Generating spiral gradient waveforms with a compact frequency spectrum

Abstract

Purpose To generate efficient gradient waveforms for spiral MRI which mitigate the high‐frequency attenuation inherent in gradient systems. Theory and Methods Spiral MRI has many clinical advantages, including high temporal and SNR efficiency. One of the challenges for robust spiral MRI is a high sensitivity to imperfections in the gradient system, which requires some form of correction in order to map data correctly in k‐space. A previous numerical algorithm for generating spiral gradient waveforms was modified to reduce its high‐frequency content with minimal increase in waveform duration. Results Examples are shown of compact frequency gradient waveforms. Software implementing the algorithm is made available. Conclusion An algorithm to produce gradient waveforms with a compact frequency spectrum is described. This algorithm results in greatly reduced overall error and better compatibility with gradient systems than the original algorithm from which it was derived.

Acoustic noise reduction for spiral MRI by gradient derating

“…This requires exact analytical equations of the gradient waveform and timing, made possible by WHIRLED PEAS, a variant of spiral trajectory that follows the involute of a circle and has comparable performance to numerically-derived Archimedean spiral trajectory. 12,13 The WHIRLED PEAS gradient waveform has four segments: a (1) very short (<1 ms) quarter-circle arc, followed by (2) frequency-constrained (maximum frequency f or angular frequency w = 2𝜋f );…”

“…The goal of our auto‐derating method is to determine the values of maximum slew rate $$$ \overline{S} $$$ and maximum gradient amplitude $$$ \overline{G} $$$ for desired performance and system parameters without manual tuning. This requires exact analytical equations of the gradient waveform and timing, made possible by WHIRLED PEAS, a variant of spiral trajectory that follows the involute of a circle and has comparable performance to numerically‐derived Archimedean spiral trajectory 12,13 . The WHIRLED PEAS gradient waveform has four segments: a (1) very short (<1 ms) quarter‐circle arc, followed by (2) frequency‐constrained (maximum frequency $$$ \overline{f} $$$ or angular frequency $$$ \overline{w}=2\pi \overline{f} $$$); (3) slew‐constrained (maximum orthogonal slew rate $$$ {\overline{S}}_{\perp } $$$); and (4) gradient‐constrained (maximum gradient amplitude $$$ \overline{G}\Big) $$$ segments.…”