Assessment of the lung microstructure in patients with asthma using hyperpolarized 3He diffusion MRI at two time scales: Comparison with healthy subjects and patients with COPD

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Abstract
Purpose To investigate short‐ and long‐time‐scale 3He diffusion in asthma. Materials and Methods A hybrid MRI sequence was developed to obtain coregistered short‐ and long‐time‐scale apparent diffusion coefficient (ADC) maps during a single breath‐hold. The study groups were: asthma (n = 14); healthy (n = 14); chronic obstructive pulmonary disease (COPD) (n = 9). Correlations were made between mean‐ADC and %ADC‐abn (abnormal) (%pixels with ADC > mean +2 SD of healthy) at both time scales and spirometry. Sensitivities were determined using receiver operating characteristic (ROC) analysis. Results For asthmatics, the short‐ and long‐time‐scale group‐mean ADCs were 0.254 ± 0.032 cm2/s and 0.0237 ± 0.0055 cm2/s, respectively, representing a 9% and 27% (P = 0.038 and P = 0.005) increase compared to the healthy group. The group‐mean %ADC‐abn were 6.4% ± 3.7% and 17.5% ± 14.2%, representing a 107% and 272% (P = 0.004 and P = 0.006) increase. For COPD much greater elevations were observed. %ADC‐abn provided better discrimination than mean‐ADC between asthmatic and healthy subjects. In asthmatics ADC did not correlate with spirometry. Conclusion With long‐time scale 3He diffusion magnetic resonance imaging (MRI) changes in lung microstructure were detected in asthma that more conspicuous regionally than at the short time scale. The hybrid diffusion method is a novel means of identifying small airway disease. J. Magn. Reson. Imaging 2008;28:80–88.

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