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EEG Montages
| Question | Answer |
|---|---|
| What is a montage? | Also called arrays, montages are combinations of multiple derivations (electrode recording combinations). |
| What are the 2 different types of montages that are used? | 1. Monopolar (Referential) 2. Bipolar |
| What are some types of referential montages that are used? | 1. Common average reference 2. Cz reference 3. Ear reference (contralateral or ipsilateral) |
| What are some types of bipolar montages that we use? | 1. Longitudinal (anterior to posterior) 2. Transverse (left to right) |
| What is a referential montage? | A series of derivations in which the same electrode is used in input 2 of each amplifier. |
| How are potentials localized on a referential montage? | Amplitude. |
| What is important about the placement of the reference? | The reference must be placed in an electrically quiet spot on the patient. If placed in an electrically busy area, there will be contamination of all the other leads. |
| What is reference contamination? | This occurs when the reference is no longer neutral, meaning it has been obscured with an overriding potential, whether mechanical or biological. |
| What are the disadvantages to a CAR montage? | 1. Contamination 2. Distortion of brain signals - if the CAR becomes part of the electrical field, the electrodes nearest will cancel out and those farthest will give false localization. |
| What is the advantage of a CAR montage? | Equal interelectrode distances between the two hemispheres. |
| What is the advantage of a Cz reference montage? | Equal interelectrode distances. |
| What is the disadvantage of a Cz reference montage? | Can't be used when the patient is asleep. Sleep potentials come from the vertex and therefore would contaminate all other leads with sleep potentials. |
| What are the advantages to an ear reference montage? | 1. Little to no cancellation when using a contralateral ear montage due to long interelectrode distances. 2. Long interelectrode distances allow potentials to appear higher amplitude than usual, making it easier to read. |
| What are the disadvantages to an ear reference montage? | 1. Contamination with EKG potentials. 2. Cancellation (when ipsilateral) due to reference becoming a part of the electrical field. |
| What is a bipolar montage? | A montage that consists of an adjacent pair of electrodes of the 10-20 system of electrode placement. |
| How are potentials localized on a bipolar montage? | Phase reversal. |
| What is an advantage of a bipolar montage? | Best for analysing low to medium amplitude waveforms that are highly localized. |
| What are some disadvantages of a bipolar montage? | 1. Cancellation 2. End of chain |
| What is cancellation? | Cancellation is when two inputs are of equipotential, therefore, producing a flat line on the EEG. This occurs because the differential amplifier filters out potentials that are common between two inputs. |
| What is the end of chain phenomenon? | This occurs when potentials appear with greatest voltage in the last electrode in the chain of electrodes producing waveform deflections that are all in the same direction (no phase reversal). |
| What is a transverse bipolar montage? | This montage has derivations going from left to right across the head. Channels are usually arranged from front to back. |
| What are the advantages of a transverse montage? | 1. Easy comparison of left and right hemispheres. 2. Easy comparison of amplitude gradient between anterior and posterior head. |
| What is a longitudinal bipolar montage? | This montage has derivations arranged from anterior to posterior. |
| What is a laplacian montage? | This montage is similar to the common average reference, but instead on refers one electrode to the nearest neighbouring electrodes. Creates a local weighted average reference. |
| What is the disadvantage of a laplacian montage? | Edge electrodes are not symmetrically surrounded by other electrodes and therefore, cannot be uniform for all input 1 electrodes. |
| What is an average reference montage? | This montage adds all the activity of all electrodes together in input 2 at every amplifier to serve as a reference for each of the individual electrodes in input 1. |
| What is the disadvantage of an average reference montage? | If one electrode has a much higher potential than the rest of the electrodes, it will contribute much more to the reference causing contamination of the EEG. |
| What can prevent contamination in an average reference montage? | More electrodes contributing to the reference. |
| What is a weighted average montage? | Similar to average reference montage except the electrodes in input 2 do not contribute equally to the reference and input 1 is not included in the reference. Electrodes closer to input one contribute more the reference than those further away. |
| What is the advantage of a weighted average montage? | It reduces the possibility of a widespread activity contaminating the reference. |
| What are the 3 good montage requirements? | 1. Left hemisphere derivations over the right. 2. Derivations are organized in an anatomical order (ant to post). 3. Common electrode reference montages should have long interelectrode distances. |
Created by:
akesselman
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