Medical physics 2017 02 16() doi 10.1002/mp.12160
Recent pulmonary imaging research has revealed that in patients with chronic obstructive pulmonary disease (COPD) and asthma, structural and functional abnormalities are spatially heterogeneous. This novel information may help optimize treatment in individual patients, monitor interventional efficacy and develop new treatments. Moreover, by automating the measurement of regional biomarkers for the 19 different anatomical lung segments, there is an opportunity to embed imaging biomarkers into clinically-acceptable clinical workflows and improve lung disease clinical care. Therefore, to exploit the regional structure-function information provided by thoracic imaging, and as a first step towards this goal, our objective was to develop a fully-automated registration pipeline for thoracic x-ray computed tomography (CT) and inhaled-gas functional magnetic resonance imaging (MRI) whole lung and segmental structure-function biomarkers.
Thirty-five patients including 15 severe, poorly-controlled asthmatics and 20 COPD patients (classified according to the Global Initiative for chronic Obstructive Lung Disease (GOLD) criteria) provided written informed consent to a study protocol approved by Health Canada and underwent pulmonary function tests, MRI and CT during a single 2-hour visit. Using this diverse patient dataset, we developed and evaluated a joint deformable registration approach to simultaneously co-register CT with both (1) H and (3) He MRI by enforcing the similarity of the deformation fields from the two individual registrations. We derived a simpler model that was equivalent to the original challenging optimization problem through variational analysis and the simpler model gave rise to an efficient numerical solver that was parallelized on a graphics processing unit. The co-registered CT-(3) He MRI and whole lung/segmental lung masks were used to generate whole lung and segmental (3) He MRI ventilation defect percent (VDP). To estimate fiducial localization reproducibility, a single observer manually identified 109 pairs of CT and (3) He MRI fiducials for 35 patient images on five separate occasions and determined the fiducial localization error (FLE). CT-(3) He MRI registration accuracy was evaluated using the target registration error (TRE). Whole lung VDP generated using the algorithm was compared with VDP generated using a previously validated semi-automated approach and computational efficiency was evaluated using run time.
In 35 patients including 15 with severe asthma and 20 with COPD, mean forced expiratory volume in 1 second (FEV1 ) was 63±24%pred and FEV1 /forced vital capacity (FVC) was 54±17%. FLE was 0.16mm and 0.34mm for (3) He MRI and CT, respectively. TRE was 4.5±2.0mm, 4.0±1.7mm, 4.8±2.3mm for asthma, COPD GOLD II and GOLD III groups, respectively, with a mean of 4.4±2.0mm for the entire dataset. TRE was significantly improved for joint CT-(1) H/(3) He MRI registration compared with CT-(1) H MRI rigid registration (p<0.0001). Whole lung VDP generated using the pipeline was not significantly different (p=0.37) compared to a semi-automated method with which it was strongly correlated (r=0.93, p<0.0001). The fully automated pipeline required 11±0.4 min to generate whole lung and segmental VDP. CONCLUSIONS
For a diverse group of patients with COPD and asthma, whole-lung and segmental VDP was measured using an automated lung image analysis pipeline which provides a way to incorporate lung functional biomarkers into clinical research and patient care. This article is protected by copyright. All rights reserved.