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dc Magnetoencephalography: Direct measurement in a magnetically extremely-well shielded room
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View: Figures


Image of FIG. 1.
FIG. 1.

Sensor arrangement of the vector magnetometer (see Ref. 13). Sixteen identical integrated SQUID magnetometers developed at PTB with a pick-up loop of are positioned in four groups (see Ref. 14). Six sensors are placed at the Dewar bottom, four sensors at , three sensors at and three sensors at , where is the distance between the sensor plane and the lowest sensor plane. The SQUID loops are oriented in such a way that vector components of the magnetic field can be calculated for the mid points between the four SQUID planes by combining two or more magnetometer signals. Sensors are labeled corresponding to the magnetic field component which they are sensitive for (Z for the component, X for the component, and Y, A, V for the component).

Image of FIG. 2.
FIG. 2.

(Color online). Frequency spectra of four of the 16 channels without any subject. Channels X7 and Y7 measure horizontal field components, while channels Z2 and Z7 measure vertical field components. Note increased noise level around 10 Hz due to mechanical vibrations.

Image of FIG. 3.
FIG. 3.

(Color online). Motor evoked direct 16 channel dc MEG measurement in BMSR-2. 30 epochs of evoked activity were averaged and filtered by ICA. The bandwidth of signals was from dc to 100 Hz. The two vertical lines indicate the beginning and the end of the finger motion.

Image of FIG. 4.
FIG. 4.

(Color online). (a) Motor evoked direct dc MEG measured in BMSR-2 with channel Z2 of Fig. 3 in a full bandwidth from dc to 100 Hz, (b) digitally low-pass filtered to a bandwidth from DC to 1 Hz. In (c), a modulated measurement of the same subject in a normal magnetically shielded room is also shown for comparison (bandwidth from dc to 0.2 Hz).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: dc Magnetoencephalography: Direct measurement in a magnetically extremely-well shielded room