Synthesis of Respiratory Phase from Image Phase in Resting-State Functional Magnetic Resonance Imaging

Functional Magnetic Resonance Imaging (fMRI) is routinely acquired using gradient-echo sequences with long echo times and short repetition time. Such sequences encode information about the magnetic field in the often discarded image phase. We demonstrate a method for processing the phase of reconstructed fMRI data to isolate temporal fluctuations in the harmonic fields associated with respiration by solving a blind source separation problem. Computed respiratory phase from the fMRI-derived field fluctuations was shown to be in strong agreement with breathing belt data acquired during the same scan. This work thus presents a hardware free measurement of respiratory phase.