Area measurement using 3DSlicer?

I’m trying my best to use Polygon to mark the borders of Midbrain and Pons and then, calculate these areas. However, I didn’t find out.

The similar research “Manual MRI morphometry in Parkinsonian syndromes - PubMed” in 2017 using 3D-Slicer with version for Windows. I have attached a figure below to illustrate my point.

Would you please help me out? Thank you so much

Just a reminder, the figure seems not be attached successfully?