Continuous-wave Functional Near-infrared Spectroscopy Research Articles

Reliability Evaluation for Continuous-Wave Functional Near-Infrared Spectroscopy Systems: Comprehensive Testing from Bench Characterization to Human Test.

In recent years, biomedical optics technology has developed rapidly. The current widespread use of biomedical optics was made possible by the invention of optical instruments. The advantages of being non-invasive, portable, effective, low cost, and less susceptible to system noise have led to the rapid development of functional near-infrared spectroscopy (fNIRS) technology for hemodynamics detection, especially in the field of functional brain imaging. At the same time, laboratories and companies have developed various fNIRS-based systems. The safety, stability, and efficacy of fNIRS systems are key performance indicators. However, there is still a lack of comprehensive and systematic evaluation methods for fNIRS instruments. This study uses the fNIRS system developed in our laboratory as the test object. The test method established in this study includes system validation and performance testing to comprehensively assess fNIRS systems' reliability. These methods feature low cost and high practicality. Based on this study, existing or newly developed systems can be comprehensively and easily evaluated in the laboratory or workspace.

Retrieval of chromophore concentration changes in a digital human head model using analytical mean partial pathlengths of photons.

Continuous-wave functional near-infrared spectroscopy has proved to be a valuable tool for assessing hemodynamic activity in the human brain in a non-invasively and inexpensive way. However, most of the current processing/analysis methods assume the head is a homogeneous medium, and hence do not appropriately correct for the signal coming from the scalp. This effect can be reduced by considering light propagation in a layered model of the human head, being the Monte Carlo (MC) simulations the gold standard to this end. However, this implies large computation times and demanding hardware capabilities. In this work, we study the feasibility of replacing the homogeneous model and the MC simulations by means of analytical multilayered models, combining in this way, the speed and simplicity of implementation of the former with the robustness and accuracy of the latter. Oxy- and deoxyhemoglobin (HbO and HbR, respectively) concentration changes were proposed in two different layers of a magnetic resonance imaging (MRI)-based meshed model of the human head, and then these changes were retrieved by means of (i)a typical homogeneous reconstruction and (ii)a theoretical layered reconstruction. Results suggest that the use of analytical models of light propagation in layered models outperforms the results obtained using traditional homogeneous reconstruction algorithms, providing much more accurate results for both, the extra- and the cerebral tissues. We also compare the analytical layered reconstruction with MC-based reconstructions, achieving similar degrees of accuracy, especially in the gray matter layer, but much faster (between 4 and 5 orders of magnitude). We have successfully developed, implemented, and validated a method for retrieving chromophore concentration changes in the human brain, combining the simplicity and speed of the traditional homogeneous reconstruction algorithms with robustness and accuracy much more similar to those provided by MC simulations.

Scalable, modular continuous wave functional near-infrared spectroscopy system (Spotlight).

We present a fiberless, portable, and modular continuous wave-functional near-infrared spectroscopy system, Spotlight, consisting of multiple palm-sized modules-each containing high-density light-emitting diode and silicon photomultiplier detector arrays embedded in a flexible membrane that facilitates optode coupling to scalp curvature. Spotlight's goal is to be a more portable, accessible, and powerful functional near-infrared spectroscopy (fNIRS) device for neuroscience and brain-computer interface (BCI) applications. We hope that the Spotlight designs we share here can spur more advances in fNIRS technology and better enable future non-invasive neuroscience and BCI research. We report sensor characteristics in system validation on phantoms and motor cortical hemodynamic responses in a human finger-tapping experiment, where subjects wore custom 3D-printed caps with two sensor modules. The task conditions can be decoded offline with a median accuracy of 69.6%, reaching 94.7% for the best subject, and at a comparable accuracy in real time for a subset of subjects. We quantified how well the custom caps fitted to each subject and observed that better fit leads to more observed task-dependent hemodynamic response and better decoding accuracy. The advances presented here should serve to make fNIRS more accessible for BCI applications.

Brain Connectivity Analysis in Distinct Footwear Conditions during Infinity Walk Using fNIRS.

Gait and balance are an intricate interplay between the brain, nervous system, sensory organs, and musculoskeletal system. They are greatly influenced by the type of footwear, walking patterns, and surface. This exploratory study examines the effects of the Infinity Walk, pronation, and footwear conditions on brain effective connectivity patterns. A continuous-wave functional near-infrared spectroscopy device collected data from five healthy participants. A highly computationally efficient connectivity model based on the Grange causal relationship between the channels was applied to data to find the effective relationship between inter- and intra-hemispheric brain connectivity. Brain regions of interest (ROI) were less connected during the barefoot condition than during other complex walks. Conversely, the highest interconnectedness between ROI was observed while wearing flat insoles and medially wedged sandals, which is a relatively difficult type of footwear to walk in. No statistically significant (p-value <0.05) effect on connectivity patterns was observed during the corrected pronated posture. The regions designated as motoric, sensorimotor, and temporal became increasingly connected with difficult walking patterns and footwear conditions. The Infinity Walk causes effective bidirectional connections between ROI across all conditions and both hemispheres. Due to its repetitive pattern, the Infinity Walk is a good test method, particularly for neuro-rehabilitation and motoric learning experiments.

Single-leg stance on a challenging surface can enhance cortical activation in the right hemisphere – A case study

Maintaining body balance, whether static or dynamic, is critical in performing everyday activities and developing and optimizing basic motor skills. This study investigates how a professional alpine skier's brain activates on the contralateral side during a single-leg stance. Continuous-wave functional near-infrared spectroscopy (fNIRS) signals were recorded with sixteen sources and detectors over the motor cortex to investigate brain hemodynamics. Three different tasks were performed: barefooted walk (BFW), right-leg stance (RLS), and left-leg stance (LLS). The signal processing pipeline includes channel rejection, the conversation of raw intensities into hemoglobin concentration changes using modified Beer-Lambert law, baseline zero-adjustments, z-normalization, and temporal filtration. The hemodynamic brain signal was estimated using a general linear model with a 2-gamma function. Measured activations (t-values) with p-value <0.05 were only considered as statistically significant active channels. Compared to all other conditions, BFW has the lowest brain activation. LLS is associated with more contralateral brain activation than RLS. During LLS, higher brain activation was observed across all brain regions. The right hemisphere has comparatively more activated regions-of-interest. Higher ΔHbO demands in the dorsolateral prefrontal, pre-motor, supplementary motor cortex, and primary motor cortex were observed in the right hemisphere relative to the left which explains higher energy demands for balancing during LLS. Broca's temporal lobe was also activated during both LLS and RLS. Comparing the results with BFW– which is considered the most realistic walking condition–, it is concluded that higher demands of ΔHbO predict higher motor control demands for balancing. The participant struggled with balance during the LLS, showing higher ΔHbO in both hemispheres compared to two other conditions, which indicates the higher requirement for motor control to maintain balance. A post-physiotherapy exercise program is expected to improve balance during LLS, leading to fewer changes to ΔHbO.

Low-dissipation optimization of the prefrontal cortex in the -12° head-down tilt position: A functional near-infrared spectroscopy study.

Our present study set out to investigate the instant state of the prefrontal cortex (PFC) in healthy subjects before and after placement in the -12°head-down tilt (HDT) position in order to explore the mechanism behind the low-dissipation optimization state of the PFC. 40 young, right-handed healthy subjects (male: female = 20: 20) were enrolled in this study. Three resting state positions, 0°initial position, -12°HDT position, and 0°rest position were sequentially tested, each for 10 minutes. A continuous-wave functional near-infrared spectroscopy (fNIRS) instrument was used to assess the resting state hemodynamic data of the PFC. After preprocessing the hemodynamics data, we evaluated changes in resting-state functional connectivity (rsFC) level and beta values of PFC. The subjective visual analogue scale (VAS) was applied before and after the experiment. The presence of sleep changes or adverse reactions were also recorded. Pairwise comparisons of the concentrations of oxyhemoglobin (HbO), deoxyhemoglobin (HbR), and hemoglobin (HbT) revealed significant differences in the aforementioned positions. Specifically, the average rsFC of PFC showed a gradual increase throughout the whole process. In addition, based on graph theory, the topological properties of brain network, such as small-world network and nodal degree centrality were analyzed. The results show that global efficiency and small-world sigma (σ) value were differences between 0°initial and 0°rest. In this study, placement in the -12°HDT had a significant effect on PFC function, mainly manifested as self-inhibition, decreased concentration of HbO in the PFC, and improved rsFC, which may provide ideas to the understanding and explanation of neurological diseases.

Load-Dependent Prefrontal Cortex Activation Assessed by Continuous-Wave Near-Infrared Spectroscopy during Two Executive Tasks with Three Cognitive Loads in Young Adults.

The present study examined the evolution of the behavioral performance, subjectively perceived difficulty, and hemodynamic activity of the prefrontal cortex as a function of cognitive load during two different cognitive tasks tapping executive functions. Additionally, it investigated the relationships between these behavioral, subjective, and neuroimaging data. Nineteen right-handed young adults (18-22 years) were scanned using continuous-wave functional near-infrared spectroscopy during the performance of n-back and random number generation tasks in three cognitive load conditions. Four emitter and four receptor optodes were fixed bilaterally over the ventrolateral and dorsolateral prefrontal cortices to record the hemodynamic changes. A self-reported scale measured the perceived difficulty. The findings of this study showed that an increasing cognitive load deteriorated the behavioral performance and increased the perceived difficulty. The hemodynamic activity increased parametrically for the three cognitive loads of the random number generation task and in a two-back and three-back compared to a one-back condition. In addition, the hemodynamic activity was specifically greater in the ventrolateral prefrontal cortex than in the dorsolateral prefrontal cortex for both cognitive tasks (random number generation and n-back tasks). Finally, the results highlighted some links between cerebral oxygenation and the behavioral performance, but not the subjectively perceived difficulty. Our results suggest that cognitive load affects the executive performance and perceived difficulty and that fNIRS can be used to specify the prefrontal cortex's implications for executive tasks involving inhibition and working memory updating.

Word Frequency Is Associated With Cognitive Effort During Verbal Working Memory: A Functional Near Infrared Spectroscopy (fNIRS) Study.

PurposePsycholinguistic models traditionally view verbal working memory capacity as independent from linguistic features; connectionist models suggest otherwise. Moreover, lexical processing studies show high frequency words differ in cognitive effort from low frequency words, although these effects during concurrent processing of words in working memory are unknown. This novel study examines potential differences in cognitive effort, as measured by differences in HbO2 and Hb, for high frequency versus low frequency words during a working memory paradigm.MethodsA total of 21 neurologically typical participants (age 18–23) completed an auditory, n-back, working memory task comparing performance with high- as compared to low- frequency words. Hemodynamic changes in the prefrontal cortex were recorded with a continuous-wave functional near-infrared spectroscopy (fNIRS) device. Behavioral data (accuracy, reaction time) were recorded using E-prime.ResultsDifferences in word frequency were evident at both behavioral and neurological levels. Participants were more accurate, albeit slower in identifying the target two back in a sequence for low- as compared to high-frequency words. Patterns of hemodynamic changes were also significantly different between HF and LF conditions.ConclusionThe results from this study indicate that the behavioral and neurological signatures inherent in holding high- versus low-frequency words in working memory differs significantly. Specifically, the findings from this study indicated that words differing in frequency place different demands on cognitive processing load in memory updating tasks.

Exploring Neuroergonomic Fit of Passive Exoskeletons during Manual Handling Tasks

Approximately 40 percent of the work-related musculoskeletal disorders (MSDs) are low back injuries. Recent advances in human-robotic cooperation, across the spectrum of passive assistance to powered augmentation, have shown strong potential to reduce MSD risks by reducing or transferring biomechanical loadings from targeted joints. However, exoskeletons could negatively impact users’ gaits and postures, and significantly increase users’ metabolic costs (Gregorczyk et al., 2010; Jin, Prado, &amp; Agrawal, 2018). It has been shown that some industrial exoskeletons reduce loads on targeted parts of the body, such as shoulders, but increase loadings on other regions, such as spine (Picchiotti, Weston, Knapik, Dufour, &amp; Marras, 2019; Weston, Alizadeh, Knapik, Wang, &amp; Marras, 2018). Thus, the rapid application of exoskeletons and robotic interventions to the industry without proper ergonomic evaluations is likely to exacerbate current MSDs or introduce new risks to the workplaces such as cognitive overloads (NIOSH, 2018). In this study, the neuroergonomic fit of an industrial passive low-back exoskeleton (Laevo, Delft, The Netherlands) will be evaluated during simulated manual handling tasks with varying levels of physical and cognitive demands of twelve healthy adults (gender-balanced). Neuroergonomic fit is defined as a human-robotic fitness that minimizes the physical load while maximizes the neural (cognitive) availability of a user. An exoskeleton that demands minimum biomechanical loads and mental efforts is considered to be a neuroergonomic fit product. We hypothesized that using low-back exoskeleton will reduce the biomechanical loads on users’ low backs but increase users’ cognitive efforts while performing manual handling task. The objective of this study is to examine the neuroergonomic fit of exoskeletons during the manual handling tasks. During each 30-minute session, a subject will be instructed to perform a manual handling task of lifting a 16-pound medicine ball from the knees to the waist level asymmetrically (45o) at a frequency of 6 lifts per minute. The whole experiment consists of four sessions which is a combination of two experimental conditions (with/without an exoskeleton and with or without cognitive demands). The cognitively demanding task will be an arithmetic task of a serial 13 subtraction from a random number between 500 and 1000 in each cognitive intervention session. Each subject will participant in two random sessions per day for two separate days with at least one resting day in between. There will be a 30-minute resting period between two sessions to reduce any fatigue effect. The neural efforts of each subject will be calculated by measuring the brain activation patterns using a 21-channel portable continuous wave functional near-infrared spectroscopy (fNIRS) system NIRSport2TM (NIRx Medical Technologies, NY, USA). Multiple physical and cognitive task-related brain regions are measured. The regions include dorsolateral prefrontal cortex (dlPFC) which is correlated with working memory, supplementary motor area (SMA) and premotor cortex (PM) which are both in charge of motor planning. A 2 exoskeletons (1 control and 1 exoskeleton) x 2 tasks (physical and physical-cognitive condition) x 2 phases (early and late phases) analysis of variance (ANOVA), with a significance level of alpha at 0.05, will be used to assess their main and interaction effects on physical and cognitive task performance. The brain activation data will be used to identify functional and effective connectivity patterns among the regions which are related to different cognitive and motor functions under four conditions. Neural efficiency metric that integrates neural effort and task performance data will be used to monitor human-robotic cooperation at different phases of each session. The ultimate goal of this study is to improve exoskeleton-workplace safety and productivity by understanding, assessing, and augmenting the neuroergonomic fit exoskeletons during occupational manual handling tasks.

Differential pathlength factor in continuous wave functional near-infrared spectroscopy: reducing hemoglobin's cross talk in high-density recordings.

Functional near-infrared spectroscopy (fNIRS) estimates the functional oscillations of oxyhemoglobin and deoxyhemoglobin in the cortex through scalp-located multiwavelength recordings. Hemoglobin oscillations are inferred through temporal changes in continuous-wave (CW) light attenuation. However, because of the diffusive multilayered head tissue structures, the photon path is longer than the source-detector separation, complicating hemoglobin evaluation. This aspect is incorporated in the modified Beer-Lambert law where the source-detector distance is multiplied by the differential pathlength factor (DPF). Since DPF estimation requires photons' time-of-flight information, DPF is assumed a priori in CW-fNIRS. Importantly, errors in the DPF spectrum induce hemoglobin cross talk, which is detrimental for fNIRS. We propose to estimate subject-specific DPF spectral dependence relying on multidistance high-density measurements. The procedure estimates the effective attenuation coefficient (EAC), which is proportional to the geometric mean of absorption and reduced scattering. Since DPF depends on the scattering-to-absorption ratio, EAC limits the spectral dependence assumption to scattering. This approach was compared to a standard frequency-domain multidistance procedure. A good association between the two methods ( ) was obtained. This approach could estimate low-resolution maps of the DPF spectral dependence through large field of view, high-density systems, reducing hemoglobin cross talk, and increasing fNIRS sensitivity and specificity to brain activity without instrumentation modification.

Continuous wave functional near-infrared spectroscopy: Various signal components and appropriate management

Continuous wave functional near-infrared spectroscopy: Various signal components and appropriate management

Crucial aspects for the use of silicon photomultiplier devices in continuous wave functional near-infrared spectroscopy.

In this work, we investigate some major issues for the use of silicon photomultiplier (SiPM) devices in continuous wave functional near-infrared spectroscopy (CW fNIRS). We analyzed the after-pulsing effect, proposing the physical mechanism causing it, and determining its relevance for CW fNIRS. We studied the SiPM transients occurring as the SiPM device goes from the dark (LED in off state) to the illumination (LED in on state) conditions, and vice-versa. Finally, we studied the SiPM SNR in standard CW fNIRS operation.

Process-specific analysis in episodic memory retrieval using fast optical signals and hemodynamic signals in the right prefrontal cortex

Objective. Memory is formed by the interaction of various brain functions at the item and task level. Revealing individual and combined effects of item- and task-related processes on retrieving episodic memory is an unsolved problem because of limitations in existing neuroimaging techniques. To investigate these issues, we analyze fast and slow optical signals measured from a custom-built continuous wave functional near-infrared spectroscopy (CW-fNIRS) system. Approach. In our work, we visually encode the words to the subjects and let them recall the words after a short rest. The hemodynamic responses evoked by the episodic memory are compared with those evoked by the semantic memory in retrieval blocks. In the fast optical signal, we compare the effects of old and new items (previously seen and not seen) to investigate the item-related process in episodic memory. The Kalman filter is simultaneously applied to slow and fast optical signals in different time windows. Main results. A significant task-related HbR decrease was observed in the episodic memory retrieval blocks. Mean amplitude and peak latency of a fast optical signal are dependent upon item types and reaction time, respectively. Moreover, task-related hemodynamic and item-related fast optical responses are correlated in the right prefrontal cortex. Significance. We demonstrate that episodic memory is retrieved from the right frontal area by a functional connectivity between the maintained mental state through retrieval and item-related transient activity. To the best of our knowledge, this demonstration of functional NIRS research is the first to examine the relationship between item- and task-related memory processes in the prefrontal area using single modality.

Characterization of a fiber-less, multichannel optical probe for continuous wave functional near-infrared spectroscopy based on silicon photomultipliers detectors: in-vivo assessment of primary sensorimotor response.

We report development, testing, and in vivo characterization of a multichannel optical probe for continuous wave (CW) functional near-infrared spectroscopy (fNIRS) that relies on silicon photomultipliers (SiPMs) detectors. SiPMs are cheap, low voltage, and robust semiconductor light detectors with performances analogous to photomultiplier tubes (PMTs). In contrast with PMTs, SiPMs allow direct contact with the head and transfer of the analog signals through thin cables greatly increasing the system flexibility avoiding optical fibers. The coupling of SiPMs and light-emitting diodes (LEDs) made the optical probe lightweight and robust against motion artifacts. After characterization of SiPM performances, which was proven to provide a noise equivalent power below 3fW, the apparatus was compared through an in vivo experiment to a commercial system relying on laser diodes, PMTs, and optical fibers for light probing and detection. The optical probes were located over the primary sensorimotor cortex and the similarities between the hemodynamic responses to the contralateral motor task were assessed. When compared to other state-of-the-art wearable fNIRS systems, where photodiode detectors are employed, the single photon sensitivity and dynamic range of SiPMs can fully exploit the long and variable interoptode distances needed for correct estimation of brain hemodynamics using CW-fNIRS.

Tryptophan hydroxylase 1 gene polymorphisms alter prefrontal cortex activation during response inhibition.

The tryptophan hydroxylase 1 gene (TPH1) catalyzes the formation of 5-hydroxytryptophan, a precursor to the neurotransmitter serotonin. Variations in the gene encoding this enzyme may underlie difficulties in impulse control; however, the proximate relationship between risk alleles for polymorphisms in the TPH1 gene and the neural correlates of response inhibition remain poorly understood. The present study examined the relationship of 2 single nucleotide polymorphisms in the TPH1 gene (rs1799913 and rs4537731) to prefrontal cortex (PFC) activation on a response inhibition task. Evoked hemodynamic oxygenation in the PFC was measured in 30 unrelated healthy adult women using 16-channel continuous-wave functional near-infrared spectroscopy while they completed a manual go/no-go task. TPH1 alleles showed no association with demographic characteristics, general intelligence, impulsive personality traits, or accuracy and response latency indices on the go/no-go task. Participants carrying the risk alleles, however, showed less activity primarily in bilateral inferior frontal gyri and medial PFC under conditions of response inhibition. Polymorphisms in the TPH1 gene may be represented by diminished activity in lateral areas of the PFC underlying response inhibition. Reduced activity in medial PFC might represent altered self-monitoring of performances on the response inhibition task.

Linking trait-based phenotypes to prefrontal cortex activation during inhibitory control.

Inhibitory control is subserved in part by discrete regions of the prefrontal cortex whose functionality may be altered according to specific trait-based phenotypes. Using a unified model of normal range personality traits, we examined activation within lateral and medial aspects of the prefrontal cortex during a manual go/no-go task. Evoked hemodynamic oxygenation within the prefrontal cortex was measured in 106 adults using a 16-channel continuous-wave functional near-infrared spectroscopy system. Within lateral regions of the prefrontal cortex, greater activation was associated with higher trait levels of extraversion, agreeableness and conscientiousness, and lower neuroticism. Higher agreeableness was also related to more activation in the medial prefrontal cortex during inhibitory control. These results suggest that personality traits reflecting greater emotional stability, extraversion, agreeableness and conscientiousness may be associated with more efficient recruitment of control processes subserved by lateral regions of the prefrontal cortex. These findings highlight key links between trait-based phenotypes and neural activation patterns in the prefrontal cortex underlying inhibitory control.

Transcranial direct current stimulation induced modulation of cortical haemodynamics: A comparison between time-domain and continuous-wave functional near-infrared spectroscopy

Transcranial direct current stimulation induced modulation of cortical haemodynamics: A comparison between time-domain and continuous-wave functional near-infrared spectroscopy

Decision-making conflict and the neural efficiency hypothesis of intelligence: A functional near-infrared spectroscopy investigation

Research on the neural efficiency hypothesis of intelligence (NEH) has revealed that the brains of more intelligent individuals consume less energy when performing easy cognitive tasks but more energy when engaged in difficult mental operations. However, previous studies testing the NEH have relied on cognitive tasks that closely resemble psychometric tests of intelligence, potentially confounding efficiency during intelligence-test performance with neural efficiency per se. The present study sought to provide a novel test of the NEH by examining patterns of prefrontal activity while participants completed an experimental paradigm that is qualitatively distinct from the contents of psychometric tests of intelligence. Specifically, participants completed a personal decision-making task (e.g., which occupation would you prefer, dancer or chemist?) in which they made a series of forced choices according to their subjective preferences. The degree of decisional conflict (i.e., choice difficulty) between the available response options was manipulated on the basis of participants' unique preference ratings for the target stimuli, which were obtained prior to scanning. Evoked oxygenation of the prefrontal cortex was measured using 16-channel continuous-wave functional near-infrared spectroscopy. Consistent with the NEH, intelligence predicted decreased activation of the right inferior frontal gyrus (IFG) during low-conflict situations and increased activation of the right-IFG during high-conflict situations. This pattern of right-IFG activity among more intelligent individuals was complemented by faster reaction times in high-conflict situations. These results provide new support for the NEH and suggest that the neural efficiency of more intelligent individuals generalizes to the performance of cognitive tasks that are distinct from intelligence tests.

A problem-solving task specialized for functional neuroimaging: validation of the Scarborough adaptation of the Tower of London (S-TOL) using near-infrared spectroscopy.

Problem-solving is an executive function subserved by a network of neural structures of which the dorsolateral prefrontal cortex (DLPFC) is central. Whereas several studies have evaluated the role of the DLPFC in problem-solving, few standardized tasks have been developed specifically for use with functional neuroimaging. The current study adapted a measure with established validity for the assessment of problem-solving abilities to design a test more suitable for functional neuroimaging protocols. The Scarborough adaptation of the Tower of London (S-TOL) was administered to 38 healthy adults while hemodynamic oxygenation of the PFC was measured using 16-channel continuous-wave functional near-infrared spectroscopy (fNIRS). Compared to a baseline condition, problems that required two or three steps to achieve a goal configuration were associated with higher activation in the left DLPFC and deactivation in the medial PFC. Individuals scoring higher in trait deliberation showed consistently higher activation in the left DLPFC regardless of task difficulty, whereas individuals lower in this trait displayed less activation when solving simple problems. Based on these results, the S-TOL may serve as a standardized task to evaluate problem-solving abilities in functional neuroimaging studies.

Measuring tissue hemodynamics and oxygenation by continuous-wave functional near-infrared spectroscopy—how robust are the different calculation methods against movement artifacts?

Continuous-wave near-infrared spectroscopy and imaging enable tissue hemodynamics and oxygenation to be determined non-invasively. Movements of the investigated subject can cause movement artifacts (MAs) in the recorded signals. The strength and type of MAs induced depend on the measurement principle. The aim of the present study was to investigate the quantitative relationship between different single-distance (SD) and multi-distance (MD) measurement methods and their susceptibility to MAs. We found that each method induces MAs to a different degree, and that MD methods are more robust against MAs than SD methods.