Correction of gradient echo images for first and second order macroscopic signal dephasing using phase derivative...

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Medical Physics
• Image Processing

Background:

• Gradient echo (GRE) imaging is susceptible to signal dephasing caused by magnetic field inhomogeneities.
• Existing methods to correct these phase variations often require longer acquisition times, additional scans, or are limited in applicability.
• These limitations hinder the diagnostic utility of GRE techniques in the presence of field perturbations from shimming or biological tissues.

Purpose of the Study:

• To develop a universally applicable post-processing technique for evaluating and compensating signal alterations due to macroscopic phase incoherences in GRE imaging.
• To address the drawbacks of current correction methods by offering a faster and more accurate solution.

Main Methods:

• A novel post-processing technique utilizing the Fourier derivative theorem on complex MRI data.
• Determines phase derivatives directly from complex signal data without requiring phase unwrapping.
• Validated on phantom experiments with controlled magnetic field disturbances and in vivo human brain imaging.

Main Results:

• The proposed method effectively evaluates and compensates for first and second-order macroscopic phase incoherences.
• Phase derivatives are obtained without compromising spatial resolution.
• Demonstrated successful application in both single- and multi-echo GRE acquisitions, including human brain data.

Conclusions:

• The presented post-processing technique offers a generally applicable and efficient solution for correcting phase variations in GRE MRI.
• It overcomes limitations of existing methods by avoiding additional acquisitions and preserving image resolution.
• First-order correction is generally sufficient, with higher-order corrections proving beneficial near significant magnetic field gradients.