Regional ventilation changes in severe asthma after bronchial thermoplasty with ³He MR imaging and CT

Materials and With approval of the local institutional review board, in-Methods: formed consent, and an Investigational New Drug Exemption, six healthy volunteers and 10 patients with severe asthma were imaged in compliance with HIPAA regulations by using both multidetector CT and ³He MR imaging. Individual bronchopulmonary segments were labeled voxel by voxel from the CT images and then registered to the ³He MR images by using custom software. The ³He signal intensity was then analyzed by evaluating the volume-weighted fraction of total-lung signal intensity present in each segment (segmental ventilation percentage [SVP]) and by identifying the whole-lung defect percentage and the segmental defect percentage. Of the 10 patients with asthma, seven received treatment with bronchial ther-moplasty and were imaged with ³He MR a second time. Changes in segmental defect percentages and whole-lung defect percentages are presented.

Purpose: To quantify regional lung ventilation in healthy volunteers and patients with severe asthma (both before and after thermoplasty) by using a combination of helium 3 (³He) magnetic resonance (MR) imaging and computed tomography (CT), with the intention of developing more effective image-guided treatments for obstructive lung diseases.

Results: Ventilation measures for healthy volunteers yielded smaller segment-to-segment variation (mean SVP, 100% ± 18 [standard deviation]) than did the measures for patients with severe asthma (mean SVP, 97% ± 23). Patients with asthma also demonstrated larger segmental defect percentages (median, 13.5%; interquartile range, 8.9%-17.8%) than healthy volunteers (median, 6%; interquartile range, 5.6%-6.3%). These quantitative results confirm what is visually observed on the ³He images. A Spearman correlation of r = 20.82 was found between the change in whole-lung defect percentage and the number of days between final treatment and second ³He imaging.

Conclusion: Regional quantification of lung ventilation is indeed feasible and may be a useful technique for image-guided treatment of obstructive lung diseases, such as bronchial ther-moplasty for severe asthma. In these patients, ventilation defects decreased as a function of time after treatment.