📐 ctpelvimetry

The first open-source Python package for fully automated CT pelvimetry and body composition analysis.

ctpelvimetry turns the manual, ~15-minute-per-scan process of measuring mid-pelvic dimensions and body composition into a fully automated 2-minute pipeline. Built for surgical data science, preoperative risk assessment, and large-scale ML training datasets, it integrates with TotalSegmentator to extract anatomical metrics directly from raw CT scans — eliminating inter-observer variability.

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📑 Contents

• Quick Start
• Installation
• CLI Usage
• Python API
• Output Structure
• Measured Metrics
• Quality Control
• Hardware Requirements
• Body Composition License (Optional)
• Architecture
• Troubleshooting
• Citation

---

🚀 Quick Start

# Install
pip install "ctpelvimetry[seg]"

# Process a single DICOM folder
ctpelvimetry pelv \
  --dicom_dir /path/to/Patient_001 \
  --patient Patient_001 \
  --output_root ./output

# Or a directory full of NIfTI files (Medical Decathlon, KiTS, etc.)
ctpelvimetry pelv \
  --nifti_root /path/to/niftis \
  --output_root ./output

You get back a CSV with ISD, inlet/outlet AP, sacral metrics, plus QC images. ~2 minutes per scan on a GPU.

---

📦 Installation

# Basic — for analysis when you already have segmentations
pip install ctpelvimetry

# Full — includes TotalSegmentator for end-to-end automation
pip install "ctpelvimetry[seg]"

Requires Python 3.10+.

For body composition (VAT/SAT/muscle), one extra step is required — see Body Composition License. Pelvimetry works without it.

---

🖥️ CLI Usage

ctpelvimetry ships two subcommands:

Subcommand	Purpose
pelv	Pelvimetry: mid-pelvic dimensions (ISD, inlet/outlet AP, sacrum)
body-comp	Body composition: VAT, SAT, skeletal muscle area at L3 and ISD levels

pelv — Pelvimetry

The pelv subcommand has 5 input modes. Pick the one that matches your data layout:

Mode	Flags	Use when
1. Existing seg	--seg_folder (+ --nifti_path)	You already have TotalSegmentator output
2. Single DICOM	--dicom_dir + --patient	One patient's DICOM folder on disk
3. Single NIfTI	--nifti_path + --patient	One NIfTI file
4. DICOM batch	--dicom_root (+ --start / --end)	Folder of Patient_001/, Patient_002/, ...
5. NIfTI batch	--nifti_root (+ optional --pattern)	Folder of *.nii.gz files (one per patient)

Examples

# Mode 1 — analysis only (skip segmentation)
ctpelvimetry pelv \
  --seg_folder /path/to/seg \
  --nifti_path /path/to/ct.nii.gz \
  --patient Patient_001 \
  --output_root ./output

# Mode 2 — single patient, full pipeline from DICOM
ctpelvimetry pelv \
  --dicom_dir /path/to/Patient_001 \
  --patient Patient_001 \
  --output_root ./output

# Mode 3 — single patient, full pipeline from NIfTI
ctpelvimetry pelv \
  --nifti_path /path/to/ct.nii.gz \
  --patient Patient_001 \
  --output_root ./output

# Mode 4 — batch DICOM (expects ./DICOMs/Patient_001/, ./DICOMs/Patient_002/, ...)
ctpelvimetry pelv \
  --dicom_root /path/to/DICOMs \
  --output_root ./output \
  --start 1 --end 250

# Mode 5 — batch NIfTI (expects *.nii.gz directly under nifti_root)
ctpelvimetry pelv \
  --nifti_root /path/to/niftis \
  --output_root ./output

# Custom glob pattern (e.g. uncompressed NIfTI, or non-default naming)
ctpelvimetry pelv \
  --nifti_root /path/to/niftis \
  --pattern "case_*_ct.nii" \
  --output_root ./output

Common flags

Flag	Default	Description
--output_root	./pelvimetry_output	Root directory for all outputs
--output	combined_pelvimetry_report.csv	Output CSV filename
--fast	off	Use TotalSegmentator --fast mode (faster, slightly less accurate)
--no-tissue	off	Skip the body composition (tissue_types) task
--qc / --no-qc	on	Generate QC images

Run ctpelvimetry pelv --help for the full list.

body-comp — Body Composition

Computes VAT, SAT, and skeletal muscle area at the L3 and mid-ISD levels. Requires pelvimetry to have already run (so it knows where the ISD level is).

# Single patient
ctpelvimetry body-comp \
  --patient Patient_001 \
  --seg_root ./output/Segmentation \
  --nifti_root ./output/NIfTI \
  --pelvimetry_csv ./output/combined_pelvimetry_report.csv \
  --output ./output/body_comp_001.csv \
  --qc

# Batch
ctpelvimetry body-comp \
  --seg_root ./output/Segmentation \
  --nifti_root ./output/NIfTI \
  --pelvimetry_csv ./output/combined_pelvimetry_report.csv \
  --output ./output/body_composition_report.csv \
  --start 1 --end 250 \
  --qc_root ./output/body_comp_qc

Run ctpelvimetry body-comp --help for all flags.

---

🐍 Python API

For custom pipelines or integration into existing data-science workflows.

Public API surface

Function	Use case
run_combined_pelvimetry	Existing segmentation → measurements
run_full_pipeline	DICOM folder → NIfTI → seg → measurements (one patient)
run_nifti_pipeline	NIfTI file → seg → measurements (one patient)
run_pelvimetry_batch	DICOM batch (parent dir of Patient_xxx/ folders)
run_pelvimetry_nifti_batch	NIfTI batch (directory of *.nii.gz)
process_single_patient	Body composition for one patient
PelvicConfig	Tuneable detection thresholds

Single-patient examples

from ctpelvimetry import (
    run_combined_pelvimetry,
    run_full_pipeline,
    run_nifti_pipeline,
)

# A. Already have segmentation (fastest path; just measurement + QC)
result = run_combined_pelvimetry(
    patient_id="Patient_001",
    seg_folder="/path/to/segmentation_masks",
    nifti_path="/path/to/ct.nii.gz",
    qc_dir="./output/QC",  # optional
)
print(f"ISD: {result['ISD_mm']} mm")
print(f"Inlet AP: {result['Inlet_AP_mm']} mm")

# B. From a DICOM folder (end-to-end)
result = run_full_pipeline(
    patient_id="Patient_001",
    dicom_path="/path/to/Patient_001",
    output_root="./output",
    use_fast=False,      # set True for quick previews
    skip_tissue=False,   # set True to skip body comp
)

# C. From a NIfTI file (end-to-end, skips DICOM conversion)
result = run_nifti_pipeline(
    patient_id="Patient_001",
    nifti_path="/path/to/ct.nii.gz",
    output_root="./output",
)

Batch examples

from ctpelvimetry.batch import (
    run_pelvimetry_batch,
    run_pelvimetry_nifti_batch,
)

# DICOM batch — expects /data/DICOMs/Patient_001/, /data/DICOMs/Patient_002/, ...
df = run_pelvimetry_batch(
    dicom_root="/data/DICOMs",
    output_root="./output",
    output_csv="./output/results.csv",
    start=1, end=250,
)

# NIfTI batch — expects /data/niftis/case_001.nii.gz, case_002.nii.gz, ...
df = run_pelvimetry_nifti_batch(
    nifti_root="/data/niftis",
    output_root="./output",
    output_csv="./output/results.csv",
    pattern="*.nii.gz",  # default
    use_fast=False,
    skip_tissue=False,
)

# Filter to fully successful patients
success = df[df["Status"] == "Success"]
print(success[["Patient_ID", "ISD_mm", "Inlet_AP_mm"]].describe())

Both batch functions return a pandas.DataFrame and write a CSV to output_csv. Per-patient errors are isolated — one failure won't abort the run.

Body composition

from ctpelvimetry import process_single_patient

body_comp = process_single_patient(
    patient_id="Patient_001",
    seg_root="./output/Segmentation",
    nifti_path="./output/NIfTI/Patient_001/Patient_001.nii.gz",
    pelvimetry_csv="./output/combined_pelvimetry_report.csv",
    qc_dir="./output/body_comp_qc",  # optional
)
print(f"VAT @ L3: {body_comp['L3_VAT_cm2']} cm²")
print(f"V/S ratio @ L3: {body_comp['L3_VS_ratio']}")
print(f"SMA @ L3: {body_comp['L3_SMA_cm2']} cm²")

Custom thresholds

from ctpelvimetry import run_combined_pelvimetry, PelvicConfig

config = PelvicConfig(
    rotation_warn_deg=3.0,    # tighter QA than the default 5°
    tilt_warn_deg=3.0,
    sacrum_offset_warn_mm=3.0,
)

result = run_combined_pelvimetry(
    patient_id="P001",
    seg_folder="./seg",
    nifti_path="./ct.nii.gz",
    config=config,
)

---

📂 Output Structure

After running the pelvimetry pipeline, --output_root looks like:

output/
├── NIfTI/                       # DICOM → NIfTI conversions (DICOM modes only)
│   └── Patient_001/
│       └── Patient_001.nii.gz
├── Segmentation/                # TotalSegmentator masks
│   └── Patient_001/
│       ├── hip_left.nii.gz
│       ├── hip_right.nii.gz
│       ├── sacrum.nii.gz
│       ├── femur_left.nii.gz
│       ├── femur_right.nii.gz
│       ├── vertebrae_S1.nii.gz
│       ├── ...
│       ├── subcutaneous_fat.nii.gz   # only with TOTALSEG_LICENSE_KEY
│       ├── torso_fat.nii.gz
│       └── skeletal_muscle.nii.gz
├── QC/                          # Visual QC images (PNG)
│   ├── Patient_001_Sagittal_QC.png
│   └── Patient_001_Extended_QC.png
└── combined_pelvimetry_report.csv   # The aggregated results

CSV schema (key columns)

Column	Type	Description
Patient_ID	str	Patient identifier
Status	str	Success, Partial_N/6, Failure, or Error
Error_Log	str	Per-metric error codes (semicolon-separated), if any
ISD_mm	float	Inter-Spinous Distance
Inlet_AP_mm	float	Pelvic inlet AP diameter
Outlet_AP_mm	float	Pelvic outlet AP diameter
Outlet_Transverse_mm	float	Intertuberous diameter
Sacral_Length_mm	float	Sacral length (promontory → coccygeal apex)
Sacral_Depth_mm	float	Maximum sacral concavity depth
Pelvic_Rotation_deg	float	Axial rotation (quality flag)
Pelvic_Tilt_deg	float	Coronal tilt (quality flag)
Promontory_x/y/z	float	RAS world coordinates (mm) of detected landmarks
Upper_Symphysis_x/y/z	float	(and similar columns for all detected landmarks)
CT_NIfTI, Seg_*	str	File paths to inputs/intermediates for traceability

Status semantics:

• Success — all 6 pelvimetric metrics computed
• Partial_N/6 — N of 6 metrics computed; the rest in Error_Log
• Failure — 0 metrics computed (segmentation produced but unusable)
• Fail_NIfTI — DICOM → NIfTI conversion failed (DICOM modes only)
• Fail_Seg — TotalSegmentator failed to produce required masks
• Fail_NIfTI_Missing — input NIfTI file does not exist (NIfTI modes only)
• Error — uncaught exception during processing (batch mode only); full message in Error_Message

---

🔬 Measured Metrics

Pelvimetry (Mid-Pelvic Workspace)

Metric	Description
ISD (mm)	Inter-Spinous Distance — narrowest mid-pelvic width, critical for deep pelvic dissection
Inlet AP (mm)	Promontory → upper symphysis distance
Outlet AP (mm)	Coccygeal apex → lower symphysis distance
Outlet Transverse (mm)	Intertuberous diameter (between ischial tuberosities)
Sacral Length (mm)	Promontory → coccygeal apex along the sacral curve
Sacral Depth (mm)	Maximum concavity depth from the inlet-outlet chord

Body Composition (requires license)

Metric	Description
VAT / SAT (cm²)	Visceral / subcutaneous adipose tissue area
V/S Ratio	VAT / SAT ratio — indicator of visceral obesity
SMA (cm²)	Skeletal Muscle Area at L3 and mid-pelvis levels

---

👁️ Quality Control

ctpelvimetry generates two QC panels per scan so you can spot-check landmark detection visually before trusting the numbers.

Sagittal QC: sacral length (magenta), inlet AP (green), outlet AP (orange), sacral depth (cyan).

Extended QC: outlet transverse diameter, ISD, and tabular measurement summary.

The pipeline also writes quality flags to the CSV:

• Pelvic_Rotation_Flag / Pelvic_Tilt_Flag — ok, warn, high (axial rotation and coronal tilt of the patient on the table)
• Sacrum_Offset_Flag — sacrum-to-symphysis midline offset in mm

These flags don't block measurement but signal when manual review is wise.

---

⚙️ Hardware Requirements

End-to-end automation runs deep-learning segmentation. A GPU is strongly recommended.

Setup	Time per scan	Notes
NVIDIA GPU 8GB+ VRAM (T4, RTX 3060+, A100)	< 2 min	Recommended. 16GB+ for high-res CTs.
CPU only	10–30+ min	Will work but slow; may OOM on large series
Google Colab (free T4)	< 2 min	Easy cloud option for clinical researchers

If you only run analysis on pre-existing segmentations (Mode 1), a standard CPU is fine — no GPU needed.

---

🔑 Body Composition License (Optional)

Body composition (VAT/SAT/muscle) requires TotalSegmentator's tissue_types task, which needs a free academic license. Pelvimetry works without it.

# 1. Register (free, takes 30 seconds): https://backend.totalsegmentator.com/license-academic/
# 2. Set the env var (add to ~/.bashrc or ~/.zshrc to persist):
export TOTALSEG_LICENSE_KEY=aca_xxxxxxxxxxxx

If TOTALSEG_LICENSE_KEY is unset, the pipeline silently skips body composition and reports pelvimetry only. No errors, no warnings beyond a one-line info message.

Note: Versions ≤ 1.4.1 shipped with a hard-coded license key. That key has been removed (see CHANGELOG); please register your own.

---

🏗️ Architecture

ctpelvimetry/
├── cli.py               # Unified CLI entry point (pelv + body-comp subcommands)
├── pipeline.py          # End-to-end orchestration:
│                        #   - run_combined_pelvimetry  (seg → measurements)
│                        #   - run_full_pipeline         (DICOM → measurements)
│                        #   - run_nifti_pipeline        (NIfTI → measurements)
├── batch.py             # Batch processors with per-patient error isolation:
│                        #   - run_pelvimetry_batch
│                        #   - run_pelvimetry_nifti_batch
│                        #   - run_body_composition_batch
├── conversion.py        # DICOM → NIfTI conversion
├── segmentation.py      # TotalSegmentator integration wrapper
├── landmarks.py         # 3D geometric landmark detection
├── metrics.py           # Pelvimetric calculations (ISD, AP, sacral, etc.)
├── body_composition.py  # Fat / muscle area quantification
├── qc.py                # QC image generation (matplotlib)
├── io.py                # Mask I/O with canonical (RAS) reorientation
└── config.py            # PelvicConfig dataclass: tuneable thresholds

---

🛠️ Troubleshooting

Patient_xxx: Status = Failure, Error_Log = ALL: ISD_NO_HIP_MASK

TotalSegmentator didn't produce hip masks. Usually the CT FOV doesn't include the pelvis, or the scan is corrupted. Inspect the input NIfTI in a viewer (3D Slicer, ITK-SNAP).

Tissue Types: Requires license

You're trying to run body composition without a license. Either set TOTALSEG_LICENSE_KEY (see Body Composition License) or pass --no-tissue to skip explicitly.

Segmentation is extremely slow

Either you don't have a GPU or PyTorch isn't seeing it. Verify with:

import torch; print(torch.cuda.is_available())

If False, reinstall PyTorch with the CUDA build for your driver.

Status = Partial_5/6 with Sacral_Depth: SACRAL_NO_LANDMARKS

Promontory or coccygeal apex wasn't detected. The other 5 metrics are still valid. Check the Sagittal QC PNG.

Segmentation results look wrong despite no error

Patient is probably rotated or tilted on the table. Check Pelvic_Rotation_deg and Pelvic_Tilt_deg columns — the pipeline flags values > 5° (default) as warn, and these often indicate unreliable measurement. Tighten the thresholds via PelvicConfig if you want stricter automatic flagging.

CSV Status column is missing or empty

You're probably reading a body-composition CSV (different schema). Pelvimetry results are in combined_pelvimetry_report.csv.

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🤝 Contributing

PRs welcome from both the surgical and data-science communities. The package follows semantic versioning; tag pushes (v*) auto-trigger PyPI publishing via GitHub Actions.

git checkout -b feature/your-feature
# ... make changes, add tests in tests/
pytest                            # all should pass
git commit -am "feat: ..."
git push origin feature/your-feature
# Open a PR

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📝 Citation

If ctpelvimetry enables your research, please cite:

@software{huang2026ctpelvimetry,
  author    = {Huang, Shih-Feng},
  title     = {ctpelvimetry: Automated CT Pelvimetry and Body Composition Analysis},
  year      = {2026},
  url       = {https://github.com/odafeng/ctpelvimetry},
  version   = {1.6.0},
}

A peer-reviewed manuscript on the clinical validation of this pipeline is in preparation.

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License: Apache License 2.0 | Author: Shih-Feng Huang, MD (@odafeng)