Circuitry design and magnetic susceptibility evaluation of 7T fMRI implantable RF coil

Implantable coils have been widely utilized in functional magnetic resonance imaging (fMRI) owing to their superior signal to noise ratio. To effectively minimize the magnetic field distortion and image artifacts, the magnetic susceptibility of the implantable coil needs to be evaluated before practical use. In this work, we experimentally identify the magnetic susceptibility of each component of the implantable coil with the 7T Bruker NMR imaging scanner and provide useful guidelines for the following manufacturing. A 5 × 5 mm
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implantable surface coil with a tunable frequency range is subsequently introduced for the 7T fMRI of the rat primary somatosensory cortex (S1FL). A detachable external tuning circuit for the implantable coil is employed to facilitate in-vivo measurements in the rat model.