Bias field correction in hyperpolarized ¹²⁹ Xe ventilation MRI using templates derived by RF-depolarization mapping

Area of Science:

• Medical Imaging
• Magnetic Resonance Imaging
• Pulmonary Function Testing

Background:

• Radiofrequency (RF) inhomogeneity is a significant challenge in quantitative 129-Xenon (Xe) ventilation MRI.
• Conventional bias field correction methods like N4ITK may inadvertently remove physiologically relevant information.

Purpose of the Study:

• To develop and evaluate RF-depolarization and flip-angle mapping techniques for correcting RF inhomogeneity in 129-Xe ventilation MRI.
• To compare these novel methods against conventional N4ITK correction for quantitative ventilation analysis.

Main Methods:

• RF-depolarization mapping was implemented using randomized 3D radial acquisitions in 51 subjects.
• A flip-angle map template approach was developed for broader applicability across acquisition strategies.
• Quantitative ventilation metrics (mean, coefficient of variation, gradient) were compared between corrected datasets.

Main Results:

• RF-depolarization and template-based methods accurately reflected expected RF inhomogeneity patterns.
• Novel methods retained the physiologically expected anterior-posterior ventilation gradient, unlike N4ITK.
• N4ITK correction erroneously eliminated the physiological anterior-posterior gradient.

Conclusions:

• Randomized 3D 129-Xe MRI ventilation acquisitions can be corrected for bias field using flip-angle mapping.
• The developed methods offer a more favorable alternative to N4ITK by correcting RF heterogeneity while preserving physiology.
• Flip-angle map templates can be created for coil-specific correction, independent of acquisition strategy.