The entropy in fractional anisotropy mapping of healthy and injured spinal cord of human beings

Abstract

Purposes: Diffusion MR imaging has been employed to delineate the functional ultrastructure of spinal cord (SC) experimentally and clinically. The ultrastructural complexity of SC builds the foundation of its normal function of spinal cord. Loss of the ultrastructural complexity would lead to functional abnormality. In the present study, we aimed to introduce the concept of entropy to describe the ultrastrucral complexity of spinal cord in fractional anisotropy (FA) mapping among healthy and cervical spondylotic myelopathy (CSM) patients. Subjects: Total 30 volunteers were recruited in this study with informed consent, including 13 adult healthy subjects (group A, 25±3 yrs), 12 elderly healthy subjects (group B, 53±7 yrs) and 5 CSM patients (group C, 53±15 yrs). Diffusion MR Imaging: MR imaging of cervical spinal cord were performed with a 3T Philips MR system (Philips Medical System, Netherlands). Diffusion MRI images were taken using pulsed gradient, spin-echo-echo-planar imaging (SE-EPI) sequence(data acquisition parameters: TR/TS=5000/60 ms; 13 slices (7mm slice thickness, 2.2mm gap); fi eld of view (FOV) = 80 (RL) ×36 (AP) mm; matrix size =128×128; non-collinear diffusion encoding directions=16, b=600s/ mm2; reconstruction resolution= 0.63×0.64×7.0mm3; acquisition time=8 minutes). Image analysis: Fractional anisotropy mapping of cervical spinal cord was generated via DTI studio. Region of interest was defi ned based on B0 images to cover the cord in. The mean and Shannon entropy of FA values were calculated for comparison. Statistics: The comparisons were performed among three groups using one-way ANOVA and post-hoc test. The p value was set at 0.05. Results: As compared with adult and aged healthy subjects, the entropy was signifi cantly lower in CSM patients (group A: 6.07±0.18; B: 6.01±0.23; C: 5.32±0.44; p<0.05). Whereas there were no signifi cant difference in FA values among groups (group A: 0.62±0.08; B: 0.64±0.09; C: 0.64±0.12). Among the healthy subjects, the coeffi cient of variance (CV) for the entropy was 34% yet the CV of FA was 1314%. Conclusion: Loss of entropy in fractional anisotropy mapping of cervical spinal cord in CSM patients. Entropy might be a new index in diffusion MR imaging for the diagnosis of CSM.