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Advanced EEG Analysis
- Corticography/Topographic Analysis
- Universal EEG Review
- ICU and EMU Long Term Monitoring
- Spike and Seizure Detection
- Reporting
FAQ / Application Notes
The Application Notes section is divided into sections for each of the components of the EEG Suite, and sub-divided into Clinical and Program application notes. If there are items you would like to see added to the Application Notes let us know via the Suggestions page.
You may also use the Persyst Site Search engine to see if there is a match to your query on this Web site. Then, use your browser's page search (e.g., Edit|Find on your browser's menu) to locate the search term on the page itself.
The Persyst EEG Suite version 4.0.0 and later incorporates a new help file that contains the Persyst EEG Suite User's Guide V4.0. Be sure to check the Insight help file in addition to the Application Notes.
Clinical Application Notes:
Insights Newsletters Index
Persyst EEG Suite General FAQ's
Insight
Reveal/SpikeReview
Prism
MagicMarker
Applications notes appear below. Use the links above to jump to the section of interest
Insight
Montage Priority: Have Insight montage settings override recorded montage.
Insight can be configured to automatically display the montages that were used during the recording by selecting View|Display Options from the Insight menu, and selecting "as recorded".
The acquisition system montages can be "overridden", so that the montages switch automatically and use your custom review settings (e.g., channel colors, gain, filters, etc.).
- Open a recording.
- Page forward until the montage you wish to customize is displayed.
- Edit the displayed montage (see the help topic Edit or Create a New Montage in the EEG Suite Help File: From Insight select Help|Help Topics).
- Right-click on the Montage Bar (left side of screen) and select Save Montage. Do not change the acquisition system's montage name.
When Insight encounters this montage name during review, it will use your customized montage settings in favor of those from the acquisition instrument.
Insight can be set to ignore acquisition parameters altogether and remain in the montage you select. Select View|Display Options, then de-select "as recorded".
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Calibration is displayed as a flat line in Insight.
Calibration performed on digital instruments is done with a referential montage. To view the calibration in Insight review, it must also be displayed in a referential montage. By definition, a referential calibration displayed in a bipolar montage is a flat line: Since the calibration pulse is applied equally to the cephalic inputs (G-1) to reference (G-2), then switching to a bipolar montage should display a flat line. Input 1-ref = Input 2-ref, so the difference between Input 1 and Input 2 is zero. If you did see any deflection, this would indicate an error in re-montaging.
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Poly channels are displayed as a flat line in Insight.
After opening a Nihon Kohden 2100 format file, and saving the montage within Insight using the original name, some traces may be displayed as flat lines. Specifically EKG-EKG and HAN-HAN traces may be displayed as flat-lines.
The solution is to not record data files with duplicated channel names. The above problem is the result of two input channels having the same assigned label name (e.g., just as Fp1-Fp1 will display a flat trace, so will EKG-EKG). When creating Patterns on the Nihon Kohden 2100 system, use unique names to label all channels, especially EKG, EMG, and HAN (e.g., EKGA-EKGB, EMG1-EMG2, etc.).
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Saving clustering results from SpikeReview
Spikes are grouped and artifacts are removed in SpikeReview. The resulting spike groups can be saved by choosing Export Groups to EEG Page from the Tools menu. The spikes are placed in Insight as @VPlot comments with the perception and group number. These events can be reviewed in more detail with Prism: VoltagePlot. Choose Select Group from the Edit menu to display the average traces and voltage topograph of a group.
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Prism
Coherence measurements in Prism
Coherence is difficult to understand. Here are a couple of references that may help: x Nunez et al., EEG Journal, 103 (1997) 499-515. x Daly and Pedly, Current Practice of Clinical EEG 2nd Edition, 66-67.
Let me also offer another more graphical description that I find useful. Coherence measures the stationarity of the phase difference between two signals at each FFT frequency. If the two signals share an “electrical generator” then we expect that the phase difference (of the frequencies for that generator) will be constant, and the coherence will be high. The cross-spectrum amplitude and phase difference is calculated for each epoch, summed, and finally normalized by the absolute cross-spectrum amplitude. If the phase difference between the two signals is random from one epoch to the next, then the coherence will tend to zero as many epochs are averaged.
Here is the graphical description to match what is described above.
Create a two-dimensional graph using radial coordinates. The graph will depict the coherence calculated for a single FFT frequency.
Calculate the cross spectrum of the two channels for the first epoch, and draw a line starting from the center of the radial graph. The length of the line is equal to the cross spectrum amplitude (combined power of the two signals at this frequency) and the angle of the line is equal to the phase difference of the two signals over this epoch.
Calculate the cross spectrum for the next epoch and draw a line starting at the end of the previous line. If the phase difference has changed, then the resulting line will have a bend in it.
Continue this process for all the epochs, each time adding the new epoch line to the end of the previous epoch line. If the resulting multi-epoch line is perfectly straight, then the coherence between the two signals is 1. If the resulting line circles around the origin of the graph, then the coherence is near 0.
The actual coherence value is calculated by dividing the distance from the start to the end of the line “as the crow flies” by the total length of all the epoch line segments. The final coherence plot displays the results of this calculation for each frequency running from 0 to the sampling-rate/2. If only a single epoch is used, the coherence is by definition 1(for all frequencies) because the multi-epoch line has no bends, and this is why Prism requires 2 or more epochs to calculate the coherence.
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CSA on-line
Prism Spectrum does provide the ability to perform CSA online, both Hidden Line CSA and Contour CSA. This is accessed from the Insight menu under "Tools" and "Prism: Spectrum".
For online CSA, scroll Insight to the EEG page where you would like the CSA to begin.
From the chart definition dialog box, choose "Hidden Line CSA" or "Contour CSA", then the channels of interest from the "Channels" tab. Next, select the number of seconds of data you would like to appear in the CSA display from the "Duration" dialog from the "Range" tab and uncheck the "Use Events" box (this is the default).
The CSA plot can be set to set to "Online CSA" by selecting "Tools" from the menu and "Online CSA". The plot will update as quickly as it can calculate and draw until it reaches the end of the recording. At that point it will update as new data is written to the EEG file.
Note: For more comprehensive on-line EEG trending that can handle and display a wider variety of parameters check out MagicMarker.
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Multiple short-epoch FFT measurements.
You can specify short epoch lengths by going to Prism: Spectrum, and selecting the FFT tab. Decreasing the points per window / windows per epoch will decrease the epoch length. Note that as you decrease the points per window your frequency resolution will also decrease.
Prism can use @Spectrum events placed in Insight to determine the start time and duration of FFT calculations. You may place these events yourself in Insight, or you can edit the comments in the Persyst .lay file to "automate" the process. It may be the case that you want to have overlapping epochs, e.g., a 125 ms epoch calculated every 10 ms. The way to accomplish this is to create @Spectrum events at the desired times and with durations of 125 ms or less. You might have noticed the *.lay file that gets created in the record’s directory when you add a comment or tab to an EEG record. This is a simple text based format that includes a section that describes the comments added from within Insight. Here is the section of a *.lay file where I have added two @Spectrum comments.
[Comments]
3.39362,60,0,100,@Spectrum
76.266,60,0,100,@Spectrum
You can create the @Spectrum comments in a text editor or on a prototype file and copy the comments into other *.lay files of interest. The fields in the comment line are time (in seconds), duration (in seconds), 0 (unused), 100 (unused), and the comment name.
As mentioned in the first paragraph, sampling rate will affect your frequency resolution, so given the short epoch length you will probably want to sample at a high rate, e.g., 1000 Hz. This will allow you to reduce the window length and keep a reasonable frequency resolution. This tradeoff of window length and frequency resolution is fundamental to FFT calculations.
Also, when using the @Spectrum events, the calculation for the first epoch will start at the start time of the event. The number of epochs is chosen to cover the complete range, so will normally be a little longer than the duration of the @Spectrum event unless its duration is an integer multiple of the epoch duration.
In the Insight help file there is additional information on setting FFT parameters, exporting the results, and the FFT parameters themselves (Prism: Spectrum: Quick Tour / Export FFT Data to a File / Technical Considerations).
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Persyst EEG Suite (Insight+SpikeDetector+Prism)
Frequently Asked Questions
When does the 30 day counter for the free trial begin?
The counter starts when the program is installed. A unique key is generated for each computer, so the same disks can be used for any number of installations.
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How do I purchase the software?
You can purchase the EEG Suite directly from Persyst, or you may purchase from one of our distributors. We will be happy to answer any questions you have, and you can reach us via e-mail at sales@eeg-persyst.com or phone at (928) 708-0705.
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What is the "Renew" date?
This shows the Software Version Date you can install with your current subscription upgrades. For example, if your Renew date is "2004.04.01", you can install any version with a number lower than this.
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Can I continue to use the software after the "Renew" date?
Yes, your software will work in every respect after the Renew date. (This is used only to show upgrade status.)
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What features are missing in the free trial, demo program?
None, there is no difference between the demo program and the retail software.
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What do I receive when I purchase the program?
Each package includes the new Persyst EEG Suite User's Guide, the new Persyst CD-ROM, and a Software Registration/Purchase form. (Floppy disks are available upon request).
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How do I get updates of the software?
Updates are free for one year after purchase, and are posted on the download page. If it is not possible to upgrade your software via the Internet, contact Persyst and we will arrange for you to receive the software update on CD-ROM. After the first year, software upgrades may be purchased for 35% of the list price for the EEG Suite components purchased originally (see the Persyst Software Subscription page for details).
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Do I have to by a Software Upgrade Subscription?
No, this is optional.
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What do I get when I purchase a Software Upgrade Subscription?
A full year of software upgrades with new features, new EEG file format support, and support for new Operating Systems.
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What changes can I expect to see in an update?
We continually add new features and support for new EEG file formats as they are requested, and fix bugs as they are found.
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Does the registration number change when I update the program?
No, you will not need to get a new unlock code when you install an update. After your one-year free upgrade period, you will need to purchase a Software Subscription from Persyst to obtain unlock codes that will enable another year of upgrades.
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Can I move my software to a new computer?
Yes, we're happy to help you move your software to a new computer. (If your software is many years old, a software upgrade may be recommended.)
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How do I find out what version of Persyst EEG Suite I have?
Select About Insight from the Help menu. The version number is shown in the lower-left corner of the Copyright screen. Compare this number to that on the download page to see if you have the current version.
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Do I get support after the first year even if I don't purchase a Software Upgrade Subscription?
Yes, we are always happy to answer any questions you have about the Persyst EEG Suite software, no matter how long ago it was purchased.
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Are bug fixes free?
Yes.
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How do I learn how to use the software?
Feel free to contact us with any questions. There is computer-based training on the CD-ROM and built into the software, and we can get you started right over the phone. Plus, there are formal EEG Suite workshops available right here at Persyst.
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What file formats are supported?
The Persyst EEG Suite supports a variety of different file formats. For a complete list of file formats, please feel free to look at our Formats Supported page
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Can I use the software to diagnose my cat?
You can try. Dogs are much friendlier when you try and attach the electrodes.
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Persyst EEG Suite Integration Notes
Reveal Spike and Seizure Detection: Relay Box for Nurse Call Systems
MPD Engineering, (19 Chestnut Drive Aliso Viejo, CA 92656 (949-362-0360) manufacturers relay boxes supported by Reveal’s parallel-port output specification (specification available from Persyst upon request).
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Accessing files on instruments running the QNX operating system over a network connection.
Access to computers running the QNX operating system is accomplished with third-party software (e.g., NFS) that establishes a connection between Windows-based PC's and QNX-based PC's. Contact your instrument manufacturer for information on obtaining and installing the software needed before altering your network instrument's configuration.
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Accessing files recorded on Cadwell DOS-based systems with the Persyst Patient Database.
Accessing the patient demographics for this file type requires that you have the Paradox drivers loaded for Windows 32bit ODBC. The Paradox 32bit ODBC drivers can be installed from any Microsoft Office CD via "add/remove options" under the "data access" category of Office setup. Cadwell customers without MS Office can contact Cadwell for the appropriate installation files.
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Copying montages created on an NK 2100 series EEG to Persyst Insight.
On the NK2100, the montages are kept in a file called eeg2100.set in a folder called Nfx. To read your NK2100 files "as recorded", use Windows Explorer to create a folder on your hard drive named Nfx, then copy the eeg2100.set file from the NK instrument to this folder on your review station.
IMPORTANT: Insight will only read a montage "set" file if it is named "eeg2100.set". If you use a montage "set" file with a name other than eeg2100.set (e.g., routine.set), be sure to copy your current "set" file to the Nfx folder on the computer running Persyst Insight. After copying the "set" file, rename the file as "eeg2100.set".
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