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Acinar determinants of the apparent diffusion coefficient for helium-3
Sylvia Verbanck1, Manuel Paiva
1Respiratory Division, University Hospital UZ Brussel, Vrije Universiteit Brussel, Brussels, Belgium. sylvia.verbanck@uzbrussel.be
Journal of Applied Physiology (Bethesda, Md. : 1985)
|February 20, 2010
Summary
Numerical simulations show that intra-acinar structure significantly impacts gas diffusion measurements, mimicking apparent diffusion coefficient (ADC) behavior in helium-3 MRI. Accounting for this branching is crucial for accurate ADC simulations.
Area of Science:
- Pulmonary physiology
- Medical imaging physics
- Computational biology
Background:
- Apparent diffusion coefficient (ADC) from helium-3 MRI reflects diffusion impairment.
- Intra-acinar and interacinar structures influence ADC.
- Emphysema alters intra-acinar collateral channels.
Purpose of the Study:
- Simulate intra-acinar gas mixing and effective diffusion.
- Evaluate the impact of intra-acinar branching on diffusion.
- Assess the influence of collateral channels on diffusion.
Main Methods:
- Developed a multiple-branch-point model of the human acinus.
- Computed instantaneous effective diffusion over time (up to 5s).
- Simulated diffusive attenuation using coupled acinar models (up to 50s).
Main Results:
- Intra-acinar collateral channels increased effective diffusion by 40-142% over 0.2-5s.
- Simulated diffusion showed biphasic time dependence, sensitive to structural changes.
- Neglecting intra-acinar branching leads to significant errors in simulated ADC.
Conclusions:
- Simulated effective diffusion mimics experimental ADC behavior.
- Intra-acinar diffusion significantly affects gas transport dynamics.
- Accurate ADC simulation requires incorporating intra-acinar structural complexity.
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