Electroencephalogram

EEG: electro + encephalo + gram:

Electro: Represented in electrical units like Voltagr or Current.

Encephalo- Related to brain.

Gram- The record book of brain signals.

EEG

Electroencephalogram is a noninvasive test for measuring the electrical activity (patterns) of the brain, where Electroencephalography is the technique for recording and interpreting it.

EEG Machine, Components and Resources Information Page

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Machine, Equipment Components, Manufacturers & Resources

3. EEG Machine, Components and Resources  

Background & Intro

After getting here, with the hope that you have reviewed the previous pages, you must now have known that EEG device is the one used to record electrical signals of the brain, and then processes it to be displayed and read on a computer monitor or screen as of wavy lines.

How this is done, and what are the electro- electronics by which it was done, is what you will get to know here, in addition to the information related to EEG proprietary commercial equipment’s and manufacturers.

The present EEG Technology is not born of the moment. On the contrary, it is the result of an accumulated years of relentless work, research and development in the recognition, recording, display, and analysis of brain electrical activity, represented by the EEG. Initially, needle electrodes along with a string galvanometer and a photographic recording process produced the first human EEG.

Albert Grass started building a three‐channel EEG recorder for the Harvard Medical School laboratory upon request from Frederic Gibbs in 1935. Grass work resulted in a galvanometer with a new moving‐coil associated with improved design of the amplifier, better known as Model 1, where EEG could be done on rolls of paper using ink and a pen‐writer. Eng. Albert Grass ambition did not stop at this point, but his research continued to culminate in the establishment of a Grass Instrument Company with his wife Ellen Robinson Grass, who had trained as a neurophysiologist, to meet the growing demand for EEG by healthcare providers, scientists, researches and academics. This dedication to the EEG cause by Grass and his wife had let to the availability of supported and trusted EEG machines in the 1940's and 1950's.

Besides the great efforts made by Grace in the development of EEG systems, we must also review other efforts that are no less important, which in turn contributed to establishing the first blocks of what we are now witnessing of the tremendous development of the EEG devices.

Along with Grass, Franklin Offner was one of the main researchers whose work contributed to the building of a high-speed piezoelectric ink-writer (Offner and Gerard, 1936). Later In 1937, he discussed a variety of differential amplifiers. He established a commercial EEG instrument company. In the 1950s, Offner was the first to introduce electronic components into EEG, which aided the machine’s safety and portability.

In 1936, the first EEG laboratory opened at the Massachusetts General Hospital as a research facility. The clinical laboratory opened there a year later.

Historically, German physiologist and psychiatrist Hans BergerBerger made the first EEG (electrocorticogram) recording on July 6, 1924, during a neurosurgical operation on a 17-year-old boy. With more refined amplifiers, Berger was later able to obtain reactive alpha rhythms and other waveforms from intact subjects.

In the period between the discovery of EEG in 1929 and the late 1960’s EEG was mainly inspected visually until digital equipment became available.
In the following decades, EEG spread worldwide. It would be impossible to name all those who contributed to its development as a clinical and research tool.

Generally, the electroencephalogram (EEG) machine has been used for both medical diagnosis and neurobiological research.
Note that, the manufacturing typically involves separate production of the various components, assembly, and final packaging. The essential components of EEG device include:

  • Amplifier (with or without headbox).
  • Sophisticated advanced software.
  • Electrodes (or caps).
  • Computer control module.
  • PC and peripherals.
  • Display device.

Optional components include:

  • Flashing light for photic stimulation.
  • Camera for recording video .
  • Connectivity for local review or through HIS.
This is how they look like!
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Images source: Mitsar Co. LTD.
Note that, images are for illustrative purpose only without endorsing or recommending the use of any particular company.

Human brain tiny μV electrical signal and the EEG Device:

Here is how the EEG machine gets use of Brainwaves signal in microvolts "μV".

"1" Volt = 1,000,000 microvolts

Our super-complex human body relies on nerve cells called neurons. These tiny nerve cells are constantly producing tiny electrical signal, and in fact transmit information throughout the body electrically. They create electrical impulses by the diffusion of calcium, sodium, and potassium ions across the cell membranes. Each human activity (mind states—alertness, rest, sleep, and dreaming) stimulates different parts of the brain lobes. These activities produce different electrical signals that can be recorded by an EEG machine and then interpreted by the clinician. To achieve this, conductive electrodes are used (routinely 16 to 21) where one side of each one of them is connected to an electronic device called “amplifier”, whereas the other side with metal disc is placed on the scalp. The main reason to use these electrodes is to pick and transmit the tiny microvolt brain signal produced by the nerves.

Once the acquired signal arrives at the amplifier, it is amplified, filtered and processed to be big and clear enough to be displayed as a wavey lines on the computer screen (geometrical picture of the brain's activity).

Amplifier used in EEG equipment is differential amplifier. It is the key component of the machine. It magnifies the difference between two inputs, where unwanted signal that is common to the two inputs will be subtracted. Amplifiers can be with regard to channel numbers as: 20+, 32, 44, 64, 128, 256 channels, but the commonly used one is 32 or 44 with AC and DC inputs.

The brainwaves of concern are: alpha, beta, theta, and delta. Each of these wave patterns has different frequencies, amplitudes and indications.

Science and Engineering Behind the EEG Device

How The EEG differential amplifier deals with the signal?

How to prevent the possibility of electric shock?

As discussed earlier, the basic EEG machine includes PC with peripherals, display, electrodes, connecting wires, amplifier (with built in or sperate headbox), a computer control module and an optional photic stimulator and a camera (mounted or portable).

The EEG differential amplifier (useful when measuring relatively low-level signals) does the main job of the mission. It successfully converts the very small signal acquired from the scalp into a more discernable signal for the output device.

The simple and basic way of amplifier handling the signal received from the electrodes, is to firstly stabilize it by the buffer and amplifies it by a factor of five to 10. Then, it is filtered and amplified by a differential pre-amplifier by a factor of 10-100. After going through these amplifiers, the signals are multiplied by hundreds or thousands of times.

For patient safety, special measures are implemented in the amplifier design (use of optical isolators to separate the main power circuitry from the patient) to prevent electric shock. The amplifier converts the analog signal to a digital output signal.

The software provided with EEG machine is essential to display the brainwaves in patterns and therefore creates a readable map of the brain.

Watch our video to know the EEG Localization and Amplifier More Videos?

Accessories used with an EEG machine

  • Various sensors.
  • Patient event button.
  • Electrolytic pastes or gels.
  • Mounting clips.
  • Different cap sizes.
  • Additional software analysis options.

EEG machines used in sleep studies are equipped with:

  • Snoring Sensor.
  • Respiration Sensor.
  • Sensory stimulation devices such as headphones and LED goggles.

Electrodes: More details

There are different types of electrodes used in EEG procedures, where each one of them is favorited and used by different group of technicians. But generally, all of them serve the same purpose, which is to acquire the brainwave signal and then transmit it.

The use of the most appropriate electrode may not be random as some believe based on a personal sense, but rather, other factors must be included in it such as: The type of information that is intended to be measured can significantly influence the decision; the device that is used; the conditions of the place in which the device is located; the type of test; and other factors specific to the patient on which the test will be performed.
Conclusion: There is no perfect choice of electrodes for all cases and situations, each has merits and demerits, which we will discuss, but firstly, let us list them as mainly as the following:

# Type Enlarge Description
1 Wet electrodes image This is the conventional widely used electrodes in EEG procedures and in the clinical practice. (available as reusable and disposable, as well as cap embedded). They are small, non-reactive metal discs or cups. Several types of metals are used including gold, silver/silver chloride material (Ag / AgCl), tin, and platinum. Electrolytic gel or paste material is used with it to facilitate conduction between the scalp and the electrode. Also, there are plastic electrodes which are MRI compatible. Wet electrodes require skin abrasion, gel application, and a trained technician.
2 Dry electrodes image Dry electrodes are mostly stainless steel with a single metal that acts as a conductor between the scalp and the electrode. They do not require skin abrasion, gel application, and a trained technician. therefore, they might be useful for EEG recording in the home setting. Dry electrodes are mostly used in research and BCI with little approved among them for clinical use. Dry electrodes do no use conductive paste; therefore, they have higher impedance than wet electrodes, causing a reduction in signal quality.

Wet Electrodes Vs Dry Electrodes:.

A disadvantage of wet electrodes is that after several hours of use, the paste or conductive gel dries out (dehydrated) causing a reduce of signal quality. This may require then a re-fill for the attached electrodes, or re-application (the removal of the electrodes requires a little more time for cleaning the electrodes, as well as the skin where they were placed.). This in turn, will impact the stability and continuity of the recording.

For long time monitoring EEG, electrodes are used and glued on the skin using collodion. By doing so, the signal quality is maintained even for longer time of recording. This method works well if the patient is admitted in the hospital, and monitored by the nursing staff or EEG technicians, but at home and in case it is ambulatory, this procedure might not be possible nor practical. Therefore, special measures are always taken to ensure electrodes don’t move out from their fixed positions. New approaches suggest using dry electrodes for long period of times, and argue that since they do not need conductive gel or paste application, their signal quality is maintained over longer periods of time. However, Dry electrodes are mostly used in research, neurofeedback BCI applications and very few of them is approved by FDA or EMA for clinical use.

The real concern regarding dry electrodes is whether their signal quality can substitute the one recorded by wet electrode in the clinical context, given that, dry electrodes are placed directly on the skin without any gel application, resulting in a larger impedance compared to conventional wet electrodes used in EEG tests.

Watch our video to know the fundamentals of EEG, components used and accessories. More Videos?

Variables used in EEG machine

Filtering

“The less the better” ……. This describes the common opinion about using filters and applying them to the EEG recording. But, should we take it as a rule?

The answer cannot be direct with Yes or No as an answer. There are drawbacks and merits of filtering to consider, and circumstances and factors reinforcing the saying “filtering is most often a necessary evil”, but if used correctly (case by case), can help obtaining a reliable EEG data.

The main benefit of filters is that they can appear to “clean up” the EEG tracing, making it easier to interpret and physically easier to be readable and distinguishable.

To describe filtering in brief, it is a method used to enforce the EEG recording software through the amplifier circuity to what to show and not to show of the time series above and below certain specified frequencies. By doing so, undesirable changes or misleading one’s of the displayed waves can occur, affecting the latency of our ERP data.

Filtering a noise associated with EEG data in a way that non- brainwaves not to be shown is a theoretical idea which is not available practically as an option. No such filter exists that removes all of the electrical noise or artifact from the EEG and only allows true cerebral activity to pass through.

Filter types

The common filter types used in clinical EEG are:

.   Low frequency filter (LFF) also called low filter (LF) as a shorthand abbreviation: By applying this filer, the low-frequency activity is filtered out and the higher frequencies are left as they are.
The standard settings for LFF is 1 Hz

.   High frequency filter (HFF) also called high filter (HF) as a shorthand abbreviation: By applying this filer, the high-frequency activity is filtered out and the low-frequency activity is allowed to pass through (left as they are).
The standard settings for HFF is 50-70 Hz

.   Notch filter: It is used to filter out activity at a specific frequency rather than a frequency range. Specifically, 60- or 50-line frequency (depending on countries alternating current “AC” in electric outlets oscillation. Where Europe is at 50 Hz; North America oscillates at 60 Hz, etc.). If we take 60 Hz as an example here, electric fields produced by the 60-Hz activity in the environment that surrounds indoor environments frequently contaminates the EEG. Sixty-Hz notch filter which is designed particularly to filter out 60-Hz undesirable activity are used to attenuate or eliminate this unwanted signal. The same literally applies if the line frequency is 50 Hz.

If we take 60 Hz as an example here, electric fields produced by the 60-Hz activity in the environment that surrounds indoor environments frequently contaminates the EEG. Sixty-Hz notch filter which is designed particularly to filter out 60-Hz undesirable activity are used to attenuate or eliminate this unwanted signal. The same literally applies if the line frequency is 50 Hz.
The standard settings for Notch filter is OFF. It should be used only when other measures against 60 Hz interference fail, as it can distort or attenuate spikes if switched ON.

Sensitivity

Sensitivity is defined as the ratio of input voltage to trace deflection. It is expressed in microvolts per millimeter (μV/mm). A commonly used sensitivity is 7 uV/mm, which, for a calibration signal of 50 μV, results in a deflection of 7.1 mm. The sensitivity of the EEG equipment for routine recording should be set in the range of 5—10 uV/ mm of trace deflection. {Citation: acns}.

Impedance

Interelectrode impedances should be checked as a routine prerecording procedure. Impedances up to 10 k Ohms are acceptable, but optimal recording still requires impedances that are balanced. Unbalanced impedances compromise the ability of an EEG amplifier to reject potentials that are the same at a pair of electrodes while amplifying those that are different (common mode rejection). Impedances should also not be below 100 Ohms, as this usually indicates a shunt or short circuit, possibly related to a salt bridge on the scalp. {Citation: acns}.

Electroencephalography “EEG” System Manufacturers

Market Overview

Based on estimates issued by Business Wire and Technavio, the electroencephalography (EEG) devices market is poised to grow by USD 886.40 million during 2020-2024 progressing at a CAGR of about 9% during the forecast period. The growth in 2020 was estimated 5.81%, where 41% of growth coming from North America. The healthcare sector will see positive impact due to the Covid-19 outbreak, and the industry is expected to register a high growth rate compared t the global GDP growth. The market will have positive impact due to the pandemic.

Based on report issued by Grand View Research, the global electroencephalography devices market size was valued at over USD 829.3 million in 2018 and is anticipated to expand at a CAGR of 8.7% over the forecast period (2019 – 2026). Increasing prevalence of neurological disorders and rising awareness about them are major factors contributing to the growth. High incidence of Alzheimer’s, epilepsy, dementia, multiple sclerosis, Parkinson’s disease, and stroke has been key in the rising adoption of electroencephalography (EEG) devices.

Manufacturers offering EEG systems and products are:

Please note that, companies are randomly listed here and not based on our assessment nor market share.

Key manufacturers operating in the global EEG equipment market

Other Neuro Manufacturers

Here is another selected list of companies that manufacture and develop EEG, BCI, Neurofeedback, dry EEG headsets and sensors.

Note that, Some of the products are intended to be used for research applications only and not in clinical practice. they are not sold as Medical Device as defined in EU directive 93/42/EEC nor FDA. The products are not designed or intended to be used for diagnosis or treatment of diseases.

EEG equipment’s key hardware component manufacturers

Most of EEG companies do not make or produce all the parts supplied with their systems, nor have a dedicated production line for each one of them. Instead, they usually outsource them from third party companies through exclusive (or non) contracts to manufacture these parts on their behalf according to given specifications, and then print the product name and company logo with identification numbers (lot and part number) on these parts.

Another aspect prevalent in the world of manufacturing is that a company specialized in manufacturing of a specific product is not keeping it exclusively for itself, but rather providing the opportunity to other companies to market it with their brand names. Therefore, it is common to see the same product being sold with different brand names by different marketers.

Below is a list of key EEG device hardware manufacturers such as amplifiers, control modules, boards, etc., and software

Computer Assisted Review of EEG (CARE) Software

Each EEG system is usually equiped with its own analysis and review software. This is an essential part of the package, but there are very specialized software’s in the market which goes away far on what to offer compared to the conventional software provided with EEG systems. These revolutionary sophisticated software’s’ in terms of review and analysis deliver a complete set of tools such as seizure detection; spike detection; trending ; artifact reduction; monitoring; Electrical Source Imaging (ESI), etc., needed for C.A.R.E (Computer Assisted Review of EEG), resulting in accurate, efficient and rapid review of EEG data from various different available data formats and vendors (universal reader).
Overall, automating EEG data review would save time and resources if it works according to approved regulatory algorithms, thus enabling more people to receive reference standard monitoring and also potentially heralding a more quantitative approach to therapeutic outcomes.

Here is a shortlist which we do recommend from our personal experience in neurophysiology and EEG in particular:

Biomedresearches (bmr’S) EEG Educational Materials.

Understanding EEG Video Series:  

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