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The present inventions relate generally to an apparatus and method for
displaying a topographical map of brain characteristics of a patient. More
particularly the inventions relate to a novel method and apparatus for
evaluating physiological functions and behavioral patterns of a patient's
brain. Computer software is used for processing measured test information
from a patient, and the processed test information is output in the form
of various topographical maps which provide functional information
characteristic of a patient's brain.
Information on neurophysiological processes in conscious patients can be
obtained by, for example, x-ray computerized tomography ("XCT,"
hereinafter) and nuclear magnetic resonance ("NMR," hereinafter) for
anatomical information and positron emission tomography ("PET,"
hereinafter), regional cerebral blood flow ("rCBF," hereinafter), and
measurement of evoked electrical and magnetic activity and
magnetoencephelogram electroencephelogram measurements ("EEG,"
hereinafter) for physiological information. Such measurements often yield
a complicated information, such as, for example, EEG time varying outputs.
A detailed and thorough analysis of complicated EEG information requires
computer manipulation to determine differences of brain electrical
activity of a patient compared to a normal population. A number of
limitations currently exist for computer manipulation and analysis of all
brain measurement.
Each particular brain analysis technique provides selected information on
different aspects of regional brain function, and each technique has its
inherent advantages and limitations. For example, although the XCT method
provides excellent spatial resolution and bone to soft tissue contrast,
the XCT method has poor soft tissue contrast for gray and white matter
imaging. The XCT method also provides virtually no information on the
physiology of the brain. The PET method provides images which primarily
depict physiological activity of the patient. Integration of anatomical
and physiological information has not generally been achieved by these
techniques.
There are methods of reconstructing three dimentional images from
tomographic information both for anatomical information obtained in XCT
methods and for physiological information obtained by PET or single photon
emission computed tomography ("SPECT," hereinafter). These methods do not
apply to non-tomographic techniques, such as, the isotope clearance method
for measuring rCBF or the measurements of the electrical potential (such
as EEG measurements) and magnetic potentials on the scalp. The clinical
utility of EEG is fairly well established, and techniques to generate
topographic maps from the EEG data have been developed (see, for example,
U.S. Pat. No. 4,408,616, which is incorporated by reference herein).
Studies in the recent past have indicated that the measurements of the rCBF
may be informative in assessing brain function in normal subjects, as well
as in patients with neurologic and psychiatric disorders. Several brain
techniques such as nitrous oxide inhalation (see, for example, S. D. Kety,
R. B. Woodford, M. M. Hamel et al., Cerebral blood flow and metabolism in
schizophrenia, American Journal of Psychiatry, 104, pp. 765-770, (1948))
intra-carotid a 133-Xenon injection (see, for example, D. H. Ingram and G.
Frazer, Distribution of cerebral activity in chronic schizophrenia,
Lancet, 2, pp. 1984-1986, (1975)) and recently 133-Xe inhalation technique
(see, for example, B. L. Mallet and W. Veall, Measurement of regional
cerebral clearance rates in man using Xenon-133 inhalation and
extra-cranial recording, Clinical Scieces, 29, pp. 179-197, (1965) and E.
F. Duffy, J. L. Burchfiel, and C. T. Lombroso, Brain electrical activity
mapping (BEAM): a method for extending the clinical utility of EEF and
evoked potendial data, Annals of Neurology, 5, pp. 309-321 , (1979)) have
been applied to measure the rCBF. The 133-Xe inhalation technique provides
non-invasive measurements of rCBF in both hemispheres of the brain
simultaneously. The 133-Xe gas in trace amounts is inhaled by the patient,
and clearance of 133-Xe from the brain is measured by conventional
extra-cranial scintillation detectors. This technique has been applied
extensively in the study of normal subjects and in clinical populations,
and has several advantages, such as, (i) it is non-invasive, (ii) the
133-Xe isotope is inexpensive and commercially available, (iii) the
radiation dose to the patient is relatively small, (iv) it can be used for
multiple measures of rCBF on the same patient, thus allowing the study of
changes during the cognitive activation process, and (v) the equipment is
transportable making bedside evaluations feasible.
BRIEF SUMMARY OF THE INVENTION
One of the primary objects of the invention is to provide an improved
method and apparatus for analyzing behavioral, neuropsychological and
physiological functioning of a patient's brain and displaying a
topographical map of the information.
A more particular object of the invention is to provide a novel method and
apparatus for manipulating physiological information from a patient's
brain using computer software to provide a video display of topographical
maps of salient information.
A further object of the invention is to provide a novel method and
apparatus for manipulating behavioral information from a patient's brain
using computer software to provide a video display of topographical maps
of behavioral information.
An additional object of the invention is to provide a novel method and
apparatus for manipulating neuropsychological information from a patient's
brain using computer software to provide a video display of topographical
maps of information.
Another object of the invention is to provide a novel method and apparatus
for generating a topographical map of physiological information from a
patient's brain the information derived from measurement of EEG
information collected during physiological testing of a patient.
An additional object of the invention is to provide an improved method for
accumulating a data base of topographical maps of funcational information
on the human brain by comparing physiological information and behavioral
test or task results.
Another object of the invention is to provide a method of measuring EEG
activity from a patient during application of neuropsychological testing
of a patient and converting the EEG activity into a topographical map of
behavioral type information.
In accordance with the invention an apparatus and method is provided for
measuring and displaying topographical maps of brain electrical activity
signals and various information processed from selected tests and tasks
performed by a patient. Various computer software programs are employed to
process and analyze the measured signals and information to generate
interpolated topographical map outputs of the brain electrical activity
signals and other processed information. These topographical maps are used
for detailed diagnosis and evalution.
A user can select for display a plurality of topographical maps which
illustrate various characteristics of brain electrical activity signals
and other processed physiological, neuropsychological and behavioral
information. For example, such physiological information as brain
electrical activity and rCBF are measured by electrode sensors and
scintillation detectors, respectively, and produce input activity signals.
These input activity signals are interpolated to generate an expanded
finer matrix of interpolated values. Interpolation is selectively
performed every other pixel line in an interlace mode of constructing the
topographical map. The display of data includes a color code scale and
associated numerical values for determining the relative magnitudes of
regions of the topographical map. In addition to the topographical maps,
individual characteristics waveforms and other associated parameters can
be simultaneously output to a video display or printer for comparison and
association with the topographical maps.
The apparatus also operates responsive to selected software programs which
are directed to the following areas: (1) accumulation of raw test results
from selected tests or tasks, such as a battery of neuropsychological test
or behavioral tests and calculation of an output signal weighted in terms
of the expected spatial location for the information on the scalp area for
a particular test, (2) during physiological and neuropsychological
testing, comparison and correlation of EEG, EP and rCBF and other such
measurements to test and task results in terms of topographical maps, (3)
performance of montage analysis to identify by an iterative procedure
features of interest in the measured EEG or EP signals, (4) performance of
threshold activation analysis wherein the incoming signals are not
measured and analyzed until a predetermined threshold condition has been
achieved, (5) performance of a cognitive testing routine in a single
testing period by applying a plurality of stimuli and sorting the
associated responses with a computer, (6) performance of a Fourier
transformation of EEG signals to determine frequency energy band output
for the major frequency banks, and (7) performance of integration analysis
of EP responses to present an averaged sum of response amplitudes to
enable the user to isolate the most significant spatial and time segment
contributions to the EP response and to condense the EP response spectrum
to a few topographical maps. Other simple mathematical operations such as
first and second order differentials and arithmetic differences of the
signal also enable characterization of the patient response and allow
comparison with normal population responses to isolate abnormal responses
for clinical diagnostic purposes. The apparatus also can utilize external
means for processing, analyzing and output of the topographical maps at a
location removed from the locations at which signals are measured.
Further objects and advantages of the present invention, together with the
organization and manner of operation thereof, will become apparent from
the following detained description of the invention when taken in
conjunction with the accompanying drawings wherein like reference numerals
designate like elements throughout the several views.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a block diagram of an apparatus for measuring brain electrical
activity signals and for displaying topographic maps characteristic
thereof, and FIG. 1B is a functional block diagram showing the flow path
through the apparatus of measured input activity signals;
FIG. 2 shows a top view of positions of an electrode sensor arrangement
with respect to a patient head outline;
FIG. 3 is an array of electrode sensors and a superimposed matrix image of
a line-by-line interpolation of signals for the array;
FIGS. 4A and 4B are block diagrams of two alternative methods for
line-by-line interpolation and output of signals;
FIG. 5 is a display output of evoked potential (EP) response measurements
showing a topographical map, associated waveforms for selected electrode
sensor locations and a vertically positioned color code scale;
FIG. 6 is a block diagram of a noise signal evaluation procedure;
FIG. 7 is a display output of a plurality of topographical maps of evoked
potential response measurements integrated over the time intervals shown;
FIG. 8 is a lateral view of the human brain;
FIG. 9A shows a sixteen detector arrangement and FIG. 9B shows a thirty-two
detector arrangement for measuring the rCBF;
FIG. 10 is a top view projection of the human brain;
FIG. 11A shows the projection geometry used for image generation. ADCB
represents the plane containing the left side view projection and CDD'C'
is the top view projection plane in FIG. 11B which shows a triangular
approximation to reduce the compression of the regions in the temporal
lobe in the top view.
FIG. 12A is an outline of the skull projections with the superimposed grid
pattern and detector arrangement on the left side view and FIG. 12B shows
the top view; and,
FIG. 13 shows regional weights assigned to the block design subtest of the
WAIS-R (1=minimum; 10=maximum).
DESCRIPTION OF PREFERRED EMBODIMENTS
A. Brain Electrical Activity
Referring now to the drawings, and in particular to FIG. 1A, a block
diagram of a brain electrical activity mapping apparatus is indicated
generally at 10. For purposes of measuring EEG and EP type information,
the brain electrical activity mapping apparatus (hereinafter referred to
as the apparatus 10) includes sensor means, such as, for example, a set of
electrode sensors 12 (for example, Grass gold cup manufactured by Grass
Corporation) arranged on the top of a patient's head 13. In FIG. 2 is
shown an enlarged detail of an arrangement for a rectangular array or
matrix of twenty-one of the electrode sensors 12 positioned on the
patient's head 13. The arrangement illustrates one acceptable variety
selected from various conventional international formats. In response to
brain electrical activity the electrode sensors 12 generate input activity
signals 14. Remote means, such as the sensors 12, can be located at remote
sites as part of a distributed system for performing measurements of
information on the brain, such as the signals 14. These remote
measurements can be communicated through remote apparatus, such as
interface devises coupled to modems, to a central location for analysis by
the remainder of the apparatus 10 described hereinbelow.
In selected operating modes of the apparatus 10, such as in measurement of
EP response, a stimulus 16 is also applied to the patient, and in response
to the stimulus 16 the resulting brain electrical activity is sensed by
the electrode sensors 12. A detailed discussion of conventional EP
response measurements is set forth in Duffy et al., "Brain Electrical
Activity Mapping (BEAM)" A method for Extending the Clinical Utility of
EEG and Evoked Potential Data," Annals of Neurology 5, Apr., 1979,
pp.209-231; which is incorporated by reference herein. The type of
stimulus 16 used in EP response measurements is, for example, a strobe
light, a sound (such as a click generator) or a somatosensory stimulus,
such as mild electrical shock. These stimuli 16 can be periodic, aperiodic
and can also be combinations of each available type of stimulus 16. In the
illustrated embodiment of FIG. 1A, the stimulus 16 is controlled
responsive to a control signal 18 from a main computer, such as a
microcomputer unit 22. The type of stimulus 16 is selected by a user
input, such as a keyboard 23. The stimulus 16 can also be provided
responsive to a stimulus controller 20 which is a separate microcomputer
or is a remote control source.
In other modes of operation of the apparatus 10, such as in
electroencephelogram (hereinafter "EEG") measurements, the stimulus 16 is
not applied to the patient. However, the measurement of brain electrical
activity in the EEG mode otherwise follows substantially the same steps as
for EP measurement. Therefore, in general as shown in FIG. 1A, the sensed
input activity signal 14 is output from the electrode sensors 12 to
processing means which includes an analog multiplexer 24, an amplifier 26
and an analog to digital converter (A/D) 28. If a Grass or Beckman
polygraph is used, the electrode sensors 12, the multiplexer 24 and the
amplifier 26 are included in the polygraph.
In the illustrated embodiment the amplifier 26 comprises a plurality of
twenty-one amplifiers, each connected to an associated one of the
electrode sensors 12. The multiplexer 24 accepts from the amplifier 26
each of the amplified input activity signals 14, and outputs each of these
input activity signals 14 is serial fashion to the A/D converter 28 (for
example, a Dual Systems AIM 12). The A/D converter 28 provides to the
microcomputer unit 22 an amplified and digitized, or a converted, form of
the input activity signal 14. In general, processing means includes those
components of the apparatus 10 which operate on the signals output by the
electrode sensors 12 to provide the amplified and digitized form of the
input activity signals 14. The processing means can also be combined with
the sensors 12 to form a remote sensor means (for example, a commercial
polygraph) at a location remote from the remainder of the apparatus 10. In
the manner discussed hereinbefore, the data from the polygraph is then
communicated by a modem to the centrally located remainder of the
apparatus 10 which analyzes the data to provide an output for display.
The microcomputer unit 22 in FIG. 1A can be any one of a plurality of
commercially available computers, such as, for example, a Zenith Z-100,
which uses an 8088 central processor chip (see, Intel Component Data
Catalog, Jan. 1982, pp. 8-25 to 8-51, which is incorporated by reference
herein). The Zenith Z-100 also includes the keyboard 23, a display
processing until (hereinafter "DPU") 39 which will be described in detail
hereinafter, a disk drive (not shown) and on board random access memory
(hereinafter "RAM") 30, and PROM and ROM (not shown) memories. The
microcomputer unit 22 controls collection, manipulation and output of the
input activity signals 14. In a preferred embodiment, the microcomputer
unit 22 includes the RAM 30 which functions in part as an averaging means
for storing at predetermined locations a running accumulation of the
plurality of input activity signals 14. The microcomputer unit 22 adds the
incoming value for the signals 14 to the previous value and stores the
total in the RAM 30 at the predetermined locations. This accumulation of
the amplified and converted input activity signals 14 results in
statistical averaging of the input activity signals 14 which improves the
signal to noise ratio. Under typical operating conditions one to ten
minutes of data averaging is desirable to obtain statistically meaningful
values for the input activity signals 14.
The apparatus 10 controls data gathering and analysis responsive to
software programs stored on a disk or tape 29, and the program are read
into the RAM 30 and executed by the microcomputer unit 22. The user
interacts with the microcomputer unit 22 through input means to supply an
input signal responsive to a user input. Examples of input means include
the keyboard 23, a light pen 34 and a mouse 36. The user can also supply
an input signal by transfer of information already stored on a disk
storage unit 27 or stored in the disk or tape 29, or stored in a memory
external to the apparatus 10, such as the time period of data taking, the
number and type of the stimuli 16 and the desired software programs to
manipulate the data for output and display for user analyzation.
The operation of the apparatus 10 as illustrated in FIG. 1A can be better
understood by reference to the procedural and signal flow diagram of FIG.
1BA and 1BB. As illustrated in FIG. 1BA, the apparatus 10 in the first
decisional block has been initialized with user selected parameters or
default parameters, and a mode of operation is selected. If the EP
response mode is selected, then a predefined stimuli 16 is applied to the
patient as a first step. However, if the EEG mode is selected, then there
is no externally applied predefined stimuli 16, and the electrode sensors
12 detect EEG signals directly from the patient's head 13. In any event
whether the signals originate from the patient as an EEG signal, an EP
response signal or other information (such as test or task results)
collected on the brain, the next step is directed to preprocessing the
outputs from the electrode sensors 12. This preprocessing can include, for
example, a number of steps, including amplification, hardware filtering,
software filtering and fast Fourier transformation.
The preprocessed outputs from the electrode sensors 12 are then digitized,
and the digitized form of the signals 14 are placed in predefined
locations in the RAM 30 corresponding to predefined sensor positions. The
signals 14 corresponding to particular sensor positions can alternatively
or additionally be stored in secondary storage, such as the disk storage
unit 27 or the tape 29.
Once the signals 14 have been digitized and stored in the RAM 30, a
determination is made whether the apparatus 10 is in the EEG or the EP
mode. If operating in the EEG mode the procedure skips to step B shown in
FIG. 1BB. If, however, the apparatus 10 is in the EP mode, the signals 14
are accumulated in the redefined locations in the RAM 30 and/or can be
stored in the disk storage unit 27 or the tape 29. Operation of the
apparatus 10 then proceeds to determine whether the selected number of
signals 14 have been acquired in accordance with the initial setup
parameters. If the selected number of the signals 14 has been acquired in
the appropriate manner, processing proceeds to step B which continues in
FIG. 1BB. If, however, the selected number of the signals 14 has been not
acquired, then processing resumes at the step of applying the predefined
stimuli 16. This operation of the apparatus 10 in the EP mode shown in
FIG. 1BA continues until the selected number of the signals 14 have been
acquired.
Referring to FIG. 1BB, the operation continues at step B from FIG. 1BA. At
this point the RAM 30 contains data representative of the accumulation of
the digitized signals 14 at predefined locations in the RAM 30
corresponding to respective sensor positions. Alternatively, at this
point, accumulated data signals can be input from a secondary storage
source, such as the disk storage unit 27, to the RAM 30 to provide the
initial database from which further manipulation proceeds. The next step
in the operation is the selection of one of a plurality of options as to
how to operate on the signals 14. Once the option is selected, the
apparatus 10 proceeds to perform the appropriate operations on the signals
14 as stored and accumulated in the RAM 30. These operations on the
signals 14 can include, for example, attenuation or amplification, digital
filtering, smoothing, fast Fourier transformation, differentiation,
integration and statistical data analysis. These operations can also be
performed prior to storage in the RAM 30, such as after the A/D conversion
28 and prior to initial storage in the RAM 30.
After the selected option has been performed, the result of the operation
is stored again in the RAM 30, either at new locations or at the previous
locations, such as by overwriting the previous locations with the new form
of the signals 14. Alternatively or additionally, the results can be
stored in a secondary storage such as the disk storage unit 27. At this
point, the signals 14 stored in the RAM 30 provide the basis for
interpolation, either line by line or in an interlaced or alternate line
mode of output, and the interpolated form of the signals 14 is output n a
display format compatible with the DPU 39. The DPU 39 therefore receives
and stores the interpolated form of the signals 14 in the display RAM of
the DPU 39, one line at a time, as shown in the next block of FIG. 1BB.
The DPU 39 generates an image on a display means, such as a video display
43 (for example, a Zenith ZVM-133), or the image is output to another form
of the display means, such as an ink jet printer 45 (for example, a TRS 80
CGP220 manufactured by Tandy Corp.).
Interpolation Example
In the apparatus illustrated in FIGS. 1-7, the input activity signals 14
stored in the RAM 30 undergo an interpolation within the RAM 30 under
control of the microcomputer unit 22. An expanded matrix is formed of
finer resolution (for example, a forty by forty array of points in the
preferred embodiment) than the arrangement of the twenty-one electrode
sensors 12. The general technique of interpolation using three points to
form finer resolutions frames of the input activity signals 14 is known
(see, for example, Duffy et al., "Brain Electrical Activity Mapping"
referred to hereinbefore). The present example of an interpolation method
uses a set of two points to generate and output line-by-line of the
interpolated form of the input activity signals 14.
In one preferred embodiment, a line is one line of pixels, wherein a pixel
is the smallest picture element used to construct the video image. As will
be described in more detail hereinafter, each pixel color is described
completely by three bits of digital information stored in the RAM 30. A
color mapping procedure can also be used to assign color values to the
pixels. For example, each pixel can have five bits in the RAM 30 to
describe one of thirty-two possible color choices which points to a color
map also located in the RAM 30. The color map can have a preselected
number of n bits of information which describes each of 2.sup.2 possible
colors, and the color map digital description is output to the intensity
digital to analog converter part of the DPU 39 for display of the desired
pixel color.
Upon completion of the interpolation for a given line, the interpolated
values can also be stored in a disk storage unit 27 for future use and
analysis. A video output 37 of the interpolated input activity signals 14
is output line-by-line to the DPU 39 (preferably contained within the
microcomputer unit 22 as discussed hereinbefore) in preparation for output
to the video display 43. The interpolated form of the signals 14 can also
be output from the RAM 30 or the DPU 39 for hard copy printout n the
printer 45 or for completion of an additional data analysis 40 before
being displayed. These alternative operations will be discussed in more
detail hereinafter.
In the illustrated embodiments of FIG. 3 and FIGS. 4A and 4B, the
interpolation begins by generating amplitudes at four projected electrode
sensors 31 at the corners of the matrix of the electrode sensors 12 to
establish a rectangularly symmetric five by five matrix of the input
activity signals 14. The values for the four signals 14 at the projected
electrode sensors 31 are interpolated from a linear average projection
from the intersecting perpendicular lines of the electrode sensors 12
which converge n each of the projected electrode sensors 31. Once the
signals 14 have been established at each of the projected electrode
sensors 31, the interpolation proceeds by selecting a first line, such as
a line 33 in FIG. 3 along the perimeter of the matrix of the electrode
sensors 12, and starting with line 33 the line-by-line interpolation is
carried out parallel to the line 33.
The use of a commercial polygraph unit with, for example, twenty-one of the
electrode sensors 12, rather than twenty-five actual sensors for the five
by five matrix, enables of a standard unit of substantially lower cost to
the user. Further, the approximately rectangular arrangement for the
twenty-one electrode sensors 12 enables the interpolation procedure to be
simplified. In FIG. 4B interpolation is shown to proceed along lines which
are parallel to one another and which passes through the regular array of
points defined by the rectangular arrangement of the electrode sensors 12.
Therefore, the interpolation takes place along one-dimensional lines which
are easily defined in the rectangular arrangement, and interpolation
calculations are performed more easily using only two points to generate a
bracketed intermediate point. In prior conventional interpolation
approaches, three points from a non-rectangular arrangement have been used
and a set of coefficients precalculated for the expanded matrix of points
(see, for example, U.S. Pat. No. 4,417,591, which is incorporated by
reference herein).
As shown in FIG. 4A, after determination of the signals 14 at the projected
electrode sensors 31, the linear interpolation is carried out for selected
points a predetermined fraction of the distance between each nearest
neighbor pair of the signals 14 in a column 25 of the electrode sensors
12. An interpolated value for the selected point is determined by forming
a linear average of an appropriate pair of signals 14, such as the two
input activity signals 14 at a pair of the electrode sensors 12.
Alternatively, the pair is one of the signals 14 at one of the electrode
sensors 12 and one of the projected sensors 31, which bracket the location
of the selected point. For example, in the illustrated embodiment of FIG.
3 the distance between each of the electrode sensors 12 is divided into
eight parts. Thus, if the selected point is one-eighth of the distance
between a first one of the sensors 12 and a second one of the sensors 12,
then the value for the electrical activity signal 14 at the interpolated
point is seven-eighths the value of the signal 14 at the first sensor 12
plus one-eighth the value of the signal 14 at the second sensor 12. This
interpolation procedure continues sequentially up each of the columns 25
of the electrode sensors 12 until the interpolation is complete for all
five of the columns 25 which are perpendicular to the line 33. The
interpolation is then performed for all remaining lines parallel to the
line 33, proceeding incrementally from line 33 to line 35 and to the other
lines until completion.
In another form of interpolation shown in FIG. 4B, after the interpolation
along the line 33 has been completed, the interpolation proceeds point by
point for the line 35 and for each of the subsequent lines parallel to the
line 33. This procedure is accomplished by first determining the signal 14
at the selected point which is a predetermined fraction of the distance
between the electrode sensor 12 contained in the line 33 and the nearest
electrode sensor 12 in the same column 25. This process is completed for
only a first point in each of the five columns 25 of the electrode sensors
12. The resulting five points are shown in FIG. 3 as interpolated values
38 which lie at the intersections of the columns 25 and the line 35. These
values 38 are then used to complete the interpolation along the line 35 in
the same manner as described above for the embodiment of FIG. 4A.
Interpolated values 41 are constructed from a linear averaged combination
of the appropriate pair of the interpolated values 38 which bracket each
of the values 41. The line 35 is then output for presentation on the video
display 43. The outputted form of the signals 14 comprising the line 35
are therefore generated in a compatible format for the conventional video
display 43. Further details of operation of the video display 43 can be
obtained by reference to the Zenith ZVM-133 operating manual, which is
incorporated by reference herein. Alternatively, the line 35 is output for
the additional data analysis 40 prior to display, depending on the user
selected operational mode. Display of the complete frame of a
topographical map 44 shown in FIGS. 5 and 7 continues line-by-line,
incrementally completing the interpolation for each of a plurality of
lines and outputting each of the lines to the video display 43.
These interpolation procedures enable the live time line-by-line processing
of the input activity signals 14 for output to the video display 43. The
live time output and display of the signals 14 is accomplished without
having to await formation of the entire video frame and also without
having to store in the RAM 30 a plurality of the lines or a complete frame
of the input activity signals 14 before output to the video display 43.
Prior to "live time" methods have required storage of the complete frame
before the topographical map 44 could be displayed (see, for example, U.S.
Pat. No. 4,417,591, which is incorporated by reference herein). Further,
as mentioned hereinbefore, the line-by-line interpolation described herein
requires only two end points to perform the procedure, and this greatly
simplifies the calculation and storage of values in the RAM 30 and
decreases the calculation and display time.
The input activity signals 14 can also undergo other operations prior to
the data interpolation, such as the data analysis 40 (for example, data
smoothing and a digital filtering treatment to be discussed in more detail
hereinafter). Another example of the data analysis 40 is the performance
of a Fourier transformation of the EEG form of the input activity signals
14 from the twenty-one electrode sensors 12. In order to avoid performing
time consuming Fourier transformation for the larger number of values in
the expanded frame containing the interpolated values 38 and 41, only the
small numbers (twenty-one in the illustrated embodiment) of the unexpanded
input activity signals 14 undergo Fourier transformation. Interpolation
expansion to a finer matrix is generally done more efficiently on the data
after completion of any extensive or complicated form of signal treatment,
such as the Fourier transformation operation.
Video Display
In one preferred embodiment shown in FIGS. 1-7, after the interpolation and
the optional data analysis 40 of the input activity signals 14, the
resulting video output 37 is applied to the DPU 39 contained in the Zenith
Z-100 unit. Alternatively, the raw input activity signals 14 accumulated
in the RAM 30 can be output as a raw signal 25 by the microcomputer unit
22 to the DPU 39 without further processing, including interpolation. The
video output 37 input to the DPU 39 is converted into an output signal 47
suitable for the video display 43 which provides the video presentation of
the topographical map 44.
In the preferred embodiment there is one display rate, other than manually
sequencing through the set of frames, for dynamic display of the change in
EP response as a function of time elapsed after the stimulus 16 has been
applied to the patient's head 13. The display rate can also be increased
by generating reduced sizes of the topographical maps 44, in a | | |
