Biomedical Engineering Reference
In-Depth Information
8.3.2.2 Head Registration for Head Tracking
An accurate registration of the 3D laser scan to the reference image is of crucial
importance for head tracking. For evaluation of the registration, we use a human
head phantom. We now use 10 different head phantom positions and scan the head
phantom with the laser scanner. For the head phantom, we already obtained an
MRI scan from which we generated a 3D virtual head contour. We now register
the head scans to the head contour with the ICP algorithm [
3
,
5
]. For evaluation,
we estimate the registration error as the absolute mismatch of the registered laser
scan to the reference image.
8.3.2.3 Head Tracking Based on 3D Laser Scans
In order to evaluate the accuracy of head tracking with a 3D laser scanning system,
we mount the human head phantom to the Adept robot's end effector. Starting
from an initial position, we move the robot to n
ΒΌ
50 random positions. At each
position we record the robot position and perform a 3D laser scan of the head
phantom. For evaluation, we now perform an ICP registration of each 3D laser
scan to the laser scan obtained at the initial position. For an estimate of the head
tracking accuracy, we compare the absolute distances of the robot motion to the
translational distances calculated with the ICP registration.
8.3.2.4 Coil Calibration
To show the general capability of coil calibration with a laser scanning system, we
use two different TMS coils. We mount an MCF-75 small circular coil and an
MCF-B65 human figure-of-eight coil (MagVenture A/S, Farum, Denmark) to the
Adept robot and perform high resolution laser scans.
8.3.3 First Results
8.3.3.1 Calibration
For evaluation of the accuracy of the calibration of laser scanning system to robot,
we have performed hand-eye calibration with 5
;
...
;
25 data points. For evaluation,
we have tested the estimated calibration matrices on another set of 25 data points.
We have performed the hand-eye calibration method with different calibration
algorithms to identify the optimal calibration method for the specific tracking data
coming from a 3D laser scanning system.
The results from the data collected with our laser scanning system are given in
Table
8.1
and Figs.
8.5
and
8.6
. Clearly, in terms of translational accuracy, the QR
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