Removing artifacts using Signal Space Projections can sometimes be very efficient.  Here are a few tricks to help you remove artifacts from your data that are ongoing or repeating.

Ongoing artifacts can be present in the data, for example when the subject has metal on them or when a device is in the room that is not MEG compatible.

Example 1: Metal in the mouth (dental retainer) that moves when the subject breathes.

1. Identify the artifact and channel(s) that are most affected.  Scan though the data and performing a PSD can help with this:
{{attachement:dental_breathing_artifacts.png}}

Here we see channel MRT57 is strongly affected.  The topography shows a dipole below the posterior part of the sensor array.