Functional Optical Topography Analysis Using Statistical Parametric Mapping (SPM) Methodology with and without Physiological Confounds

Functional optical topography (OT) measures the changes in oxygenated and deoxygenated hemoglobin (HbO(2), HHb) across multiple brain sites which occur in response to neuronal activation of the cerebral cortex. However, identification of areas of cortical activation is a complex task due to intrinsic physiological noise and systemic interference and careful statistical analysis is therefore required. A total of 10 young healthy adults were studied. The activation paradigm comprised of anagrams followed by finger tapping. 12 channels of the OT system were positioned over the frontal cortex and 12 channels over the motor cortex while the systemic physiology (mean blood pressure (MBP), heart rate (HR), scalp flux) was simultaneously monitored. Analysis was done using the functional Optical Signal Analysis (fOSA) software and Statistical Parametric Mapping (SPM), where we utilized two approaches: (i) using only HbO(2) as a regressor in the general linear model (GLM) and (ii) using all of the explanatory variables (HbO(2), MBP, HR and scalp flux) as regressors. Group analysis using SPM showed significant correlation in a large number of OT channels between HbO(2) and systemic regressors; however no differences in activation areas were seen between the two approaches

Investigation of frontal lobe activation with fNIRS and systemic changes during video gaming.

Frontal lobe activation caused by tasks such as videogames can be investigated using multichannel near-infrared spectroscopy (fNIRS), sometimes called optical topography. The aims of this study are to investigate the effects of video gaming (fighting and puzzle games) in the brain and the systemic physiology and to determine whether systemic responses during the gaming task are associated with the measurement of localised cerebral haemodynamic changes as measured by fNIRS. We used a continuous-wave 8-channel fNIRS system to measure the changes in concentration of oxy-haemoglobin (HbO2) and deoxy-haemoglobin (HHb) and changes in total haemoglobin (ΔtHb = ΔHbO2 + ΔHHb) over the frontal lobe in 30 healthy volunteers. The Portapres system was used to measure mean blood pressure (MBP) and heart rate (HR), and a laser Doppler was employed to measure the changes in scalp blood flow (or flux). Even though we observed significant changes in systemic variables during gaming, in particular in scalp flow, we also managed to see localised activation patterns over the frontal polar (FP1) region. However, in some channels over the frontal lobe, we also observed significant correlations between the HbO2 and systemic variables

False positives and false negatives in functional near-infrared spectroscopy: issues, challenges, and the way forward

We highlight a significant problem that needs to be considered and addressed when performing functional near-infrared spectroscopy (fNIRS) studies, namely the possibility of inadvertently measuring fNIRS hemodynamic responses that are not due to neurovascular coupling. These can be misinterpreted as brain activity, i.e., "false positives" (errors caused by wrongly assigning a detected hemodynamic response to functional brain activity), or mask brain activity, i.e., "false negatives" (errors caused by wrongly assigning a not observed hemodynamic response in the presence of functional brain activity). Here, we summarize the possible physiological origins of these issues and suggest ways to avoid and remove them

Cerebral and Peripheral Tissue Oxygenation in Children Supported on ECMO for Cardio-Respiratory Failure

Extracorporeal membrane oxygenation (ECMO) is a rescue therapy for patients with cardio-respiratory failure. Establishing, maintaining and weaning from ECMO may increase the risk for intracranial injury. We used a dual channel near infrared system to monitor cerebral and peripheral tissue oxygenation in 3 venoarterial (VA) and 1 venovenous (VV) ECMO patients undergoing manipulations in the ECMO circuit flows. Spectral analysis was performed on the oxyhaemoglobin data collected from these patients with the aim of comparing oscillations at range of frequencies appearing in the two measurement sites

The role of parietal cortex in overimitation: a study with fNIRS

Previous studies have shown right parietal activation in response to observing irrational actions. Behavioural studies show that people sometimes imitate irrational actions, a phenomenon called overimitation. However, limitations on movement in fMRI mean that the neural basis of overimitation has not been studied. To address this, our study employed a less restrictive neuroimaging technique, functional near infrared spectroscopy (fNIRS). Measurements were taken while participants observed either rational or irrational movements before performing movements on a computerised puzzle task. Observing irrational actions produced greater activation in right anterior inferior parietal lobule (aIPL), replicating results from the fMRI literature. This is a proof of principle that fNIRS can be used as an alternative to fMRI in social cognition experiments, and that parietal cortex has a core role in responding to irrational actions

Hyperspectral imaging solutions for brain tissue metabolic and hemodynamic monitoring: past, current and future developments

Hyperspectral imaging (HSI) technologies have been used extensively in medical research, targeting various biological phenomena and multiple tissue types. Their high spectral resolution over a wide range of wavelengths enables acquisition of spatial information corresponding to different light-interacting biological compounds. This review focuses on the application of HSI to monitor brain tissue metabolism and hemodynamics in life sciences. Different approaches involving HSI have been investigated to assess and quantify cerebral activity, mainly focusing on: (1) mapping tissue oxygen delivery through measurement of changes in oxygenated (HbO₂) and deoxygenated (HHb) hemoglobin; and (2) the assessment of the cerebral metabolic rate of oxygen (CMRO₂) to estimate oxygen consumption by brain tissue. Finally, we introduce future perspectives of HSI of brain metabolism, including its potential use for imaging optical signals from molecules directly involved in cellular energy production. HSI solutions can provide remarkable insight in understanding cerebral tissue metabolism and oxygenation, aiding investigation on brain tissue physiological processes

A Hybrid Multi-Distance Phase and Broadband Spatially Resolved Spectrometer and Algorithm for Resolving Absolute Concentrations of Chromophores in the Near-Infrared Light Spectrum

For resolving absolute concentration of tissue chromophores in the human adult brain with near-infrared spectroscopy it is necessary to calculate the light scattering and absorption, at multiple wavelengths with some depth resolution. To achieve this we propose an instrumentation configuration that combines multi-distance frequency and broadband spectrometers to quantify chromophores in turbid media by using a hybrid spatially resolved algorithm. Preliminary results in solid phantoms as well as liquid dynamic homogeneous and inhomogeneous phantoms and in-vivo muscle measurements showed encouraging results

Investigation of in vivo measurement of cerebral cytochrome-c-oxidase redox changes using near-infrared spectroscopy in patients with orthostatic hypotension

We have previously used a continuous four wavelength near infrared spectrometer to measure changes in the cerebral concentrations of oxy- (Δ[HbO2] and deoxy- haemoglobin (Δ[HHb]) during head-up tilt in patients with primary autonomic failure. The measured changes in light attenuation also allow calculation of changes in the concentration of oxidised cytochrome c oxidase (Δ[oxCCO]), and this paper analyses the Δ[oxCCO] during the severe episodes of orthostatic hypotension produced by this experimental protocol. We studied 12 patients during a passive change in position from supine to a 60º head-up tilt. The challenge caused a reduction in mean blood pressure of 59.93 (±26.12) mmHg (Mean (±SD), p<0.0001), which was associated with a reduction in the total concentration of haemoglobin (Δ[HbT]= Δ[HbO2]+Δ[HHb]) of 5.02 (±3.81) μM (p<0.0001) and a reduction in the haemoglobin difference concentration (Δ[Hbdiff]= Δ[HbO2]-Δ[HHb]) of 14.4 (±6.73) μM (p<0.0001). We observed a wide range of responses in Δ[oxCCO]. 6 patients demonstrated a drop in Δ[oxCCO] (0.17 ±0.15μM ); 4 patients demonstrated no change (0.01 ±0.12 μM ) and 2 patients showed an increase in Δ[oxCCO] (0.21 ±0.01 μM ). Investigation of the association between the changes in concentrations of haemoglobin species and the Δ[oxCCO] for each patient show a range of relationships. This suggests that a simple mechanism for crosstalk, which might produce artefactual changes in [oxCCO], is not present between the haemoglobin and the oxCCO NIRS signals. Further investigation is required to determine the clinical significance of the changes in [oxCCO]

Analysis of the Changes in the Oxidation of Brain Tissue Cytochrome-c-Oxidase in Traumatic Brain Injury Patients during Hypercapnoea A Broadband NIRS Study

Using broadband near-infrared spectroscopy (NIRS) and cerebral micro-dialysis (MD), we investigated cerebral cellular metabolism and mitochondrial redox states, following hypercapnoea in 6 patients with traumatic brain injury (TBI). In all patients hypercapnoea increased intracranial pressure and cerebral blood flow velocity measured with transcranial Doppler. Despite the likely increase in cerebral oxygen delivery, we did not see an increase in the oxidation status of cytochrome-c-oxidase [oxCCO] in every patient. Analysis of the NIRS data demonstrated two patterns of the changes; Group A (n = 4) showed an increase in [oxCCO] of 0.34(+/-0.34)mu M and Group B (n = 2) a decrease of 0.40(+/- 0.41)mu M. Although no obvious association was seen between the Delta[oxCCO] and the MD, measured changes in lactate and pyruvate concentrations. Further work using model informed data interpretation may be helpful in understanding the multimodal signals acquired in this heterogeneous patient group

MAESTROS: A multi-wavelength time domain NIRS system to monitor changes in oxygenation and oxidation state of cytochrome-c-oxidase

CCBY We present a multi-wavelength, multi-channel, time domain near-infrared spectroscopy (NIRS) system named MAESTROS. This instrument can measure absorption and scattering coefficients and can quantify the concentrations of oxy- and deoxy-haemoglobin ([HbO2] , [HHb]), and oxidation state of cytochrome-c-oxidase ([oxCCO] ). This system is composed of a supercontinuum laser source coupled with two acousto-optic tuneable filters (AOTF). The light is collected by four photomultipliers tubes (PMT), connected to a router to redirect the signal to a single TCSPC card. The interface between the system and the tissue is based on optical fibres. This arrangement allows us to resolve up to sixteen wavelengths, within the range of 650 to 900 nm, at a sampling rate compatible with the physiology (from 0.5 to 2 Hz). In this paper, we describe the system and assess its performance based on two specifically designed protocols for photon migration instruments, the BIP and nEUROPt protocols, and on a well characterized liquid phantom based on Intralipid and water. Then, the ability to resolve [HbO2], [HHb] and [oxCCO] is demonstrated on a homogeneous liquid phantom, based on blood for [HbO2] , [HHb] and yeast for [oxCCO] . In the future, the system could be used to monitor brain tissue physiology