B₁ and magnetization decay correction for hyperpolarized ¹²⁹ Xe lung imaging using sequential 2D spiral acquisitions

Area of Science:

• Medical Imaging
• Pulmonary Medicine
• Magnetic Resonance Imaging

Background:

• Inhomogeneous radiofrequency (RF) fields and magnetization decay cause signal variations in hyperpolarized 129Xe ventilation imaging.
• These variations can obscure important physiological details in lung imaging.

Purpose of the Study:

• To develop and validate a method for mitigating signal inhomogeneities in hyperpolarized 129Xe ventilation images.
• To utilize flip-angle maps derived from rapid 2D spiral imaging for correction.

Main Methods:

• Analytical expressions from Bloch equations were used to predict signal intensity and flip-angle uncertainties.
• 2D gradient-recalled echo and 2D spiral imaging sequences were employed for hyperpolarized 129Xe phantom and human subject imaging.
• Flip-angle maps were calculated from sequential images acquired during a single breath-hold to correct ventilation images.

Main Results:

• Simulations showed excellent agreement (R² = 0.99) between measured and applied flip angles.
• In vivo and phantom experiments demonstrated good agreement of measured flip angles with applied values (∼15% difference).
• Corrected images exhibited significantly reduced signal nonuniformity compared to uncorrected images.

Conclusions:

• Flip-angle maps derived from rapid (5-second) 2D spiral hyperpolarized 129Xe ventilation images effectively correct signal intensity variations.
• This method addresses RF-coil inhomogeneity and preserves physiologically relevant signal distributions.
• The technique offers a fast and efficient way to improve the quality of hyperpolarized 129Xe ventilation images.