The rest period in between strength exercises determines how the short-term energy supplies in the muscles are replenished and metabolites are cleared. Near-InfraRed Spectroscopy (NIRS) is a proven method to study oxidative recovery kinetics following exercise. The goal of this study is to develop a model that predicts the oxygenated recovery state, this can help athletes optimize the resumption of exercise. 17 healthy subjects performed a sustained isometric hold in a hand gripper until volitional exertion, Tissue Saturation Index (TSI) was continuously monitored throughout and following exercise by a NIRS sensor (Train.Red PLUS). The oxygenated recovery state was manually categorized by three independent experts into four different phases of recovery; I - a pronounced increase, II - a gentle increase, III - the maximum oxygenated state, and IV - the return to baseline. A Recurrent Neural Network, inspired by Natural Language Processing, was trained and tested on this data, resulting in a model that predicts shifts between phases of recovery. A 5-fold cross-validation analysis resulted in the following average performance: • Recurrent Neural Network: Accuracy: 55.17%, categorical cross-entropy: 1.02351. • Multi-Layer Perceptron: Accuracy: 57.16%, categorical cross-entropy: 0.95201. • XGBoost: accuracy: 44.85%, categorical cross-entropy: 10.1119. In predicting the user’s current state of oxygenated recovery the MLP and RNN are similar in performance, however, the MLP shows erratic behavior, while the RNN generally follows the shift in phases of the ground truth. These capabilities could enable athletes with different fitness goals to design goal-tailored and therefore more efficient training.
KEYWORDS: Near infrared spectroscopy, Data acquisition, Standards development, Software development, Neuroimaging, Neurophotonics, Design and modelling, MATLAB, Data storage, Compliance
SignificanceFunctional near-infrared spectroscopy (fNIRS) is a popular neuroimaging technique with proliferating hardware platforms, analysis approaches, and software tools. There has not been a standardized file format for storing fNIRS data, which has hindered the sharing of data as well as the adoption and development of software tools.AimWe endeavored to design a file format to facilitate the analysis and sharing of fNIRS data that is flexible enough to meet the community’s needs and sufficiently defined to be implemented consistently across various hardware and software platforms.ApproachThe shared NIRS format (SNIRF) specification was developed in consultation with the academic and commercial fNIRS community and the Society for functional Near Infrared Spectroscopy.ResultsThe SNIRF specification defines a format for fNIRS data acquired using continuous wave, frequency domain, time domain, and diffuse correlation spectroscopy devices.ConclusionsWe present the SNIRF along with validation software and example datasets. Support for reading and writing SNIRF data has been implemented by major hardware and software platforms, and the format has found widespread use in the fNIRS community.
Motion is disruptive to neuroimaging methods. Motion artefacts range from large amplitude and short frequency spikes to drifts in amplitude causing cofounds in the analysis or completely invalidating any analysis, leading to epoch exclusion of data. However, we can only acquire ecologically robust information if subjects are engaging in natural interaction with their environment. Even more so in the case of sports, infants or motor disorder afflicted populations, where movement will happen. We proposed to study the relationship between channel location and Inertial Measuring Unit (IMU) quantified head movements, in order to better understand their effects in fNIRS data. Cerebral oxygenated (O2Hb) and deoxygenated (HHb) haemoglobin were measured bilaterally in prefrontal to frontal and occipital to temporo-parietal regions of healthy individuals. All participants performed controlled head movements in four conditions: Up, Down, measured by pitch IMU values; and Left, Right, measured by yaw IMU values, in varying degrees of movement. We analysed amplitude and coefficient of determination of O2Hb and HHb, within conditions and channel coordinates across subjects. Our results show that smaller angle magnitude movements (bellow 60 degrees in rotation) are significantly different than larger angle magnitude movements (above 75 degrees in rotation) with a p value of 0.0073; and that the Up condition is significantly different than other movement directions with a p value of 0.0001. We conclude that movement artefacts do not depend on area of measurement for the movement conditions studied. We recommend the application of threshold values for the future with the use of the IMU, by ignoring the effects of lower magnitudes of movement, while correcting or removing larger magnitudes. In future motion artefact removal, we recommend using an IMU for optimal head motion correction of cerebral oxygenation signals.
Functional Near-Infrared Spectroscopy (fNIRS) is gaining popularity in detection and classification of cognitive and emotional states. In addition to hemodynamic responses arising from functional activity changes in the brain areas of interest, fNIRS signals contain components related to other physiological processes, such as respiration (frequency oscillations around 0.3 Hz) and cardiac pulsation (around 1 Hz). While heart rate and respiration measures have been successfully used as separate modalities to assess mental workload, these components are often discarded in fNIRS studies during the pre-processing. In this study, we examined whether including features related to heart and breathing rate improves the accuracy of mental workload level classification. Data collected with wearable fNIRS devices from 14 healthy participants performing mental workload task (n-back) were used to extract features for the classification. Machine learning classifiers were trained and tested using conventional features separately and in combination with the features derived from the oscillatory activity of respiration and heart pulsation. By comparing the performance, we demonstrated the effect of including proposed features on the classification accuracy of mental workload. In future studies, the examined features might be beneficial for other classification problems where modulations in heart and breathing rates are expected.
Functional near infrared spectroscopy (fNIRS) is used for brain hemodynamic assessment. Cortical hemodynamics are reliably estimated when the recorded signal has a sufficient quality. This is acquired when fNIRS optodes have proper scalp coupling. A lack of proper scalp coupling causes false positives and false negatives. Therefore, developing an objective algorithm for determining fNIRS signal quality is of great importance. In this study, we developed a machine learning-based algorithm for quantitatively rating fNIRS signal quality. Our promising results confirm the efficacy of the algorithm in determining fNIRS signal quality and hence decreasing misinterpretations.
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