Proposal of self-resonance spin-lock sequence: adaptable contrast fMRI sequences

Motivation: To propose the novel spin-lock sequence employing phase modulation (self-resonance spin-lock: SR-SL). There is no report on self-resonance during the spin-lock pulse, and we would like to share this idea through this report. Goal(s): To demonstrate the feasibility of SR-SL and characterize its pros and cons. Approach: Mathematical analysis of the Bloch equation, numerical simulation, and phantom experiment. Results: All the results of three approaches agreed. We confirmed the phase modulation could control the operating point of MR image contrast, which provides us with desired contrast change depending on the target magnetic field. Impact: We proposed the novel spin-lock sequence named self-resonance spin-lock (SRSL), which can control the operating point of MR image contrast and provides desired contrasts. SR-SL has potential to improve sensitivity to magnetic fields and save saturation absorption rate.