Discussion - Robotized Transcranial Magnetic Stimulation - page 151

Our practical test has shown that the hand-assisted positioning method allows
even unexperienced users to effectively position the coil with the system. Without
hand-assisted positioning, this is hardly possible. Additionally, the hand-assisted
positioning method speeds up the positioning time for experienced users. Thus,
hand-assisted positioning greatly enhances the system's usability.
We have shown that the presented method for hand-assisted positioning com-
bined with the coil calibration method is sufficient for usage with different com-
mon TMS coils ( Sect. 5.3 ). The mean errors for forces and torques have been
1.89 N and 0.31 Nm, respectively. These errors are mostly due to the heavy TMS
supply cable that is connected to the stimulator. As the weight of the cable is
approximately 0.5-1 kg and the weight of the pure transducer head is roughly
0.5-1.9 kg, depending on the coil type, the observed results are satisfactory. Due
to the flexibility of the cable, the errors are related to the gravity compensation of
the cable's weight. However, the maximum errors are below the threshold applied
for contact pressure control. Note that for contact pressure control only the z-
directed forces (in coil coordinates) are taken into account (see below).
In contrast to standard industrial robots, recent light weighted robots are already
equipped with force-torque sensors located in the single joints [ 2 ]. In particular,
these robots are suitable for applications in the human-robot interaction. However,
future comparison studies might be performed to investigate whether these robots
are also applicable for robotized TMS due to their larger elasticity.
Using a force-torque sensor to control a robotized TMS system by hand greatly
enhances system usability. The operator (physician) is now able to (pre-)position
the TMS coil in an intuitive fashion. Knowledge of the functionality of the
industrial robot itself is not needed for system use. Beside pre-positioning, hand-
assisted positioning allows the user to perform a fast hot-spot search. The stim-
ulation points are automatically recorded for later precise re-targeting. The
robotized TMS system allows to automatically reposition the coil at previously
recorded stimulation points and can now easily be integrated in the clinical
workflow. Note that current neuro-navigation systems also record stimulation
positions. However, the user must reposition the coil at these positions manually
by hand. This cannot be achieved accurately (cf. Sect. 1.2 ) .
For the specialized TMS robot proposed by Zorn et al. [ 15 ] and Lebossé et al.
[ 9 ] the force sensor grid is attached to the coil's rear side (see also Sect. 1.3.1 ) .
Thus gravity compensation and therefore a coil calibration is not required. Even
though, this enables an easy contact pressure control, the presented hand-assisted
positioning method is not applicable to this system setup. In general, hand-assisted
positioning will not be possible with this robot setup as only the z-directed force is
detected.