Comparison of CT-based Lobar Ventilation with 3He MR Imaging Ventilation Measurements

Purpose: To compare lobar lung ventilation computed from expiratory and inspiratory computed tomographic (CT) data with direct measurements of ventilation at hyperpolarized helium 3 (He-3) magnetic resonance (MR) imaging by using same-breath hydrogen 1 (H-1) MR imaging examinations to coregister the multimodality images. Materials and Methods: The study was approved by the national research ethics committee, and written patient consent was obtained. Thirty patients with asthma underwent breath-hold CT at total lung capacity and functional residual capacity. He-3 and H-1 MR images were acquired during the same breath hold at a lung volume of functional residual capacity plus 1 L. Lobar segmentations delineated by major fissures on both CT scans were used to calculate the percentage of ventilation per lobe from the change in inspiratory and expiratory lobar volumes. CT-based ventilation was compared with He-3 MR imaging ventilation by using diffeomorphic image registration of H-1 MR imaging to CT, which enabled indirect registration of He-3 MR imaging to CT. Statistical analysis was performed by using the Wilcoxon signed-rank test, Pearson correlation coefficient, and Bland-Altman analysis. Results: The mean 6 standard deviation absolute difference between the CT and He-3 MR imaging percentage of ventilation volume in all lobes was 4.0% (right upper and right middle lobes, 5.4% +/- 3.3; right lower lobe, 3.7% +/- 3.9; left upper lobe, 2.8% +/- 2.7; left lower lobe, 3.9% +/- 2.6; Wilcoxon signed-rank test, P < .05). The Pearson correlation coefficient between the two techniques in all lobes was 0.65 (P < .001). Greater percentage of ventilation was seen in the upper lobes with He-3 MR imaging and in the lower lobes with CT. This was confirmed with Bland-Altman analysis, with 95% limits of agreement for right upper and middle lobes, -2.4, 12.7; right lower lobe, -11.7, 4.6; left upper lobe, -4.9, 8.7; and left lower lobe, -9.8, 2.8. Conclusion: The percentage of regional ventilation per lobe calculated at CT was comparable to a direct measurement of lung ventilation at hyperpolarized He-3 MR imaging. This work provides evidence for the validity of the CT model, and same-breath H-1 MR imaging enables regional interpretation of He-3 ventilation MR imaging on the underlying lung anatomy at thin-section CT. (C) RSNA, 2015