Combined T2*-weighted measurements of the human brain and cervical spinal cord with a dynamic shim update

Abstract

Important functions of the central nervous system such as sensory processing and motor execution, involve the spinal cord. Recent advances in human functional MRI have allowed to investigate spinal cord neuronal processes using the blood-oxygenation-level-dependent (BOLD) contrast. However, to assess the functional connectivity between the brain and the spinal cord, functional MRI measurements covering both regions in the same experiment are required. Unfortunately, the ideal MRI setup differs considerably for the brain and the spinal cord with respect to resolution, field-of-view, relevant receive coils, and, in particular, shim adjustments required to minimize distortion artifacts. Here, these issues are addressed for combined T2*-weighted MRI measurements of the human brain and the cervical spinal cord by using adapted parameter settings (field-of-view, in-plane resolution, slice thickness, and receiver bandwidth) for each region, a dynamic receive coil element selection where for each slice only the elements with significant signal contributions are considered, and, most importantly, the implementation of a dynamic update of the frequency and the linear shims in order to provide shim settings individually adapted to the brain and spinal cord subvolume. The feasibility of this setup for combined measurements is demonstrated in healthy volunteers at 3T. Although geometric distortions are slightly more pronounced and the temporal signal-to-noise ratio is lower as compared to measurements focusing to the brain or spinal cord only, the overall image quality can be expected to be sufficient for combined functional MRI experiments. Thus, the presented approach could help to unravel the functional coupling between the brain and the spinal cord.