Quantification of changes in regional diaphragmatic motion and shape due to surgery via free-breathing dynamic MRI in pediatric patients with thoracic insufficiency syndrome

Purpose: This study investigates Thoracic Insufficiency Syndrome (TIS) in pediatric patients, a condition impacting respiratory function due to spinal and thoracic deformities. The research focuses on the use of the Vertical Expandable Prosthetic Titanium Rib (VEPTR) surgery to address deformities hindering normal development and to promote lung growth. A unique non-invasive approach utilizing free-breathing dynamic magnetic resonance imaging (dMRI) is employed to analyze the 3D motion and shape of each hemi-diaphragm (HD) surface. Method: In this study of 49 TIS patients who underwent VEPTR surgery, free-breathing dMRI was used before and after surgery. After 4D image construction of diaphragm, we manually delineated the HDs on sagittal slice images at end-expiration and end-inspiration time points. We then constructed the 3D surface of the HDs, automatically selected 25 points on each HD surface, and estimated velocities and both sagittal curvature and coronal curvature at each point. Then, we identified 13 homologous regions for each HD surface and categorized subjects based on changes in Cobb angle to compare HD velocities and curvatures before and after surgery. Results: The study group consisted of 27 males and 22 females with mean age of 3.51 +/- 3.49 years before surgery and 5.9 +/- 3.63 years after surgery. Right HD regions exhibited statistically significantly higher velocities compared to homologous regions in the left HD, and posterior regions showed higher velocity than other regions in both HDs. The most statistically significant differences in diaphragm shape were observed in the lateral regions, with particular emphasis on the coronal curvatures. Conclusion: Through analysis of pre- and post-surgical data, we observed significant improvement in diaphragm motion following VEPTR surgery, despite minimal changes in diaphragm shape.