Optimizing the experimental design for ankle dorsiflexion fMRI.

Area of Science:

• Neuroimaging
• Motor Control
• Rehabilitation Science

Background:

• Limited research exists on blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) sensorimotor signals in the lower limbs compared to the upper limb.
• Understanding lower limb motor control via fMRI is crucial for developing effective rehabilitation strategies.

Purpose of the Study:

• To optimize experimental protocols for BOLD fMRI during lower limb (ankle) movements.
• To assess BOLD signal sensitivity and characteristics during different ankle dorsiflexion amplitudes.
• To establish the feasibility of using 1.5 T fMRI for studying lower limb sensorimotor function.

Main Methods:

• Experiment 1: Optimized protocol using an fMRI simulator with two design types and four movement types for ankle dorsiflexion.
• Experiment 2: Tested BOLD sensitivity at 1.5 T during large (40°) and small (15°) amplitude ankle dorsiflexion using an event-related design.
• Utilized MR-compatible fiberoptic tape and visual biofeedback for guided ankle movements.

Main Results:

• Electromyography (EMG) showed a 2:1 voltage ratio between large and small dorsiflexion.
• Peak BOLD signal changes were 1.04% for large and 0.89% for small dorsiflexion.
• Graded dorsiflexion produced graded BOLD signals in sensorimotor areas in 10/12 subjects.

Conclusions:

• Established the feasibility of lower-limb fMRI at 1.5 T.
• Demonstrated graded BOLD responses in sensorimotor areas correlating with ankle dorsiflexion.
• The developed paradigm shows potential for application in hemiparetic stroke subjects.