Clarification on Segment Statistics: Surface Area vs. Cross-Sectional Area (CSA) for Muscle Analysis

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Hi everyone,

I am performing a quantitative body composition analysis on single-slice CT scans (at the D10 level) using the Segment Statistics module in 3D Slicer. I would like to clarify a methodological doubt to ensure the accuracy of my data:

  1. Surface Area vs. CSA: Can you confirm that the ‘Surface Area’ (mm²) metric provided by the module refers to the total 3D surface area of the generated mesh (the “envelope” or “shell” of the segment)? In my single-slice analysis, this value is significantly higher than the expected planar area. Is it correct to assume that ‘Surface Area’ should not be used as a proxy for the Cross-Sectional Area (CSA) or Skeletal Muscle Area (SMA)?

  2. SMA Calculation: To derive the Skeletal Muscle Area (SMA) in $cm^2$, I am currently taking the ‘Volume’ (mm³) of the segment and dividing it by the slice thickness (e.g., 1 mm). Is this “Volume / Thickness” conversion considered a standard and reliable method in Slicer to obtain the 2D planar area from a single-slice segmentation?

I want to make sure I am not misinterpreting the geometric outputs of the software, as using the wrong metric would lead to incorrect Skeletal Muscle Index (SMI) calculations.

Thank you in advance for your help!