To compare lobar lung ventilation computed from expiratory and inspiratory computed tomographic (CT) data with direct measurements of ventilation at hyperpolarized helium 3 (³He) magnetic resonance (MR) imaging by using same-breath hydrogen 1 (¹H) MR imaging examinations to coregister the multimodality images.

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. ³He and ¹H 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 ³He MR imaging ventilation by using diffeomorphic image registration of ¹H MR imaging to CT, which enabled indirect registration of ³He MR imaging to CT. Statistical analysis was performed by using the Wilcoxon signed-rank test, Pearson correlation coefficient, and Bland-Altman analysis.

The mean ± standard deviation absolute difference between the CT and ³He 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 ³He 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.

The percentage of regional ventilation per lobe calculated at CT was comparable to a direct measurement of lung ventilation at hyperpolarized ³He MR imaging. This work provides evidence for the validity of the CT model, and same-breath ¹H MR imaging enables regional interpretation of ³He ventilation MR imaging on the underlying lung anatomy at thin-section CT.

^© RSNA, 2015