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

**URL:** <https://discourse.slicer.org/t/clarification-on-segment-statistics-surface-area-vs-cross-sectional-area-csa-for-muscle-analysis/45558>\
**Category:** Support\
**Tags:** segmentation, dicom\
**Created:** [December 19, 2025, 12:48pm UTC](https://discourse.slicer.org/t/clarification-on-segment-statistics-surface-area-vs-cross-sectional-area-csa-for-muscle-analysis/45558 "2025-12-19T12:48:57Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![GaetanoGazze](https://avatars.discourse-cdn.com/v4/letter/g/e56c9b/32.png) [@GaetanoGazze](https://discourse.slicer.org/u/GaetanoGazze)\
**Post date:** [December 19, 2025, 12:48pm UTC](https://discourse.slicer.org/t/clarification-on-segment-statistics-surface-area-vs-cross-sectional-area-csa-for-muscle-analysis/45558/1 "2025-12-19T12:48:57Z")

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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!