FT-Control - Robotized Transcranial Magnetic Stimulation - page 92

Table 5.1 Parameters of the used coils for evaluation
Coil Type Weight (kg) Cable length (m)
MCF-75 Circular (static cooled) 1.0 1.3
MC-B35 Figure-of-eight (for small animals) 0.6 1.5
Medium 70 mm Circular 0.5 1.7
C-B60 Figure-of-eight 0.7 1.7
MCF-P-B65 Butterfly (static cooled) 1.9 2.0
MC-125 Figure-of-eight 0.6 1.3
MC-B70 Butterfly 0.9 1.3
MCF-B65 Figure-of-eight (static cooled) 1.5 2.0
Beside coil type, individual weight of the transducer head and length of the TMS supply cable are
listed. The medium 70 mm circular coil is produced by Magstim (Magstim Ltd., Whitland,
Wales, UK). All other coils are manufactured by MagVenture (MagVenture A/S, Farum,
Denmark)
standard figure-of-eight coils, which weigh more than 1.5 kg, also small and
lightweighted coils (less than 0.6 kg) are in operation with the robotized TMS
system. In addition to the size and weight of the coil (the transducer head), the
length and therefore the weight of the supply cable varies. Note that cable length
and coil weight do not correlate.
First of all, we conduct a sensor calibration with 500 measurements as illus-
trated above in Sect. 5.1.1 . For each of the listed TMS coils, we subsequently
employ the setup for FT controlled robotized TMS. First, we mount the TMS coil
into the clamp attached to the FT sensor. Second, we perform a coil calibration as
described in Sect. 5.1.2 . Subsequently, we start the hand-assisted positioning
method and move the coil to 10 randomly chosen positions with different orien-
tations. For evaluation, we now record the forces and torques at rest at these
positions and compute the user applied forces and torques. As error quantification,
we estimate the discrepancy of the computed user applied forces and torques at
rest to zero. In case of perfect calibrations and optimal gravity compensation, the
applied forces and torques at rest should always correspond to 0.
5.2.4.2 Usability of Hand-Assisted Positioning
For evaluation of the hand-assisted positioning, we are primarily interested in the
speed-up of coil positioning with this method in comparison to coil positioning
with the current robotized TMS control software. This speed-up in positioning
time is an indicator for the increased usability with the hand-assisted positioning
method. As typically physicians, researchers and medical staff are the users of the
robotized TMS system, we also measure the effects of hand-assisted positioning
for inexperienced operators in addition to experienced users. Note that experience
in this context only refers to the knowledge of robotic systems and their control
mechanisms.