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Home < Documentation < Nightly < Modules < Watchdog

For the stable Slicer documentation, visit the 4.6 page.

Introduction and Acknowledgements

Contributors: Jaime Garcia Guevara (PerkLab, Queen's University), Andras Lasso (PerkLab, Queen's University)
Contact: Tamas Ungi,

Cancer Care Ontario  

Module Description

Module for displaying warning message to the user if continuous update of tracked tool position or update of an image stream stops.

Demo video:

The module provides the following features:

  • Display of a warning message in any of the viewer window(s), at configurable size, color, and transparency
  • Sound feedback when tracking or imaging is stopped or resumed
  • All settings are saved with the scene and when the scene is loaded into Slicer the configured watchdog is activated automatically

Use Cases

Tool positions and/or images are typically acquired through OpenIGTLink from Plus Server ( or other compatible server. When an optically tracked tool gets out of the tracker's view or an electromagnetically tracked tool gets out of the tracking field then position updates stop. As a result, the tracked tool stops moving and/or the displayed image stops updating, but this may not be immediately visible to the operator. To make sure that stopping of real-time updates is not missed by the operator, the Watchdog module is configured to provide visual and/or audible warning.

Limitation: end of warning sounds may be clipped during replay, therefore users cannot fully rely on the audio feedback.


See this 1-minute video:

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