Helium-3 MRI diffusion coefficient: correlation to morphometry in a model of mild emphysema

Area of Science:

• Pulmonary imaging
• Medical physics
• Respiratory medicine

Background:

• Hyperpolarized gas magnetic resonance imaging (MRI) offers novel image-derived pulmonary function parameters.
• The apparent diffusion coefficient (ADC) derived from these images reflects the size of lung's gas-compartmentalizing structures, such as alveolar spaces.

Purpose of the Study:

• To compare noninvasive ADC measurements with microscopic morphometric parameters in emphysema.
• To investigate the correlation between ADC and airspace size in a rat model of emphysema.

Main Methods:

• Acquisition of helium-3 gas density coronal ex vivo images and apparent diffusion maps in control and elastase-induced panacinar emphysema rat lungs.
• Utilizing total lung capacity as a reference for both imaging and lung fixation.
• Microscopic analysis using mean linear intercept and mean alveolar internal area for validation.

Main Results:

• A mild degree of emphysema was confirmed by mean linear intercept (134 ± 25 µm vs. 85 ± 14 µm in controls).
• Significantly different apparent diffusion coefficients were observed between emphysematous and control groups (0.18 ± 0.02 cm² s⁻¹ vs. 0.15 ± 0.01 cm² s⁻¹).
• Demonstrated a significant correlation between ADC and morphometric parameters in mild emphysema for the first time.

Conclusions:

• Noninvasive apparent diffusion coefficient measurements show promise for estimating absolute airspace size in the lungs.
• This technique could provide a noninvasive method for assessing lung structural changes in diseases like emphysema.