Pulmonary ventilation visualized using hyperpolarized helium-3 and xenon-129 magnetic resonance imaging: differences in COPD and relationship to emphysema

Kirby M, Svenningsen S, Kanhere N, Owrangi A, Wheatley A, Coxson HO, Santyr GE, Paterson NA, McCormack DG, Parraga G. Pulmonary ventilation visualized using hyperpolarized helium-3 and xenon-129 magnetic resonance imaging: differences in COPD and relationship to emphysema. J Appl Physiol 114: 707-715, 2013. First published December 13, 2012; doi: 10.1152/japplphysiol.01206.2012.-In subjects with chronic obstructive pulmonary disease (COPD), hyperpolarized xenon-129 (Xe-129) magnetic resonance imaging (MRI) reveals significantly greater ventilation defects than hyperpolarized helium-3 (He-3) MRI. The physiological and/or morphological determinants of ventilation defects and the differences observed between hyperpolarized He-3 and Xe-129 MRI are not yet understood. Here we aimed to determine the structural basis for the differences in ventilation observed between He-3 and Xe-129 MRI in subjects with COPD using apparent diffusion coefficients (ADC) and computed tomography (CT). Ten COPD ex-smokers provided written, informed consent and underwent MRI, CT, spirometry, and plethysmography. He-3 and Xe-129 MRI ventilation volume was generated using semiautomated segmentation, and ADC maps were registered to generate ADC values for lung regions of interest ventilated by both gases (ADC(HX)) and by He-3 gas only (ADC(HO)). CT wall area percentage and the lowest 15th percentile point of the CT lung density histogram (HU15%) were also evaluated. For lung regions accessed by 3He gas only, mean He-3 ADC(HO) was significantly greater than for regions accessed by both gases (ADC(HO) = 0.503 +/- 0.119 cm(2)/s, ADC(HX) = 0.470 +/- 0.125 cm(2)/s, P < 0.0001). The difference between He-3 and Xe-129 ventilation volume was significantly correlated with CT HU15% (r = -65, P = 0.04) and He-3 ADC(HO) (r = 0.70, P = 0.02), but not CT wall area percentage (r = -0.34, P = 0.33). In conclusion, in this small study in COPD subjects, we observed significantly decreased Xe-129 MRI ventilation compared with He-3 MRI, and these regions of decreased Xe-129 ventilation were spatially and significantly correlated with regions of increased pulmonary emphysema, but not airway wall thickness.