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Combined EEG/NIRS

Combined EEG/NIRS

In close cooperation with Artinis Medical Systems (www.artinis.com)  we are developing a dedicated EEG/NIRS head cap for the simultaneous measurement of EEG and NIRS.

EEG and NIRS (Near-InfraRed Spectroscopy) both offer information about brain function, complementing each other in their ability to resolve information about the spatial and temporal characteristics of neural activity. The electrical potentials in brain tissue can be measured by EEG with high temporal resolution. NIRS measures the changes in oxygenation and blood volume, which reflects a different aspect of neural activity with high spatial information. Our EEG amplifiers do not interfere with NIRS signals. 

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Electrocardiography (ECG)

Electrocardiography (ECG)

Several techniques are available to measure the heartbeat, with the electro-physiological measurement of the heart muscle signal or electrocardiography (ECG) being the most used one. 

An ECG is not only suitable for measuring the heart rate and the regularity of heartbeats (heart rate variability or HRV), but also to extract additional information, such as the size and position of the chambers and the presence and place of any damage to the heart. Sometimes even upt to 128 electrodes are used for cardiac mapping.

A typical ECG recording of one heartbeat consists of a P wave, a QRS complex, a T wave, and in some cases also a U wave. Usually more than two electrodes are used for measuring the ECG. The most simple is the 3-lead ECG with one electrode on the left arm (LA), one on the right arm (RA) and one on the left leg (LL). These electrodes are often used to make three bipolar leads, being lead I (LA+RA), lead II (LA+LL) and lead III (RA+LL). A more elaborate ECG recording is the 12-leads ECG, in which also the so called precordial leads are measured.

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Electroencephalography (EEG)

Electroencephalography (EEG)

Electroencephalography (EEG) is the recording of electrical activity along the scalp. The brain's electrical activity, which is measured with the EEG, is maintained by billions of neurons.

The EEG cannot pick up the electrical potential generated by a single neuron for it is far too small. Voltages measured by the EEG therefore always reflect the synchronous activity of thousands of neurons. The EEG is mostly produced by cortical neurons, because activity from deeper sources is more difficult to detect than currents near the skull. Most of the cerebral signal observed in the scalp EEG falls in the range of 1-20 Hz and have an amplitude in the range of 5-200 µV. However, meaningful activity up to several hundreds of Hz has also been reported.

An EEG can be performed by applying different electrodes on the scalp of the subject. In most clinical applications, 19 electrodes may be sufficient, but also set-ups up to 256 electrodes are used. Therefore so called EEG headcaps are often applied in which the electrodes are already integrated in a standard configuration. Most often the electrode configuration is according to the International 10-20 system, an internationally recognized method to describe and apply the location of scalp electrodes in the context of an EEG test or experiment.

Measurement of EEG is often performed in the fields of Psychology and Neurology, but also in BCI (Brain Computer Interfacing), Neurofeedback or Neuro-Marketing.

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Electromyography (EMG)

Electromyography (EMG)

Suppose we want to measure the electro-physiological signal of a muscle, the so called electromyogram (EMG). There are two main types of EMG: surface EMG and intramuscular (needle and fine-wire) EMG.

Most applications of EMG only require the surface EMG, which has the advantage that it is non-invasive. For measuring EMG we must place some surface electrodes on the skin above the muscle, to collect the signals that are generated by the large amount of muscle fibers. Typical EMG potentials range between less than 50 ┬ÁV up to 20 or 30 mV in amplitude.

To measure the EMG of a certain muscle, two electrodes are necessary to get a bipolar montage. With our systems this can be done by using a bipolar input channel of one of our devices. Another possibility is to use two unipolar input channels with one unipolar electrode each and then do the montage (electrode1-electrode2) in software (e.g. TMSi Polybench). Of course, in both cases a patient ground electrode is also needed.

We also offer the possibility to measure High Density (HD) EMG, with multiple electrodes covering one muscle (see relevant accessories below). 

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High Density EMG

High Density EMG

Traditionally, neuromuscular disorders have been diagnosed with needle EMG, often in combination with motor-nerve conduction studies. In the latter, surface electrodes are widely used to record the compound muscle action potentials.

Other than this, single bipolar surface recordings are not being used in routine electro-diagnosis, because of inherent limitations. They are being used, however, in other fields, such as kinesiology, ergonomics, rehabilitation and sports medicine, where it is important to record on-off switching of muscles or to estimate muscle force.

Obviously, needle EMG also has disadvantages, the most prominent being the invasiveness and the lack of spatial information.

With the above in mind, a number of research groups around the world have started to evaluate the possibilities of high density surface EMG (HDsEMG), using dense arrays of individual electrodes, to obtain information from the muscle. This information is sometimes overlapping, but often complementary to the information extracted by needle EMG

At this point, HDsEMG is still very much in the research phase. It is thought, however, that it may become clinically useful in the assessment of for example motor fiber conduction velocity (MFCV) measurements (see specifications below).

Obvious advantages of HDsEMG are its non-invasiveness (especially attractive in pediatric applications) and its ability to record over very long time periods.

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