5.1 DC offset voltage and resistance measurements
5.2.1 Quality compared to hospital electrodes
In the following pictures the two top channels are hospital Ag/Ag-Cl electrodes (Hospital electrodes), and the four following are from the BrainCare electrodes, and the bottom trace is the subject’s heartbeat (i.e., ECG)
FIGURE 31. Surface measurements for the rapid eye blinking tests (looking up and down).
in the above figure 31, we can see the traces of EEG measurement from rapid eye blinking (in the middle) and then looking upwards and downwards and after that some of the EEG signals look inverted compared to each other, but it is due to traces being on both sides of the head.
FIGURE 32. surface measurements from the rapid eye blinking tests (looking from left to right)
In the traces, above figure 32, we can see EEG measurement from rapid eye blinking and then looking from left to right. The top two channels are from the golden standard electrode and the rest four from UltimateEEG.
FIGURE 33. surface measurements for an alpha wave test (upper two traces belong to golden standard electrodes and the rest four belong to UltimateEEG and the bottom trace is the heart rhythm (ECG).
In the above figure 33, Here we see measurements from an alpha wave test, during a normal wake test. The subject’s eyes were closed, and they were told to relax. We can clearly see the alpha wave differences from regular EEG.
FIGURE 34. Measurement from the VEP-checkerboard pattern-reversal The above figure 34 represents the Visually evoked potential (VEP) the channels (Oz, O1, O2) belong to golden standard electrodes (Hospital eelctrode) and( Pz, P3, and P4) channels stand for UltimateEEG (BrainCare electrode).
In epilepsy measurements it is often needed to artificially induce a seizure, as the patient is not in his/her natural environment in the hospital and might not have any seizures during the stay otherwise. One of the common tests is a visually evoked potential test, where either a flashing light or a changing checkerboard pattern is displayed to the subject, and they focus on keeping their gaze to a specific spot on the screen. In the figure above, we can see a checkerboard pat-tern test. The channels marked with Oz, O1, O2 are hospital Ag/Ag-Cl electrodes and the channels marked Pz, P3, P4 are showing platinum i.e., the BrainCare electrode. As we see, there are differences in the electrodes are not visible, even though the BrainCare electrodes are not meant for surface measurements and the hospital electrodes are the best one’s hospitals use in Finland.
FIGURE 35. Real time impedance measurement from the subject.
In the figure 35, above we can see a real-time impedance measurement from the subject. The setup for the measurement is that the back of the subject’s head is shaved, measurement electrodes placed there, and the reference electrode is placed next to the subject's nose. This way the impedance measurement goes all the way through the head. The electrodes marked with O, are hospital elec-trodes and the elecelec-trodes marked with P are BrainCare elecelec-trodes. As we see there was something wrong with channel P3 as its impedance is close to the 5000
ohm (Ω) maximum limit. This is due to a bad connection to the back of the head due to hair stubbles being in the way. We can see that the BrainCare electrode performs better than the hospital electrodes (impedance lower) in channels Pz and P4.
FIGURE 35. The reference electrodes connected for Real time impedance.
In the above figure 35, the subjects head is shaved so that the reference elec-trodes can be attached to the head when shaved there are tiny hair stubbles the red wires signify the UltimateEEG and the white wires mean golden standard electrodes. This is done to take the real time impedance measurements from both the reference electrodes.
FIGURE 36. Depicting the same impedance measurements after some time
Here in the figure 36, we can see the same impedance measurement a little later, the channel P3 still had some problems that could not be solved. It was still a bad connection between the electrode’s measurement pad and the scalp.
6 DISCUSSION
The project was partly done in the Tampere university hospital (Tays) using EEG equipment’s available in the neurology department. The hospital electrodes known as Golden standard electrodes are industrially available, they were col-lected from Tampere University hospital for experimental purposes. The Ulti-maateEEG electrodes belong to BrainCare oy and they are coated with the plat-inum metal and these electrodes were designed and laser etched in the Tampere universitiy (TAU) sakhotalo laboratory.
Then to study the DC off voltage of both the electrodes Golden standard and UltimateEEG electrode, a small saline homemade experimental set up was made. Salt stimulates the conditions under the skin. The main idea was to take the voltage and resistance measurement from both the electrodes and to test their compatibility, functionality and analyse their stability. At the beginning the electrodes gave negative results due to misplacing of the digital multimeter lead probes and due to slight cracks formed within the UltimateEEG electrodes. The DC offset measurements were not standard at the beginning and later the exper-iment was repeated with a solution by placing the tape around the electrode. Here the tape acted as a protective barrier and as an insulator so the experiment could continue further.
As discussed earlier in the protocol the experiment was supposed to be contin-ued for a month and the electrodes resistance were to be measured in 2,4, and 6 weeks with electrodes A, B, and C. Due to lack of time the same experimental set up was done for two weeks (14 days) under different random temperature conditions. The voltage readings were taken every day and the resistant meas-urements was measured at the end of every consecutive week. After removing the electrodes from the saline solution to measure the opposition flow of the al-ternate currents. with the results it was significant that with the home-based ex-periment the resistance of the Ultimate EEG (BrainCare electrode) pads was un-der 200 ohms(Ω) and the DC offset voltage was below 200millivolts (mv) which means the electrode is standard and is fit to use for surface implantation. If the voltage value would have exceeded above 200 millivolts (mv) then the Ulti-mateEEG electrode would not have functioned properly.
The reference electrodes impedance measurements (Surface EEG measure-ments) were done with the Natus NicoleteOne amplifier available in Tampere University Hospital (TAYS) video EEG lab in the neurology department. To get the appointment to use the equipment’s there was delay two months due to the busy schedule of the doctors and the nurses. The measurements were taken to check if the UltimateEEG electrode could work along the golden standard elec-trode and if it is suitable for surface measurements because the ultimateEEG electrode is designed for long term monitoring. So, there were different tests done with the healthy and non-healthy individuals (people suffering from epilepsy) and their surface and real time impedance measurements were compared. when the measurement results were compared to check the functionality of the Ulti-mateEEG to the golden standard electrode it showed that the UltiUlti-mateEEG elec-trode worked equally to the golden standard elecelec-trode and in fact, the ulti-mateEEG performed better than the golden standard electrode. In all the meas-urements every upper two traces belong to the Golden standard electrode (Hos-pital electrode, TAYS) and the rest four traces stand for the UltimateEEG elec-trode.
According to pirhonen 2015, a superior quality electrode must have the imped-ance measurement under 5000 ohm’s (Ω) and the DC offset voltagef should be under 200 millivolts (mv). From the above results it was evident that the Ulti-mateEEG electrode is a standard quality electrode as it meets the values for a quality electrode. If the impedance measurements would have exceeded more than the required value, then the Ultimate EEG electrodes would be useless.
Recently BrainCare Oy, got CE marked for their device.BrainCare oy in future has a plan to do the pilot study with the actual people suffering from epilepsy and implant the electrode for long term monitoring. Because of the results it was clear that the UltimateEEG electrode can also be used for surface measurements. The future of BrainCare is to use the UltimateEEG electrode for various neurological disorders and to help people to have stress free life and a better future. Hopfe-fully, one day the UltimateEEG electrode can be commercially available in the market as a solution for the neurological disorders.
CONCLUSIONS
To conclude with the comparative study, the UltimateEEG electrodes were suc-cessful for the surface measurements and performed better than the Golden standard electrode according to the real time impedance measurements. There were few challenges at the beginning to analyse the voltage measurements and to get access to the video EEG laboratory in Tampere University Hospital (TAYS) with almost two-month delay. With all odds at the end real time impedance and DC offset voltage measurements show that the UltimateEEG electrodes per-formed better than the Golden standard electrodes. It is shown that the ulti-mateEEG can be also used for surface measurements when in actual Ulti-mateEEG electrode was meant for long term EEG monitoring.
The next step is to do a pilot study, with the UltimateEEG electrode to implanted on the patients suffering with epilepsy for long term monitoring with a software named Soenia application, this is like a diary where the seizure information can be stored, and it will be automatically updated in the cloud through the recording and measuring system from the electrode. From here it will be easy for the neu-rologists to access the seizure information. Hopefully, there will be a day that ultimateEEG will be in the commercialized giving solution to many patients suf-fering from epilepsy.
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APPENDICES
Appendix 1.Measurements from the DC offset Voltage, Black probe on silver with