Mapping and correcting hyperpolarized magnetization decay with radial keyhole imaging.

Area of Science:

• Biomedical Imaging
• Magnetic Resonance Imaging (MRI)

Background:

• Hyperpolarized (HP) media offer advanced biomedical imaging capabilities beyond conventional MRI contrast agents.
• Quantifying HP images is difficult due to spatially varying signal decay caused by relaxation and radio-frequency pulsing during acquisition.

Purpose of the Study:

• To develop a method for generating voxel-by-voxel maps of regional HP magnetization decay.
• To address the challenge of quantifying HP images by correcting for signal decay.

Main Methods:

• Utilized center-out k-space sampling combined with postacquisition keyhole reconstruction.
• Reconstructed datasets from digital phantoms, HP ¹²⁹ Xe phantoms, and in vivo human HP ¹²⁹ Xe imaging (N=6).
• Generated temporally resolved images to create regional magnetization decay maps using an analytical model.

Main Results:

• Keyhole-derived decay terms strongly agreed with simulated and phantom imaging decay values (R² > 0.97).
• In vivo regional decay maps showed spatial heterogeneity consistent with physiological variations and agreed with global decay.
• Demonstrated the ability of these maps to correct for variable signal decay across image volumes.

Conclusions:

• Center-out trajectories and keyhole reconstruction effectively map regional HP signal decay.
• This technique enables quantitative correction of HP images, enhancing accuracy.
• The method is generalizable to various hyperpolarized agents beyond the demonstrated HP ¹²⁹ Xe.