Validation of a Hyperspectral NIRS Method for Measuring Tissue Oxygen Saturation

Brain injury during preterm infancy can cause serious intellectual and behavioral disabilities, as such, measurements of cerebral health are needed to aid in the diagnosis and treatment of these injuries. Near infrared spectroscopy (NIRS) is considered ideal for this purpose because it is non-invasive and provides a continuous measure of tissue oxygen saturation (StO2), a key marker of cerebral health. Current commercial NIRS systems have considerable variability between devices and between infants restricting them to monitoring trends. Time-resolved (TR) NIRS is considered the gold standard in biomedical optics for quantifying tissue optical properties, but the technology is more complex and has struggled with integration into clinical settings. As an inexpensive alternative, the present study investigated using a hyperspectral NIRS (H-NIRS) method to quantify StO2. Experiments were conducted using newborn piglets and StO2 measured at different oxygenation levels by H-NIRS and by TR-NIRS for validation. Measurements were acquired at step-wise reduction in StO2 caused by reducing the fraction of inspired oxygen. Across eight animals, there was no significant effect between StO2 measurements from the two techniques (F5,35 = 1.591, p \u3e 0.05). The strong agreement (R2 = 0.95) in the StO2 measurements suggests that H-NIRS is a strong candidate for clinical use considering it is both quantitative and technically simple

Acoustic liner optimisation and noise propagation through turbofan engine intake ducts

The research in this thesis explores the prediction of fan noise propagation through turbofan engine intakes and its radiation to the far-field. The performance of acoustic liners installed in intakes to attenuate noise is the focus of the study. A commercial CAA (Computational AeroAcoustics) code ACTRAN/TM and an in-house shell code ANPRORAD developed at the ISVR are used to predict the performance of acoustic liners throughout the studies presented in this thesis. An automated system for running computations for a large number of cases with different liner impedance and engine operating conditions has been developed and applied for optimising liners for maximum noise benefit. The intake liner configuration of main interest is an intake lip liner. The performance of liners are investigated for broadband and tone noise source components of fan noise. In the study for an intake lip liner, an optimum single layer was identified based on the optimisations. A series of no-flow scale rig tests were conducted in the anechoic chamber at the ISVR and the test data have been appraised by comparing with numerical predictions. Reasonable agreements have been achieved, and the lip liner showed measurable noise benefit. Numerical predictions of a lip liner performance have also been performed for a fan rig intake tested in the presence of flow

Assessing cerebral blood flow, oxygenation and cytochrome c oxidase stability in preterm infants during the first 3 days after birth

A major concern with preterm birth is the risk of neurodevelopmental disability. Poor cerebral circulation leading to periods of hypoxia is believed to play a significant role in the etiology of preterm brain injury, with the first three days of life considered the period when the brain is most vulnerable. This study focused on monitoring cerebral perfusion and metabolism during the first 72 h after birth in preterm infants weighing less than 1500 g. Brain monitoring was performed by combining hyperspectral near-infrared spectroscopy to assess oxygen saturation and the oxidation state of cytochrome c oxidase (oxCCO), with diffuse correlation spectroscopy to monitor cerebral blood flow (CBF). In seven of eight patients, oxCCO remained independent of CBF, indicating adequate oxygen delivery despite any fluctuations in cerebral hemodynamics. In the remaining infant, a significant correlation between CBF and oxCCO was found during the monitoring periods on days 1 and 3. This infant also had the lowest baseline CBF, suggesting the impact of CBF instabilities on metabolism depends on the level of blood supply to the brain. In summary, this study demonstrated for the first time how continuous perfusion and metabolic monitoring can be achieved, opening the possibility to investigate if CBF/oxCCO monitoring could help identify preterm infants at risk of brain injury

Perfusion and Metabolic Neuromonitoring during Ventricular Taps in Infants with Post-Hemorrhagic Ventricular Dilatation.

Post-hemorrhagic ventricular dilatation (PHVD) is characterized by a build-up of cerebral spinal fluid (CSF) in the ventricles, which increases intracranial pressure and compresses brain tissue. Clinical interventions (i.e., ventricular taps, VT) work to mitigate these complications through CSF drainage; however, the timing of these procedures remains imprecise. This study presents Neonatal NeuroMonitor (NNeMo), a portable optical device that combines broadband near-infrared spectroscopy (B-NIRS) and diffuse correlation spectroscopy (DCS) to provide simultaneous assessments of cerebral blood flow (CBF), tissue saturation (

Liner optimisation for turbofan ducts - towards a fully automated procedure

Validated computational methods exist which can predict sound propagation and absorption in turbofan intake and bypass ducts. In this article, the practicability of embedding such methods within automated and semi-automated liner optimisation schemes for realistic nacelle geometries, liner definitions and noise source spectra is investigated. Two different strategies are used to demonstrate the feasibility of applying such an approach to intake liner optimisation

Hybrid broadband NIRS/Diffuse correlation spectroscopy system for simultaneous monitoring of cerebral perfusion and cytochrome c oxidase

© OSA 2018. This article reports on the development and demonstration of a novel optical system combining broadband near-infrared spectroscopy and diffuse correlation spectroscopy to provide simultaneous acquisition of cerebral perfusion and cytochrome c oxidase

Evaluation of hyperspectral NIRS for quantitative measurements of tissue oxygen saturation by comparison to time-resolved NIRS

© 2019 Optical Society of America. Near-infrared spectroscopy (NIRS) is considered ideal for brain monitoring during preterm infancy because it is non-invasive and provides a continuous measure of tissue oxygen saturation (StO2). Hyperspectral NIRS (HS NIRS) is an inexpensive, quantitative modality that can measure tissue optical properties and oxygen saturation (StO2) by differential spectroscopy. In this study, experiments were conducted using newborn piglets to measure StO2 across a range of oxygenation levels from hyperoxia to hypoxia by HS and time-resolved (TR) NIRS for validation. A strong correlation between StO2 measurements from the two techniques was observed (R2 = 0.98, average slope of 1.02 ± 0.28); however, the HS-NIRS estimates were significantly higher than the corresponding TR-NIRS values. These regression results indicate that HS NIRS could become a clinically feasible method for monitoring StO2 in preterm infants

Simultaneous monitoring of cerebral perfusion and cytochrome c oxidase by combining broadband near-infrared spectroscopy and diffuse correlation spectroscopy

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement. Preterm infants born with very low birth weights are at a high risk of brain injury, in part because the premature brain is believed to be prone to periods of low cerebral blood flow (CBF). Tissue damage is likely to occur if reduction in CBF is sufficient to impair cerebral energy metabolism for extended periods. Therefore, a neuromonitoring method that can detect reductions in CBF, large enough to affect metabolism, could alert the neonatal intensive care team before injury occurs. In this report, we present the development of an optical system that combines diffuse correlation spectroscopy (DCS) for monitoring CBF and broadband near-infrared spectroscopy (B-NIRS) for monitoring the oxidation state of cytochrome c oxidase (oxCCO) – a key biomarker of oxidative metabolism. The hybrid instrument includes a multiplexing system to enable concomitant DCS and B-NIRS measurements while avoiding crosstalk between the two subsystems. The ability of the instrument to monitor dynamic changes in CBF and oxCCO was demonstrated in a piglet model of neonatal hypoxia-ischemia (HI). Experiments conducted in eight animals, including two controls, showed that oxCCO exhibited a delayed response to ischemia while CBF and tissue oxygenation (StO2) responses were instantaneous. These findings suggest that simultaneous neuromonitoring of perfusion and metabolism could provide critical information regarding clinically significant hemodynamic events prior to the onset of brain injury

Multimodal measurements of brain tissue metabolism and perfusion in a neonatal model of hypoxic-ischaemic injury

© 2019 SPIE. This is the first multimodal study of cerebral tissue metabolism and perfusion post-hypoxic-ischaemic (HI) brain injury with broadband near-infrared spectroscopy (bNIRS), diffuse correlation spectroscopy (DCS), positron emission tomography (PET) and magnetic resonance spectroscopy (MRS). In 5 piglet models of HI, we measured cerebral tissue saturation (StO2), cerebral blood flow (CBF), cerebral oxygen metabolism (CMRO2), changes in the mitochondrial oxidation state of cytochrome-c-oxidase (oxCCO), cerebral glucose metabolism (CMRglc), and tissue biochemistry (Lac+Thr/tNAA). At baseline, the parameters measured were: 64±6 % StO2, 35±11 ml/100g/min CBF, and 2.0±0.4 μmol/100g/min CMRO2. After HI the parameters measured were: 68±6% StO2, 35±6 ml/100g/min CBF, 1.3±0.1 μmol/100g/min CMRO2, 0.4±0.2 Lac+Thr/tNAA, and 9.5±2.0 CMRglc. This study demonstrates the capacity of a multimodal set up to interrogate the pathophysiology of HIE using a combination of optical methods, MRS, and PET