PMJ - PMJ Distance and Extent

SCT
1

Hi,
I hope you’re well.

I am trying to figure out PMJ labelling with brain scans, so the spinal cord is much shorter. On the SCT website there are four steps. However, I am confused about how the distance 64 and extent 30 were generated. What would be the steps to find these units to be able to compute CSA using PMJ.

Thank you.

2

Hi @K.M,

Welcome to the forum, and thank you very much for your thoughtful question! :slight_smile:

Additional context for the default PMJ methodology can be found in the corresponding publication (which can also be found on the “Citing SCT” page):

SC CSA was computed at the mean distance between the C2–C3 disc and the PMJ across all participants, which corresponds to 64 mm. SC CSA was computed along the SC centerline and then averaged on a 20 mm extent as presented in Figure 2.

This at least provides justification for the ‘64mm’ value, though I’m not entirely sure of the justification for the ‘20mm’ value in the publication (as compared to the ‘30mm’ value used in tutorials). I will mention this to my colleagues and see if we can provide a more detailed response. :slight_smile:

Kind regards,
Joshua

3

Hi @K.M,

You can choose the extend depending on how much averaging you want in your CSA measure. In the paper, 20mm to approximates vertebral level length, but you can decide if you want a smaller or larger extent.

Best,

Sandrine