Optimizing the experimental design for ankle dorsiflexion fMRI.
Compared to motor studies of the upper limb, few experiments have sought a relationship between blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) sensorimotor signals and the resulting lower limb output. In Experiment 1, using an fMRI simulator system, we determined the optimized experimental protocol based on two design types and four behavioral movement types during ankle dorsiflexion. Experiment 2 involved testing the BOLD sensitivity at 1.5 T during ankle movements. Subjects performed large- and small-amplitude dorsiflexion movement types using an event-related design, with the intent of contrasting spatial and temporal features of the BOLD signal. In both experiments, the subject's behavior was guided by visual biofeedback of their ankle flexion angle, using an MR-compatible fiberoptic tape. From Experiment 1, we found electromyography (EMG) difference voltage ratio of approximately 2:1 for large (40 degrees ) and small (15 degrees ) dorsiflexion, 0.13 mV and 0.07 mV, respectively. In Experimental 2, we found the peak BOLD % signal changes of 1.04% and 0.89%, for large (40 degrees ) and small (15 degrees ) dorsiflexion, respectively. In addition, graded dorsiflexion produced graded BOLD signals in the primary sensorimotor and supplementary motor areas in 10 of 12 healthy young subjects, attesting to the feasibility of lower-limb fMRI at 1.5 T. This study provides insight into the cortical network involved in dorsiflexion using an experimental paradigm that is likely to translate effectively to hemiparetic stroke subjects.
MacIntosh
Bradley J
BJ
Imaging Research, Sunnybrook and Women's College Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada. brad.macintosh@utoronto.ca
Mraz
Richard
R
Baker
Nicole
N
Tam
Fred
F
Staines
W Richard
WR
Graham
Simon J
SJ
D000328:Adult; D000842:Ankle / Q000294:innervation*; D001676:Biofeedback, Psychology / Q000502:physiology; D001931:Brain Mapping; D004576:Electromyography; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted; D007537:Isometric Contraction / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009415:Nerve Net / Q000502:physiology; D010100:Oxygen / Q000097:blood*; D013003:Somatosensory Cortex / Q000502:physiology*
D010100:Oxygen