Concurrent excitation and detection in magnetic resonance using voltage-controlled oscillators.

Abstract

Dead time following radio frequency excitation limits pulsed magnetic resonance (MR) experiments by obscuring early-time spin dynamics and short-lived signals. We demonstrate continuous concurrent excitation and detection using two oscillator-based MR detectors: a high-frequency (477 megahertz) injection-locked voltage-controlled oscillator (VCO) array enabling a scalable segmented-coil architecture and a low-frequency (17 megahertz) single-coil VCO. Both detectors are embedded in custom-designed phase-locked loops, enabling phase-coherent multipulse operation. Using a planar segmented coil driven by a chip-integrated VCO array operating at 477-megahertz proton frequency, we perform conventional Fourier transform nuclear MR, continuously monitor driven Rabi oscillations throughout the excitation pulse, and observe the immediate onset of free-induction decay, all without dedicated transmit-receive switches or receiver gating. We further demonstrate phase-coherent, phase-cycled multipulse operation, including a Hahn echo sequence realized on a second system operating at 17 megahertz. Together, these results demonstrate the general applicability and versatility of the oscillator-based detection principle across pulse sequences and operating frequencies.