Based on a stimulated-echo technique, a method to construct an apparent diffusion coefficient (ADC) map of hyperpolarized (3)He in a long-range diffusion scale is presented with a phase-cycle alternative to remove all unwanted echoes. The approach was successfully applied to determine in vivo diffusion constants in rat lungs. The ADC values in healthy rats show a good agreement with reported values for diffusion times of approximately. These long diffusivity measurements may be sensitive to detect emphysema progression or tissue remodeling and thus have enormous potential for the diagnosis and tracking of disease progression and for drug evaluation.