Examining lung microstructure using ¹⁹ F MR diffusion imaging in COPD patients

Area of Science:

• Pulmonary Medicine
• Medical Imaging
• Biophysics

Background:

• Assessing lung microstructure is crucial for understanding pulmonary diseases.
• Current methods like hyperpolarized ¹²⁹Xe MRI and lung function tests provide valuable but distinct insights.
• A novel, repeatable imaging technique for lung microstructure could enhance diagnostic capabilities.

Purpose of the Study:

• To evaluate the time-dependent diffusion of inhaled Fluorine-19 (¹⁹F) gas in human lungs.
• To determine the pulmonary surface-to-volume ratio (S/V) using ¹⁹F diffusion MRI.
• To compare these findings with hyperpolarized ¹²⁹Xe diffusion MRI and standard lung function tests in healthy volunteers and COPD patients.

Main Methods:

• Utilized multiple gradient-echo sequences with trapezoidal gradient pulses to measure ¹⁹F gas diffusion in the short-time regime.
• Calculated pulmonary S/V using a first-order approximation of time-dependent diffusion.
• Assessed repeatability of measurements and correlation with ¹²⁹Xe MRI and spirometry in 20 healthy volunteers and 22 COPD patients.

Main Results:

• ¹⁹F diffusion MRI revealed a significantly decreased S/V in COPD patients (median 126 cm⁻¹) compared to healthy volunteers (median 164 cm⁻¹; p < 0.0001).
• Measurements demonstrated good repeatability within 7 days for both healthy (CV 4.3%) and COPD (CV 6.7%) subjects.
• Strong linear correlations were observed between ¹⁹F-derived S/V and both ¹²⁹Xe-derived S/V (r=0.85; p=0.001) and forced expiratory volume in 1 second (r=0.68; p < 0.0001).

Conclusions:

• Time-dependent diffusion measurement of inhaled ¹⁹F gas is a feasible and repeatable method for examining lung microstructure.
• This ¹⁹F diffusion MRI technique provides quantitative insights into lung S/V.
• The findings correlate well with established diagnostic measurements, suggesting potential for clinical application in pulmonary disease assessment.