DSI Guidelines for EEG, EMG, and EOG Applications
Applications involving sampling of electrical signals like EEG require telemetry implants with adequate technical specifications to accurately acquire and analyze data. The purpose of this document is to provide definitions of key terms and clearly outline what telemetry implants are appropriate for certain applications.
Definitions
| Term | Definition | Notes |
| Channel Bandwidth | The frequency range between the lowest and highest attainable frequency, measured in Hertz (Hz) |
For DSI products, this focuses on the range of frequencies for which the reported signal amplitude remains within an error power band of 3 dB The two values of a published channel bandwidth indicate the low and high frequencies where the response has fallen by no more than 3dB
|
| Nominal Sampling Rate | Nominal implant sampling rate: The rate at which data points are sampled by the implant. Higher sample rates enable accurate response to higher signal frequencies, but at the cost of shorter battery life | |
| Aliasing | Arises when a signal is discretely sampled at a rate that is insufficient to capture the changes in the signal (see Appendix B) | |
| Nyquist Sampling Theorem | The sampling frequency should be at least twice the highest frequency contained in the signal to avoid aliasing | For DSI implants, we choose to sample sometimes higher than a factor of 2. We typically sample 4-5x higher than highest targeted frequency content |
| Software Sampling Rate | The rate at which the raw data is reconstructed in the application software (e.g. Ponemah) for plotting and feature extraction |
Higher software sample rates (relative to the nominal sampling rate of the implant) will include more points along an interpolated representation of the raw telemetry data Select a software sampling rate that is at least equal to the nominal implant sampling rate. |
| Interpolation (upsampling) | The insertion of additional data points between points collected via the nominal sampling rate | Interpolation allows for a more continuous representation of the physiological data, but it cannot increase the accuracy of the signal reconstruction. |
| Impedance | the measure of the opposition which a circuit presents to a current when a voltage is applied. |
Best Practices
Acquisition
- Input voltage range must accommodate full amplitude of ECG signal
- Minimum input voltage for mouse ECG is ±2.5 mV, rat is ±5 mV, large animal is ±10 mV
- Impedance is important to consider for EEG recordings because the source impedance of EEG electrodes is inversely proportional to the electrode contact between the target tissue and electrode material; a high source impedance may attenuate the lower EEG frequencies
- EEG electrodes have a higher source impedance than ECG electrodes because the contact area between electrode and target tissue tends to be smaller than ECG electrodes
- Source input impedance is most consistent across multiple cortical recordings by anchoring the biopotential electrodes to screws and contacting the dura
Use of Screws for EEG Leads
DSI recommends the use of lead anchor screws for EEG monitoring to ensure
- Consistent and high-quality signal acquisition
- Stable Mechanical Interface between electrode lead and skull
- Minimize signal noise due to movement
- Maintain electrode impedance, crucial for accurate low-frequency EEG Waveforms
EEG Screw Compatibility
DSI offers specific EEG screws compatibility with the following telemetry implants:
| Implant Model | Key Features |
| SoHo-X02/SoHo-S02 | EEG signal acquisition with sufficient bandwidth for most studies. |
| HD-X02 | Captures EEG frequencies down to 0.5 Hz, enabling Delta band monitoring |
| F50-EEE, L03, L04 |
Compatible Screw Part Numbers
These screws are only sold by DSI and may not be compatible with other systems.
| Part Number | Description |
| 012005-001 | Uncoated mouse EEG screw |
| 01102006-001 | Uncoated rat EEG screw |
| 012007-001 | Uncoated large animal EEG screw |
Implant Specifications
|
Implant Family |
Implant Model |
# of Channels |
Input Voltage Range |
Bandwidth (Hz)5 |
Signal Type |
Notes |
| SoHo |
X02, S02 |
2 | ±1.25 mV | 1-100 | ECG, EEG, EMG | |
|
PhysioTel |
F50-EEE |
3 |
±2.5 mV |
1-100 |
ECG2, EEG, EMG |
|
|
PhysioTel HD |
HD-X02 |
2 |
±1.25 mV |
0.5-80 |
EEG, EMG (ECG2) |
Channel 1 should be used for the EEG
|
|
HD-S02 |
2 |
±1.25 mV |
0.5-100 |
EEG, EMG (ECG2) |
||
|
PhysioTel Digital4 |
L033 |
3 |
Programmable (Ch. 1-2) ±2.5, 5, 10, 201 mV |
0.5-100 |
EEG, EMG, ECG |
Channel 4 has a reduced bandwidth and isn't recommended for ECG.
|
|
L04 |
4 |
Programmable (Ch. 1-2) ±2.5, 5, 10, 201 mV |
Ch. 1-3: 0.5-100 Ch. 4: 0.5-50 |
EEG, EMG, ECG |
120 mV input voltage may be selected when solid tip lead placement results in ECG amplitude exceeding 10 mV.
2If there is a need to record ECG, EMG, or EOG with these devices, channel 1 should not be used. This is due to the signal potentially railing if the signal amplitudes is above the ±1.25 mV. Additionally, a small ECG signal artifact may be seen in other channels.
3The L03 6-lead configuration has no common leads. Each pair of leads is coupled into an instrumentation amplifier (differential inputs). The common-mode specs apply to each input. Our specification is that each biopotential channel shall have a Common Mode Rejection Ratio (CMRR) of -40dB or better. This common-mode response test shall be met for each biopotential channel at test frequencies of 0.5Hz and 10Hz, and the common mode signal applied to the biopotential channel under test will be generated with respect to the implant housing connection.
4it is not recommended to use intravenous negative lead placement (solid tip lead) combined with diaphragmatic positive lead placement when EEG data will be collected concurrently with ECG data due to the concern over cross-talk between the biopotentials channel (i.e. ECG artifact on the EEG channels).
5Only signal frequency content within the specified channel bandwidth of the telemetry implant is acquired accurately
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