Biomedical Engineering Reference
Fig. 3.6 Example of the
threshold increase with
distance (subject 10, coil
MC-B70) and fitted
exponential function. The
threshold is expressed in % of
the exponential fit is significantly better (p \ 0 : 05) and for the MC-B70 coil the
exponential fit just misses significance (p ¼ 0 : 066). In Fig. 3.6 the measured
thresholds with respect to the coil-to-scalp distance are plotted (open circles).
Additionally, the fitted exponential function is shown.
3.2.3 Robotized TMS for Accurate Coil Positioning
The robotized TMS system facilitates to precisely measure the relation between MT
and scalp-to-coil distance in vivo. In contrast to the previous studies, we have mea-
sured MTs up to a maximum scalp-to-coil distance of 24 mm. Based on these accurate
measurements, it becomes clear that an exponential relationship is much more likely
than a linear function as previously suggested. The exponential function is also in
accordance with measurements of the induced electric fields in air and phantoms.
Furthermore, realistic simulations also reported an exponential relationship [ 29 ].
Our study shows that without robotized TMS the discovery of the exponential
relationship is not possible. This might be due to the inaccurate coil positioning
and holding the coil by hand. Furthermore, head motion during the experiment
might be another reason for linear findings in the previous studies [ 8 , 25 , 26 ].
3.3 Practical Evaluation of Robotized TMS
The presented TMS studies show that robotized TMS is a very powerful tool for
performing TMS as it allows for precise coil positioning even within very small
steps. Furthermore, it allows to accurate re-accessment of previous stimulation