MRI-COMPATIBLE OPTICAL FIBER FOR CHRONIC OPTOGENETIC FMRI MAPPING

Optogenetic functional magnetic resonance imaging (ofMRI) enables cell-type–specific modulation with simultaneous whole-brain readout of circuit dynamics. In small-animal ofMRI, optical stimulation is typically delivered via silica-based fibers. However, their mechanical rigidity and magnetic susceptibility mismatch with brain tissue can impose critical limitations in high-field MRI. These fibers induce susceptibility-related image distortion and signal dropout. Moreover, their chronic implantation leads to tissue damage and inflammatory responses, which increase light scattering and absorption. Consequently, effective light delivery becomes unstable, reducing reproducibility across animals and over time. To address these issues, we developed a shape-memory polymer-based optical fiber optimized for high-field (≥9.4T) small-animal ofMRI. The fiber remains rigid during implantation but softens at physiological temperature, enabling compliance with brain tissue while preserving precise targeting. Its non-magnetic polymer composition minimizes susceptibility artifacts, while its high numerical aperture (NA ≈ 0.65) supports efficient light delivery.
We systematically evaluated the optical transmission, thermo-mechanical behavior, MRI compatibility and in-vivo bio-compatibility of the fiber. Compared with conventional silica fibers, the proposed fiber significantly reduced geometric distortion and signal loss in high-field MRI, while maintaining stable light output and minimizing chronic tissue responses. In vivo ofMRI experiments further showed improved signal stability and reproducibility. Together, these results demonstrate that the shape-memory polymer optical fiber provides an MRI-compatible optical interface for reliable circuit-level interrogation in high-field ofMRI.