Hyperpolarised 3He MRI and 81mKr SPECT in chronic obstructive pulmonary disease

Purpose. During recent years, magnetic resonance imaging (MRI) using hyperpolarised (HP) He-3 gas has emerged as a promising new method for the imaging of lung ventilation. However, systematic comparisons with nuclear medicine techniques have not yet been performed. The aim of this study was to compare ventilation imaging methods in 26 patients with chronic obstructive pulmonary disease (COPD) and nine lung healthy volunteers. Methods: HP He-3 MRI, Kr-81m single-photon emission computed tomography (SPECT), high-resolution computed tomography (HRCT) and pulmonary function tests were performed. The three scans were scored visually as percentage of non-ventilated/diseased lung, and a computer-based objective measure of the ventilated volume in HP He-3 MRI and Kr-81m SPECT and an emphysema index in HRCT were calculated. Results: We found a good correlation between HP He-3 MRI and Kr-81m SPECT for both visual defect score (r=0.80, p < 0.0001) and objective estimate of ventilation (r=0.45, p=0.0157). In addition, both scans were well correlated with reference methods for the diagnosis of emphysema (pulmonary function test and HRCT). The defect scores were largest on Kr-81m SPECT (the score on HP He-3 MRI was one-third less than that on Kr-81m SPECT), but the difference was reduced after normalisation for different breathing depths (HP He-3 MRI at total lung capacity; Kr-81m SPECT at tidal breathing at functional residual capacity). Conclusion: HP He-3 MRI provides detailed ventilation distribution images and defect scores are comparable on HP He-3 MRI and Kr-81m SPECT. Additionally, new insights into the regional pulmonary microstructure via the apparent diffusion coefficient measurements are provided by HP He-3 MRI. HP He-3 MRI is a promising new diagnostic tool for the assessment of ventilation distribution.