Our Systems

With the addition of the KIT child MEG system, our lab is the first in the world to house two MEG systems inside the same magnetically shielded room. We are currently optimizing our newly acquired system. More technical specifications will be added shortly.

The KIT-Macquarie adult MEG System

Our MEG system, the KIT-Macquarie MEG160 system, is housed in a magnetically shielded room or MSR. It consists of three layers of permalloy (an alloy of iron and zinc), one layer of copper. The room frame is made of aluminum. The MSR was built by Fuhijira Co. Ltd. on May 2006.

The KIT-Macquarie MEG160 system, was developed and installed by the Applied Electronics Laboratory (AEL) at the Kanazawa Institute of Technology. It consists of 160 coaxial first-order gradiometers (50mm baseline). The magnetic signal is sent to the SQUID sensors placed at 75mm from the pick up coil. This separation between SQUID and pick up coil may cause magnetic flux trapping(1) and therefore it is necessary to keep the MSR clean of magnetic materials (eyeglasses, jewelery, flash photography, etc.). We ask everybody including researchers to remove all magnetic material from their bodies including shoes to keep our MSR clean of magnetic residue.

The system also has 64 external channels for simultaneous acquisition of additional analog signals. These additional signals include TTL pulses used as event triggers by the MEG160 Laboratory acquisition software (Yokogawa). In order to record event timings while recording data, the presentation software must send output codes to the MEG 160 system. This must be done via analog signals. Codes are sent as TTL pulses via the parallel port on the stimulus computer and mapped to the external channels on the MEG system.

On July 2008, we have installed a 64-channel MEG system, specially designed by AEL and Yokogawa to work with children. Details about the setup of this system will be specified shortly.

Stimulus Presentation

Software:

The visual presentation system includes a presentation PC that runs Presentation (Neurobehavioral Systems), and Psychotoolbox (Matlab) (if lab users are interested in using other types of software to deliver their stimuli please contact Craig Richardson or the lab staff for help).

Visual delivery:

Our current LCD projector (Sharp PG-B 10S) with a specially fitted lense. The image sent by the projector is reflected on a mirror, which in turn reflects onto a screen placed around 40cm above the participant's face.

Signal detection devices:

Our stimulus presentation system also incorporates a luminosity detection device (photodetector), which is placed on the MSR screen. We also have an audio signal detection device (voice onset detector). These signal detection devices can be used to send triggers to the MEG system when precise timing information is required.

Audio delivery:

Auditory stimuli is delivered by a set of Etymotics E30 earphones.

Response devices:

We currently record subject's responses with two fibre optic response buttons (subjects are required to lift one of their fingers to provide a response). We also use a button box with four buttons each. Lab users should be aware that the key presses on this box make a distinctive loud click. The fiber optic response buttons connect to a conversion box that splits the signal between the presentation PC and the MEG system. The 4-button response box only connects to the presentation PC by USB port. Therefore, only the signal from the fibre optic buttons can be converted to analog input to be recorded directly by the KIT-Macquarie MEG 160 system.

Co-registration of MEG and Structural MRI

Some researchers will wish to localize MEG activity. If so, the researcher must provide the lab staff with a structural MRI (DICOM) or a digitised headshape for each subject that will participate in their MEG study. To be able to co-register structural MRI or digitised headshape with the MEG data, we use a template to mark five fiducial points in the subject's forehead and side of the head. We place five coils in the marked positions to record their location once the subject is inside the MSR. The KIT-Macquarie Brain Research Lab has a Polhemus Fastrak digitizer, which researchers can use to digitise the subject's head.

Data Acquisition and Running Subjects

The system can record continuously for blocks of up to 20 minutes at a time, with a sampling rate of up to 1,000Hz. The system can also record averaged data online.

We usually perform two tests with each subject before the experiment begins, in order to identify the position of the subject's head in the MEG dewar. These experiments consist in the elicitation of an auditory M100 response and a visual M100 response. These pre-test experiments take about 5 minutes.

Data Analysis

The MEG lab has a PC computer for data analysis with a copy of the Yokogawa MEG160 software. This program allows researchers to apply digital filters, perform data averaging, data localization, dipole fitting, and other functions for analysis. The lab staff plan to offer workshops for researchers on how to apply filters, average the data and localize brain activity using the MEG160 software. Please contact the lab manager if you have further questions. The analysis computers must be booked in advance.

The lab has one analysis computer on site that can be used for processing the data offline with the following analysis software:

• MEG160 Laboratory (offline copy)
• BESA 5.2
• MATLAB 7.5
• Matlab toolboxes: Signal processing, SPM, Statitics

Data files (*.con/ *.ave) can be exported as txt files and then imported into Matlab. Also, the files can be exported in BESA format using MEG160. SPSS is available for statistic analysis as well as the Statistics toolbox.

 

References

(1) H. Kado, M. Higuchi, M. Shimogawara, Y. Haruta, Y. Adachi, J. Kawai, H. Ogata, G. Uehera. (1999) Magnetoencephalogram systems developed at KIT. IEEE Transactions on Applied Superconductivity, Vol 9 (2), 4057-4062.

 

Contact staff

Christopher Sewell (Research Assistant)

Craig Richardson (System Administrator)

Dr Graciela Tesan (MEG Lab Manager)