EEG-fMRI 3 EEG, Exg and Checklist
See also:Using the BrainAmp ExG MR for bipolar and sensor data acquisition
The BrainAmp ExG MR is a bipolar amplifier which can be used for peripheral physiology and polygraphic measurements. The BrainAmp ExG MR is part of the BrainAmp MR family of amplifiers and is subject to the same safety guidelines as the BrainAmp MR and BrainAmp MR plus. As such, the general safety guidelines and restrictions presented in this document also apply to using the ExG amplifier in the MR environment.
In the MR environment only ever use the BrainAmp ExG MR together with the ExG AUX Box and special MR conditional electrodes and sensors. For bipolar measurements (e.g. EMG, ECG) only use Brain Products MR electrodes / cable sets. For polygraphic signals only use Brain Products MR conditional auxiliary sensors (GSR MR Sensor, 3D Acceleration Sensor MR, Respiration Belt MR). All MR Conditional sensors have been tested for use in MR environments up to 3T.
The general safety rule applies that no cable is permitted to be routed through more than 50 % of the length of the bore of the scanner. In practical terms, when using multiple amplifiers e.g. for EEG and for peripheral physiology, this means that it may be necessary to position amplifiers at the foot end and head end of the bore
ExG - Bipolar measurements - EMG
Combined EMG-fMRI measurements are somewhat different to EMG measurements under laboratory conditions. Such measurements require particular care with respect to the choice of suitable electrodes and the routing of the cables. All cable displacement must be avoided. This also applies to respiratory movements that can be transferred to the EMG cables.
EMG signals can be measured at a wide variety of sites on the body. We distinguish between two fundamental application scenarios: EMG measurements on the upper or lower limbs and EMG measurements on the face.
For EMG on the upper or lower limbs only use Brain Products EMG-fMRI electrodes (Multitrode MR electrodes for EMG). The cables have 15 kOhm current-limiting resistors and are bundled in a spiral tube so that they cannot come into direct contact with the test subject. Never use the bipolar EMG-fMRI electrodes for EMG acquisition on the head of the test subject.
For EMG on the face we are able to provide custom EMG-fMRI caps for correct, safe routing of cables. Please contact the Brain Products Technical Support team for guidance if you are considering measuring EMG on the face.
We recommend that you do not use a body coil as the RF transmitter coil for combined EMG-fMRI measurements because this limits where you can place the electrodes; they can only be placed outside of the RF field.
ExG - Positioning of the amplifier
Position the BrainAmp ExG MR at the foot end of the scanner table, distal to the feet of the test subject.
The standard version of the BrainCap MR is fitted with a drop-down electrode for recording the ECG signal from the subject's back during an EEGfMRI measurement. However, should you require additional ECG measurements, you can use a BrainAmp ExG MR positioned at the foot end of the scanner bore to record a bipolar ECG measurement. The Brain Products Multitrode MR for EMG can also be used to record ECG. The same safety guidelines regarding electrode placement, lead length and transmit coils apply as for the combined limb EMG-fMRI measurements
ExG - Polygraphic measurements via the auxiliary channels
All MR sensors are MR conditional and must be used outside of the RF transmit field. Therefore, we recommend that you do not use a body transmit coil for measurements using the auxiliary channels of the BrainAmp ExG MR.
If you do choose to use a body transmit coil please be aware that this limits where you are able to place the sensors; you will only be able to use them on the lower limbs and the extremities of the upper limbs.
ExG - GSR Sensor MR
The GSR-MR Module is a part of our MR product line and is subject to the same safety regulations and restrictions as all the other components of the BrainAmp MR amplifier system.
The GSR module is MR conditional and must be used outside of the RF transmit field. Use the GSR-MR Module only in combination with the BrainAmp ExG MR amplifier and the ExG AUX Box. These devices offer electrical isolation and can be used in MR scanners.
The GSR electrodes should be applied only to the hand of the subject. The correct position of the GSR electrodes and the appropriate cable routing, to avoid loops, is shown in th next slide.
ExG - Respiration Belt MR
The Respiration Belt MR is a part of our MR product line and is subject to the same safety regulations and restrictions on use as all the other components of the BrainAmp MR amplifier system.
Use the Respiration Belt MR only in combination with the BrainAmp ExG MR amplifier and the ExG AUX Box.
The transducer is MR conditional. Therefore, always position the transducer outside the RF transmit field. The pneumatic sensor is MR safe. It does not contain ferromagnetic or electrically conductive material, therefore it is safe to use inside the scanner bore.
The correct positioning of the pneumatic sensor and transducer in relation to the ExG Aux Box and BrainAmp ExG MR is shown in the next slide.
ExG - 3D acceleration sensor
The 3D Acceleration Sensor MR is a part of our MR product line and is subject to the same safety regulations and restrictions on use as all the other components of the BrainAmp MR amplifier system.
Use the 3D Acceleration Sensor MR only in combination with the BrainAmp ExG MR amplifier and the ExG AUX Box.
The 3D Acceleration Sensor MR is MR conditional. Therefore, always position the sensor outside the transmit RF field. The correct position of the acceleration sensor in relation to the ExG Aux Box and BrainAmp ExG MR is shown in the next slide.
Phantom measurements in MR environments
The 3D Acceleration Sensor MR is a part of our MR product line and is subject to the same safety regulations and restrictions on use as all the other components of the BrainAmp MR amplifier system.
Use the 3D Acceleration Sensor MR only in combination with the BrainAmp ExG MR amplifier and the ExG AUX Box.
The 3D Acceleration Sensor MR is MR conditional. Therefore, always position the sensor outside the transmit RF field. The correct position of the acceleration sensor in relation to the ExG Aux Box and BrainAmp ExG MR is shown in the next slide.
Phantom measurements are useful to assess the impact of the EEG equipment on MR image quality. Special care must be taken if you are to obtain reliable imaging results and avoid damage to the amplifier.
Imaging phantoms as provided by the scanner manufacturer usually have a non-conductive surface. As a result, when you attach the electrode cap to the phantom and connect it to the amplifier, all the electrodes show high impedances. The amplifier can be destroyed by antenna effects if pulse sequences are run with open or high impedance channels
Phantom measurements in MR environments
Proceed as follows to avoid destroying the amplifier:
- Before you attach the BrainCap MR, ensure that the entire surface of the phantom is coated with a conductive layer of Abralyte gel.
- After you have attached the BrainCap MR to the fully gel-coated phantom, ensure that the cap fits as tightly as possible to the surface by tightening the chin strap.
- Attach the EOG and ECG electrodes under the edge of the cap.
- Make sure that all electrodes show low impedances. Use impedance mode to check the electrode impedances while you reduce the impedances using a syringe and a further quantity of Abralyt gel, in the same way that you would for measurements with human volunteers.
- Once you have prepared all electrodes in this way, take the phantom into the scanner room and position it and the amplifier in the same way as with a normal measurement.
- We recommend that you check the impedances again before starting the scan.
- All the conditions regarding the setup and position of the amplifiers given in Positioning the EEG amplifier on page 37 also apply for phantom measurements.
Working with special populations and specific states
While due care and attention is always required for simultaneous EEG-fMRI measurements particular attention/supervision is recommended for populations that may not be able to easily detect or communicate any heating or discomfort during the measurement. This is important for the following special test populations and specific states:
- Children and babies
- Test subjects in a poor state of health
- Uncooperative test subjects
- Test subjects with reduced vigilance (e.g. pharmacological studies)
- Sleep EEG
- Epilepsy
- Sedation.
Sumary Checklist for EEG-fMRI
Before starting a measurement please check that the following criteria are fulfilled:
1. Route all cables correctly:
- straight
- no loops
- in line with the z axis of the scanner.
2. Only use scanners with the specified field strengths:
- up to 3T
- for >3T only with guidance from the Brain Products Technical Support team.
Sumary Checklist for EEG-fMRI
3. Only use permitted head coils:
- Ideal = cable duct for EEG cable
- Appropriate = cable routing option at the side or top
- No-go = completely closed coil
- Use Transmit-Recieve head coil whenever possible
4. Only use permitted sequences:
- Single-shot GRE-EPI BOLD sequences
- Magnetization Prepared Rapid Gradient Echo (Siemens: MPRAGE, Philips: TFE, General Electric: FSPGR)
- Spoiled Gradient Echo (Siemens: FLASH, Philips: T1-FFE, General Electric: SPGR).
5. Only use permitted electrode caps:
- Standard BrainCap MR
- Customised BrainCap MR with Liability Waiver.
6. Minimize the impedance of all electrodes. There should be no open electrodes, so, no electrodes that are not in contact with the subject.
Behavior in emergencies
The scanner operator must know how to:
- follow the emergency procedures for the facility regarding turning off the scanner
- release the scanner table
- shut down the amplifier.
The user documentation provided by the scanner manufacturer and local safety regulations also apply without restrictions for combined EEG-fMRI measurements.
Behavior in emergencies
Release the test subject from the scanner in an emergency
If you are required to stop the experiment and release the subject from the scanner in an emergency situation please do the following:
1. Stop the scan.
2. Disconnect the electrode cap, sensors and other equipment from the amplifier(s).
3. Move the scanner table out of the bore.
4. Remove the head coil.
5. Help the subject up from the scanner bed and escort them from the room.
6. Remove the cap and sensors from the subject.
Shut down the amplifier
If you must abort the measurement due to a malfunction or fault in the EEG components, proceed as follows:
1. Switch off the amplifier and disconnect amplifier from battery (PowerPack).
2. Disconnect the electrode cap, sensors and other equipment from the amplifier(s).
3. Move the scanner table.
4. Remove the head coil.
5. Help the subject up from the scanner bed and escort them from the room.
6. Remove the cap and sensors from the subject.
7. Check if the amplifier system is working properly and if all the system components are installed correctly. Please refer to the troubleshooting section of the BrainAmp user manual for details of how to test the amplifier.
8. If it is not possible to eliminate the malfunction or if the problem persists, send a detailed description of what has occurred to the Brain Products Technical Support team.
References
Performing simultaneous EEG-fMRI measurements, Conditions for the safe use of BrainAmp MR amplifiers and accessories in the MR environment, Document version: 002, Publishing date: 4/9/2020. Brain Products GmbH.
Standard Practice for Marking Medical Devices and Other Items for Safety in the Magnetic Resonance Environment, ASTM F2503-13, ASTM International, West Conshohocken, PA; 2013.
International Electrotechnical Commission. IEC 60601-2-33:2010 + COR1:2012 + A1:2013 + A2:2015 + COR2:2016. Medical electrical equipment. Part 2-33: Particular requirements for the basic safety and essential performance of magnetic resonance equipment for medical diagnosis.
Faulkner W. (2016) New MRI Safety Labels & Devices. https://www.ismrm.org/smrt/E-Signals/2016FEBRUARY/eSig_5_1_hot_2.htm
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