Chapter 2 Tracking Devices

Tracking devices are an essential component of an image-guided surgery system. These devices are used to track the position of instruments relative to the patient anatomy. Although early tracking systems were essentially mechanical digitizers, the field quickly adopted optical tracking systems because of their high accuracy and relatively large workspace. However, optical tracking systems require that a line-of-sight be maintained between the tracking device and the instrument to be tracked, which is not always convenient and precludes tracking of flexible instruments inside the body. Therefore, electromagnetic tracking systems were developed that had no line-of-sight requirement and could track instruments such as catheters and the tips of needles inside the body. The choice of tracking system is highly application dependent and requires an understanding of the desired working volume and accuracy requirements. To meet these needs, a variety of tracking devices and techniques have been introduced as described in this chapter.