MB-SWIFT as a novel approach for simultaneous functional imaging of the brain and spinal cord

ABSTRACT Our goal is to establish a novel MRI approach to acquire functional MRI (fMRI) data simultaneously from brain and spinal cord. Unlike standard MRI readouts, our approach does not require a dedicated shimming procedure, as it is based on the newly developed zero echo time MRI pulse sequence entitled Multi-Band SWeep Imaging with Fourier Transformation (MB-SWIFT) which is inherently resilient to magnetic field inhomogeneities. Comprehensive evaluations of the central nervous system (CNS) function will tremendously benefit from this imaging modality, particularly in areas of research such as spinal cord injury, neurodegenerative diseases, pain and aging. Thus far, functional neuroimaging of the CNS has been an untapped area of research due to several technical challenges, the biggest of which is the need to efficiently shim a field of view large enough to cover both brain and spinal cord. Solutions of per-slice dynamic shimming approaches have been proposed. However, they are limited by the settling-time of eddy currents, they considerably prolong the experimental session, and they have been applied only to cover cervical (but not lower) spinal cord. Furthermore, dynamic shimming allows only inefficient sequential rather than simultaneous acquisitions of brain and spinal cord, posing additional challenges for CNS fMRI. As proven by our preliminary data, MB-SWIFT can instead image two fields of view (FOVs) at distant locations in brain and lumbar spinal cord in a true simultaneous fashion (i.e., within 1 ms of each other), thus allowing unprecedented functional imaging of the CNS that is unattainable with standard imaging modalities for fMRI. The current project is a proof-of-concept study conducted in rats, designed to first optimize the MB-SWIFT protocol including the dual RF coil and the dual FOV acquisition, then to demonstrate that fMRI of CNS with MB-SWIFT provides robust fMRI outcomes in absence of dedicated shimming solutions. Moreover, we will optimize spoke order of MB-SWIFT and post-processing pipeline for handling physiological noise, and demonstrate that MB-SWIFT provides surrogate markers of neuronal activity in spinal cord. Finally we will establish inter-subject, intra-subject and inter-site reproducibility of task-based and resting-state fMRI outcomes extracted from the CNS with dual FOV MB-SWIFT. Once completed, the study will provide an invaluable tool for pre-clinical research, and will set the stage for translation to humans.