brain-extraction-qc

name

brain-extraction-qc

description

Validate brain extraction / skull stripping results. Generate a QC PNG mosaic, perform AI visual evaluation against a structured rubric, and produce a matching human verification form for reliability comparison. Invoke after brain extraction completes, or standalone on any existing brain mask with "check brain extraction", "QC the mask", "validate skull strip", "review brain extraction", "evaluate the mask", or "brain-extraction-qc". Also invoke when the user references a file ending in `_brain.nii.gz`, `_mask.nii.gz`, or `_brain_mask.nii.gz` and asks to check, review, or validate it.

Skill: brain-extraction-qc

Validate brain extraction results through three steps: generate a PNG mosaic with mask overlay, visually evaluate the PNG using AI vision, and save a paired human verification form so that AI-human agreement can be measured over time.

Steps

1. Identify inputs

   Read the invocation arguments or current user request for: (1) original NIfTI path, (2) brain mask NIfTI path, (3) optional output prefix (used for naming QC files). If arguments are missing, ask the user to provide them.

   Verify both files exist:

   ls "<original_path>" "<mask_path>"
   

   Stop and report any missing file. Do not proceed.

   Infer the tool name from context or the mask filename if possible (used for output file naming). Default to unknown-tool if not determinable.

2. Generate the QC PNG

   Load references/qc-generation.md from this skill directory for the full Python script. Write it to a temporary file qc_brain_extraction.py in the current directory (overwrite if it exists already).

   Create the output directory:

   mkdir -p qc/
   

   Before running the script, verify required Python dependencies are available:

   python3 -c "import nibabel, matplotlib"
   

   If this fails, tell the user to run pip install nibabel matplotlib and verify the import succeeds before proceeding.

   Capture the timestamp once and store it — this exact value must be reused verbatim in Steps 4 and 5 to ensure all three output files share the same timestamp:

   TIMESTAMP=$(date +%Y%m%d-%H%M%S)
   echo "$TIMESTAMP"
   

   Construct the output filename using $TIMESTAMP:

   qc/<output_prefix>_<tool>_${TIMESTAMP}_qc.png
   

   Run the script:

   python3 qc_brain_extraction.py "<original_path>" "<mask_path>" "<qc_png_path>"
   

   The script prints quantitative stats (brain volume cm³, voxel count, coverage fraction) to stdout — capture and retain these for the evaluation report.

   Verify the PNG was produced:

   ls "<qc_png_path>"
   

   If the file is absent or empty, stop and report that the QC script failed to produce output. Do not proceed to Step 3.

3. AI visual evaluation

   Load references/ai-evaluation-criteria.md from this skill directory to review the rubric definitions before evaluating.

   The PNG was verified to exist at the end of Step 2. Open and visually inspect it using the image-viewing capability available in the current agent/runtime.

   Examine the image carefully: check each plane (axial, coronal, sagittal), inspect the mask boundary (red overlay), and assess each criterion below. Do not infer from metadata alone — the visual read is required.

   Produce the following structured report, filling in all fields:

   ## AI Brain Extraction QC
   
   **Subject:** <output_prefix>
   **Tool:** <tool>
   **Timestamp:** <YYYYMMDD-HHMMSS>
   **Original image:** <original_path>
   **Brain mask:** <mask_path>
   
   ### Quantitative
   | Metric | Value | Reference range |
   |--------|-------|-----------------|
   | Brain volume | X cm³ | 900–1800 cm³ (adult T1w) |
   | Voxel count | N | — |
   | Coverage fraction | X% | 95–105% of expected |
   
   ### Visual Criteria
   | Criterion | Rating | Notes |
   |-----------|--------|-------|
   | No residual skull or scalp signal | Pass / Borderline / Fail | <observation> |
   | No excessive tissue loss at poles (frontal, temporal, occipital) | Pass / Borderline / Fail | <observation> |
   | Symmetric left-right and anterior-posterior coverage | Pass / Borderline / Fail | <observation> |
   | No internal holes or disconnected mask regions | Pass / Borderline / Fail | <observation> |
   | Boundary tightness (not over-dilated into dura/CSF) | Pass / Borderline / Fail | <observation> |
   
   ### Overall Verdict
   **<Pass / Borderline / Fail>** — Confidence: <High / Medium / Low>
   
   ### Notes
   <Free-text observations about image quality, unusual features, or artefacts>
   
   ### Recommended action
   <none | re-run with adjusted parameters: <suggest specific flag changes> | manual mask editing recommended>
   

4. Save AI evaluation

   Write the completed report to:

   qc/<output_prefix>_<tool>_<timestamp>_ai_eval.md
   

5. Write human verification form

   Load references/human-verification-form.md from this skill directory for the template. Write a blank (unfilled) instance to:

   qc/<output_prefix>_<tool>_<timestamp>_human_eval.md
   

   The criterion labels must be identical to those in the AI evaluation table so that agreement can be computed later.

   Tell the user:

   "Please open qc/<...>_qc.png to review the extraction visually, then fill in qc/<...>_human_eval.md with your assessment. The AI evaluation is at qc/<...>_ai_eval.md for comparison. Use identical ratings (Pass / Borderline / Fail) so agreement can be scored."

6. Summarise

   Report:

   • Overall AI verdict and confidence
   • Path to the QC PNG
   • Any criteria rated Borderline or Fail, with the specific recommendation
   • Reminder that the human form needs to be filled in

Constraints

• ALWAYS visually inspect the PNG before writing the evaluation — never fill in criteria from metadata or quantitative stats alone.
• ALWAYS save both _ai_eval.md and _human_eval.md before reporting complete.
• The criterion labels in the AI eval and the human form MUST be identical word- for-word — this is required for downstream agreement scoring.
• If brain volume is outside 900–1800 cm³ for an adult T1w scan, flag it explicitly in the Quantitative section notes even if the visual rating is Pass.
• Confidence should reflect actual uncertainty: use Low when image quality, contrast, or unusual anatomy makes visual criteria hard to assess.
• Do not delete qc_brain_extraction.py after running — it serves as a reproducible record of exactly which QC script was used.