🧭 Workshop Week 4 Outline

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

---

🧠 Session 1: Differential Tractography

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

📂 Example Dataset:

• SCA2 study: QSDR .fz files

---

🧪 Hands-On Exercises

🔧 Create a Population-Average Template

📊 Cross-Sectional Analysis

• Build a population average template
• Compare patient vs. average and control vs. average
• Compute false discovery rate:
  (Findings in controls) / (Findings in patients)

🧬 Longitudinal Analysis

• Compare follow-up vs. baseline for patients and controls
• Compute false discovery rate similarly

---

🧠 Session 2: Correlational Tractography

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

---

📂 Prepare the Database

Aggregate metrics (e.g., FA, QA) from:

1. QSDR reconstructed files (*.qsdr.fz)
2. MNI-space NIfTI files (*.nii.gz)

📌 Example Dataset: SCA2 study

---

🧪 Analysis Types

📊 Cross-Sectional Analysis

• Correlate diffusion metrics with variables across subjects
• Post-tracking analysis

🧬 Longitudinal Analysis

• Correlate within-subject changes across timepoints