FT-Control - Robotized Transcranial Magnetic Stimulation - page 81

Chapter 5
FT-Control

Even though the introduced robust real-time robot/camera calibration ( Chap. 4 )
contributes to the system's usability during system start and system safety, it
cannot solve all the deficits of the current robotized Transcranial Magnetic
Stimulation (TMS) system. As shown during the practical evaluation of the
robotized TMS system ( Sect. 3.3 ), target accessibility, coil positioning on the head
and general system safety are still open deficits of the current system

implementation.
To achieve a maximum of patient safety with the current system, the permitted
robot trajectories are strongly restricted [ 3 ]. Any potentially dangerous trajectory
from the current robot pose (coil pose) to the coil target position on the head is
prohibited by the control software [ 2 ]. In many cases, a manual robot pre-posi-
tioning is therefore required. As this must be done with the robot controller, this
can only be effectively achieved by experienced robot operators. However, these
robot trajectory restrictions combined with the implemented robot velocity limits
cannot achieve general system safety, neither can the robust real-time calibration.
Furthermore, to position the coil on the patient's head, the coil is first placed
roughly 10 mm above the target. Subsequently, the coil is moved on the head in
steps of 1 mm until the patient confirms the coil on the head. This procedure is
chosen to compensate for noise in the head scans and for the potential positioning
error of the robotized TMS system (cf. Sect. 4.3.2.3 ) . The positioning approach
requires therefore the feedback of the patients and often results in suboptimal coil
positioning. Some patients wait until the coil strongly touches the head before they
confirm contact to the head. This results in a heavy force on the head which leads
to pushing the head by the robot during stimulation. On the contrary, hair can lead
to a gap between coil and scalp which is also suboptimal for coil positioning. As
the coil touches the hair, the patients feel the contact and confirm the coil on the
head, even though there is still a gap of a couple of millimeters. Thus, optimal coil
placement on the scalp can be difficult.

Parts of this chapter have been already published in [ 4 - 7 ].