Active Markers; Filter Spectral Response - Northern Digital Polaris Vicra User Manual

The passive markers can only be sterilized one time. NDI does not recommend that a passive marker
be used if it has been sterilized more than once, as multiple cycles of sterilization may adversely
affect the marker's performance. Testing has shown that there is no significant degradation in the
performance of these markers after one cycle of ETO, STERRAD 100S, or STERIS SYSTEM 1
sterilization. The passive markers cannot be autoclaved. Pre-sterilized passive sphere markers are
also available; contact NDI for details.
Do not use markers without inspecting them for cleanliness and damage both before and during a procedure.
Reliance on data produced by unclean or damaged markers may lead to inaccurate conclusions. If your
Warning!
application involves personal safety, inaccurate conclusions increase the possibility of personal injury.
Caution!
Do not handle the passive sphere markers with bare hands as this will leave residue from skin that affects the
marker's reflectivity. Take care not to drop or scuff the markers, as this also affects the reflectivity of the markers.
3.13

Active Markers

Active markers are physically smaller than passive sphere markers. They consist of an Infrared
Light Emitting Diode (IRED) mounted on a ceramic base. The Position Sensor codes ("chirps") the
IR pulses emitted from its illuminators. These coded IR pulses are received by the IR receiver on the
tool which then activates the IREDs. The Position Sensor receives the IR emitted by the IREDs and
processes it in the same manner as passive tool reflections.
Active markers are mounted in active wireless tools. The ceramic base allows them to be sterilised
by auto-claving as required. The power for active wireless tools is supplied by battery. For detailed
information on active markers and active wireless tools, refer to the "Polaris Tool Design Guide".
3.14

Filter Spectral Response

The lenses on the Position Sensor filter out visible light, allowing only certain amounts of light at
specific frequencies to pass through to the CCDs. The CCDs are sensitive only to light below certain
frequencies. The result is a band pass filter from 800 nm to 1100 nm. Environmental light in this
range can affect the performance of the Polaris Vicra System. The more intense the environmental
light in this range, the higher the probability that it will interfere with the system.
Note
It is important to reduce environmental IR, to prevent interference with the system. Some operating room lights
may emit IR.
The amount of light at various frequencies that passes through the lenses to the CCDs, and then is
detected by the CCDs, as illustrated in
Polaris Vicra User Guide - Revision 2
Figure 3-9.
How the Polaris Vicra System Works
39