Feasibility and SNR Performance of Hyperpolarized ¹²⁹Xe Gas Exchange Imaging Using a Balanced SSFP Sequence

Area of Science:

• Magnetic Resonance Imaging
• Pulmonary Imaging
• Hyperpolarized Gas MRI

Background:

• Dissolved-phase ¹²⁹Xe MRI allows for detailed lung tissue characterization.
• Previous methods struggled with separating signals from red blood cells and cell membranes.
• Optimizing imaging sequences is crucial for improving SNR and diagnostic accuracy.

Purpose of the Study:

• To develop and validate a balanced steady-state free precession (bSSFP) sequence for ¹²⁹Xe dissolved-phase pulmonary MRI.
• To compare the SNR performance and imaging capabilities of the new bSSFP sequence against a conventional FLASH sequence.
• To assess the feasibility of using bSSFP for separating red blood cell and membrane signals.

Main Methods:

• Developed a dual-echo bSSFP sequence for hyperpolarized ¹²⁹Xe MRI.
• Acquired data from 12 healthy volunteers using both bSSFP and FLASH sequences.
• Quantified SNR using pseudo-multiple replica method and performed chemical shift separation in k-space.

Main Results:

• The bSSFP sequence demonstrated significantly greater normalized SNR compared to FLASH at the same flip angle.
• The effective number of signal averages was significantly higher with bSSFP, improving SNR efficiency in signal decomposition.
• Approximating echo time as constant in k-space analysis introduced bias in RBC-M ratios but reduced noise amplification.

Conclusions:

• Dual-echo bSSFP is a feasible technique for hyperpolarized ¹²⁹Xe dissolved-phase lung imaging.
• The bSSFP sequence offers superior SNR efficiency for signal decomposition compared to FLASH.
• Future research should focus on applying this advanced technique to patients with lung diseases.