three types of NIRS data; spectra obtained in NIRFAST simulations in a layered neonatal head mesh, measurements in a dynamic optical phantom and a neonate with hypoxic-ischaemic encephalopathy (HIE) treated at the NICU
Summary
Tissue oximetry with near-infrared spectroscopy (NIRS) is a non-invasive technique for assessing tissue oxygenation and haemodynamics through the measurement of tissue oxygen saturation StO2. The absorption of light in tissue in the near-infrared region (650–900nm) is dominated by oxygenated haemoglobin (HbO2) and deoxygenated haemoglobin (HHb), whose concentrations can be quantified using NIRS. Cerebral tissue oximetry can be used in various settings in the hospital including the intensive care unit, during cardiac surgery, anaesthesia or in brain injury management. One area of significant interest is the use in the neonatal intensive care (NICU) for assessment of neonatal brain injury in term [1] or in preterm infants [2]. Despite the ongoing research efforts to demonstrate benefits of tissue oximetry in neonatal intensive care, including clinical trials like SafeBooosC [2], a lack of consistency among instrumentation makes associating tissue oximetry with clinical outcomes challenging [4]
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