Comparison of hyperpolarized 3He MRI with Xe-enhanced computed tomography imaging for ventilation mapping of rat lung

Lung ventilation was mapped in five healthy Brown Norway rats (210-377 g) using both hyperpolarized He-3 MRI and Xe-enhanced computed tomography (Xe-CT) under similar ventilator conditions. Whole-lung measurements of ventilation r obtained with He-3 MRI were not significantly different from those obtained from Xe-CT (p = 0.1875 by Wilcoxon matched pairs test). The ventilation parameter r is defined as the fraction of refreshed gas per unit volume per breath. Regional ventilation was also measured in four regions of the lung using both methods. A two-tailed paired t-test was performed for each region, yielding p > 0.05 for all but the upper portion of the right lung. The distribution of regional ventilation was evaluated by calculating ventilation gradients in the superior/inferior (S/I) direction. The average S/I gradient obtained using the He-3 MRI method was found to be 0.17 +/- 0.04 cm(-1), whereas the average S/I gradient obtained using the Xe-CT method was found to be 0.016 +/- 0.005 cm(-1). In general, S/I ventilation gradients obtained from both methods were significantly different from each other (p = 0.0019 by two-tailed paired t-test). These regional differences in ventilation measurements may be caused by the manner in which the gas contrast agents distribute physiologically and/or by the imaging modality. Copyright (C) 2011 John Wiley & Sons, Ltd.