Tomographic
Quantitative EEG Analysis (qEEGT)
The system performs quantitative
electroencephalogram (EEG) analysis (qEEG) in the
frequency domain in order to estimate spectral activity
at the electrodes (topography) as well as at the
sources (tomography).
The traditional Broad Band Spectral Model (which
defines a small number of broad bands to summarize
the spectral activity of the EEG) is included. The
user has the option to select the number as well
as the frequency range limits for each band. The
system also includes the more attractive and informative
Narrow Band Spectral Model, which gives the possibility
of analyzing the spectra of the EEG at each frequency.
One of the most significant feature available in qEEGT
is the comparison with a normative database for obtaining
a Z transformation correlated with age in the range
5-90 years. These norms are available for the 10/20
system.
With the calculation screen it is possible to set
the parameters for calculating the different qEEGT
models: Narrow Band, Broad Band and Electrical Tomography
with or without Z transformation. It is possible also
to select the physiological state as well as the montage
to use for calculating. qEEGT is calculated according
to a new method for 3D tomography in the frequency
domain: a variant of statistical parametric mapping
for source log spectra. In the new tomographic method
sources are estimated by means of a discrete spline
EEG inverse solution known as Variable Resolution
Electromagnetic Tomography (VARETA). Anatomical
constraints are incorporated by the use of the Montreal
Neurological Institute (MNI) probabilistic brain
atlas. Efficient methods were developed for frequency
domain VARETA in order to estimate the source spectra
for the set of 103 – 105 voxels that comprise
a EEG/MEG inverse solution. High resolution source
Z spectra are then defined with respect to the age
dependent mean and standard deviations of each voxel,
which are summarized as regression equations calculated
from the EEG normative database. The system offers
two electrical tomography variants: computed only
for brain cortex and brain cortex plus basal ganglia.
Deviations from normality are shown both as Z values
and by superimposing the actual activity of the
subject/patient with the mean and standard deviations
obtained from the equation regressions of the normative
database as shown in the figure. Together with the
spectra the electrical tomography corresponding
to the current frequency is shown to the right side
in low resolution. BET Viewer system can be used
to inspect in full detail and high resolution the
electrical tomograpy calculated.
Broad Band measures are represented by means of
topographic maps. In qEEGT topographic maps can
e visualized with 5 different views and the color
palette can be changed and edited as well as the
scale type in order to improve maps interpretation
Movie generation is available at the Narrow Band
screen. Movies are saved in standard Windows AVI
format allowing further playing on any movie player.
Another new feature in qEEGT is the correction
by means of the Geometric Power factor. This factor
allows to eliminate scale differences among EEG
data from different subjects due to system differences
making them more comparable.
qEEGT system accepts EEG data from native format
as well as Neuroscan formats (CNT and EEG) and ASCII
format (according to some predefined structure)
making the system very easy to use EEG recorded
from different EEG devices. Follow-up studies can
be visualized and compared in another screen making
comparisons among different subjects possible.
|
![](javascript:Abrir_ventana("../../imagenes/softwares/imagenes/qeegt1.jpg"))
![](javascript:Abrir_ventana("../../imagenes/softwares/imagenes/qeegt2.jpg"))
![](javascript:Abrir_ventana("../../imagenes/softwares/imagenes/qeegt3.jpg"))
