EEG Montages
Summary
TLDREl vídeo explica los diferentes tipos de montajes en el EEG, esenciales para una interpretación precisa. Se destacan los montajes bipolares, como el anterior-posterior, y su utilidad en la detección de focos cerebrales. También se discuten los montajes de referencia común, especialmente útiles para hallazgos difusos, y el montaje de referencia promedio, que puede sufrir contaminación de referencia. Se presenta el montaje de referencia promedio vecinal (LASSAN), ideal para focos focales, pero menos efectivo en campos eléctricos amplios. Finalmente, se subraya la importancia de la experimentación con diferentes montajes para una interpretación precisa del EEG.
Takeaways
- 🧠 La clave para una comprensión más profunda de la interpretación del EEG es entender la base de los montajes EEG, que se basan en el amplificador diferencial.
- 🔍 Los montajes bipolares son los más comunes en la interpretación del EEG, comparando una sola traza de electrodo con su vecino inmediato.
- 📊 El montaje bipolar anterior-posterior se organiza como si miráramos la parte superior de la cabeza del paciente, mostrando cadenas de electrodos en el temporal, parasagital y temporal derecho.
- 🌐 El montaje bipolar transversal se enfoca en el centro de la cabeza, útil para observar tránsitos de sueño que son más prominentes en el centro.
- 📍 El montaje de referencia común compara la señal de cada electrodo con una referencia común, como el CZ, destacando la utilidad para hallazgos difusos.
- 🔌 La contaminación de referencia es un concepto clave en los montajes de referencia promedio, donde la actividad de un electrodo se compara con el promedio de los demás, pudiendo generar interpretaciones erróneas.
- 🌐 El montaje de referencia promedio es versátil y puede ser usado para hallazgos focales y difusos, pero es susceptible a la contaminación de referencia.
- 📉 El montaje de referencia al mastóideo ipsilateral es útil para focos eléctricos amplios, ya que la referencia está lejos del área de interés.
- 🔎 El montaje LASSAN (Local Averaging Reference) es excelente para focos eléctricos focales, pero no es adecuado para campos eléctricos amplios.
- 📚 La elección del montaje depende del tipo de hallazgo que se está observando, y la experimentación y la experiencia son clave para comprender las fortalezas y debilidades de cada uno.
Q & A
¿Qué es un montaje EEG y por qué es importante para la interpretación de EEG?
-Un montaje EEG es una configuración específica de los electrodos en el cerebro, que permite visualizar y analizar las señales cerebrales de manera diferente. Es crucial porque permite comparar señales de un electrodo con otro, lo que ayuda a identificar patrones y eventos específicos en el cerebro.
¿Cuál es la diferencia fundamental entre un montaje bipolar y un montaje de referencia común en EEG?
-En un montaje bipolar, se compara una señal EEG de un electrodo con su vecino inmediato, mientras que en un montaje de referencia común, cada señal de electrodo se compara con una referencia común que puede ser un electrodo específico o el promedio de todos los electrodos.
¿Qué es el montaje bipolar anterior-posterior y cómo se organiza?
-El montaje bipolar anterior-posterior se organiza comparando electrodos consecutivos a lo largo de la línea temporal y parasagital, desde el frente hacia atrás. Se muestran en una disposición que parece mirar hacia la parte superior del cabezal del paciente, con cadenas temporales, parasagitales y una cadena central.
¿Cómo se utiliza el montaje bipolar transversal en la interpretación de EEG?
-El montaje bipolar transversal se organiza como si se mirara hacia la parte superior de la cabeza con el paciente mirando hacia arriba. Se enfoca en la parte central del cerebro, lo que es útil para observar eventos como los tránsitos de sueño, que a menudo son más prominentes en el centro del cerebro.
¿Qué es la contaminación de referencia y cómo afecta la interpretación de EEG?
-La contaminación de referencia ocurre cuando una señal anormalmente alta o baja en un área del cerebro distorsiona el promedio de la actividad cerebral, lo que puede hacer que otras áreas parecieran tener una actividad eléctrica anormal. Esto puede llevar a conclusiones erróneas sobre la actividad cerebral.
¿Cuál es la ventaja de usar un montaje de referencia común con una referencia distante para la interpretación de EEG?
-Un montaje de referencia común con una referencia distante puede aumentar el contraste entre la actividad cerebral en un área de interés y la referencia, lo que puede hacer que los eventos focales o grandes sean más evidentes en la lectura del EEG.
¿Qué es el montaje de referencia promedio y cómo se relaciona con la contaminación de referencia?
-El montaje de referencia promedio compara la señal en cada posición del cerebro con el promedio del resto del cerebro. Sin embargo, está sujeto a la contaminación de referencia, ya que eventos focales pueden distorsionar el promedio y hacer que otras áreas parecieran tener una actividad eléctrica anormal.
¿Cómo se utiliza el montaje de referencia contralateral mastoides en la interpretación de EEG?
-El montaje de referencia contralateral mastoides compara todos los electrodos de un lado del cerebro con un electrodo en el mastóideo opuesto. Esto puede ser útil para enfocarse en eventos focales en un hemisferio específico, ya que la referencia está lejos del área de interés.
¿Qué es el montaje LASSAN y cómo se diferencia de otros montajes en la interpretación de EEG?
-El montaje LASSAN compara cada electrodo con el promedio de sus vecinos más cercanos. Es muy bueno para identificar eventos focales, pero no es adecuado para eventos de campo amplio, ya que no hay mucha diferencia entre un electrodo y sus vecinos cercanos en un campo amplio.
¿Por qué es importante experimentar con diferentes montajes al interpretar EEG?
-Es importante experimentar con diferentes montajes porque cada uno tiene fortalezas y debilidades específicas. Al usar varios montajes, se pueden visualizar diferentes aspectos de la actividad cerebral y se pueden obtener conclusiones más precisas sobre la función cerebral.
Outlines
🧠 Montajes en EEG: Concepto y tipos
El primer párrafo explica la importancia de comprender el concepto de los montajes en el análisis de EEG. Se menciona que la base del EEG es el amplificador diferencial y que la salida EEG es siempre relativa. Se discuten cuatro tipos de montajes: bipolar, con referencia común y con referencia promedio común. El montaje bipolar compara un electrodo con su vecino adyacente, y se describen ejemplos de montajes bipolares como el anterior-posterior y el transverso. También se exploran variaciones institucionales en la organización de los montajes.
🔍 Contaminación de referencia y el Montaje Lassan
Este párrafo profundiza en el concepto de la contaminación de referencia en EEG, explicando cómo afecta la interpretación de los datos cuando se utiliza un promedio. Se utiliza la analogía de un grupo de hombres con una altura promedio para ilustrar cómo un outlier puede distorsionar la percepción de la altura promedio. Se describe cómo esto se refleja en los campos eléctricos en el EEG y cómo el Montaje Lassan, que compara un electrodo solo con sus vecinos más cercanos, puede ayudar a evitar esta contaminación. Se discuten los límites del Montaje Lassan, especialmente con campos eléctricos ampliamente distribuidos.
🌐 Montajes y su aplicación en la detección de anomalías
El tercer párrafo explora cómo diferentes tipos de montajes pueden ser utilizados para detectar anomalías focales o difusas en el EEG. Se discuten las ventajas y desventajas de los montajes bipolares, de referencia común y de referencia promedio común, así como del Montaje Lassan. Se enfatiza la importancia de no utilizar solo un tipo de montaje al interpretar EEGs y se sugiere que la experimentación y la experiencia son clave para comprender las fortalezas y debilidades de cada tipo de montaje. Se presentan ejemplos de cómo los montajes pueden afectar la percepción de eventos como ondas K durante el sueño y lentitud en una región cerebral específica.
Mindmap
Keywords
💡EEG
💡Montajes
💡Amplificador diferencial
💡Montaje bipolar
💡Montaje de referencia común
💡Contaminación de referencia
💡Montaje de promedio común
💡Montaje de referencia promedio
💡Contaminación de referencia
💡Mastóides
💡Campo eléctrico
Highlights
理解EEG解读的关键在于理解EEG蒙太奇的基础
EEG输出始终是相对的,这是由差分放大器原理决定的
介绍了五种EEG蒙太奇,重点讲解了四种最常用的蒙太奇
双极性蒙太奇基于比较单个EEG电极追踪与其相邻电极的原理
介绍了前-后双极性蒙太奇,从FP2到F8开始比较生成追踪
通过一系列电极链生成蒙太奇,展示了前-后双极性蒙太奇的布局
双极性蒙太奇在机构间有不同的排列方式,但通常左半球电极显示在右半球上方
横向双极性蒙太奇的布局,特别适用于观察睡眠中的脑电活动
共同参考蒙太奇将头部每个电极位置的信号与单一共同参考点比较
CZ共同参考蒙太奇是最常见的共同参考蒙太奇之一
共同参考蒙太奇的局限性在于对焦点放电的观察不如其他蒙太奇
平均参考蒙太奇通过将每个头部位置的信号与头部其他位置的平均值比较
参考污染是平均参考蒙太奇中需要考虑的一个重要概念
Lassan蒙太奇通过比较电极位置与其最邻近的邻居的平均值来减少参考污染
Lassan蒙太奇非常适合观察焦点放电,但不适合广泛分布的异常
远距离参考蒙太奇可能有助于观察广泛分布的电活动
通过比较不同蒙太奇在观察不同异常时的表现,强调了实验和经验的重要性
总结了不同蒙太奇的优势和局限性,强调了在EEG阅读中不应仅使用一种蒙太奇
Transcripts
one of the keys to a deeper
understanding of the interpretation of
EEG is understanding the basis of EEG
montages one of the things we have to
remember is that the basis of EEG is the
differential amplifier we have to keep
at the top of our minds the fact that
EEG output is always relative for this
reason we have a variety of ways of
looking at EEG which we call
montages we will go through four of
these five montages in this video video
the most commonly used montages in EEG
interpretation are bipolar montages a
bipolar montage is based on the
principle of comparing a single EEG
electrode tracing to its adjacent
neighbor one of the commonest bipolar
montages is the anterior posterior
bipolar Montage going through this
systematically we may start by comparing
fp2 to f8 this will generate a tracing
which we call a channel this can also be
called a derivation we will then
continue posteriorly starting at f8 and
going to T8 generating another Channel
or derivation we will continue
posteriorly to generate a chain of
electrodes along the temporal aspect of
the head eventually we put a number of
these chains together to generate a
montage this is an example of an
anterior posterior bipolar Montage going
through this systematically we can see
that this particular montage is AR
arranged as if we are looking at the top
of this patient's head while they are
facing rightward first we have the left
temporal
chain then the left parasagittal chain
then a midline chain in the middle then
a right parasagittal chain and finally a
right temporal chain there are
institutional variations in the
arrangement of these chains within a
montage however in general left
hemisphere electrodes are shown on top
of right hemisphere electrodes another
type of bipolar montage is the
transverse bipolar Montage this
transverse bipolar montage is arranged
as if we are looking at the top of the
head and the patient is facing
upward first we have a short chain over
the forehead then a longer chain
extending from left to right over the
front of the head then a very long chain
extending from ear to ear left to right
then a parietal chain and finally a
short Pari occipital chain the
transverse bipolar montage is
particularly good at focusing one's
attention to the center of the head many
sleep transients are maximal at the
center of the head and so transverse
bipolar Montage can be useful at looking
at sleep the second type of Montage we
will discuss is the common reference
Montage in this situation we compare the
signal at every electrode position on
the head to a single common reference
one of the most common common reference
montages is the CZ Montage in this
situation we compare every electrode on
the head to CZ the first channel or
derivation we will look at is f8 to ZZ
we then move posteriorly comparing T8 to
ZZ and then finally p8 to CZ in this way
we generate a chain much in the same way
as we generated a chain in the anterior
posterior bipolar Montage this
particular CZ reference montage is
arranged in the same way as the anterior
posterior bipolar Montage first we start
with a left temporal chain then a left
parasagittal chain then a midline chain
then a right parasagittal chain and then
a right temporal chain there are many
other types of common reference montages
and in fact we can compare signals on
the head to any reference we like for a
reference that is not very close to the
middle of the head another option is the
ipsilateral mastoid Montage you can see
here that all of the electrodes on the
left side of the head are being compared
to a single electrode attached to the
left mastoid we can also compare Electro
positions to the contralateral Mard
there is a tremendous amount of freedom
in organizing EEG montages and we will
discuss a little bit about why we might
choose looking at one Montage compared
to another the next type of montage is a
common average reference Montage in this
situation we compare the signal at each
position in the head to the average of
the rest of the head let's first look at
F7 what we would do in this situation is
compare F7 to the signal everywhere else
in the head divided by the number of
electrodes however because fp1 and fp2
are very susceptible to IM movement
artifact and because o1 and O2 are very
susceptible to head movement artifact
they are generally excluded from the
average reference Montage therefore we
are actually comparing each electrode
position to a smaller sample of of the
electrodes on the head one of the main
considerations with average reference
montage is a concept called reference
contamination one way to conceptualize
reference contamination is to look at
how we deal with averages in this
situation let's take an averaged sized
man if we compare him to a group of
other average sized men we will say that
he is of average height however if one
of the men in the comparison group is
larger than the other men then we would
come to the conclusion that our
gentleman is of below average height
this is actually the effect of the
outlier in the comparison group and has
nothing to do with our man who as we
said before is of average height in fact
this will make all other men within the
group appear to be of below average
height which can be very misleading now
let's look at how this might affect
findings on
EEG this is an anterior posterior
bipolar Montage during sleep in a young
person here we can see a number of
vertex waves maximal along the center of
the head if we look at these vertex
waves more carefully we see that the
maximum is at C3 CZ and
C4 therefore we have an electrical field
that looks something like this because
this is a very high voltage field in a
very limited area it acts like our very
tall man changing the average of the
rest of the head so that the average
over the entire head is is negative now
when we take an electro position that is
not involved in this field and compare
it to the average of the rest of the
head we can say that 01 in this example
is neutral and the average as we said
before is relatively negative for the
rest of the head therefore it will
appear like o1 is positive with respect
to the average of the rest of the head
o1 appearing electropositive is very
similar to the average men in our
previous example appearing small now if
we change to an average reference
Montage we can see that while it is true
that C3 C4 and CZ are relatively
electronegative there is also the false
impression that all other waveforms are
electropositive this is not a reflection
of any true electrical phenomenon but
rather an example of reference
contamination one way to get around
reference contamination is to use
something called the lassan Montage the
llan Montage is probably used least
often among eegs mainly because it is
very difficult to conceptualize this
Montage in general terms we are always
comparing one electrode position to an
average of its nearest Neighbors in this
example we would compare CZ to its four
closest neighbors we express this as a
first input which is CZ and a second
input which we call CZ Prime
CZ Prime is an average of the four
adjacent neighbors special consideration
has to be given to electrode positions
on the edge of the head where there are
fewer adjacent Neighbors when looking at
t7 for example we would derive t7 Prime
as an average of its three most adjacent
neighbors here is an example of how a
llan montage might be laid out again it
is laid out in a very similar way to our
other montages left over right with
temporal chains then parasagittal chains
then the midline let's take the example
of a right temporal sharp wave as seen
in this example on an anterior posterior
bipolar
Montage the sharp wave can be seen best
in the right temporal regions with some
extension into the right frontal regions
if we mapped out the field it might look
something like
this the phase reversal is at f8 and so
we would say that this field is likely
maximal at f8 and so we might include a
maximal negative Contour at f8 when we
look at this on average Montage we see
that indeed we do have maximal electr
negativity at f8 we also have a field
that extends to fp2 F4 and T8 which are
all involved in our theoretical field
but then we see a lot of electr
positivities in electrodes that are not
anywhere close to our field because of
reference contamination if we instead
change to the lassan Montage where we
are only considering most adjacent
neighbors we can see that the field is
very focal involving f8 with some
involvement of fp2 and T8 as we had
hypothesized before but no reference
contamination you can see here on the
left the lassan Montage and on the right
the common average reference Montage
with reference contamination seen best
in the left hemisphere the lassan
Montage has some limitations especially
with very broadly distributed electrical
discharges one example would be this
normal K complex during sleep again I
have shown it in an anterior posterior
bipolar Montage you can see that this K
complex has a very broad field extending
throughout much of the anterior aspect
of the head let's say that the field
involves this general area and is
approximately maximal in the frontal
Central region of the head because the
lassan Montage Compares One electrode to
only its closest Neighbors in an
electrical field that is very broad
there might not be much difference
between one electrode and its most
adjacent neighbors and we can see that
when we switch to the llan Montage for
this K complex things flatten out and it
is very difficult to see to summarize
llan montages are not good for broad
electrical Fields so we can ask the
question what if we choose a distant
reference a distant reference might have
the advantage of being very far from our
broad electrical field so that the
comparison between the activity within
our field and at the distance electrode
will be greatest one type of Montage
that we might want to consider is a
common reference Montage to the
ipsilateral mastoid process this is far
away from the area of interest and so we
would hypothesize that this would
generate the maximal amount of contrast
between our large area of interest and
the reference and we can see that when
we do apply the ipsilateral mastoid
Montage we get very high voltage
activity accentuating the K complex
again if we compare the ipsilateral
mastoid a distant reference Montage to
the lassan which Compares only adjacent
neighbors we can see a dramatic
difference in the electrical activity we
can also look at how different types of
montages can look at a broad area of
slowing in one hemisphere in this
example I have included A short segment
of a recording of a patient patient who
just had a seizure arising in the right
temporal region it is difficult to see
but there is some polymorphic Theta and
Delta activity in the right temporal
region again this has a very broad field
and if we were going to hypothesize the
field we might show it something like
this again when we use the lassan
Montage where we are comparing only to
closest adjacent neighbors it's very
difficult to see the slowing but we may
apply a distant reference Montage such
as the CZ montage and we can see a
dramatic change and the focal slowing is
much better seen in a short video it is
very difficult to give a comprehensive
view of the strengths and weaknesses of
different montages your ability to
recognize the relative strengths and
weaknesses of these montages will come
with experience and with
experimentation however we can make some
broad statements about the strengths and
weaknesses based on what we have looked
at so far a bipolar montage in
particular the anterior posterior
bipolar montage is used most frequently
for screening of EEG recordings because
it is very
versatile however it is not the best
Montage for either focal or diffus
findings and for this reason you have to
consider using other montages when you
read the common reference Montage as we
have shown can be very good for broadly
distributed abnormalities particularly
if you use an appropriate reference
distant to the area of Interest however
a common reference montage is not
particularly good at looking at focal
discharges and this is the main
limitation in using this as a screening
Montage the average reference montage is
generally very versatile and can also be
used as a screening Montage however it
is susceptible to reference
contamination as we have shown which can
lead to some misleading findings the
lassan Montage is extremely good at
looking at focal discharges but not very
good for broadly distributed
abnormalities
as I have said already I think it is
important to experiment with different
montages looking at different
abnormalities and comparing how they
look with one Montage compared to
another now that you have a good
understanding of the strength and
weaknesses of each of the montages I
hope that you understand that it is
important to never read EEG with just
one montage
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