Diploma thesis: Error Classification and Propagation for Electromagnetic Tracking
Student:
Julian Much
Advisor:
Nassir Navab
Supervision by:
Joerg Traub and
Marco Feuerstein
Abstract
The negative influence of electromagnetic tracking errors on the accuracy of a number of
image-guided surgery applications encourages the consideration of erroneous measurements
on a lower level. An error classification methodology is described in this thesis and allows
to group occurring errors into subclasses, to draw conclusions about their origins, and to
propagate them for the prediction of the final error in the application. Positional and
orientational errors can be classified into both static and dynamic distorted data, where
static errors are grouped into jitter and field distortions caused by the influence of nearby
metallic objects in the operating volume. Dynamic errors are subdivided into sensor velocity
and errors caused by dynamically induced metals or electrical devices in the tracking area.
Error propagation models help to predict the resulting error based on the initially reported
tracking errors in a specific application.
Robotic devices, measurement tools and optical tracking systems can be used to classify an
occuring electromagnetic error and to measure the magnitude of its components. To compensate
the faulty tracking data, a number of error correction approaches can be applied
and are described in this thesis. Several experiments were accomplished to classify occuring
tracking errors in a distortion-free environment by using both a standardized assessment
protocol with a high-precision measurement plate and a co-calibrated magneto-optical system.
In general the flat transmitter showed an increased performance at orientation determination
and metallic distortion experiments in comparision to the mid-range transmitter,
however, with drawbacks at jitter errors and positional determinations. Furthermore, the
error value provided by Ascension was observed throughout the experiments and its magnitude
strongly depends on the distance between receiver and transmitter. The implemented
applications of electromagnetic tracking systems in the field of navigated bronchoscopy and
augmented camera systems were used to apply the error detection and correction models
within this thesis. Additionally, the assessment experiments were performed in the bronchoscopy
room and distortions were observed caused by metallic objects in the operating
volume.
Documents