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Select the topic that interests you, or submit your own question: How are trackers used in medicine? What is the benefit of using a magnetic tracker with an imaging system? What is the difference between optical and magnetic trackers? What should I look for when choosing a medical tracker? Aren’t all magnetic trackers about the same? I’ve heard that magnetic trackers are hard to use in medical environments. Is this true? Can Ascension customize a tracker to my needs? When should I start thinking about incorporating a tracker into my medical device? 1) How are trackers used in medicine? A. Motion trackers measure the position and orientation (X, Y, Z, Yaw, Pitch, Roll) of one or more sensors in 3D space. Measurements are used to track the real-time motion of medical instruments and devices for localization and targeting purposes. In one prominent application, an Ascension pciBIRD™ sensor is attached to an ultrasound scanhead for freehand data acquisition and subsequent viewing of 3D reconstructions of multiple 2D image planes. Ascension trackers are also used in minimally invasive procedures for measuring anatomy, guiding interventions, and navigating inside the body. 2) What’s the benefit of using a magnetic tracker with an imaging system? A. The combination of miniaturized magnetic sensors with imaging systems lets clinicians follow a real-time graphic display of the current and projected position of interventional tools onto real-time ultrasound or recently acquired CT images. Using it, clinicians can quickly and precisely guide biopsy needles or ablation tools to soft-tissue lesions within the human body. The risk of hitting delicate, adjacent anatomy is also minimized. Magnetically guided intervention shortens procedures through pre-visualization of target trajectory and single needle insertion. When used with CT imaging, it reduces radiation exposure by minimizing the number of verification CT scans. In CT procedures, a spare position/orientation measurement sensor is placed on the patient so the true anatomical position of the target can be continuously monitored during procedure. Ascension's new pciBIRD is the choice for such imaging procedures. It offers highly accurate tracking of multiple miniaturized sensors without performance loss due to the presence of nearby conductive metals. 3) What’s the difference between optical and magnetic trackers? A. Optical trackers operate by emitting a light source that is sensed by one of more detectors. While highly accurate, they are obtrusive and require a clear line-of sight between source and detector at all times. If an occlusion occurs, measurements are lost. This precludes use within the body and limits usefulness in application in which heads and hands move freely within a tracking volume. Magnetic trackers transmit magnetic fields that permeate all non-metallic surfaces. These sensors have been miniaturized for medical applications and can be placed inside the body and even inside some instruments. Its transmitter possesses a small form factor and can be draped to avoid sterilization. As a result, magnetic trackers minimize clutter in procedural fields. 4) What should I look for when choosing a medical tracker? A. First, seek a company that focuses on developing medical tracking products and presents a robust record of bringing products to market. Making a tracker work in medicine requires clear understanding of technology tradeoffs, interface issues, and customization requirements. It is one thing to make a tracker work in a vacuum; it is a far different issue to make it work successfully in a medical application. Second, evaluate competing trackers before making a decision. At least one major medical company has come to regret not performing due diligence before making a major investment. Finally, look for expertise and versatility in tracking solutions. With the recent expiration of first generation AC magnetic tracking patents, a number of start-ups have built AC trackers and rushed into the medical market. While their intentions are good, their track records are poor. Your safest bet is to deal with an experienced tracking company offering multiple trackers, and configurations that can be readily modified to meet your requirements. 5) Aren’t all magnetic trackers about the same? A. No, there are several generations of trackers on the market. These range from 1st generation AC electromagnetic technology patented by Polhemus in the 1970s; 2nd generation pulsed DC magnetic technology patented by Ascension in the 1990s; and now 3rd generation magnetic technology patented by Ascension. The latter features the latest improvements and innovations in magnetic technology. First generation trackers are notoriously susceptible to distorted measurements in the presence of environmental metals, such as carbon steel, aluminum, and even stainless steel. Second generation DC trackers exhibit only 1/5 the sensitivity to conductive metal as their earlier counterparts. As a result their sensors can be attached to ultrasound scanheads, titanium instruments and stainless steel objects without discernable loss of accuracy. Third generation trackers represent the state-of-the art in tracking. These include alarms to warn of any accuracy distortion, special transmitters that screen distortions emanating below the tracking volume, miniaturized transducers for close-in operation, and advanced calibration techniques that yield sub-millimeter accuracies. 6) Is it true that magnetic trackers are hard to use in medical environments? A. Yes, they can be, especially if the technology is first generation vintage. In the last 10 years many medical device manufacturers have evaluated these early trackers and found them inadequate, usually because of accuracy distortion and improper placement. When developing the 3rd generation tracking technology the focus was and is to address the previous generation’s inadequacies. One of the major improvements has been metal compensation techniques. The improvement of these techniques continues. Bottom line: don’t give up on electromagnetic tracking due to its previous limitations. 7) Can Ascension customize a tracker to my needs? A. Yes. Ascension has a long and successful record of modifying tracker configurations to meet stringent medical requirements. In 2001, Ascension designed and developed for General Electric Medical Systems a new BIRD tracker with a pci bus interface and custom cabling in under six months. This tracker, pciBIRD™, is now available as an option for their Logiq 9 Ultrasound system. This year, Ascension added miniaturized transmitters and sensors to the pci platform to meet customer’s requirements. 8) When should I start thinking about incorporating a tracker into my medical device? A. During the development stage, if possible. Integrating a tracker into an existing medical device without forethought can be the recipe for trouble. This approach can be expensive, time consuming, and will most likely not provide optimal system performance. For instance, the present configuration of the medical device may require the tracker to operate beyond its specified range, resulting in degraded performance. The best approach is to design the tracker in during the development stage. The end result is a robust tracker specifically designed and optimized for your medical application.

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