Digitizer issue

Yesterday evening, someone had a lot of localization noise (imprecise positions) during digitization, leading to unusable results. This morning it was definitely not as bad, but there might still have been more noise than usual.

I will investigate when I can, probably after the holidays. In the meantime, please let me know how it behaves today, and if anybody perhaps dropped one of the components (stylus, glasses, emitter cube), so that I have a clue which part might be damaged.

For most studies, you can still run if it’s not working. In that case, just make sure to take good pictures of the placement of fiducials, e.g. dots or the head coils themselves, so they can be marked on the MRI later. This is harder and not as accurate, but not an uncommon way to do co-registration.

Here’s a picture of what it looked like when it didn’t work properly yesterday:
It also gave errors for pairs of fiducial points being too far apart.

Here are things to double check that could cause localization problems:

  1. Emitter cube not attached at the back of the chair, or too far from the head*.
  2. Goggles unstable. If you hit them by mistake, probably best to start over.
  3. MSR door open or chair not placed in center of space. This is a magnetic system; metal will distort localization.
  4. Damaged part (emitter or receiver on goggles or stylus).
  5. System misconfiguration. (It only detects in half a sphere around the emitter, but this should not change on its own.)

*We haven’t had issues with this since I reconfigured the system, but it’s possible if someone is very tall or sitting at the front of the chair that we would get more error. I’ll look into getting a stand to improve this.

We have confirmed that the receiver attached to the goggles is the problem. It will likely be replaced within a week.

We have received the new receiver and the digitizer works well again.