In this project, we aim to implement a lumbar fMRI technique to track sensorimotor function in the lumbosacral cord after spinal cord injury (SCI).
Functional MRI (fMRI) is a non-invasive technique to probe neuronal activity at a high spatial resolution. fMRI has been routinely applied in the brain and (since more recently) in the cervical spine to investigate motor, sensory, and cognitive function.
However, direct adoption of fMRI in the lumbosacral cord is challenging due to the lower size of the cord, lower signal to noise ratio, and higher level of breathing artifacts. The established lumbar fMRI protocol enables us to measure remaining sensorimotor function after incomplete SCI in the lumbar cord at a high spatial specificity. Motor-related activities at L2-S1 are compared to healthy volunteers. Alterations in the activation pattern of the lumbar gray matter will shed light on the trans-synaptic neurodegeneration of the lower motor neurons occurring after SCI.
We started our effort to develop a lumbar fMRI protocol by optimizing the anatomical reference scan. A high-resolution axial reference scan with good gray and white matter contrast is necessary for signal localization and region of interest definition (for example, localizing the ventral horn at L4 neurological level).
In particular, we found that a 3D multi-echo gradient-echo sequence provides good time-efficiency, tolerable artifact level, and allows high in-plane resolution in the lumbosacral cord.
We performed parameter tuning to find optimal trade-off between gray/white matter contrast, white matter/liquor contrast, and artifact level. The implemented sequence encompasses the whole lumbosacral region (lumbar enlargement plus conus medullaris) by 20 slices of 5 mm (Fig. 1).