New Application, Development and Aerospace Prospect of fNIR

doi:10.4236/eng.2013.55B010

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Engineering, 2013, 5, 47-52

doi:10.4236/eng.2013.55B010 Published Online May 2013 (http://www.scirp.org/journal/eng)

New Application, Development and Aerospace

Prospe c t of fN IR

Jinjin Pan, Xuejun Jiao

National Key Laboratory of Human Factor Engineering, China Astronaut Research and Training Centre, Beijing, China

Email: [email protected]

Received 2013

ABSTRACT

Functional near-infrared imaging (fNIR) is a non-invasive, convenient, safe and stable imaging method to test

biological state. It can obtain the biological tissue hemodynamic data, thus becoming a powerful tool to measure brain

activities, mental workload , metabolism and cognitive activities state. First of all, we introduced the characteristics an d

current situation of fNIR in this article. Then we focused on the applications of fNIR, discussed some existing problems

and future directions, including the prospect in aerospace field. Our purpose is to give a comprehensive description of

fNIR and show its potential in aerospace field.

Keywords: fNIR; Brain Activity; Hemodynamics; Neuro-imaging Technology

1. Introduction

Neural science develops rapidly in recent years. Lots of

researches in human cognition and behavior performance

have been carried out. Neuroscience research field is

very wide, including nervous system structure, nervous

function, pathological and so on. Among these aspects,

the researches on nervous structure and function are key

and fundamental. So neural imaging technology is very

important. It developed rapidly these years. And there are

several technology methods can be used to observe brain

structure and activity. FNIR technology is an excellent

neural imaging method of brain observation. It can

observe biological state effectively, non-invasively, and

easily.

1.1. Characteristics of fNIR

FNIR is a newly developed technology that utilizes light

from 700 nm to 900 nm to monitor the state of biological

tissue. This technique can be portable, safe, relatively

cheap and noninvasive. [1,2]

It was firstly introduced by Jobsis[24] in his research

paper that relatively high degree of brain tissue

transparency in the NIR range enables the real-time

non-invasive detection of hemoglobin (Hb) oxygenation

using transillumin ation spectroscop y. For about ten years

later, this technology had been remarkable developed.

Researchers found that the near infrared spectroscopy

could be used to monitor brain fun ctional activities, such

as monitoring cognitive activities in normal condition

and war environment. [3] Early researchers carried out

some simple exercise and cognitive tasks, to verify this

possibility used for non-invasive monitoring of brain

regional activities. Some researchers later began to try to

monitor some complex cognitive tasks, such as war

management [4] and planes landing simulation [5].

Chance [6], Hoshi [7], and Villringer [8] are firstly

proved the possibility of NIR’s brain activity monitoring.

1.2. Principle

The wavelength range of fNIR is 700 nm to 900 nm.

Most biological tissues are relatively transparent to light

in this wavelength, so relatively little scattering of

photons oc curs when these wave length s are introduced to

tissue. It makes fNIR very suitable for tissue imaging. [1]

The main chromophores in the optical window of 600 to

900 nm are oxy- and deoxy-hemoglobin (denoted HbO

and Hb respectively), water, lipids and

cytochrome-coxidase. HbO and Hb are mainly of interest

because they are related to the regional cerebral blood

flow. [9] Using the modified Beer-Lambert law and fNIR

measurements conducted at two different wavelengths

within the near infrared light range at two adjacent times,

the relative changes in concentrations of deoxy-and

oxy-Hb can be obtained. [2] These physiological

parameters are closely related with human oxidation and

metabolism, and can be used for the detection of

cognitive activities and mental workload, so fNIR is a

ideal tool to detect cerebral cortex function.[4]

There are several neuroimaging methods can realize

the monitoring of brain structure and function. They can

J. J. PAN, X. J. JIAO

be divided into invasive and non-invasive imaging

methods on the basis of whether harmful or not to human

body. At present, some high-resolution mode require

invasive methods or injection of pharmacological (such

as CT, MRI), these are not ideal choice. So many

invasive neuroimaging methods become research focus,

such as fNIR, EEG, fMRI, MEG, PET etc. [10] Among

these techniques, fMRI, EEG and PET are widely used.

Compared with other existing neuroscience imaging

methods, fNIR has several advantages. First of all, fNIR

can provide some physiological parameter information

while other methods cannot, such as oxidation

information. In addition, from Figure 1, we can find

fNIR has a better time resolution compared with fMRI

and P E T . FNIR and fMRI can both provide hemodynamic

responses information, but the fMRI measurements have

much restriction, its equipment is very large. The

subjects need supine measurement, and the image

acquisition time is long. However, fNIR can acquire data

quickly, its time resolution is very high, but it cannot

replace fMRI in the aspect of spatial resolution. [11]

Compared with EEG, fNIR can offer higher spatial

resolution for better observing brain structure. At the

same time, fNIR is less susceptible to motion artifacts

than EEG. Meanwhile it does not rely on ionizing

radiation, therefore it is safer than PET. Some

continue-wave fNIR equipment system is very portable,

and can be used for telemeasurement. [10,11] In

conclusion, fNIR is safe, convenient, unrestricted, green,

quick, and balanced. The subjects have no body

limitation, and can realize telemeasurement. Especially,

its balanced characteristics of time and sp atial resolution,

anti-jamming and portable advantages make it quite

suitable for application in the relative field.

Figure 1. Comparisons of neuroscience technologies [30].

2. Application of fNIR

Because of the advantages of fNIR, it develops rapidly in

recent years. The researchers take full advantage of fNIR,

study and produce many relative applications. Especially

in the near year, with the development of neuroscience,

some new and advanced applications appeared. FNIR

application fields include brain structure and function

research, brain-computer-interface, adaptive interface,

mental workload assessment, monitoring of newborn,

mental fatigue, depth of anesthesia monitoring, medical

rehabilitation, cognitive enhancement etc as shown in

Table 1.

Table 1. Main fields of fnir applications [28]

2.1. Brain-computer-interface (BCI)

BCI is an interface system which can obtain signal from

the brain, and control the external device or computer

through the signal. Application of fNIR in BCI is a

relatively new method, it can be used to help evaluate the

attention and cognitive load. [12] EEG, fNIR and other

methods can be used comprehensively in BCI to evaluate

the cognitive state based on neurophysiology and

physiology, [13] and to monitor cognitive activities such

as attention, working memory, motor nerve activity in

clinical and natural conditions. [14]

2.2. Cognitive Load and Professional Skills

Measurement

Here is an example research of monitoring professional

skill development and cognitive load. Kurtulus and

several researchers monitored subjects’ cognitive load

J. J. PAN, X. J. JIAO 49

and development of professional skill in a simulation

UAV environment. The monitor system used was a

16-channel cw-fNIR system. The results showed that the

operators’ total HB decreased significantly when they

transited from beginner to professional status. At the

same time, they believed that fNIR had great potential

application in research and production, and could also be

used to help optimize performance in adverse

circumstances.[15] Hasan Ayaz et al also conducted

same UAV test, and they got the similar results.

2.3. Mental Workload Assessment

Human mental workload plays a very important role in

many complex control systems. Villringer.A proved that

under natural conditions, fNIR could be used for the

evaluation of mental workload in standard experiment

(n-back) and complex cognitive tasks (ATC). They also

showed that fNIR can evaluate the operators’ skill

progress in a complex cognitive task. They regarded

N-back experiment as a reference to verify the

availability of fNIR application in mental workload.

They used the 16 channels’ data to calculate oxidation

information based on MBLL. The results further proved

that the degree of expertise indeed affect the prefrontal

cortex (PFC) hemodynamic changes of left back.[16]

2.4. Mental Fatigue Research

Jiao xuejun and several researchers simulated a

mircrogravity environment, and studied the relationship

between fNIR sample entropy and power spectrum in

normal and fatigue states. The results showed that fNIR

signal sample entropy and power spectral entropy

decreased obviously during fatigue status. So fNIR has

the potential to monitor mental fatigue.[17]

2.5. Medical Rehabilitation

FNIR can be used to help monitor cognitive diseases

rehabilitation.[18] There were dozens of years since

fNIR’s first application in monitoring of brain oxidation

and metabolism. However, fNIR’s history as a mean of

monitoring cognitive process and helping monitor nerve

repair is relatively short, only 10 years. Similarly to

fMRI, the output of fNIR can also be used to produce a

brain activation map, thus can be compared by some

software. Patricia M described several application

examples in nerve recovery field. These examples

showed that fNIR could be applied to monitor brain

function recovery after impact effectively, as well as

evaluation of brain iniury (TBI) function. He also

proposed that a series of united and standard

measurement methods were necessary. And we also need

to further develop connection device, in order to achieve

an integration of a variety of functions. [18] Study of

Kurtulus Izzetoglu showed that fNIR could be used to

tell the difference between healthy people and patients

with TBI.[12] Darren Roblyer conducted a research

related to breast cancer, the results showed obvious

changes of Hb after treatment. So we can quickly

determine the possible reaction source by using fNIR to

monitor the changes or alter the breast cancer treatment

plan.[19]

2.6. Brain Functional Imaging of Newborn

There was about 10 years since fNIR’s first application

in newborn brain functional imaging. S. Lloyd-Fox

summarized the development of fNIR application in

newborn brain functional imaging, and had summed up

38 applications in this field just up to the end of

2009.[11]Fengyu and JiaoXuejun from Tsinghua

university and ACC developed a multichannel fNIR

system, the system was applicable to neonatal head blood

oxygen state bedside monitor. After ensuring system

safety, they verified the effectiveness of the system

through forearm occlusion and ValSalva’s experiments.

The experimental results accorded with physical laws,

were similar with the relatively results other researchers

got, and supplied the blood volume (CBV) information.

At the same time, they carried on ValSalva’s experiment

on adults, which proved the effectiveness of the

apparatus for measuring the human head CBV. Their

research provided a basis for the further study of neonatal

head blood oxygen activity and brain response

characteristics, and will promote the study in early

diagnosis of neonatal hypoxic ischemic encephalopathy.

[20]

2.7. Pediatric Pain Assessment

Dr Harel Rosen et al designed a set of pediatric pain

assessment by using fNIR. They found obvious growth

of oxy-Hb and deoxy-Hb when during pain stimulation.

The head blood volume growth under stimulation they

showed was consistent with the prior research.[12]

2.8. Muscle and Brain Oxidation Process

Monitor

Related researchers tested and verified that fNIR can be

used for understanding the metabolism process of healthy

muscle, the effects of disease on muscle’s oxidation and

metabolism, and evalu ating the efficiency of intervention

treatment.[21] Especially in the field of aerospace,

muscle oxygen monitoring can be used for guiding the

training of athletes, and the astronaut muscle strength

change mechanism analysis.

2.9. Depth of Anesthesia Monitor

J. J. PAN, X. J. JIAO

School of medicine in Drexel University conducted an

experiment about monitoring depth of anesthesia by

fNIR. The results showed that the content of deoxy-Hb

had obvious difference between deep and superficial

anesthesia, thus proved that fNIR could be used for

clinical anesthesia depth monitoring. [12]

2.10. Social Science and Medicine in the Future

Relevan t rese arc her focu ses on the applicatio n of fNIR in

neonatal and adult language processing. [28] And there

are also some research directions are about the brain

responses of social people.[27] Andreas Fallgatter is

carrying out a research about psychiatry using fNIR.[28]

these research directions of fNIR will contribute to the

development of social science and medicine. With the

development of fNIR, it can also be used in learning

environment. It will help constitute personalized training

mechanism, and evaluate th e operators’ effort in multiple

tasks circumstance.[29]

2.11. Space Environment

In space environment, fNIR can be used for astronauts to

monitor their working load and cognitive performance.

Many studies showed that in space environment, the

cognition and operation ability of astronauts will change .

Study of Stefan Schneider et al demonstrated that fNIR

could provide brain structure and functional information

in extreme circumstances. And we could use fNIR to

explore oxidation information in different regions of the

cerebral cortex. So we could realize the measurement of

human brain hemodynamic data and function

information in space environment.[26]

There are two available methods to measure brain

functions in aerospace field, EEG and fNIR. And fNIR

has many advantages when compared with EEG. FNIR

do not use to apply conductive paste, is not sensitive to

motion interference, and is comfortable to objects etc.

There are many application fields in apace environment,

such as cognition function, mental workload, emotion,

adaptive human-machine interaction, training

performance assessment in orbit, mental fatigue,

operating force varying mechanism analysis and so on.

3. Problems and Development Trend of fNIR

FNIR has lots of advantages, such as safe, convenient,

little restriction, fast imaging, green, it has balanced time

and spatial revolution, and it can be used freely not only

in daily life, but also in extreme circumstance like space

environment. However, it still exist some problems that

need further to develop, such as MA (motion aircraft),

physiological noise, resolution, unified analytical method

and so on.[25]

3.1. Motion aircraft (MA)

FNIR can monitor the changes of HbO and Hb in the

brain. However, any physiological phenomenon or

activity occurred from head or other parts of the body,

can lead to changes in the fNIR indexes, and bring the

fNIR signals some interference. In particular, the motion

of human body can lead to this change, which is called

MA. Eliminating the interference of human motion on

fNIR signal, is very necessary for the reliable use of

cognitive activity evalu ation.[22]

Some researchers are doing related study about fNIR

MA, Meltem Izzetoglu proposed a Kalman filter to solve

the movement interference for fNIR signals. In fNIR field,

there are only adaptive filer and Wiener filter methods

before, which were widely used in biology,

communication, and voice processing etc. However,

adaptive filter needs additional sensor an d hardware, and

changes the transmission function according to the

characteristics of input signals. And Wiener filter need

fixed data, it cannot be effectively used in real-time

environment. This newly proposed method could reduce

the motion interference in fNIR signal effectively. FNIR,

which combines the advantages of adaptive filter with

the Wiener filter, has higher SNR, ne eds no extra sensor,

and is applicable for real-time use. [23]

In addition, Behnam Molavi proposed a fNIR MA

elimination method based on wavelet. This method relies

on the difference of cycle and amplitude between motion

artifacts and fNIR signals, and is designed specially for

long motion artifacts. Through fNIR experiments on 3

infants, they confirmed that this method could effectively

eliminate the motion artifacts, and obtain a better artifact

reduction. This method is very suitable for eliminating

fringy motion artifacts, and artifacts with short cycle and

high amplitude. And the wavelets are changed adaptively

based on the changes of noise. [22]

These methods are effective, but they also have some

limitations. Therefore, one development direction of fNIR

signal should be to minimize interference as weak as

possible. Little MA is an advantage for fNIR compared

with other imaging methods (such as EEG, fMRI etc), so

it is important to constantly develop and strengthen this

advantage.

3.2. Resolution Problem

From fig [1] we can see that, fNIR has higher spatial

resolution than EEG, and higher time resolution than

fMRI. It is a balanced and comprehensive method.

However, fNIR may be less excellent than EEG or fMRI

in some extreme required conditions, such as in very

high spatial or time resolution conditions. Therefore, we

should combine and use their advantages. A very good

method is to combine the fNIR with EEG or fMRI, make

full use of their advantages, so can we deal with the

J. J. PAN, X. J. JIAO 51

resolution problem and get accurate and quick brain

information presentation.

3.3. Sensor

Compared to the existing fixed hood type fNIR sensor,

future design of sensor should include modular sensor

and hairbrush sensor. The modular sensor can adapt to

adult and children, and all kinds of forehead size. And

hairbrush sensor can install light source and perceptron

in the hairbrush, it can make the light source and detector

contacted to skin directly by separated the hair. This

design will allow fNIR to measure information of

forehead and all other cortex area in brain, which has

never been realized before.[2] And we should also focus

on the issue about how to detect the comfort and

accuracy of sensor.

3.4. Develop toward More Convenient Direction

FNIR develops from wired style to wireless style. There

was only cable fNIR equipment before Maurico

Rodriguez published an article about wireless fNIR

device in 2011. He studied and designed a wireless fNIR

system. Science develops quickly, and now we can find

many excellent wireless fNIR products. [1]

Although fNIR is very smart and convenient when

compared with other imaging modalities, it still needs to

develop toward a more convenient, compact, and light

direction. Thus it can be more suitable for using in

learning and training.

3.5. Establish a Standardized Method of Data

Analysis

Although we have made remark able progress in the field

of light propagation in brain tissue, and the field of image

reconstruction from optical data, there is no standard data

analysis method to establish DOT image by multi-chan-

nel system, and no standard data analysis method to

determine statistical characteristics and cortical oxidative

changes.[28] So establishing unified data analysis

methods is also a very important development direction

for fNIR technology application.

3.6. Combination with Other Techniques

By combining the eye-movement apparatus and fNIR

technology, we can capture the attention points and get

relative brain activities simultaneou sly. This function can

be easily realized by combining convenient fNIR and

accurate eye-movement apparatus.[27]

In addition, we can achieve more accurate and quick

presentation of brain structure and function by combining

fNIR with EEG, fMRI etc.

4. Application Prospect of Aerospace

Neuroscience is developing very rapidly, and fNIR will

no doubt pl ay a key role i n fut ure as a h uman brain activity

measurement tool in neuroscience, especially in aerospace

field.

Aerospace comprises the atmosphere of earth and

surrounding space. Typically, aerospace industries

combine aeronautics and astronautics to design and

maintain vehicles moving through air and space. The

environment in aerospace is very extreme, such as

weightlessness, radiation, vacuum, large temperature

difference, vibrancy, and long distance. Aerospace

activities are hard, large and expensive. So each kilogram

in weight must be seriously considered in aerospace

field.

The equipment used in space circumstance must be

portable, safe, simple and no much restriction, and fNIR

has these characteristics. Thus fNIR is competitive in the

field of aerospace. FNIR may be used to monitor the

astronauts’ performance and skills duri ng traini ng and learn-

ing process. FNIR may also be used to acquire

astronauts’ cognitive state when they were in space work.

To sum up, there are many application fields in apace

environment, such as cognition function, mental

workload, emotion, adap tive human-machine interaction,

training perform a nce assessment in orbit， mental fatigue,

operating force varying mechanism analysis and so on.

With the development of science and technology,

people pay more attention to human being themselves.

We can see more and more human-centric training,

learning, and human-centered machine and equipment

emerge, and these new things also obey the ergonomics

law of safety, efficiency, and comfort.

The technology of fNIR not only obtains human physic-

ology and brain activity information, but also has the

characteristics of safe, green, convenient, quick, and

ergonomics trait. These proved the considerable

development space of fNIR. We can see its fine vitality

and development prospect in aerospace and many other

fields.

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