Elektroenkefalografia

AMI offers simultaneous EEG measurements with fMRI. Information such as EEG equipment storage, maintenance, ordering accessories, wiring and use of EEG inside the scanner are demonstrated in below. The manual is also available in PDF.

Manual for simultaneous EEG and fMRI at AMI

This manual is for the simultaneous use of EEG and fMRI at AMI centre, TKK. The EEG and MRI equipment is shown in Figure 1.

Figure 1. Left: Customized 32-channel BrainCap MR, BrainAmp MR plus amplifier, PowerPack rechargeable battery, BrainProducts GmbH, Munich, Germany. Right: MRI scanner, GE Signa 3.0T with Excite, 8HRBRAIN headcoil; General Electric.

Information is provided for

EEG equipment storage and maintenance
Ordering of EEG accessories
Wiring of EEG and stimulus computers
Using the EEG equipment inside the scanner
Allowed MR imaging sequences
Check-up list for experiments

Manuals for the usage of the EEG cap and software can be found in the Appendix. In case you have questions, please consult AMI Technical Director (phone 050 344 2657, office IM213).

EEG Equipment

Make sure you leave the EEG equipment clean and ready for the next user. If the equipment is not clean when you start using it, please inform AMI Technical Director.

Storage

The EEG equipment is kept in the cupboard above the sink (Fig.2). The EEG cap is kept stretched over the styrofoam head next to the electrode paste container, and other equipment are kept in smaller boxes. Extra cables and this manual are on the upper shelf. The battery box is usually kept on table on the left side of the sink.

The padded box contains the amplifier marked with MRI SAFE, power adapters, and flat cables. The small items box contains items such as chin straps, washers (electrode stickers), syringes for electrode paste, and a toothbrush for cleaning the cap. The battery box contains two identical PowerPack rechargeable batteries marked with MRI SAFE, power adapters, and cables for connecting the batteries to the amplifier (see Fig.2).

Figure 2. From left: Cupboard, amplifier box, small items box, battery box.

Maintenance

After each experiment, gently wash the EEG cap with the toothbrush, rinse, press dry with a soft towel, and stretch it back on the styrofoam head. Wash also the syringes. Dried paste is easy to remove if the cap is soaked in water for a while. Mild children's shampoo can be used as well. The chin straps are washed only when needed.

Note! The EEG connector needs to be kept absolutely dry!

Should any damage happen to the equipment, notify AMI Technical Director immediately.

Ordering new material

If some consumable is running low, please ask Mia Illman (phone 451 8286, email mia(at)neuro.hut.fi), or Marita Kattelus (phone 451 6163, email marita.kattelus(at)tkk.fi) to acquire more in time. Syringes and cotton swabs can be bought from pharmacies. Styrofoam head was purchased from Apuhara Oy (http://www.apuhara.fi). Electrode paste and washers (electrode stickers) are ordered from Algol Pharma, the BrainProducts' supplier in Finland. Preferably order more at once to save shipping costs and time (can take as long as a few weeks).

Wiring of EEG and stimulus computers

Two computers are needed: the EEG PC and the stimulus PC (Fig.3). Start them both. The computers have separate screens. The EEG computer (username amiuser) has no password, so just press <enter>, and then start the EEG recording software VisionRecorder. The username and the password of the stimulus PC are printed in the lower part of the screen.

Figure 3. Left: EEG computer. Middle: Stimulus computer: Right: The screens of the two computers.

Stimuli, responses and fMRI triggers to EEG PC

The branched cable shown in Figure 4 is connected as follows:

Figure 4. Branched cable.

26-pinned male (EEG) to EEG PC above optic fibre (Fig.5, Left). Function: all stimulus, response, and fMRI markers to VisionRecorder via this connector.
25-pinned male (STIM.) to stimulus PC parallel port (Fig.5, Right). Function: stimulus markers from Presentation to VisionRecorder.

Figure 5. Left: Connections to the EEG PC; dongles on the left, connector EEG and optic fibres on the right. Right: Connections to the stimulus PC; colorful cable on the top, connector STIM. at the bottom.

Coaxial cable (MRI) with T-connector to the lower leftmost place “TRIG J9” of the “Unidirectional trigger interface” -box on the wall (Fig.6, Left). Function: fMRI slice onset triggers to VisionRecorder.
25-pinned female (RESP.) to mid-way connector of colorful flat cable (Fig.6, Middle). One end of the colorful cable is connected to the parallel port of the stimulus PC (Fig.5, Right), and the other to the “Parallel port interface” -box on the wall (Fig.6, Right). Function: responses from user to Presentation, from which the response markers are bounced to VisionRecorder via connector.

Figure 6. Left: Connector MRI with T-connector to unidirectional trigger interface (lower leftmost place “TRIG J9”. Middle: Connector RESP. to colorful cable. Right: Colorful cable to paraller port interface.

EEG data from amplifier to EEG PC

EEG data is transmitted via the optic fibres shown in Figure 5 (Left). The upper slot is used when using 32 channels. By default, the slot is occupied by a long optic fibre which goes into the imaging room. In addition, two BrainProducts dongles (black and green in Fig.5, left) need to be connected to the parallel (printer) port of the EEG PC in order to run VisionRecorder and VisionAnalyzer.

Presentation port settings

Basically three things need to be set in Presentation: two output ports, LPT1 (address 0x378) and LPT 3 (address 0xCC88) (Fig.7), and the active buttons for the parallel port device i.e. user response pad (Fig.8).

Figure 7. Presentation output port settings. Port 1: LPT1, address 0x378, port 2: LPT3, address 0xCC88. It is important that the ports are in this order.

Figure 8. Presentation active button settings. Include as many active buttons as in your Presentation script.

Amplifier

Use either the power adapter of the amplifier or the rechargeable battery (PowerPack, marked MRI SAFE) for testing and when preparing the subject. Connect a short optic fibre (found in the cupboard shown in Figure 2) from the amplifier to the back of the EEG PC (Fig.5, Left, upper fibre slot).

Testing connections and other program features

The stimulus and response connections can be tested using the Presentation file D:/Users/EEGfMRI/PortTesting.exp. Press “Start recording” in VisionRecorder and run PortTesting.sce in Presentation. Press response (mouse) buttons as instructed. EEG data should include several markers (Fig. 9). You can also try imaging the phantom, which should result in fMRI markers (marker R128).

Figure 9. Stimulus and response markers in EEG data by Porttesting.sce.

There are 8 markers for stimuli (typically named S1, S2, S4, S8, S16, S32, S64, S128), and 4 user-defined markers for user responses (typically named R1, R2, R4, R8). The limitation to 4 is due to the parallel port interface.

The Presentation scenario file should include at least the following (see also PortTesting.sce):

# output port for responses is the default port
default_output_port = 1; # 0x378, standard parallel port

# number of response buttons
active_buttons = 2; # maximum 4

# response codes, markers R1, R2 ...
button_codes = 1,2; # also 4,8,16,32, or 64 are ok.

And in all stimulus events need to include port and port_code:

begin;

# marker S64
stimulus_event {
nothing stim;
port = 2; # stimuli output port, important!!!
port_code = 64; # results in marker S64
code = "stim 64";
time = 1000;
};

# responses are sent to port 1 automatically

There is also a default workspace file for recording and analyzing EEG data (EEG PC, C:/Vision/Workfiles/BrainCap\_MR32\_customized.rwksp and Standard Workspace.wksp, respectively). These files include the numbering and naming of EEG channels (Appendix A). You can copy these example workspaces to be a base for your own work.

EEG preparation

The subject is prepared outside the shielded room. Place a towel on the back of the chair and/or on the subject's shoulders to keep them clean. In case the subjects wish to wash their hair after the experiment, please provide a clean towel for this purpose, or instruct them to bring their own.

Cap and electrode placement

In addition to normal MRI experiment procedures, the subject must be fitted with the electrode cap. Instructions to do that are provided in Appendix E. Read them carefully.

Please note that there is no need to press hard with the cotton swabs. Ask the subject if there is any discomfort, and before you do anything, explain the subject what you are about to do. When finished applying the electrode paste, check the electrode-skin impedances and press “monitor” in VisionRecorder to assure all channels are working properly.

There are 4 detachable electrodes. The one at the back is intended for recording ECG (important when removing artefacts from EEG data), and the three in the front can be used for EOG, EMG, or offline re-referencing. Use the white plastic adapters with the washers (stickers) to connect these electrodes to the skin (see Figure 10). Note! Match the colors of the electrode lead connectors and make sure they are properly attached. Do not pull from the electrode leads! Check that the electrode leads do not form loops or cross each other!

Figure 10. Connecting detachable electrodes with adapters and washers.

EEG recording inside the scanner

This chapter tells you how to proceed inside the scanner. See also the check-up list in the end of this document and fill it every time you use the system.

Note! The only EEG items you need (and are allowed) to take into the shielded room are the items marked with MRI SAFE. These include the amplifier, the rechargeable battery pack, the cable connecting the amplifier and the battery pack, the 12-cm long flat cable, and the 32- channel EEG cap with detachable electrodes.

The amplifier is placed behind the head coil as far back as possible with the front facing towards the monitoring room. The power switch of the amplifier is at the back panel.
The battery pack is placed on the amplifier and they are connected with a cable (marked with MRI SAFE).
Place a disposable pillow case within the head coil to keep it clean from electrode paste.
Electrode lead bundle comes out through one of the coil openings and is connected to the amplifier using the 12-cm long flat cable (Figure 11, Middle)
Secure amplifier, battery pack, flat cable and electrode lead bundle with sand bags and tape (Figure 11, Right). Cables should be as straight and tight as possible without causing strain.
Make sure all electrode leads are as straight as possible (no loops). Check the ECG electrode lead at the subject's neck extra carefully.
Once the bed is slid in the scanner, connect the optic fibre to the amplifier. The optic fibre is stored inside the cupboard in the imaging room (Fig.11, Left), and the other end is connected to the EEG PC. Avoid bending the fibre.
Notify Securitas (phone number on the phone) that you are going to switch off the cryogenic pump and for how long. Turn off cryogenic pump and fan because they cause artefacts (see also Appendix D). Afterwards remember to do the reverse. The pump should be turned off only when absolutely needed, for 3 hours maximum to avoid danger and damage. If there is any confusion with respect to the time limit and in cases of whole-day imaging sessions, consult AMI Technical Director.

Figure 11. Left: Optic fibre cupboard. Middle: Electrode lead bundle. Right: Sandbags.

Safe imaging sequences

Allowed low-SAR imaging sequences with their duration and peak-SAR limitations are listed in Table 1.

Table 1: Approved imaging sequences with their corresponding maximum durations and maximum estimated peak SAR values.

Sequence	Duration (minutes)	Estimated Peak SAR (W/kg)
Localizer	max 2:00	max 1.0
GRE-EPI	max 30:00	max 1.0
SPGR	max 15:00	max 1.

Take any other images without the EEG cap.

WARNING: MR sequences with high SAR values may cause heating of the EEG equipment and the subject. Never use any other MR sequences than localizer, GRE-EPI, or SPGR!!!

The manual was originally written by Iina Tarnanen. It was modified by Nuutti Vartiainen 30th November 30, 2008.

Advanced Magnetic Imaging -keskus (AMI)