Purpose: Thoracic insufficiency syndrome (TIS) affects ventilatory function due to spinal and thoracic deformities limiting lung space and diaphragmatic motion. Corrective orthopedic surgery can be used to help normalize skeletal anatomy, restoring lung space and diaphragmatic motion. This study employs free-breathing dynamic MRI (dMRI) and quantifies the 3D motion of each hemi-diaphragm surface in normal and TIS patients, and evaluates effects of surgical intervention.
Materials and methods: In a retrospective study of 149 pediatric patients with TIS and 190 healthy children, we constructed 4D images from free-breathing dMRI and manually delineated the diaphragm at end-expiration (EE) and end-inspiration (EI) time points. We automatically selected 25 points uniformly on each hemi-diaphragm surface, calculated their relative velocities between EE and EI, and derived mean velocities in 13 homologous regions for each hemi-diaphragm to provide measures of regional 3D hemi-diaphragm motion. T-testing was used to compare velocity changes before and after surgery, and to velocities in healthy controls.
Results: The posterior-central region of the right hemi-diaphragm exhibited the highest average velocity post-operatively. Posterior regions showed greater velocity changes after surgery in both right and left hemi-diaphragms. Surgical reduction of thoracic Cobb angle displayed a stronger correlation with changes in diaphragm velocity than reduction in lumbar Cobb angle. Following surgery, the anterior regions of the left hemi-diaphragm tended to approach a more normal state.
Conclusion: Quantification of regional motion of the 3D diaphragm surface in normal subjects and TIS patients via free-breathing dMRI is feasible. Derived measurements can be assessed in comparison to normal subjects to study TIS and the effects of surgery.