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A comparison of phase encoding ordering schemes in T2-weighted GRASE imaging | JoVE Visualize

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A comparison of phase encoding ordering schemes in T2-weighted GRASE imaging

G Johnson¹, D A Feinberg, V Venkataraman

¹Department of Radiology, New York University Medical Center, New York 10016, USA.

Magnetic Resonance in Medicine|September 1, 1996

View abstract on PubMed

Summary

Optimizing Gradient and Spin Echo (GRASE) imaging involves changing phase encoding orders to reduce ghosting artifacts. The k-banded (kb) GRASE ordering generally shows the lowest artifact levels, improving image quality.

Area of Science:

Magnetic Resonance Imaging (MRI)
Medical Imaging Physics

Background:

Gradient and Spin Echo (GRASE) imaging combines gradient and RF refocusing, leading to phase modulations.
Linear phase encoding orders in GRASE sequences are susceptible to severe ghosting artifacts due to these modulations.

Purpose of the Study:

To compare different phase encoding orders for T2-weighted GRASE sequences.
To evaluate artifact levels and spatial resolution across various GRASE implementations.

Main Methods:

Comparison of linear, partially randomized, standard GRASE, and k-banded (kb) GRASE ordering.
Utilized computer simulations for resolution and artifact analysis.
Presented phantom and volunteer images for validation.

Main Results:

Linear order is highly sensitive to ghosting from chemical shift, susceptibility, and field inhomogeneities.
Standard GRASE order is robust against these but vulnerable to short T2 signal artifacts.
kb-GRASE offers a balance, generally exhibiting the lowest artifact levels.
Partially randomized order results in diffuse artifacts.

Conclusions:

Phase encoding order significantly impacts artifact levels in GRASE imaging.
kb-GRASE ordering provides a favorable trade-off, minimizing artifacts while maintaining resolution and contrast.
The choice of phase encoding order is crucial for optimizing GRASE image quality.

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A Comparison Of Phase Encoding Ordering Schemes In T2-weighted Grase Imaging