Gradient-Echo and Spin-Echo BOLD FMRI of Rat Spinal Cord Insight Into Its Hemodynamic Response to Neuronal Activity

Fuqiang Zhao¹, Denise Welsh¹, Xiangjun Meng¹, Mangay Williams¹, Jacquelynn J. Cook¹, Alise S. Reicin¹, Richard Hargreaves¹, Donald S. Williams¹

The mechanisms of hemodynamic response to neuronal activity in spinal cord have not been clearly elucidated. Whether the hemodynamic response in spinal cord is similar to that in brain is unknown. In this study, spin-echo and gradient-echo BOLD fMRI were performed in the rat cervical spinal cord to answer this question. Based on different vessel size dependence of SE and GE BOLD signals, by comparing the SE and GE BOLD measured by EPI, the vasculature involved in BOLD fMRI response in the cortex has been investigated. In this study, GE and SE BOLD measurements in cervical spinal cord of rat were performed. The stimulation-induced relaxation rate ratio R2* / R2 for GE vs SE is 1.25 / 0.35 =3.52, which is consistent with the ratios of 3.3-4.0 observed in various cerebral cortical regions. The similarity of these ratios between spinal cord and cortex supports the concept that the hemodynamic response and the vasculature of the spinal cord are similar to those of cerebral cortex.