Removing artifacts using Signal Space Projections can sometimes be very efficient.  Here are a few tricks to help you remove artifacts that are ongoing (dental work, breathing, noise from a device in the room, etc) or transient.

Ongoing artifacts can be present in the data with the subject has metal on them or when a device is in the room that is not MEG compatible.  Here I will show you two examples.  The techniques used here can be applied to most ongoing artifacts.

Metal in the mouth (denal retainer) that moves when the subject breathes.