Optimized FT-Control with FTA Sensor - Robotized Transcranial Magnetic Stimulation - page 125

Table 7.1 Errors in forces and torques of optimized coil calibration and gravity compensation
for different TMS coils
70 mm MC-125 CB-60 MC-B70 MCF-75 MCF-B65 MCF-P-B65

Forces (N)
Mean

0.92 0.96 0.92 1.08 1.06 1.16 1.80

SD 0.31 0.44 0.37 0.38 0.40 0.59 0.68

Max 2.16 2.11 2.12 2.21 2.11 3.06 3.57

Torques (Nm)
Mean 0.21 0.16 0.24 0.20 0.25 0.31 0.59
SD 0.07 0.05 0.09 0.05 0.07 0.17 0.21
Max 0.42 0.34 0.55 0.44 0.47 1.01 1.31
The average error (mean), the standard deviation (SD) and the maximum error (max) are listed.
The values are illustrated in Fig. 7.7

(from left to right) (cf. Table 5.1 ). We see that with increasing coil weight also the
errors for gravity compensation increase. The mean overall error is 1.1 N for
forces and 0.3 Nm for torques with standard deviations of 0.55 N and 0.18 Nm,
respectively. Table 7.1 lists the detailed values of each coil for forces and torques.
When comparing these calibration results with the results of the previous coil
calibration method (cf. Sect. 5.2.4.1 ), we see that the mean calibration error
decreased of roughly 0.8 N for forces. There was only a slight decrease in the
mean torque error.
For instance, the average force error for a standard passively cooled figure-of-
eight coil is 1.2 N with the optimized calibration method. The mean torque error
for that coil is 0.3 Nm.

7.5.2 Precision of Optimized Hand-Assisted Positioning

In order to evaluate the optimized hand-assisted positioning method with the FTA
sensor, inexperienced users perform realistic coil placements. After a brief
familiarization task, the users place the TMS coil at different targets on a human
head phantom and we measure the absolute positioning error.
The ten inexperienced users get familiar with the system within a few minutes.
Directly after the familiarization task, they have easily and intuitively performed
the positioning task on the human head phantom. The results of the positioning
task for optimized hand-assisted positioning are shown in Fig. 7.8 as a boxplot.
The results for each single target on the head phantom are presented. The overall
mean positioning error is 0.79 mm with an Standard Deviation (SD) of 0.61 mm.
The maximum error is 2.8 mm. For instance, the M1-HAND area as one of the
most important regions for TMS proves best for targeting. The average positioning
error reaches roughly 0.3 mm. Table 7.2 summarizes the mean positioning error
with the SD and the maximum positioning error for each single target.