Department Of Medical Imaging

17/12/2025

12/12/2025

🧲 Thursday's MRI Discussion 🧲
🤔 What is Partial Fourier in SIEMENS MRI?

📝Phase Partial Fourier in SIEMENS MRI (also called Partial Phase, Half Fourier, or Asymmetric Sampling) is a technique where the scanner acquires less than 100% of phase-encoding lines in k-space and mathematically reconstructs the missing part.
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✅ Simple Definition

Phase Partial Fourier = acquiring 60–80% of phase-encoding data and estimating the rest using symmetry of k-space.

It reduces scan time but may slightly reduce SNR and increase image noise if too much is skipped.
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🔍 How it works

k-space is symmetric about its center.

SIEMENS collects only the low-frequency + some high-frequency lines.

The missing high-frequency phase lines are reconstructed using:

Homodyne detection

POCS (Projection Onto Convex Sets)
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📌 Where Phase Partial Fourier is used

Used in almost all sequences:

T1, T2 spin echo

Fast GRE sequences

3D sequences

DWI/EPI
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🎯 Benefits

Benefit Explanation

Shorter scan time Fewer phase lines → faster TR loops
Less motion artifact Shorter time reduces patient movement
Useful for thin slices & 3D scans Improves feasibility
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⚠️ Disadvantages

Issue Why it happens

Slight SNR loss Less data acquired
Phase artifacts If too much reconstruction needed
Ghosting In EPI if PF too high
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💡 SIEMENS Settings You’ll See

In Siemens protocol, Phase PF appears as:

Partial Fourier (Phase): 6/8, 7/8, 5/8

Sometimes written as PF = 0.75 or 0.625

Common setting:
👉 6/8 (75%)
giving best balance of speed and image quality.
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📘 Practical Example

If phase matrix = 320
Partial Fourier = 6/8

Scanner actually acquires: 320 × 0.75 = 240 lines

Remaining 80 lines = reconstructed.
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🧠 Quick Summary (Easy to Remember)

Phase Partial Fourier = 60–80% phase data.

Purpose = Faster scan + less motion.

Cost = Slight SNR drop + possible artifacts.
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12/12/2025

10/12/2025

10/12/2025

Sensitivity and specificity of blood-fluid levels for oral anticoagulant-associated intracerebral haemorrhage.

https://www.nature.com/articles/s41598-020-72504-7

10/12/2025