ImagentFunctional brain imaging system

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Overview of Imagent

Imagent provides a balance between temporal and spatial resolution for the cognitive study of superficially located areas of human brain by addressing two main applications techniques:

  1. Functional Near Infrared Spectroscopy (fNIRS), which detects changes in the absorption of the optical signal in response to a stimulus and provides a map of the areas where the changes occur. The changes in the optical signal (time scale > 100 ms), are due to local variations of oxy- and deoxy-hemoglobin concentrations.

  2. Event Related Optical Signal (EROS), which detects changes in the scattered component of the diffuse signal subsequent to a stimulus. The changes (time scale < 100 ms) are due to the variation in the shape of the glia and neurons and/or in the optical properties of the membrane.

Brain imaging techniques can be broadly classified in two groups. One group includes the techniques that have a good spatial resolution (up to 1 - 2 mm) but a poor temporal resolution, such as functional Magnetic Resonance Imaging (fMRI) and Positron Emission Tomography (PET). The second group includes techniques featuring an excellent temporal resolution (of the order of milliseconds) but providing a limited spatial information. This group includes the Event Related Brain Potential (ERP) and the Magneto-encephalography (MEG). Imagent captures both the slow signals (hemodynamic changes) and the fast signals (EROS).

Notice: Investigational device. Limited by Federal (or United States) law to investigational use. The ISS Imagent is presently used for research only.

Key Features of Imagent

Measures Both Amplitude & Changes in Average Transit Time

Measures Both Amplitude & Changes in Average Transit Time

Fast Measurements Up to 50 Hz

Fast Measurements Up to 50 Hz

Applicable to a Wide Range of Research

Applicable to a Wide Range of Research

Applications for Imagent

fNIRS

Cognitive Neuroscience

  • Auditory cortex
  • Motor cortex
  • Visual cortex
  • Language centers

Physiological monitoring

  • Stress studies
  • Working memory in aging
  • Mapping epileptic areas in the brain

Virtual Reality

Brain Computer Interface

EROS

Cognitive Neuroscience

  • Auditory cortex
  • Motor cortex
  • Visual cortex
  • Language centers

How Imagent Works

Imagent's working principle is based on the use of near infrared light for probing the cortical surface. The main tissue absorbers in the wavelength region spanning from 700 nm to 900 nm are oxy-hemoglobin (HbO2) and deoxy-hemoglobin (Hb); on a smaller scale, water, fat and cytochrome oxidase contribute to the partial absorption of the light. The penetration depth of light in tissues is quite significant in this wavelength range. For typical head tissue (skin/scalp, skull and cortical layer), with an absorption coefficient of μa = 0.1 cm-1 and a scattering coefficient μs' = 8 cm-1, the maximum optical penetration can be estimated to be about 1.5 cm when a detector is placed at 4 cm from the source. The penetration depth can be increased by increasing the distance between the source and the detector, although, eventually, the signal-to-noise ratio of the measurement deteriorates.

Main Tissue Absorbers Wavelengths
Figure 1. Main tissue absorbers in the 600 - 1100 nm region.

Imagent utilizes laser diodes emitting at 690 nm and 830 nm. The light is delivered by fiber optics positioned on the head. Upon entering the tissue, the near infrared light, albeit weakly absorbed, is highly scattered by the tissue in homogeneities. A fraction of the light leaves the tissue and it is collected by the collecting fiber that carries it back to the light detectors housed in the unit for data processing. The fibers are kept in place by a headgear, which is available for adults and children; for the study of specific areas, pad sensors are available. Up to 128 fibers and up to 60 detectors bundles (for a total of 3,840 optical channels) can be positioned on the head of an adult. Different patterns (montages) of the excitation and collection fibers can be used.

Light penetration in brain tissue
Figure 2. Light penetration in brain tissue using Imagent.

Imagent utilizes the frequency domain technology; whereas, the light sources are modulated at high frequency (of the order of 100 MHz) and three parameters of the detected signal are measured: the intensity, the modulation depth and the time it takes to traverse the tissue (phase delay). Any two combinations of the three measured quantities can be utilized to provide changes in the physiological parameters, the choice being dictated by the specific parameter to be measured, by the need to reduce physiological noise and by the time scale of the event to be measured.

Product Specifications for Imagent

Operations:
  • Method: frequency domain
  • Modulation frequency 110 MHz
  • Sampling time: minimum 15 ms
  • Number of optical channels: 16 to 960
Measured Parameters: fNIRS
  • Changes in O2Hb oxygenated hemoglobin
  • Changes in HHb deoxygenated hemoglobin
  • Changes in Hb total hemoglobin
Measured Parameters: EROS
  • Signal intensity
  • Signal phase delay
Light Sources:
  • Fiber coupled laser diodes
  • Wavelengths: 690 nm and 830 nm
  • Laser power: 10 mW average
Light Detectors:
  • Photomultiplier tubes
Optodes:
  • Paired fibers in excitation, 400 µm diameter
  • Fiber bundle in collection, 3 mm diameter
Interface:
  • Interfaceable to FastTrack by Polhemus for Talairach registration technique of brain coordinates
Pre-Amplifier Discriminators:
  • 600 MHz bandwidth, TTL output
Computer and Operating System:
  • Intel-type CPU, Windows 10 operating system
Power Requirements:
  • Universal power input: 110 - 240 V, 250 W
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