isoPhasor: a generic and precise marker visualization, localization, and quantification method based on phase saddles...

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biomedical Engineering
• Medical Physics

Background:

• Accurate localization and characterization of susceptibility markers are crucial in MRI.
• Existing methods often lack compatibility with diverse pulse sequences and acceleration techniques.

Purpose of the Study:

• To develop a generic approach for accurate localization and characterization of susceptibility markers in MRI.
• The method aims for compatibility with common pulse sequences, sampling trajectories, and acceleration methods.

Main Methods:

• Utilized the dipolar phase evolution of susceptibility markers, which creates three phase saddles in k-space.
• Developed a marker detection algorithm based on focusing signal from these saddles for positive contrast.
• Validated the method numerically and experimentally across various spherical susceptibility marker sizes and magnetic susceptibilities.

Main Results:

• Achieved an average localization error below one-third of the voxel size.
• Demonstrated an average magnetic strength quantification error of 7%.
• Successfully validated across diverse conditions including gradient echo, spin echo, free induction decay, Cartesian, radial, echo planar imaging (EPI), and turbo spin echo (TSE) sequences.

Conclusions:

• Spherical markers can be reliably identified using their characteristic phase saddles.
• The developed method enables clear visualization, precise localization, and accurate quantification of magnetic marker strength.
• The approach is broadly applicable to clinically relevant MRI pulse sequences and sampling strategies.