Imagent™

Functional Brain Imaging System

Imagent™: Brain Imaging using Infrared Photons

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 millimeters) 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).

The ISS Imagent™ provides a balance between temporal and spatial resolution for the study of superficially located areas of human brain. Imagent™ detects variations in the oxygenation levels of activated brain areas and provides a map of the areas where the changes occur. The technique is called Diffuse Optical Tomography (DOT).

Imagent™ is an instrument capable of detecting changes in areas of the brain activated by an external stimulus; the detected signal is processed and produces a map of the activated area.

The instrument working principle is based upon the use of infrared light to probe changes in the brain hemodynamic response. Infrared light at a wavelength in the range from 670 nm to about 850 nm penetrates fairly freely in tissues; it can go through the bone of the skull, traverse the dura matter and the arachnoid matter. Infrared photons can reach about 2 cm below the skull’s surface all the way to the cortex area where most of the grey matter is located; from there, some of them are scattered back throughout the tissue all the way to the surface and escape out. Whenever a change in the relative concentration of oxy- and deoxy-hemoglobin occurs in the cortex, a change in the number of photons escaping the brain is detected.

Imagent™ delivers photons by using fiber optics that are positioned on the head of the patient (emitters); other fiber cables (collectors) are positioned at proper distances from the emitters to collect the photons that escape the tissue. Up to 64 fiber sources and up to 8 fiber collectors can be positioned on the head.

Imagent™ utilizes the frequency domain technology whereas the light sources are modulated at high frequency and three parameters of the detected signal are measured: the intensity, the modulation depth and the phase delay. Any two combination 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.

Functional information, versus structural, derives from the slow (> 100 ms) and fast (< 100 ms) optical signals observed during brain stimulation. Functional measurements have been reported on the motor cortex during motor stimulation; on the visual cortex during visual stimulation; on the frontal region during mental work; and on the monitoring of cerebral hemodynamic during sleep. These are some of the techniques utilized:

1. For fast signals: EEG, MEG, NIRS measurements: scattering, neuronal membrane
2. For slow signals: fMRI, PET, NIRS measurements: Hemoglobin concentration, changes in blood flow, Neurovascular coupling

Imagent™ captures both the slow signals (hemodynamic changes) and the fast signals (the event related optical signal, or EROS).