Optical tracking systems pioneered the use of position sensors in surgical navigation. The requirement to maintain a clear
line-of-sight between the emitters and detectors, however, renders them unsuitable for tracking flexible invasive
instruments. On the other hand, advances in electromagnetic tracking systems permit a key-enabling role in imageguided
procedures. First-generation magnetic systems present a significant challenge for tracker designers to improve
both performance and acceptance. Troublesome magnetic problems include inaccuracies due to the presence of metallic
distorters in the tracking volume and to dynamic motion of the tracked object. A new magnetic tracker (3D GuidanceTM),
recently developed at Ascension Technology, seeks to address these problems. Employing third-generation pulsed-DC
magnetic tracking technology and new signal processing techniques, the new tracker overcomes the distorting effects of
non-magnetic conductive metals (300-series stainless steel, titanium and aluminum) and composite tables experienced by
AC trackers. Ascension has developed a break-through flat transmitter that negates ferrous metal distortion emanating
from procedural tables. The tracker development has also significantly advanced the state of the art in sensor
miniaturization. The 3D GuidanceTM features the world's smallest electromagnetic tracking sensors, opening the door to
new applications for minimally invasive procedures. Finally, dynamic accuracy has been significantly improved with the
implementation of Kalman based algorithms. Test results are reported.
KEYWORDS: Sensors, Magnetism, Electromagnetism, Magnetic sensors, Antennas, Chemical elements, Detection and tracking algorithms, Calibration, Magnetic tracking, Transmitters
A low frequency AC electromagnetic tracking system is presented that is capable of determining the position and orientation of a catheter tip. Advantages of using magnetic tracking for this application is that magnetic fields are non-ionizing and pass through the human body with minimal attenuation. Low frequency fields are used to mitigate the effects of eddy currents induced in conductive materials found in the environment. There are two significant differences between this and other magnetic tracking technologies, these being (1) the use of a single magnetic sensing coil for position and orientation determination and (2) the eliminating of range restrictions between the sensing antenna and the magnetic field generators. This paper will discuss the general theory of electromagnetic tracking, why it is that researchers have an intense interest for internal tracking and a comparison of the new and old tracking technologies. Some applications of this tracking technology will also be presented.
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