| Combined NIRS / EEG solution |
| ANT has collaborated with NIRx Medical Technologies, LLC since the start of 2010 to develop a solution for combined NIRS tomography / EEG acquisition. This solution combines the best features of the DYNOT-232 imager WaveGuard cap, ASA-Lab EEG/ERP and Xensor 3D digitizer systems. The first system is taken into use at the University of Goettingen. |
NIRS tomography NIRS tomography makes use of the fact that light penetrates up to several centimeters of biological tissue. This is demonstrated by an experiment such as depicted in the image to the right. Here, a bright white light source is directed toward a hand, causing a reddish glow in places where light is transmitted through the tissue. The red color is caused by the pigment hemoglobin in the red blood cells, which primarily absorbs wavelengths outside the red and near infrared spectrum. It is seen that no inner structures such as bones or veins are readily revealed by this simple transillumination technique. |  |
| NIRS tomography employs sensitive instrumentation to precisely measure the amount of light that is transmitted through a body site of interest. Many transmission measurements (hundreds or thousands) are performed in different locations on the target surface creating large data sets which are then used to compute an image of the underlying tissue composition. It is known from e.g. fMRI research that neural activation has a vascular response that serves to replenish activated tissue with improved blood flow. Functional studies have shown that the brain activation produces a spatially distributed and temporally varying response. Techniques such as electroencephalography (EEG) and its magnetic equivalent, magnetoencephalography (MEG), provide a high degree of temporal resolution but have markedly reduced spatial resolution, especially for EEG, compared to anatomic imaging techniques (e.g., MR, CT). An imaging modality that is proving to have significant impact in investigative studies is functional MRI (fMRI). This technique is sensitive to the vascular response resulting from brain activation, specifically to the level of deoxyhemoglobin. While the utility of fMRI continues to expand, it is also clear that the technique has a number of limitations that are not encountered using near infrared techniques. Value/Advantages of NIRS tomography are: *) High temporal resolution. *) Excellent intrinsic sensitivity to hemoglobin. *) 3D imaging capability. *) Measurements possible with a variety of tasks. *) Economical, portable, scalable. |
Combined NIRS / EEG acquisition ANT and NIRX have integrated their NIRS and EEG / ERP systems. The fibers that are a part of the DYNOT-232 system can be connected onto a NIRS compatible WaveGuard cap. The positions of the optodes are placed according to an equidistant layout where the EEG is positioned according to the 10/20 system. There is also the possibility of measuring EEG at the same positions as NIRS optodes. The EEG is measured using the ASA-Lab amplifier and acquisition software. EEG and NIRS measurements run simultaneously: trigger information that comes from stimulation experiments are acquired in both datastreams. |  |
3D Xensor digitization Xensor provides an approach to 3d electrode digitization for combined NIRS / EEG measurements. This way topographical map of EEG / ERP or EEG spectrum can be visualized but also topographical maps of hemodynamic response. The sensor digitizer system uses a very accurate technique based on infrared light to track tools (like a digitizer pen or head tracker). The system takes care of the sensor digitization procedure and records, visualizes and stores the digitized electrode and optode positions. The sequence of the digitization procedure is pre-defined by the user. Positions are acquired by locating the respective sensor at the scalp, placing the digitizer pen at that location and pressing a button. Markers (nasion, left and right pre-auricular points) are digitized as well. This way, the 3D sensor positions are transformed to the nasion-ear coordinate frame.For more information about the NIRS / EEG system, contact ANT International Sales. |
| written by Ruud Kalis |
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