Functional Analysis in Single-Lung Transplant Recipients: A Comparative Study of High-Resolution CT, ^sup 3^He-MRI, and Pulmonary Function Tests

OBJECTIVE: To develop and evaluate a postprocessing tool to quantify ventilated split-lung volumes on the basis of (3)He-MRI and to apply it in patients after single-lung transplantation (SLTX). High-resolution CT (HRCT) was employed as a reference modality providing split air-filled lung volumes. Lung volumes derived from pulmonary function test results served as clinical parameters and were used as the "gold standard." MATERIAL AND METHODS: Eight patients (mean age, 54 years) with emphysema and six patients (mean age, 58 years) with idiopathic pulmonary fibrosis. All patients were evaluated following SLTX. HRCT was performed during inspiration (slice thickness, 1 mm; increment, 10 mm). For correlation with (3)He-MRI, HRCT images were reconstructed in coronal orientation to match the same anatomic levels. Aerated lung was determined by threshold-based segmentation of CT. (3)He-MRI was performed on a 1.5-T scanner using a two-dimensional, fast low-angle shot sequence in coronal orientation covering the whole lung after inhalation of a 300-mL bolus of hyperpolarized (3)He gas followed by normal room air for the rest of the tidal volume. Lung segmentation on (3)He-MRI was done using different thresholds. RESULTS: In emphysematous patients, (3)He-MRI showed excellent correlation (r = 0.9) with vital capacity, while CT correlated (r = 0.8) with total lung capacity. (3)He-MRI correlated well with CT (r > 0.8) for grafts and native fibrotic lungs. In emphysematous lungs, MRI showed a good correlation (r = 0.7) with the nonemphysematous lung volume from CT. Increasing thresholds in (3)He-MRI reveal differences between aerated and ventilated lung areas with a different distribution in emphysema and fibrosis. CONCLUSIONS: (3)He-MRI is superior to CT in emphysema to demonstrate ventilated lung areas that participate in gas exchange. In fibrosis, (3)He-MRI and CT have a similar impact. The decrease pattern and the intraindividual ratio between ventilation of native and transplanted lungs will have to be investigated as a new surrogate for the ventilatory follow-up in patients undergoing SLTX.