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    Analysis of task-evoked systemic interference in fNIRS measurements: Insights from fMRI
    (Academic Press Inc Elsevier Science, 2014) Erdogan, Sinem B.; Yucel, Meryem A.; Akin, Ata
    Functional near infrared spectroscopy (fNIRS) is a promising method for monitoring cerebral hemodynamics with a wide range of clinical applications. INIRS signals are contaminated with systemic physiological interferences from both the brain and superficial tissues, resulting in a poor estimation of the task related neuronal activation. In this study, we use the anatomical resolution of functional magnetic resonance imaging (fMRI) to extract scalp and brain vascular signals separately and construct an optically weighted spatial average of the fMRI blood oxygen level-dependent (BOLD) signal for characterizing the scalp signal contribution to fNIRS measurements. We introduce an extended superficial signal regression (ESSR) method for canceling physiology-based systemic interference where the effects of cerebral and superficial systemic interference are treated separately. We apply and validate our method on the optically weighted BOLD signals, which are obtained by projecting the fMRI image onto optical measurement space by use of the optical forward problem. The performance of ESSR method in removing physiological artifacts is compared to i) a global signal regression (GSR) method and ii) a superficial signal regression (SSR) method. The retrieved signals from each method are compared with the neural signals that represent the 'ground truth' brain activation cleaned from cerebral systemic fluctuations. We report significant improvements in the recovery of task induced neural activation with the ESSR method when compared to the other two methods as reflected in the Pearson R2 coefficient and mean square error (MSE) metrics (two tailed paired t-tests, p <0.05). The signal quality is enhanced most when ESSR method is applied with higher spatial localization, lower inter-trial variability, a clear canonical waveform and higher contrast-to-noise (CNR) improvement (60%). Our findings suggest that, during a cognitive task i) superficial scalp signal contribution to fNIRS signals varies significantly among different regions on the forehead and ii) using an average scalp measurement together with a local measure of superficial hemodynamics better accounts for the systemic interference inherent in the brain as well as superficial scalp tissue. We conclude that maximizing the overlap between the optical pathlength of superficial and deeper penetration measurements is of crucial importance for accurate recovery of the evoked hemodynamic response in (NIRS recordings. (C) 2013 Elsevier Inc. All rights reserved.
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    DETECTING LATERIZATION OF HAEMODYNAMIC RESPONSE DURING EXECUTIVE MOTOR TASK AND MOTOR IMAGERY WITH FNIRS
    (IEEE, 2014) Gokdag, Yunus Engin; Sansal, Firat; Dumlu, Seda Nilgun; Erdogan, Sinem Burcu; Yilmaz, Ozge; Akin, Ata
    In this study, haemodynamic response strength during motor imagery and executive motor tasks are investigated through a general linear model using functional near infrared spectroscopy (fNIRS) data to discriminate neural correlation of right and left hand movement. A 16-channel fNIRS system is used over the prefrontal cortex during motor imagery and motor execution. Preliminary results shows that the activation of the prefrontal cortex during motor imagery task is related with high levels of cognitive processing, namely attentional engagement, rather than motor execution from the measurements using generalised linear model. Results show that fNIRS holds great promise as a tool for clinical studies, cognitive and behavioural neuroscience research.
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    Detecting the Functionality of Executive Motor Task and Motor Imagery Through Electroencephalography (EEG)
    (IEEE, 2014) Dumlu, Seda; Sahin, Duygu; Vardar, Bige; Akin, Ata; Duru, Adil Deniz
    In this study, electrical activity of the brain is measured to assess the changes due to motor function, namely during motor execution and motor imagery tasks. First group of experiment covers motor execution task which subjects are required to clench the ball according to the direction of right or left arrows whereas in second group of experiment, subjects carried out a motor imaginary task which subjects imagine as if they are clenching the ball with their left or right hand. In motor execution task, subjects were asked to clench a tennis ball according to left or right cue arrow indicating, which hand the subject, should use. In motor imaginary task, subjects were asked to 'imagine' as if they clench a tennis ball according to left or right cue arrow. mu rhythm is the indicator of suppression during motor execution and imagery in alpha band. As a neurophysiologic marker of the electrical activity of the brain, during motor execution mu rhythm is suppressed with a higher rate as opposed to motor imagery. According to our results, it is shown that there is statistical significance between motor movement and motor imagery, in upper alpha band of the power spectral density.
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    Effective channels in classification and functional connectivity pattern of prefrontal cortex by functional near infrared spectroscopy signals
    (Elsevier Gmbh, 2016) Einalou, Zahra; Maghooli, Keivan; Setarehdan, Seyed Kamaledin; Akin, Ata
    In this paper, we apply support vector machine (SVM) based classification of functional near-infrared spectroscopy (fNIRS) which is non-invasive monitoring of human brain function by measuring the changes in the concentration of oxyhemoglobin and deoxyhemoglobin. Data collected from 11 healthy volunteers and 16 schizophrenia subjects. Signals were first preprocessed and decomposed by using discrete wavelet transform DWT to eliminate systemic physiological interference. A preliminary analysis based on Genetic Algorithm (GA) favored eight channels of the reconstructed fNIRS signals for further analysis. Energy in these 8 reconstructed signals was computed and used for classification of signals. SVM based classifier was employed to diagnosis schizophrenia. The results show the promising classification accuracy of nearly 84% in detection of schizophrenia from healthy subjects. The major finding of this study is that selected channels were able to identify differences in functional connectivity patterns of prefrontal cortex (PFC) elicited by Stroop task. (C) 2015 Elsevier GmbH. All rights reserved.
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    Frontal Brain Activation During A Go/NoGo Response Inhibition Task: An fNIRS Study
    (IEEE, 2014) Sansal, Firat; Gokdag, Yunus Engin; Sahin, Duygu; Keskin, Yasemin; Yilmaz, Ozge; Akin, Ata
    It has been known that in human brain, prefrontal cortex intensively controls the cognitive processes. In this study, functional near infrared spectroscopy (fNIRS) system has been used which is a promising method and has a relatively easier application. The aim of this study is to measure the prefrontal activity of the human brain using a Go-Nogo paradigm which is a common task to measure inhibitory activity in neuroscience field. We have investigated the inhibitory activity triggered by a Go-Nogo paradigm for the first time using fNIRS method with general linear model (GLM) analysis.
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    Use of the Color Spaces in Determining the Level of Hemolysis in Blood under Storage
    (Springer-Verlag Berlin, 2015) Can, Osman Melih; Ulgen, Yekta; Akin, Ata
    Quality of the transfused blood units are needed to be controlled, because severe storage lesion leads to clinical adverse effects on critically ill patients. Currently, visual assessment of hemolysis is used to control the quality of the blood units by inspecting the pink discoloration in blood bag. However, the color of blood units can be uniquely and more accurately defined by a set of tristimulus values or color coordinates in a color space. The objective of the study is to monitor daily changes in the color parameters of stored blood and relate them with the changes in hemolysis index. Red blood cell (RBC) suspensions collected from 7 male volunteers were used for the study. On each day of storage, 24 colorimetric parameters in various color spaces were measured. Besides, each week of storage, standard hemolysis measurements were performed by taking blood samples from blood bags. Colorimetric parameters: tristimulus X, u', u-v saturation, Hunter a, CIE a*, CIELAB chroma and the correlated color temperature (CCT) that mostly correspond to red contents of the color stimuli changed significantly (p<0.05) for each sample after the third week of storage. Except CCT, hemolysis showed good correlation (r>0.65) (p<0.005) with those parameters. However u', u-v saturation and CIE a* are not sensitive enough to detect hemolysis in the first two weeks of the storage.