Assessment of Regional 3D Hemi-diaphragmatic Motion Via Free-breathing Dynamic MRI in Pediatric Thoracic...

Thoracic insufficiency syndrome (TIS) affects ventilatory function due to spinal and thoracic deformities limiting lung space and diaphragm motion. Corrective surgery helps normalize skeletal anatomy, restoring diaphragm 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 the effects of surgical intervention.

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 both right (RHD) and left hemi-diaphragm (LHD) surface, estimated 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. Velocity changes after surgery (mean follow-up: 2.4±1.8 years) were assessed compared to before surgery, and compared with velocities in healthy controls.

After surgery, the mean diaphragm velocity increased by 311.9% in 71.4% of subjects in the RHD (P=0.013), and by 93.9% in 61.2% of subjects in the LHD (P=0.078). The posterior-central region of the RHD exhibited the highest average velocity post-operatively. Posterior regions showed greater velocity changes after surgery in both RHD and LHD. Surgical correction of thoracic spinal curve displayed stronger correlation with changes in diaphragm velocity than correction in lumbar spinal curve. Following surgery, the anterior regions of the LHD tended to approach a more normal state.

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.