Effects of diffusion time on short-range hyperpolarized (3)He diffusivity measurements in emphysema

Area of Science:

• Pulmonary Medicine
• Radiology
• Medical Imaging Physics

Background:

• Emphysema is a chronic lung disease characterized by alveolar destruction.
• Hyperpolarized helium-3 (³He) magnetic resonance imaging (MRI) is a promising technique for assessing lung structure and function.
• Apparent diffusion coefficient (ADC) measurements in ³He MRI can quantify diffusion characteristics within the lungs.

Purpose of the Study:

• To investigate the influence of varying diffusion times on short-range ³He MRI diffusion measurements.
• To evaluate this effect across a spectrum of emphysema severities.

Main Methods:

• ³He diffusion MRI was performed on 19 human lung specimens with diverse emphysema levels.
• Three diffusion times (1.6, 5.0, and 10.0 msec) were used at a constant b value.
• Emphysema severity was assessed using mean ADC and an ADC index, with quantitative histology (mean linear intercept) obtained for comparison.

Main Results:

• Mean ADC values decreased significantly with increasing diffusion time (1.6 msec: 0.46 cm²/sec, 5.0 msec: 0.40 cm²/sec, 10.0 msec: 0.37 cm²/sec; P < 0.0001).
• The observed decrease in ADC with longer diffusion times was not correlated with emphysema severity.
• Strong correlations were found between ADC values (at all tested diffusion times) and quantitative histology (mean linear intercept), indicating ADC's robustness in reflecting emphysema.

Conclusions:

• The effect of diffusion time on ADC in ³He MRI is independent of emphysema severity.
• ADC measurements in ³He MRI are a reliable indicator of emphysema, correlating well with histological findings.
• These findings are crucial for standardizing diffusion time parameters in ³He MRI for accurate emphysema assessment.