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Questions and answers about the GES 250.
FAQS:
How long does it take to apply a 64-, 128-, or 256-channel
HydroCel Geodesic Sensor Net?
How do I apply the electrodes?
Do you have recommended protocols for Net application
and Net cleanup?
Don't I need to abrade the scalp to get good impedances?
Where can I find support for what you say about
impedances?
Can the patient lie down wearing a Geodesic Sensor
Net?
Can LTM be done using HydroCel Geodesic Sensor Nets?
What about video EEG?
Is this like those "caps"?
What about salt bridges?
Don't the electrodes move around?
What about thick hair?
Are there different GSN sizes?
How do you replace electrodes?
How does it compare with the 10-20 system?
Can I view the data in standard EEG montages?
How are the GSNs cleaned?
What about training?
Who do I contact for support?
How does this change the EEG technician's role?
How do patients like the HydroCel GSN?
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How long does it take to apply a 64-, 128-, or 256-channel HydroCel Geodesic Sensor Net?
An experienced EEG technician can apply the 64- or 128-channel HydroCel GSN in about 10 minutes; 256 channels take about 15 minutes. The tension structure itself goes on in about 1 minute—the rest of the time is spent making sure that each electrode pedestal is upright and touching the scalp.
How do I apply the electrodes?
Application involves six steps:
- Dip the HydroCel GSN in electrolyte formulation.
- Measure the patient's vertex.
- Put your hands inside the Net tension structure and position it over the patient's head.
- Drape the Net over the patient's head using the nasion, vertex, and ears as your guides—remove your hands when the Net is aligned correctly.
- Make sure that each electrode pedestal is upright and touching the scalp.
- Check to make sure that the HydroCel GSN is on evenly and no electrodes are mispositioned.
For more guidance, watch our HydroCel Net application movie.
Do you have recommended protocols for Net application and Net cleanup?
Yes. EGI has reference placards for posting in the relevant work areas. Topics covered include procedures for general GSN application, specific HydroCel GSN application, and GSN rinsing and disinfecting (for HydroCel GSNs with sponges and for HydroCel GSNs without sponges), as well as Control III disinfection information.
Don't I need to abrade the scalp to get good impedances?
- No. EGI's Geodesic EEG Systems are specially designed to handle high scalp impedance without signal loss or extra noise. It works because the Net Amps have been designed with high front-end input impedance that allows it to handle high-impedance electrodes. Signal quality is excellent, with impedances in the 50-100 KOhms range.
Where can I find support for what you say about impedances?
- Read Ferree, T., Luu, P., Russell, G. S., & Tucker, D. M. (2001). Scalp electrode impedance, infection risk, and EEG data quality. Clinical Neurophysiology, 112(3), 536-544, available here as a pdf.
Can the patient lie down wearing a Geodesic Sensor Net?
- Yes. Please contact us regarding recommended practice.
Can LTM be done using HydroCel Geodesic Sensor Nets?
Yes. For this purpose, LTM Hydrocel Nets use standard electrolyte gels for extended recording times. With the LTM HydroCel GSN, recordings can last twelve hours.
What about video EEG?
Video EEG is available with a variety of cameras, depending on your needs.
Is this like those "caps"?
No. EGI's HydroCel GSNs are completely different from "caps."
Unlike caps, Nets can be worn for days without pain. The geodesic structure allows evenly distributed pressure over the head, eliminating any painful pressure points on the scalp.
Unlike caps, the HydroCel GSN's open structure allows you to see the electrodes on the scalp, reducing the chances of electrolyte spread and bridging.
Unlike caps, hair does not affect the tension structure.
Unlike caps, the HCGSN tension structure can fit to any head shape.
Finally, the HydroCel GSN requires no scalp abrasion.
What about salt bridges?
Salt bridges rarely occur with EGI's HydroCel system.
Both our HydroCel Saline and HydroCel HS formulations will evaporate quickly, once outside the HydroCel Hydrating Skin Interface Chamber of the GSN.
Even if spilled, these formulations will evaporate within a few minutes.
Furthermore, Net Station allows you to check for salt bridges, much in the same manner that you measure electrode impedances.
- Not an issue! Thick hair actually helps keep the GSN in place. The Net design allows the hair to come out from between the sensors, and to remain out of the way. The pedestal design also helps to part the hair, facilitating good contact with the scalp.
- 7 infant sizes
- 4 pediatric sizes
- 3 adult sizes
Don't the electrodes move around?
Again, the difference is the HydroCel GSN.
The Net applies even pressure across the head. The pressure holds the electrodes in place.
Furthermore, our electrode designs are low profile and very stable, thus reducing the chances of movement artifact. Experience shows that the stability of the GSN electrodes is comparable with that of colloidal applications.
What about thick hair?
Are there different GSN sizes?
Yes. EGI has GSN sizes from neonate to large adult. In all, there are:
The GSN will conform to all varieties of head shape within the tolerance for each size.
How do you replace electrodes?
With our higher-channel-count systems, EGI's Net Station software can replace the data in a few channels using "spline interpolation."
The GSNs can also be returned to EGI for a fast factory replacement.
How does it compare with the 10-20 system?
The HydroCel GSN uses an electrode placement system that is inherently different from the 10-20 international system.
The HydroCel GSN emphasizes even placement of the electrodes across the entire head surface. The best method for doing this is the geodesic structure. Placement of the entire Net is based on identification of the Cz position. Therefore, the HydroCel GSN will not have exact equivalence to the 10-20 system, with the exception of the Cz position.
However, because the HydroCel GSN has many electrodes (depending of channel count) there are sensor positions that are approximately equivalent (defined as being less than 1 cm from the actual 10-20 position, which is within the acceptable error bounds for electrode applications according to ABRET standard) to the 10-20 positions.
Can I view the data in standard EEG montages?
All EEG data can be viewed in standard clinical montages, such as bipolar pairs, double banana, etc., using the approximate 10-20 equivalent positions.
How are the GSNs cleaned?
First, remember that there is no scalp abrasion, so the risk of infection is already greatly reduced from standard systems.
Still, EGI suggests a disinfection protocol lasting about 10 minutes, using an FDA-cleared disinfection solution (Control III).
The GSN should not be used on patients with open wounds.
What about training?
Each Geodesic EEG System purchase includes several opportunities for training.
During the installation visit, the support engineer will spend a full day training the EEG technician.
Additional refresher courses are offered at regional sites at least once a year.
EGI has a technical support staff ready to answer questions 24/7.
During regular business hours, from 7:00 a.m. to 5:00 p.m. PST, phone and email support are available.
After-hours support is available on a per-incident fee; calls will be forwarded to the support engineer on-call.
Email support is always available. Response time is usually 1 hour during regular business hours or the first thing the next morning, if after-hours.
Additionally, our support staff can, if requested, log into your Geodesic EEG System remotely to implement software fixes and to diagnose hardware problems.
- With EGI's HydroCel GSNs, a trained EEG technician can apply as many as 256 electrodes in 10-15 minutes (from the time the patient enters the room to when you start recording). EGI's Geodesic EEG technology allows for longer recordings in the same amount of time. EEG technicians can focus on the patient and on recording the data the doctor needs, not on measuring and cleaning up.
How does this change the EEG technician's role?
How do patients like the HydroCel GSN?
Patients report that they prefer EEGs performed with Geodesic Sensor Nets, compared with conventional EEG sensor arrays. Patients report that the GSN is more comfortable, and the electrolyte formulation does not smell or mess up their hair.
