fNIR BrainSpy 28
Newmanbrain fNIR BrainSpy 28 is a portable neuroimaging device capable of measures changes in the metabolic activity of specific areas during various mental processes.
Functional Near-Infrared Spectroscopy (fNIR or fNIRS), is the use of NIRS (near-infrared spectroscopy) for the purpose of functional neuroimaging. Using fNIR, brain activity is measured through hemodynamic responses associated with neuron behaviour.
Neuroimaging technologies have contributed a great deal over recent years to our current understanding of brain functions. The most common modalities of neuroimaging techniques are functional magnetic resonance imaging (fMRI), positron emission tomography (PET) imaging, both based on the indirect imaging of hemodynamic changes resulting from neuronal activity. Magneto-encephalography (MEG) and electro-encephalography (EEG) are, direct imaging technologies based on the electrical / magnetic manifestations of neuronal activity. Many of the aforementioned techniques have a high temporal resolution but little spatial resolution (MEG and EEG) or vice versa (fMRI and PET), which restricts in the explanation of the neuronal bases of biological processes.
Near-infrared functional spectroscopy (fNIR) is an emerging technology that uses near-infrared light to measure changes in the concentration of oxygenated and deoxygenated hemoglobin in the cerebral cortex. FNIR has a temporal resolution in the order of seconds and a spatial resolution in the order of centimeters. Among other advantages, a major benefit is the fact that is a non-invasive, safe device. In addition, our fNIR BrainSpy 28 is also portable, wireless and relatively affordable.
The fNIR methodology is based on recording local hemodynamic changes, specifically changes in blood oxygenation, as an indirect measure of changes in neuronal activity. Neuron activity consumes energy derived from glucose metabolism, so an increase in neuronal activity implies an increase in the glucose and oxygen consumption of the local capillary bed. A reduction of local glucose and oxygen stimulates the brain to increase local arteriolar vasodilation, which increases local cerebral blood flow (CBF) and cerebral blood volume (CBV); This relationship between hemodynamic changes and neuronal activity is known as “neurovascular coupling”. Over a period of several seconds, the increase in CBF brings glucose and oxygen, transported via oxygenated hemoglobin, to the area. Increased oxygen in the area usually exceeds the rate of local oxygen utilization, resulting in an over-abundance of cerebral blood oxygenation in the active areas. Although the initial increase in brain activity is thought to be a result of local increase in deoxygenated hemoglobin in the capillary bed, since oxygen is withdrawn from hemoglobin to be used to metabolize glucose, this characteristic of the vascular response Is very difficult to measure and is currently controversial.
Biological tissues absorb very little NIR light allowing it to penetrate several centimeters into the tissue before being detected. The main chromophores of the tissues are water, lipids, melanin and hemoglobin. Water, lipids and melanin have an absorption spectrum that escapes the range of infrared light (also called “optical window”), comprising wavelengths between 700nm and 900nm (Figure 1) behaving as if they were transparent as well. The chromophores that do absorb inside the optical window of infrared light are oxygenated hemoglobin (HbO) and deoxygenated hemoglobin (HBR), both with characteristic optical properties. The wavelengths we use to maximize sensitivity when detecting the full amount of absorption of HbR and HbO are 740nm and 860nm, respectively.
The propagation of light in tissues is governed by the absorption or dispersion of light photons. The photons follow an optical path that travels the “banana-shaped” tissue from the light source (LEDs) to the detector (D). The depth that this banana-shaped path reaches in the cerebral cortex depends directly on the distance between LED and D. The greater the distance between the two, the more light will penetrate the tissue, but it will also imply that the signal arrives with more interference; Therefore the range of distances between LEDs and D that is usually used oscillates between 2 and 7 cm.
The depth also influences the thickness of the skull and superficial layers of each individual, so we take 2 registers at two different LED-D distances of 2.5 cm and 5.5 cm (Figure 2), to ensure that the Hemodynamic changes that we are measuring correspond to changes in the activity of the cerebral cortex and not to those corresponding to the more superficial areas (vasculature of the meninges and skin).
It should be noted that the fNIR system does not predict absolute oxygen and hemoglobin concentrations, but rather the relative changes in these parameters as a function of time, thus reflecting the relative changes in neuronal activity in response to specific stimuli. What we are actually measuring are the changes in the number of photons that are absorbed and the photons that are dispersed due to changes in the concentration of the chromophores. The relationship between the light absorbed by the tissue and the amount of chromophores possessed by the medium is given by the Law of Lambert-Beer.
A = εʎ c d
A = Absorbance or optical density (OD)
εʎ =Molar extinction coefficient for a wavelength ʎ. It is expressed in cm-1 μM -1.
c = Concentration of the chromophore (micro moles, μM)
d = Distance between light source and detector (centimeters, cm)
– The same equation can also be expressed as follows (Figure 3):
ΔOD = – log (Io / I) = ε Δc d DPF
ΔOD = increase in optical density
Δc = increase in concentration
I = input light intensity
Io = output light intensity
DPF = wavelength-dependent differential path length factor. It is a correction factor of the average distance that the photon has traveled.
In this way, the continuous wave fNIR system allows us to measure the optical densities of oxygenated hemoglobin (HbO) and deoxygenated hemoglobin (HbR) with regards to time; Thus, by applying the modified Lambert-Beer law, we can calculate the changes in HbO and HbR concentrations in the tissue of interest, and changes in oxygenation.
Oxygenation = Δ CHbO – ΔCHbR
Why fNIR BrainSpy 28?
The underlying difficulty in designing a good system for recording brain activity lies in the knowledge of neurophysiological processes. It is not easy to have this “know-how” which can only be acquired after many years of dedication to science. The fNIR Brainspy 28 from Newmanbrain has been designed from the outset with integration in mind. A simple addition of elements is not the right solution since it complicates the scalability of the system as well as the client training.
Our system can be easily worn, fundamental for recording in environments outside the laboratory, “Wireless”, fundamental to allow freedom of movement to the patient, has 28 channels, fundamental to obtain good spatial resolution, is a “Multidistance channel” device which allows the separation of superficial and deep signals and incorporates a “Patient Motion Detector”, fundamental for eliminating artifacts in the registry.
The fNIR BrainSpy 28 is ideal for capturing brain activity while having the freedom to perform daily activities including exercise. The device consists of 28 channels covering the full prefrontal cortex. The fNIR BrainSpy 28 measures changes in oxygenation in terms of oxyhemoglobin, deoxyhemoglobin and total hemoglobin. This device can be applied in a variety of dynamic settings as often required in neuroscience and sports science research.
The research published to date is based on the establishment of the fNIR technique as a neuroimaging technology with valid and reliable results. Our fNIR BrainSpy 28 can be used to evaluate cognitive and emotional functions with normal subjects and patients with different pathologies (attention deficit and learning, neurodegenerative diseases) as well as the evaluation of staff (work or sports) and activities of practical education for college students of neuroscience, psychology, psychiatry, sports medicine, etc. It can be used in different environments including daily life situations of the patient thanks to its portability, comfort and ease of use. In summary, the fNIR methodology is a novel, non-invasive, portable and secure imaging technique; which allows the evaluation of brain activity in response to motor, visual, auditory stimuli and cognitive tasks in adults and children.
Included with fNIR BrainSpy 28
|NIRS TECHNIQUE USED||Continious wave near infrared spectroscopy using modified lambert-beer law.|
|MEASURES||Brain activity based on hemodynamic responses obtained by the relative changes in oxy-deoxyhemoglobin of the prefrontal cortex.|
|LIGHT SOURCES||Dual infrared LEDs with 256 different power levels.
740nm and 860nm wavelengths.
|LIGHT SENSORS||10 High sensitivity preamplified sensor.|
|CHANNELS||Up to 16 superficial channels with optode distance of 12 mm.
Up to 12 deep channels with of optode distance of 32 mm./td>
|RESOLUTION||16 bits for every channel.|
|COMMUNICATION||Wireless connection to computer via Bluetooth.|
|SAMPLING FREQUENCY||10 Hz for all channels.|
|SOFTWARE||Specialized software with real-time filtering, visualization and analysis.|
|STORAGE||Real-time, unlimited data storage in experiments of up to 30 minutes.|
|POWER||At leat 10 hours of non stop recording with included lithium battery pack.|
|DIMENSIONS||Device: 18 x 6.5 x 4.5 cm (WxHxD)
Battery Pack: 7.2 x 2.2 x 3 cm (WxHxD)