Continuous-wave Near-infrared Spectroscopy System Research Articles

Movement artefact removal from NIRS signal using multi-channel IMU data

BackgroundThe non-invasive nature of near-infrared spectroscopy (NIRS) makes it a widely accepted method for blood oxygenation measurement in various parts of the human body. One of the main challenges in this method lies in the successful removal of movement artefacts in the detected signal. In this respect, multi-channel inertia measurement unit (IMU) containing accelerometer, gyroscope and magnetometer can be used for better modelling of movement artefact than using accelerometer only, which as a result, movement artefact can be more accurately removed.MethodsA wearable two-channel continuous wave NIRS system, incorporating an IMU sensor which contain accelerometer, gyroscope and magnetometer in it, was developed to record NIRS signal along with the simultaneous recording of movement artefacts related signal using the IMU. Four healthy subjects volunteered in the recording of the NIRS signals. During the recording from the first two subject, movement artefacts were simulated in one of the NIRS channels by tapping the photodiode sensor nearby. The corresponding IMU data for the simulated movement artefacts were used to estimate the artefacts in the corrupted signal by autoregressive with exogenous input method and subtracted from the corrupted signal to remove the artefacts in the NIRS signal. Signal-to-noise ratio (SNR) improvement was used to evaluate the performance of the movement artefacts removal process. The performance of the movement artefacts estimation and removal were compared using accelerometer only, accelerometer and gyroscope, and accelerometer, gyroscope and magnetometer data from IMU sensor to estimate the artefact in NIRS reading. For the remaining two subjects the NIRS signal was recorded by natural movement artefacts impact and the results of artefacts removal was compared using accelerometer only, accelerometer and gyroscope, and accelerometer, gyroscope and magnetometer data from IMU sensor to estimate the artefact in NIRS reading.ResultsThe quantitative and qualitative results revealed that the SNR improvement increases with the number of IMU channels used in the artefacts estimation, and there were approximately 5–11 dB increase in SNR when nine channel IMU data were used rather than using only three channel accelerometer data only. The artefact removal from natural movements also demonstrated that the combination of gyroscope and magnetometer sensors with accelerometer provided better estimation and removal of the movement artefacts, which was revealed by the minimal change of the HbO2 and Hb level before, during and after movement artefacts occurred in the NIRS signal.ConclusionThe movement artefacts in NIRS can be more accurately estimated and removed by using accelerometer, gyroscope and magnetograph signals from an integrated IMU sensor than using accelerometer signal only.

Reduced Deoxyhemoglobin Threshold In The Prefrontal Cortex In Obese vs. Healthy Children

A growing body of evidence suggests that a neural component influences exercise tolerance. During exhaustive exercise, the prefrontal cortex (PFC) has been shown to switch from a steady state of deoxygenated blood levels (HbR) to a state of rapidly increasing HbR preceding exercise termination. We report alterations to the threshold at which HbR changes within obese (Ob) relative to normal-weight (Nw) children. PURPOSE: To compare, in Ob vs Nw children, PFC HbR thresholds in response to incremental exercise, as measured non-invasively with Diffuse Optical Spectroscopy (DOS). METHODS: A DOS probe was placed on the left forehead of 7 Ob children (13 ± 0.3 yrs, 97 ± 0.6 BMI%, 3F) and 12 Nw children (13 ± 0.2 yrs, 44 ± 8.7 BMI%, 10F). DOS measurements of HbR were obtained via a continuous wave near-infrared spectroscopy system (pocket NIRS, Hamamatsu) as the children underwent an incremental exercise test until exhaustion. HbR thresholds were calculated via linear segmented regression. Comparisons were made using one-tailed, independent Student’s t-tests. RESULTS: The HbR threshold occurred in Ob not only at a lower absolute work-rate (watts, W) (82 ± 9 vs.106 ± 8W, p<0.05) as could be expected by a lower aerobic capacity (27 ± 2 vs. 38 ± 2 ml O2/kg/min, p<0.05), but also at a lower % of peak work rate (60 ± 3 vs. 70 ± 3%, p<0.05), suggesting an additional, obesity-related component to this reduction. CONCLUSION: Our cohort of Ob children experienced earlier HbR thresholds in incremental exercise relative to Nw children. Our findings are consistent with the concept that alterations in HbR threshold are related to exercise tolerance, highlighting the PFC’s potential role in the volitional control of exercise termination.NIH NICHD P01HD048721 & UL1 TR000153

Design and Development of Two Channel Portable Near Infrared Spectroscopy System for Studies of Cerebral Oxygenation in Prefrontal Cortex of Human Brain

Functional near infrared spectroscopy is a noninvasive, non harmful, low cost and safe optical technique that can be used to study the functional activities in the human brain. This paper describes the development of two channel Near InfraRed Spectroscopy (NIRS) system and the results of the cerebral oxygenation changes during the different cognitive tasks. The objective of the study is to design, develop a portable non-invasive continuous wave NIRS system with dual wave length for determining the hemoglobin content of the blood chromophores during different activities of the prefrontal cortex of the brain. The two channel NIRS system designed and it was tested with 20 healthy, ie.,15 males and 5 females with an average age group of 21±2.25, they were given a 2 different mental tasks such as sequential subtraction (mathematical task) and spot the difference (Visuo-spatial task) and their Oxy &amp; de-Oxy hemoglobin concentration was measured which showed more changes during the task period when compared to relaxation in both left and right part of pre-frontal cortex.

A DAQ-device-based continuous wave near-infrared spectroscopy system for measuring human functional brain activity.

In the last two decades, functional near-infrared spectroscopy (fNIRS) is getting more and more popular as a neuroimaging technique. The fNIRS instrument can be used to measure local hemodynamic response, which indirectly reflects the functional neural activities in human brain. In this study, an easily implemented way to establish DAQ-device-based fNIRS system was proposed. Basic instrumentation components (light sources driving, signal conditioning, sensors, and optical fiber) of the fNIRS system were described. The digital in-phase and quadrature demodulation method was applied in LabVIEW software to distinguish light sources from different emitters. The effectiveness of the custom-made system was verified by simultaneous measurement with a commercial instrument ETG-4000 during Valsalva maneuver experiment. The light intensity data acquired from two systems were highly correlated for lower wavelength (Pearson's correlation coefficient r = 0.92, P < 0.01) and higher wavelength (r = 0.84, P < 0.01). Further, another mental arithmetic experiment was implemented to detect neural activation in the prefrontal cortex. For 9 participants, significant cerebral activation was detected in 6 subjects (P < 0.05) for oxyhemoglobin and in 8 subjects (P < 0.01) for deoxyhemoglobin.

Detection of optical neuronal signals in the visual cortex using continuous wave near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) measures slow hemodynamic signals noninvasively to indirectly infer the neuronal activity in the brain. However, it remains a controversy on whether this optical measurement technique can detect the optical neuronal signal, which reflects the optical changes directly associated with neuronal activity, within the visual cortex of human and non-human primates. By carefully reviewing the important factors in the detection of optical neuronal signals, we aim to investigate the feasibility of performing NIRS measurements of optical neuronal signals within the visual cortex in humans. To ensure a strong optical neuronal response, a full-field circular black and white reversing checkerboard stimulus was presented, and the reversal frequency was carefully chosen. We used a homemade continuous wave (CW) NIRS system with high detection sensitivity (of the order of 0.1pW) to record a large area of the visual cortex (approximately 6×14cm2). EEG was simultaneously acquired with the optical signal. Based on the mathematical morphology, we adapted the filter proposed by Gratton et al. to remove the influence of arterial pulsation and facilitate the detection and elimination of unknown artifacts from the data. We obtained reliable optical neuronal signals in 77% of the participants (10 out of 13). The amplitudes (latencies) of the obtained optical neuronal signals corresponding to the 785 and 850nm wavelengths were 0.017±0.003% (94.7±8.4ms) and 0.025±0.006% (99.0±7.7ms), respectively. There were no significant differences between the latencies of the N75 component of the visual evoked potential (VEP) and optical neuronal signals at either wavelength. This is the first study to report optical neuronal signals within the visual cortex in the intact human brain using a CW NIRS system. These results indicate the feasibility of measuring noninvasive optical neuronal signals using a CW NIRS system with high detection sensitivity.