Biomedical Engineering Reference
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Fig. 2.5 (A) The field sensor is integrated in a head phantom made of styrofoam and located
15 mm below the outer head surface. (B) The sensor consists of a plastic bar (diameter: 10 mm,
length: 220 mm) with wires. (C) The sensor measures the induced electric field in the x/y-plane
using two perpendicular wires (x and y, in dotted lines)ontop of the sensor. The connections of
the wires descend vertically and thus, they are not influenced by the electric field. (D) Top view of
the head phantom (x/y-plane). The sensor's location is marked with a filled circle
For motion replay, we use two identical Adept Viper s850 industrial robots
combined with a Polaris tracking system. The tracking system is positioned
opposite to the robots and calibrated to the second robot R 2 by hand-eye cali-
bration [ 4 ] (see also Sect. 4.1 ) . The first robot R 1 moves the head phantom
including the field sensor according to the recorded head motion. R 2 holds and
positions the TMS coil. Figure 2.6 shows this setup.
R 1 is moved to a starting position S. R 2 places the coil approximately 5 mm
above the head phantom. Moreover, the coil is aligned such that the coil is in a
tangential orientation with respect to the surface of the scalp and the induced
electric field in the target is maximal for this coil-to-head distance. This is assured
by measuring the induced electric field while moving the coil in steps of 1 mm
until the maximum induced electric field is found for this coil-to-head distance.
The first robot replays the recorded head movements relatively to S.
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