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Brain electrical activity mapping (BEAM) A method for extending the clinical utility of EEG and evoked potential data.

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ORIGINAL ARTICLES
Brain Electrical Activity Mapping (BEAM):
A Method for Extending the Clinical Utility
of EEG and Evoked Potential Data
Frank H. Duffy, MD, James I. Burchfiel, PhD, and Cesare T. Lombroso, MD
The difficulties inherent in extracting clinically useful information by visual inspection alone from the massive
amounts of data contained in multichannel polygraphic recordings have placed limits on the accuracy and range of
utility of electroencephalography and evoked potentials. A method for condensing and summarizing the
spatiotemporal information contained in recordings from multiple scalp electrodes is described. Data dimensionality is reduced and visibility increased by computer-controlled topographic mapping and display of data as color
television images. Examples are given in which such brain electrical activity mapping (BEAM) (1) localizes tumors
in patients with normal or nondiagnostic EEGs, ( 2 ) adds additional information to that visible on computerized
axial tomography, and (3) demonstrates electrophysiological abnormalities in patients with functional lesions but
normal CT scans. A sensitivity to the functional component of a neurological lesion suggests that BEAM may
provide complementary information to the anatomical definition provided by the CT scan.
Duffy FH, Burchfiel JL, Lombroso C T Brain electrical activity mapping (BEAM):a method for extending the
clinical utility of EEG and evoked potential data. Ann Neurol 5:309-321,1979
Computerized axial tomography-the
C T scan-has
largely replaced cerebral angiography and pneumoencephalography for the diagnosis of anatomical abnormalities of the brain. The impact of the
CT scan upon electroencephalography has been
more variable. This stems from the use of EEG to
diagnose not only anatomical lesions (e.g., tumor,
abscess) but functional lesions as well (e.g., epilepsy).
Whereas EEG may fail to diagnose 15% of brain
tumors [3], it remains the best or only test for epilepsy and certain other functional disorders (e.g.,
Reye syndrome, brain death).
The clinical utilization of evoked potentials (EP) to
assist in the diagnosis of various sensory disorders [6,
9, 10, 341, brainstem lesions [351, and demyelinating
diseases [22, 281 has increased. Nevertheless, the
clinical value of EEG and EP in the diagnosis of certain forms of purely functional lesions is still limited.
For instance, there are many reports of EEG and EP
abnormalities in children with dyslexia 117, 19, 33,
36, 371; however, these findings are too nonspecific
to form useful diagnostic constellations.
We do not believe that EEG and EP suffer from an
~
inherent insensitivity to underlying brain dysfunction. O n the contrary, we propose that brain electrical activity presents not too little, but too much information to be easily grasped and assimilated by
visual inspection alone. The approach we have taken
t o enhance its utility in the diagnosis of both anatomical and functional lesions is based upon topographic
mapping. In this technique, EEG and EP data recorded from multiple scalp electrodes are graphically
displayed o n a computer-driven color video screen.
Values between electrodes are obtained by interpolation. We call this technique brain electrical activity
mapping, or BEAM. This report describes the methods and results of a feasibility study illustrating the
ability of BEAM to define both anatomical and functional lesions in selected cases.
Method
Data from 24 standard EEG scalp electrodes are amplified
via a 20-channel polygraph (Grass Model 78) and recorded
on a 28-channel FM analogue tape recorder (Honeywell
5600E) for off-line computer processing (Digital Equip-
~~~~
From the Seizure Unit and Division of Neurophysiology, Department of Neurology, Children’s Hospital Medical Center and Harvard Medical School, Boston, MA.
Address reprint requests to Dr F. H. Duffy, Seizure Unit, Children’s Hospital Medical Center, 300 Longwood Ave, Bosron, MA
02115.
Accepted for publication Aug 21, 1978.
0 3 6 4 - ~ 1 3 4 / 7 ~ / 0 4 0 3 0 9 - 1 3 $ 0 1 .@
2 5 1978 by Frank
H.Duffy 309
ment Corp PDP-12). Data analysis of three types is performed under the SIGSYS-12 biomedical software package
(Agrippa Data Systems). First, spectral analysis from 0 to
32 Hz is performed o n background EEG using the fast
Fourier transform (FFT) technique. To avoid artifacts from
muscle and mains (60 Hz) activity, signals are tightly
filtered at 24 d b per octave using active Butterworth filters
(EEG Associates Mark 4 x 24). The amount of energy in
each classic EEG band (e.g., delta, theta, alpha, and beta) is
determined for each electrode and stored for future display. Second, visual EPs of 5 12 msec duration are formed
from stimulation by randomly presented strobe flashes
(Grass PS-2) set 20 cm from the subject's eyes at intensity
level 2. Trials containing muscle or blink artifact are automatically excluded. The average EP voltage over 128
epochs each lasting 4 msec is determined for each electrode
and stored for later display. Third, epochs of raw EEG
signals containing epileptic spikes are digitized. Next, a 5to 20-msec epoch containing the feature of interest (spike)
is averaged and stored for later display.
By means of a hardware digital interface (Agrippa Data
Systems 8ETV3) between the computer and an ordinary
Sony color television set, results are displayed within a
graphic outline of the head. Individual topographic displays
of four sorts are commonly prepared: (1) spectral energy in
any individual EEG band, (2) EP voltage at any 4-msec
epoch after stimulus onset, ( 3 ) EEG amplitude during the
peak of an epileptic spike, and ( 4 )results of statistical analysis on any of the preceding features (e.g., standard deviation). For each display, scalp areas around the original 24
electrode values are filled by linear three-dimensional interpolation based on the values at the three nearest electrodes (see Figure 1 for details of this process). Furthermore, the interface hardware is capable of displaying a new
video image every 100 msec; accordingly, images may be
cartooned at variable rates of up to 10 frames per second in
an endless-loop manner. Thereby, for example, one can
observe an EP in both space (a single topographic video
image) and time (a cartooned series of images representing
512 msec in real time).
Subjects and Tests
Twelve patients (7 with tumors, 1 with a suspected tumor,
3 with dyslexia, and 1 with a sociopathic personality) of the
many referred for clinical EEGs and EPs were evaluated
using the described techniques; the results of these evaluations are included in this report. These patients were carefully chosen to demonstrate the clinical utility of BEAM:
they were selected to compare the ability of BEAM to
define anatomical lesions (tumors) and functional lesions
(dyslexia and behavioral disorders). Seven right-handed
subjects with normal EEGs and normal neurological examinations were used as controls. The 12 patients were
right-handed and had either normal or nondiagnostically
abnormal EEGs containing no focal or lateralizing features.
Seven ambulatory patients with unoperated supratentorial brain tumors diagnosed by C T scan were studied with
spectral and visual EP topography. The tumors included
gliomas of all four lobes of the right hemisphere and all but
the frontal lobe of the left hemisphere. One patient, sus-
310 Annals of Neurology
Vol 5
No 4 April 1979
pected by C T scan of having a right frontal tumor, was
similarly studied. This 13-year-old girl was admitted with a
one and one-half year history of brief periods of abnormal
C N S function. These periods included episodes of bizarre
behavior, focal seizures of the right side of the face, transient left-sided hemianopia, and nominal aphasia. Due to a
more recent history of headache and lethargy, a CT scan
was performed which revealed areas of density in the right
frontal lobe with shift of the midline structures from right
to left (Fig 2). An angiogram confirmed a right frontal avascular mass. The patient was admitted for surgical exploration. Neuropsychological testing, however, revealed that in
addition to nondominant frontal abnormalities, she showed
bilateral parietal deficits.
Three neurologically intact adolescents of normal intelligence, referred with the diagnosis of specific reading disability (dyslexia), were evaluated. In addition to resting
spectral and visual EP studies, their spectral topographies
were examined while they were listening to music or
speech. O n e neurologically intact adolescent patient with a
history of sociopathic behavior was studied with resting
spectral and visual EP topography. His EEG was considered borderline due to excessive theta slowing in the anterior quadrants; however, his C T scan was within normal
limits.
Results
Controls
Figure 3 demonstrates a BEAM spectral plot for a
normal subject in the eyes-open and the eyes-closed
state. For this subject and all the control subjects,
spatial distributions were those one might predict
using classic EEG analysis. For example, beta activity
was maximal anteriorly (eyes open), and alpha activity tended to be maximal in the midline leads and
posterior leads with a slight right-sided predominance (eyes closed). Figure 4 demonstrates five representative frames of a 128-frame visual evoked potential (VEP) examination in which each frame
represents 4 msec. The symmetrical appearance
of activity in the -occipital regions should be noted;
the sequential appearance of symmetrical vertex
waves is also illustrated. All normal subjects demonstrated spectral and VEP plots similar to those
shown in Figures 3 and 4.
Tumor Patients
Figure 5 demonstrates the abnormal spectral plot for
a patient with a left occipital glioma (his CT scan is
shown in Figure 2 for comparison). Note the increased delta, decreased beta, and decreased alpha
activity over the tumor site. Six of the 7 tumor patients showed the same abnormalities that this subject demonstrated, namely, increased slow activity
and decreased fast activity overlying the tumor site.
Although the seventh subject had a normal spectral
plot, the spatial distribution of the standard deviation
P3
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73
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01
A
B
C
D
F i g I . Example of the construction of a topographic map for
E P data. Mean EPs are formed from each of 20 recordiq sites.
Each EP is divided into 128 4 - m e c intervals, and the mean
voltage value for each interval is calculated. In (A) the individual EPs are shown for the electrode locations indicated on
the head diagram. In IB) the mean voltage values at these locations are shown for the interval beginning I 9 2 msec after the
stimulus (the vertical line in A indicates this time on the EPs).
Next the head region is treated as a 64 x 64 matrix; the resulting 4,096 spatial domains are illustrated in (C).
Each
domain is assigned a voltage value by linear interpolation from
the three nearest known points. Finally, for display, the raw
voltage values are fitted t o a discrete-level equal-interval intensity scale as shown in ( D ) .An illustration of topographic maps
in two-color display for other selected intervals over the time
course of the EP is shown in Figure 6.
Duffy et al: Brain Electrical Activity Mapping
311
Fig 2. Each photograph represents the resnlts of a computerized
axial toniographic radiographic examination. ( A ) The primary lesion i n the patient u!ith the left occipital glionia shown
in Figures 5 and G is marked with un X. Note the dilatation
of the lefi lateral ventricle; this may explain the disruption of
forzrjard spread of actitJitynoted in the VEP BEAM ( F i g 6 ) .
( B ) The lesion in the patient with lymphomatoid granuloniatosis is marked by an arrow. C T scan lesions were
limited to the right frontal lobe. No abnormalities were seen i n
the parietal regions to correlate with the biparietal abnormalities obserred by neurop.ryc-hologii-altesting and V E P
BEAM (see F i g 8).
312
Annals of Neurology Vol 5
No 4
April 1979
F i g .3. Example of a normal BEAM spectral plot in the eyesopen (EO; A-D) and eyes-closed (EC; E-H) state, formed according to the method outlined in Figure 1 ; however, spectral
fiinctions instead of EPs are used as input. Each spec~irmis
dirfided u p into the classic E E G spectral bands (i.e.9 delta = 0
l o 4 H z , theta = 4 t o 8 H z , rrlphu = 8 t o 12 HL,und beta =
12 t o 20 Hz). Each plot is scaled i n d i d u a l I y . Note the ex-
pected asymmetry of alpha activity, which is greater over the
right occipzrt for this right-handed subject. Note the general
shift i n energy from the anterior to the posterior regionsfor all
frequencies with EC, a frequentjnding in normal persons.
Note the posterior beta asymmetry with EC; this i s seen when
beta includes the 12 t o 16 H z range, adjacent t o alpha. I t is
not seen fnr the 16 to 3 2 H z range (not shown here).
Duffy et
al:
Brain Electrical Activity Mapping 313
Fig 4
of his spectral energy (not illustrated) demonstrated
localization to the site of his tumor.
Figure 6 demonstrates a typical BEAM VEP plot
for tumor subjects. All 7 tumor patients showed VEP
plots demonstrating: (1) depression or absence of
early electrical activity at the site of the tumor; (2)
abnormally persistent late activity overlying the
tumor; (3) asymmetrical spread of activity; and (4)
diminished or absent vertex waves. In every patient,
the topographically demonstrated abnormalities extended beyond the strict anatomical limits of the lesion on C T scan (for example, see the lesion size in
Figure 6 as compared to the C T scan lesion in Figure
2).
The ability of measurements taken from topographic plots to differentiate tumor patients from
normal subjects is shown in Figure 7. The time spent
in asymmetry at the locus of maximum asymmetry is
plotted for all 7 controls and the 7 tumor patients.
Note that a line drawn at 7 5 msec completely separates these two groups.
Patient with Suspected Tumor
Figure 8 demonstrates the abnormal BEAM VEP
plot for the 13-year-old girl with the suspected right
frontal lobe tumor by CT scan and angiogram. This
VEP BEAM showed repetitive midline parietal ab~
F i g 4. Example of a normal BEAM VEP plot formed according
t o the method described in Figure 1. Five representative plots of
the total of 128 plots spanning 512 msec are shown. Each plot
represents a 4-msec averaged epoch. In this and all other VEP
plots, red represents positive and blue represents negative activity
with respect t o linked ear references. At 40 msec note the frontal electsoretinogram IERG). The primary EP wave begins
with maximum amplitude overlying PZ, just forward of the
occipital region 152 msec); this is a normal variant. This activity spreads to the “vertex”at CZ for the first vertex wave
(1 08 msec). Note the slight vertex wave asymmetry, which is
within normal limits. The next positive component,just beginning at 108 msec in the occipital region, sweeps up t o CZ t o
form the next vertex wave (168 msec). Much kater, another
vertex waveforms (440 msec). Normal VEPs consist of a series
of vertex waves with positive or negative wavefronts converging
on the vertex region. Asymmetries of early vertex waves are not
uncommon. The ERG is a common contaminant (40 msec), as
is some temporalis muscle activity (i.e., left ear at 52 msec).
F i g 5. Example of a tumor (left occipital glioma) demonstrated
& a BEAM spectral plot, formed as for Figure 3 in the EC
state. Note the increased leji occipital delta, markedly decreased
/eft occipital alpha, and slightly decreased lefi occipital beta
activity. Theta shows only a slight increase on the left. Although alpha asymmetries are seen in normal subjects ( F i g 31,
a marked depression of alpha activity overlying one occiput, as
in thisjigure, is not. (See also Figure 6 for the VEP plot of this
subject.)
normalities, possibly involving both medial parietal
lobes, and bifrontal abnormalities. Thus, in contrast
to the radiographic studies, BEAM demonstrated
multifocal abnormalities that were more in line with
the clinical history and with neuropsychological
testing. At operation no tumor was found. The subsequent diagnosis by examination of biopsied material was lymphomatoid granulomatosis, a disease entity that may involve the CNS in a multifocal manner
[20, 241.
Dyslexics
None o f the dyslexic patients showed abnormalities
on standard spectral plots. However, when they were
studied under special circumstances, asymmetries
were noted (not illustrated). When these subjects
were asked to listen to music, alpha activity was suppressed over the right hemisphere as in many normal
subjects [12, 21, 231. When they were asked to listen
to speech, however, the left hemisphere alpha suppression often seen in normal subjects was not noted
[12, 21, 231. The standard VEP plots of the dyslexics
were normal. Unusual visual EP features in other
special test situations will be the subject of a future
report.
Patient with Behavioral Abnormality
Although the spectral plot for the sociopathic patient
was within normal limits, his visual EP topography
showed consistent abnormalities consisting of recurring asymmetries of activity overlying the frontal
lobes (Fig 9).
Discussion
Interpretation of EEG and EP records requires correlation of large volumes of data across both space
and time. We propose that the difficulties involved in
making spatiotemporal correlations by unaided visual
inspection of multichannel polygraphic recordings
constrain the clinical utility of EEG and EP. Accordingly, we have developed a technique for the topographic display of scalp-recorded signals on a color
television monitor. Such topographic mapping reduces the dimensionality of data in a twofold manner.
First, topographic mapping presents spatial information in a more concise and summarized form. For
example, one must ordinarily examine many pages of
EEG to appreciate subtle slow-wave asymmetries.
With spectral BEAM plots, such asymmetries can be
summarized in a single image (see Figs 3 , 5 ) . Second,
linking together individual images, as in endless-loop
cinematography (cartooning), enables the visualization of temporal patterns of brain activity that are not
otherwise easily perceived. For example, EP analysis
Duffy et al: Brain Electrical Activity Mapping 315
Fig 6. BEAM VEP plot, showing 42 of the 128 frames generated from the 512-msec VEP of a patient with a kji occipital
brain tumor, formed as in Figure 4. Note the initial negativity
beginning at PZ (72 msec), which then sweeps forward
primarily on the left. The first occipital positivity appears only
on the right 188 to I12 msec). In a similar manner, the second
occipital positivity appears asymmetrically on the right. Next,
it sweeps simultaneously i n two directions: ( 1 ) forward on the
right side exclusively, and (2) across the midline t o activate the
left occipital region (I 52 to 21 6 msec). The kji occipital
positivity persists despite disappearance of the right occipital
positivity (I 60 t o 296 msec), reaching a maximum between
200 and 224 msec. The delayed activation of the &Jt occipital
region overlying the tumor and the prolonged retention of activity i n this region, once activated, are typical of abnormalities associated with tumors. Note also the lack of forward
spread of activity from the leji occipital region to the kji frontal region; we hypothesized that this might represent the electrical correlate of a functional disconnection between the k f t
occipital and frontal lobes caused by the tumor (i.e., interrup-
tion of the left occipitofrontalpatbway). The late waves then
repeat the same sequence. Note the right occipital negativity
developing at 344 msec, which then sweeps forward on the
right only (424 to 472 msec); notice also that it grws in amplitude on the right (432 t o 448 msec) well before it spreads t o
the kji occipital region 1456 to 504 msec). Again, the left side
i s late and persistently activated (504 msec +). Thus the process offirst appearance in the right occipital region, spread
forward on the right only, and late activation of the lefi occipital region from the right was repeated twice. It is of interest t o
note that this patient had a completeb normal standard neurological examination, including visual field studies; the E E G
was also normal. The chical impression was migraine headache. The significance of the peak of positivity appearing in
the left frontal region ( I 5 2 to 224 msec) is not known (perhaps
it represents the effect of deafferentationfrom the leji occipital
region). Neuropsychological tests were not performed on this
patient; therefore, one cannot comment about the possibility of a
defect of frontal lobe function. (See also Figure 5 for the spectral
plot of this subject.)
Duffy et al: Brain Electrical Activity Mapping
317
250
1
200
-
175
150
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-
125
25 5o
1
0
NORMALS
TUMORS
F i g 7 . This graph demonstrates the possibility of differentiating patients with tumor from normal subjects on the basis of a
single measurement from their topographic maps. All tumor
patients showed marked asymmetries overlying the tumor in
their VEP BEAM; most showed more than one episode of
asymmetry at the same location lsee F i g 6). In this figure we
plot the total length of time for all period of asymmetry at the
locus of the maximal asymmetry for 7 normal subjects and 7
tumor patients. Note that the tumor patients had a much
greater period of asymmetry than the normal persons. Furthermore, a line drawn at 75 msec serves t o separate all normal (<
75 msec)from all tumor subjects I> 130 msec).
usually consists of measuring amplitudes and latencies of various waveform components recorded from
several electrodes. The temporal cartooning of EP
BEAM images formed from multichannel data allows
the visualization of traveling wavefronts of positive
or negative electrical activity. Thus waveform components appearing as differing latencies at different
scalp sites may, in fact, represent the same wavefront
slowly progressing across the scalp surface (see Fig
6). BEAM does not create new data but merely presents the original spectral, EP, or EEG data in a more
concise and intuitively comprehensible format.
Despite the fact that their routine clinical EEGs
were normal or nonlocalizing, all 7 tumor patients
examined in this study were differentiated from
normal subjects on the basis of a simple measurement obtained from their BEAM studies (see Fig 7).
Although BEAM may not prove to be as accurate or
consistent as the CT scan in defining anatomical lesions, its success rate exceeds that of the routine
EEG. We suggest that BEAM may significantly increase the percentage of space-occupying lesions that
can be electrophysiologically defined. In certain instances (see Fig 8) BEAM may provide more clinically useful information than is found on CT scan.
The ability of BEAM to identify functional differences in the absence of anatomical lesions was also
demonstrated. An EP BEAM test on an adolescent
sociopath, chosen for having a normal CT scan, revealed prominent frontal lobe asymmetries (see Fig
318 Annals of Neurology Vol 5
N o 4 April 1979
9). Some authors have invoked frontal lobe dysfunction as the cause underlying abnormal behavior in
sociopaths [26, 271. Functional changes were also
observed in 3 adolescent dyslexics of normal intelligence and with normal EEGs. Although standard
spectral and EP BEAM studies were within normal
limits, alpha activity was not suppressed over the left
hemisphere by listening to speech. Many investigators have implicated the left parietal lobe as the
abnormal site in dyslexia on the basis of behavioral
observation and testing and as an analogy to aphasia
[2, 7, 8, 13, 331. The findings suggest that BEAM
may provide a useful electrophysiological tool for
studying the genesis of functional abnormalities of
the brain.
BEAM is not the first method to be used for the
topographic representation of EEG or EP activity. In
the 1950s and 1960s devices called toposcopes or
encephaloscopes, developed by pioneers such as
Harold Shipton and Grey Walter [31, 32, 391, used
multiple-intensity modulated cathode ray tubes to
display data in space and time. In recent years, others
have topographically displayed computer-processed
EEG or EP data via techniques varying from handdrawn contour plots [ l , 14, 15, 381 to computerdrawn contour or gray-scale plots [4, 5, 11, 16, 18,
25, 29, 301. The compressed spectral array of
Bickford et al[4, 51 and the canonogram of Gotman,
Gloor, and Ray Cl61 have proved to be clinically
useful in the demonstration of localized brain lesions.
Two of the most sophisticated display systems
were implemented by Harris et al [ 181and Estrin and
Uzgalis [l 11 as early as 1969. Both systems involved
computer plotting of electrophysiological data. It is
surprising that many of the more recent articles have
used much simpler display systems, including handdrawn plots. In a 1976 review article, Petsche [25]
F i g 8 . This figure illustrates how BEAM may add additional
information to that provided by radiographic evaluation. Five
selectedframes of 128 computed images are displayed as in
Figure 4. The patient was a 13-year-old girl with a history of
multiple episodes of transient neurological dysfunction and a
more recent history of headaches and lethargy (see text). The
C T scan lsee F i g 2) and angiogram suggested a right frontal
lobe tumor. However, both neutvpsychological testing and thc
VEP BEAM revealed bilateral parietal dysfunction as well as
bifrontaldisease. The VEP BEAM, shown in this figure, reveals: (1) long-lasting bilateral prefrontal waves of both positive
(1 64 msec) and negative 1292 msec) polarity, 12) a peculiar
absence of activity (48, 116 , 164 msec) of the midparietal region, ( 3 ) an unusual period of polarity reversal between the left
and right parietal regions and the midline parietal region (84
msec),and (4) a lesser deficiency of activation over the midfrontal region I1 64 and 292 msec). No tumor was found at the
time of craniotomy. The neuropathologicaldiagnosis was lymphomatoid granulomatosis, a process that may involve the CNS
in a multifocal manner.
F i x 9. This figure shou1.r a functional abnormality demonstrated by V E P topography in the presence of a normal C T
scan (no anatomical lesion). Three selected frames of 128 computed images are displayed as in Figure 4. The patient was an
18-year-old man referred for evaluation with a hi.itory of
sociopathic behavior. Although his C T .scan was within normal limits, his behavior suggested frontal lobe dysIysfirnction. His
V E P plot. shown here, demonstrates recurring asymmetries in
the frontal lobes of both positive and negatire activity. 7'hi.r.
we believe, represents the neurophysiologicalcorrelate of-the expectedfrontal lobe beharioral dy.rfunction seen i n the presence of
a normal C T scun. Such topographic maps may protme usefir1 i n
finding electrnphysiologicalcorrelates of behacioral disorders.
Fig 8
suggested features to be incorporated into a topographic display system of the future. Many of these
features, however, had already been implemented by
Harris et a1 [18] in 1969. T h e reasons for the lack of
application of technology already developed may be
twofold. First, the early systems may have been operationally difficult, inconvenient, or expensive to use
for other than a circumscribed research project. Second, the better systems appear to have been developed by engineers, and the failure to see these
systems widely applied to clinical problems may have
reflected a comprehension or credibility gap between
engineers and physicians.
The BEAM system described in this report takes
full advantage of modern advances in solid-state
electronics technology (see Scienti$c American, Sept
1977). A key feature of BEAM is a simple and easy to
use interface between a small biomedical computer
and a standard color television set. At present, computation time for a single topographic map is under 4
seconds; thus the 128 maps of the usual EP sequence
can be created from the initial 20 EP curves in approximately 9 minutes. EEG technicians have been
trained to create BEAM images within a day's instruction. Furthermore, the prototype computed
video interface costs little more than an eight-channel
polygraph. Therefore, only a small investment would
be required for a laboratory already performing EPs
or collecting spectral data to begin to display their
results topographically.
The results of the current feasibility study suggest
that topographic display of electrophysiological data
may greatly expand their clinical utility, especially as
regards functional lesions. In this sense, data from
BEAM appear to complement the anatomical definition provided by the C T scan.
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