🧭 Workshop Week 4 Outline

1. Differential Tractography
   • Cross-sectional analysis
   • Longitudinal analysis
2. Correlational Tractography
   • Cross-sectional analysis / group comparison
   • Longitudinal analysis

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🧠 Session 1: Differential Tractography

Adds an additional termination criterion:
→ Tracking stops when the signal difference exceeds a defined threshold

🧪 Hands-On Exercises

📂 Example Dataset:

• [OpenNeuro (disease)][ds001378] SCA2 study

🧬 Longitudinal Analysis

• Compare follow-up vs. baseline for patients
• Compare follow-up vs. baseline for controls
• Compute false discovery rate:
  (Findings in controls) / (Findings in patients)

📊 Cross-Sectional Analysis

• Build a population average template
  • Download control subject’s qsdr.fz file: select matching → *control*ses-01*qsdr.fz
  • [Tractography (Batch)] → [Create Population Average]
• Compare patient vs. average and control vs. average
• Compute false discovery rate:
  (Findings in controls) / (Findings in patients)

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🧠 Session 2: Correlational Tractography

Identifies fiber tracts that correlate with a variable or condition
→ Based on Spearman correlation across subjects

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📂 Prepare the Database

Aggregate metrics (e.g., FA, QA) from: QSDR reconstructed files (*.qsdr.fz)

📌 Example Dataset: SCA2 study

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🧪 Analysis Types

📊 Cross-Sectional Analysis

• Correlate diffusion metrics with variables across subjects
• FDR v.s. tract length

🧬 Longitudinal Analysis

• Changes in patients using unfiltered changes
• Changes in patients versus healthy control using filtered changes

🧬 Post-hoc Analysis

• Segment tracts and compute associated values