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

Purpose To investigate short‐ and long‐time‐scale 3 He 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 cm 2 /s and 0.0237 ± 0.0055 cm 2 /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 3 He 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. © 2008 Wiley‐Liss, Inc.