Diffusion Tensor Imaging (DTI) of the Pediatric Spinal Cord

Abstract

Diffusion Tensor Imaging (DTI) is a technique for noninvasively examining diffusion of water molecules in each voxel of an image in directions parallel and transverse to the plane of neuronal axons. The quantitative characteristic of DTI allows for the characterization of physical properties of tissues. The unique characteristic architecture of the spinal cord allows DTI to characterize cord white matter, separate white from gray matter and assess structural damage of the cord. While studies on diffusion imaging of the spinal cord in adults, as well as in animal models have been reported, a comprehensive study of the pediatric spinal cord examining the accuracy and reproducibility of DTI measures has not yet been reported. The purpose of this study is to (a) evaluate the accuracy of cervical spinal cord DTI in children using a newly developed inner-Field-of-View (iFoV) sequence with spatially selective 2D RF excitations, (b) investigate reproducibility of the DTI measures and (c) examine correlation of DTI with standardized clinical exams. Twenty-five pediatric control subjects and ten pediatric patients with Spinal Cord Injuries (SCI) were recruited. The iFoV DTI pulse sequence was implemented on a 3 Tesla MRI scanner. The protocol was optimized for imaging the pediatric spinal cord and tested on phantom models, human cadaveric spine and adult subjects. All thirty-five pediatric subjects underwent two DTI scans of the spinal cord. Imaging results were compared between controls and patients with SCI. Statistical analysis was performed to examine reproducibility of DTI parameters and their correlation with standard clinical examinations. Results showed reduced FA and increased diffusivity values (AD, RD and MD) in patients compared to controls. Reproducibility of the different DTI parameters showed moderate to strong agreement between the repeated-measurements scans. Correlations between clinical examinations (ISNCSCI and MRI scores) and DTI values showed that DTI predicts sacral sparing outcomes, motor and MRI levels in the injured spinal cord with good to strong accuracy. Results also revealed that DTI values differ between children with and without cervical SCI and between children with SCI who have incomplete injuries and complete injuries. Finally, the study showed DTI to have relatively low specificity values for AC and DAP, compared with specificity for S4-5 sensation, and that the combination of the three DTI parameters FA, AD and RD was the strongest predictor of both motor level and MRI level of injury. This study was the first to demonstrate the feasibility of pediatric spinal cord DTI and produced accurate and reliable DTI measures.