Active Versus Passive Tracking

When choosing which Polaris® system configuration to purchase, either passive or hybrid, the following key points and differences of each technology should be considered. Some of the points are related to the system hardware and some to the tool properties that are tracked by each system.

A passive system (Vicra, passive Spectra) tracks passive and active wireless tools only. A hybrid system (hybrid Spectra) tracks active, passive and active wireleless tools. The hardware components of the hybrid system offer some additional functionality not available in a passive configuration. The number and types of tools needed to be tracked are also leading considerations. It is important to note that active and passive tools are equivalent in accuracy.

When considering which system to purchase, NDI's technical specialists can work with you to help determine the best technology for your application.

Passive System

Hybrid System

Passive tools use spherical, retro-reflective markers that reflect infrared light emitted by the illuminators on the Position Sensor No physical connection of the tool to the system Can track numerous tools at the same time without reducing the sampling rate Offers simple tool construction Requires each tool to have a unique marker geometry which means larger tool sizes with each geometry Passive spheres need to be replaced after use Difficult to clean passive spheres intra-operatively Is less expensive than the hybrid system

Active tools incorporate infrared-emitting markers that are activated by an electrical current Tools are connected to the SCU via a cable Tool marker geometries can be small since the same geometry can be used multiple times Markers can be cleaned easily Can incorporate switches and visible LEDs Tool Description File can be programmed into tool Markers have limited life and are not replaceable Sampling rate is reduced with every third active tool added More complex to build than passive tools SCU has GPIO port that can be used for devices such as a foot switch for feedback to the application SCU has multiple connectivity options (i.e. RS-232, USB) SCU has synchronization port

Subscribe or Unsubscribe

If you wish to subscribe or unsubscribe to the NDI InFocus Newsletter, visit our NDI InFocus Subscription page.

Questions, Concerns, Complaints

If you have any questions, concerns, complaints, or if you think there is an error with your subscription, please feel free contact us at infocus@ndigital.com.