Controlling diffusion of 3He by buffer gases: a structural contrast agent in lung MRI

Area of Science:

• Physics
• Medical Imaging
• Biomedical Engineering

Background:

• Laser-polarized Helium-3 (He-3) is a key contrast agent in MRI.
• Gas diffusion significantly impacts image quality and resolution in MRI.
• Controlling gas diffusion is crucial for advanced imaging applications.

Purpose of the Study:

• To investigate the effect of inert buffer gases on the diffusion coefficient of laser-polarized He-3.
• To assess the impact of altered diffusion on MRI image contrast and resolution.
• To explore the potential for controlling gas diffusion in MRI for improved imaging.

Main Methods:

• Altering the diffusion coefficient of He-3 by admixing buffer gases (He-4, N2, SF6).
• Analyzing the influence of pulse sequences and diffusion coefficients on gas MRI appearance.
• Comparing theoretical models with experimental data using gradient echoes.
• Utilizing diffusion-weighted MRI on a pig's lung with gas mixtures.

Main Results:

• Demonstrated excellent agreement between theoretical predictions and experimental observations.
• Validated a method for achieving maximum signal gain, leading to improved image resolution.
• Showcased how gas type and concentration establish a structural threshold for apparent diffusion coefficient (ADC).

Conclusions:

• Proposed a novel method to control gas diffusion in MRI using inert buffer gases.
• Buffer gas molecular mass and concentration are key parameters for structural contrast.
• Enables tunable imaging of lung structures, from individual alveoli to entire airway systems, with minimal diffusion-related signal loss.