Digitization error Neuromag 122

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1

Hi!

I’m working on a dataset acquired with a Neuromag-122 system ( MacOs 12.6.3, MNE 1.2.0 (conda env)). However, reviewing the raw.info object I realized that only HPI coils and fiducals have been digitized:

raw.info[‘dig’] gives this output:

[<DigPoint | LPA : (-79.9, 0.0, 0.0) mm : head frame>,
<DigPoint | Nasion : (-0.0, 107.8, 0.0) mm : head frame>,
<DigPoint | RPA : (78.1, 0.0, 0.0) mm : head frame>,
<DigPoint | HPI #1 : (69.5, 77.0, 66.5) mm : head frame>,
<DigPoint | HPI #2 : (82.9, -1.4, 25.8) mm : head frame>,
<DigPoint | HPI #3 : (-84.7, -6.8, 25.2) mm : head frame>,
<DigPoint | HPI #4 : (-56.1, 86.6, 68.6) mm : head frame>].

Could it be that digization of the skull is saved somewhere else in this system, or maybe only these points have been digitized? If there are no additional coordinates, would it be acceptable to use scalp coordinates from a recounstructed MRI?

Best regards and thank you in advance,
Karin

2

Hi Karin,

You could use the LPA, nasion and RPA for the co-registration … it won’t be as accurate as with scalp points but probably good enough. You can use the plot_alignment function to check the quality of the co-registration.

Mainak

3

Dear Mainak,

Thank you very much! Is there a smart way of avoiding the “no digitization points found”-error that this causes (which prevents further processing)?

Best regards and thank you in advance,
Karin

4

Hi Karin,

Which function is throwing this error? Can you share some more info so we can help.

Mainak