What is tEEG and how does it differ from EEG?
Electroencephalography (EEG) is the recording of brain electrical activity using electrodes placed on the scalp. It measures the difference in potentials between electrodes which are generated by ionic currents flowing within neurons of the brain.
Conventionally, EEG is recorded with disc electrodes. When novel tripolar concentric ring electrodes (TCREs) are utilized for recording, the resulting EEG is known as the tEEG.
When only the outer ring of the TCRE is used for sensing, it provides the disc electrode emulation that is equivalent to the conventional EEG. In other words, you can simultaneously obtain both tEEG and conventional EEG with TCREs and the t-Interface.
What advantages does tEEG have over EEG?
Fundamental problems of EEG
Research and medical communities have been struggling with the following problems with EEG for decades.
- Artifacts contamination
- Poor spatial resolution
- Low communication rates of EEG systems, likely due to the smearing, spatial averaging, across many neurons with dissimilar properties.
Advantages of tEEG
- Superior artifact rejection, -75 dB one radius from the electrode [Besio et al. 2006]
- Improved signal-to-noise ratio (SNR) (375%-420%) [Besio et al. 2006, Koka and Besio 2007]
- Higher spatial resolution (approx. 10 times improvement) [Liu and Besio 2013, Koka and Besio 2007]
- Reduced mutual (overlapping) information (to only 8%), supporting higher information content in tEEG [Koka and Besio 2007]
- 1/10 time to collect event related potentials (ERPs), significantly shortening experiment time [see “Videos” section]
- Ability to record high frequency activities [Besio et al. 2013]
Read on for further explanation of the advantages of tEEG.
tEEG’s Superior Artifacts Suppression
The figure below compares the EEG and tEEG simultaneously recorded from a patient with epilepsy while the patient was moving his head. The EEG was severely contaminated by muscle and movement artifacts during movements by the patient (as seen in the signals on the left) even when bipolar pairs of disc electrodes were used to reduce noise (e.g., the F4-C4 pair). In contrast, the referential tEEG signal, recorded from t-Leads next to the same locations, was very clean (signals on the right).
tEEG’s Advantage over Software Filters
High- or low-pass filtering can reduce artifacts, but also generally removes a significant portion of the relevant signal. While software filtering solutions are available to “clean” the signal, all digital software solutions represent transformed data. As such, the data may not faithfully reflect the underlying physiology, or may inadvertently remove or attenuate the signal itself. When EEG is used as part of a pre-surgical evaluation to determine which temporal lobe to remove to cure seizures, accurate data are of critical importance.
Unlike any existing approach, tEEG suppresses artifacts and increases the interpretability of EEG through hardware innovations: (1) a transformative electrode configuration – the tripolar concentric ring electrode (TCRE) sensor; and (2) a proprietary tInterface which serves to configure the electrode elements, route, and pre-amplify the signals. Unlike software filtered data that do not represent the underlying physiology, tEEG’s artifact suppression is reality-based.
Enhanced Spatial Resolution with tEEG
Conventional EEG from disc electrodes lacks high spatial resolution primarily due to the blurring affects of the volume conduction of the head. Literature shows that EEG electrodes would need to be 10~20 mm apart to capture all the information originating from the brain [Malmivuo & Plonsey, 1995; Srinivasan et al., 1998].
Koka and Besio  placed conventional disc electrodes and tripolar concentric ring electrodes (TCREs), both 10 mm diameter, side-by-side during movement related potential experiments and found that there was very high mutual information in the conventional disc electrode EEG. High mutual information means that the signals are highly duplicative. Conversely, there was much lower mutual information when the TCREs were used, only approximately 8% of the mutual information found in the conventional disc electrode EEG. This experiment demonstrated that simply increasing the density of conventional disc electrodes does not translate to improved spatial resolution. TCREs can be spaced less than 10 mm apart thanks to their extremely low mutual information content. The minimum spacing for conventional disc electrodes is much greater than 10 mm because of their high mutual information. tEEG, the current density of the signals, is not as distorted by the volume conduction and has higher spatial resolution.
Read about detecting seizures and discovering new biomarkers with tEEG here.