Introduction - Robotized Transcranial Magnetic Stimulation - page 17

• Easy setup and safety: robust real-time calibration
For the robotized system a calibration between tracking system and robot is
required. As the system design is partially mobile, the calibration step might be
performed frequently which takes additional time. When robot and/or tracking
system shift, calibration must be re-performed. It is even worse when such a
shift occurs unrecognized during treatment. We developed an online calibration
method that is able to update and check the current calibration during appli-
cation in real-time.
• Usability: hand-assisted positioning
An industrial robot is a complex and potentially hazardous system. To guarantee
patient safety, potential dangerous robot trajectories are disabled in the robot-
ized TMS software. Therefore, quite often the user must coarsely pre-position
the robot to allow safe and automated coil positioning. We integrated a hand-
assisted positioning method, based on a Force-Torque (FT) sensor, into the
system. It enables the user to perform easy and fast coil positioning to overcome
the more cumbersome manual pre-positioning.
• Precision: contact pressure control
Motion compensation keeps the coil position stable during treatment. However,
a constant pressure of the coil on the head is not guaranteed. An optimal coil to
head distance is important for an optimal stimulation. For this reason, we
combine the existing motion compensation algorithm with contact pressure
control using the FT sensor. It allows for automated target approaching with an
optimal initial coil to head distance and maintains the contact pressure stable
during application.
• Safety: Force-Torque-Acceleration (FTA) sensor
Safety is a big challenge for medical robotic systems due to the direct interaction
with the patient and/or user. For most systems based on industrial robots, as the
robotized TMS system, safety features can only be implemented on the software
layer. In this case, robot acceleration and velocity, joint range and configuration
are restricted in software. Even though this works for most situations, safety
cannot be guaranteed. Programming faults or communication errors between
software and robot might bypass the implemented software safety measures.
This can lead to serious and dangerous situations. We design and develop an
additional safety layer for medical robotic systems, and the robotized TMS
system in particular, named FTA sensor. It combines a force-torque sensor with
an inertia measurement unit for independence from robot input. An embedded
system checks the recordings in real-time (approximately 1 ms) and is directly
linked to the robot's emergency circuit. In case of an error or collision, it stops
the robot instantaneously. Note that the FTA sensor additionally provides the
functionality of the FT control which is hand-assisted positioning and contact
pressure control.
• (User) comfort: direct head tracking
So far, indirect head tracking, using a marker attached to the patient's head, is
state-of-the-art for neuro-navigated and robotized TMS. This approach requires
the marker to be registered to the patient's head. A shift of the marker during