Safe Spirals for Your Scanner

Motivation: Vibration of gradient coils is a source of loud acoustics, signal dropout, field distortion, and potential system damage particularly at mechanical resonant frequencies. Goal(s): To design safe spiral gradient waveforms which avoid mechanical resonant frequencies and their resulting severe vibrations. Approach: Instantaneous gradient frequency during spiral readout is estimated as the rotational frequency of a circle at the current k-space radius and gradient amplitude. Amplitude is limited to drop through resonant bands quickly. A convex problem for spiral rewinders is formed minimizing the DFT at resonant frequencies. Results: Coil vibration was significantly reduced using safe spirals, and gradient field oscillations were minimized. Impact: Frequency constrained “safe” spiral waveforms were shown to avoid specified frequency bands, reducing gradient vibrations and k-space oscillations without degrading image quality. Such waveforms could potentially prolong gradient coil lifetime, reduce acoustic discomfort, and remove artefacts from persisting k-space oscillations.