Abstract
Wirelessly Amplified NMR Detectors (WAND) can utilize wireless pumping power to amplify MRI signals in situ for sensitivity enhancement of deep-lying tissues that are difficult to access by conventional surface coils. To reconfigure between selective and simultaneous activation in a multielement array, each WAND has a dipole resonance mode for MR signal acquisition and two butterfly modes that support counter-rotating current circulation. Because detectors in the same row share the same lower butterfly frequency but different higher butterfly frequency, a pumping signal at the sum frequency of the dipole mode and the higher butterfly mode can selectively activate individual resonators, leading to 4-fold sensitivity gain over passive coupling. Meanwhile, a pumping signal at the sum frequency of the dipole mode and the lower butterfly mode can simultaneously activate multiple resonators in the same row, leading to 3-fold sensitivity gain over passive coupling. When multiple rows of detectors are parallelly aligned, each row has a unique lower butterfly frequency for consecutive activation during the acquisition interval of the others. This wireless detector array can be embedded beneath a headpost that is normally required for multi-modal brain imaging, enabling easy reconfiguration between focal imaging of individual vessels and multiregional mapping of brain connectivity.
Highlights
To decipher brain dynamics from micro to mesoscales, functional MRI has been performed on rodent brain in combination with optic-mediated brain stimulation and recording [1]–[3]
To overcome signal transmission attenuation over large distance separations, Wirelessly Amplified NMR Detectors (WAND) [15]–[18] have been developed that can be embedded beneath the headpost for proximal detection of the brain cortex
Compared to a surface coil of the same dimension but with direct cable connection to a conventional preamplifier, the WAND could maintain about 80% sensitivity under 798.6-MHz activation and about 64% sensitivity under 526.3-MHz activation
Summary
To decipher brain dynamics from micro to mesoscales, functional MRI (fMRI) has been performed on rodent brain in combination with optic-mediated brain stimulation and recording [1]–[3]. Such a multi-modal imaging platform consists of a head-post that is fixed on top of the skull to restrict head motion during MR experiments and to secure fiber-optics insertion into the brain cortex through a tiny orifice. Without the need for wired connections or internal batteries, the WAND can utilize wireless pumping power to amplify locally detected MR signals in situ, before wirelessly transmitting them to an externally separated receiver coil that is connected to the MRI console
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