Discussion - Robotized Transcranial Magnetic Stimulation - page 148

Chapter 9
Discussion
We have shown with our realistic measurements of the induced electric field
( Chap. 2 ) that head motion occurs during Transcranial Magnetic Stimulation
(TMS) applications and cannot be suppressed completely. Even small changes in
the position and/or orientation of the coil with respect to the target can have a
substantial impact on the stimulus intensity and therefore on the stimulation out-
come. Robotic motion compensation, however, effectively reduces these changes,
thus maintaining the initial magnitude and orientation throughout treatment.
Many—partially unknown—factors influence the results and outcomes in all
TMS applications. As shown by our TMS studies ( Chap. 3 ), the robotized TMS
system eliminates one major factor which is accuracy of coil placement. There-
fore, it is an important tool to further investigate the principles of TMS in the
cortex, which are still not fully understood, and to determine other factors that
have an influence on TMS, making TMS a more stable technique in the future. As
shown in the described studies, robotized TMS facilitates sufficiently precise coil
positioning and orientation to study even small variations of the motor threshold
with changing coil orientation and scalp-to-coil distance.
However, our practical evaluation ( Sect. 3.3 ) has also emphasized the deficits
of the robotized TMS system in its previous state, which are:
• time consuming calibration step,
• limited target accessibility,
• difficult optimal coil positioning on the head,
• the lack of (general) system safety, and
• the potential risk of shift of head marker.
Thus, the evaluation supports the need for further improvements of the system to
bring it into the labs and clinics. Therefore, we have further improved the system
towards safe and clinical applicable robotized Transcranial Magnetic Stimulation.