Biomedical Engineering Reference
In-Depth Information
Table 2.2 Mean decrease of induced electric field magnitude and orientation change with SD at
six different time points
5 min
10 min
15 min
20 min
25 min
30 min
Magnitude decrease (%)
hold-and-restrain
8 : 4 7 : 3 : 1 11 : 823 : 1 13 : 529 : 2 13 : 827 : 6 14 : 732 : 0 14 : 9
hold-and-rest
8 : 0 10 : 117 : 7 17 : 418 : 9 15 : 120 : 9 15 : 120 : 6 13 : 719 : 7 13 : 8
robot-freely
2 : 2 2 : 4 : 4 2 : 9 : 0 1 : 1 : 9 3 : 2 : 8 2 : 7 : 9 1 : 9
robot-and-restrain
2 : 1 0 : 6 : 8 1 : 8 : 6 1 : 5 : 6 1 : 7 : 2 1 : 1 : 4 1 : 3
robot-and-rest
3 : 0 2 : 2 : 4 1 : 7 : 7 0 : 9 : 4 2 : 3 : 3 1 : 0 : 0 1 : 3
Orientation change ( )
hold-and-restrain
1 : 5 1 : 0 : 6 1 : 1 : 3 5 : 3 : 5 6 : 5 : 9 7 : 2 : 5 6 : 4
hold-and-rest
2 : 6 4 : 0 : 9 10 : 9 : 4 15 : 5 : 0 18 : 8 : 2 14 : 2 : 6 12 : 0
robot-freely
0 : 4 0 : 2 : 3 0 : 2 : 3 0 : 1 : 4 0 : 2 : 5 0 : 4 : 4 0 : 4
robot-and-restrain
0 : 3 0 : 3 : 3 0 : 2 : 5 0 : 3 : 3 0 : 2 : 3 0 : 3 : 2 0 : 4
robot-and-rest
0 : 3 0 : 3 : 2 0 : 1 : 6 0 : 5 : 4 0 : 4 : 3 0 : 3 : 2 0 : 2
initial value in the worst case after 30 min for robot-freely, robot-and-restrain and
robot-and-rest, respectively.
Figure 2.8 b visualizes the change in orientation of the induced electric fields
over time averaging the measurements for all subjects. It is clearly visible that the
error in orientation for the two common scenarios, hold-and-restrain and hold-
and-rest, increases for the first 15 min and then remains almost constant.
Surprisingly, the change for hold-and-rest is slightly larger compared to hold-
and-restrain. In contrast, the change for the motion compensated setups stays
constant at a very low level for the full duration.
After 30 min, the orientation has changed 5.5 for hold-and-restrain and 7.6
for hold-and-rest. The change in orientation is 0.4 , 0.2 and 0.2 , respectively, for
the motion compensated scenarios. Table 2.2 additionally summarizes the change
in orientation for six time points with the mean values and SDs for all measure-
ment scenarios.
Interestingly, the average decrease in induced electric field strength (Fig. 2.8 a)
shows some extreme peaks within the first 7 min of the measurements of the robot-
freely scenario. Further analysis indicates that these errors are mainly due to the
measurements of subject 3. Figure 2.9 therefore displays the induced electric field
measurements and the corresponding recorded head motion of subject 3. In this
figure some sudden extreme head movements occur within the first 7 min which
are highlighted with circles. The plots show that sudden rotational head move-
ments are recorded in addition to the translational movements. As the robot needs
a certain amount of time to compensate for the motion, this extreme sudden head
motion results in a short-term decrease of induced electric field strength. Once the
head motion has stabilized, the decrease of induced electric field strength is
minimized again due to the robot's motion compensation. Interestingly, there are
no corresponding extreme changes in the orientation of the measured orientation of
the induced electric field.
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