Ultra-fast radial encoding with oscillating gradients: Potential of a high performance ultrasound gradient insert

Motivation: Radial sampling offers motion-robust, high bandwidth MRI with incoherent undersampling, but suffers from inefficient k-space sampling. 3D radial acquisitions can be accelerated using non-conventional gradient trajectories. Goal(s): To investigate the potential improvements in point spread function and acquisition time for radial encoding using oscillating gradients. Approach: Radial spokes are modified to a conical helix trajectory using external sinusoidal gradients to increase sampling efficiency. Acceleration potential and PSF were calculated using numerical simulations. Proof-of-principle phantom measurements were performed at 3T using a field camera. Results: Radial sampling with oscillating gradients improves PSF and allows for an up to 5-fold acceleration. Impact: This study demonstrates first high-frequency conical helix spokes in 3D using high frequency oscillating gradients. Using external ultrasound (>20kHz) gradients, the proposed trajectory can significantly improve the PSF for both low-resolution and high-resolution protocols while providing extremely high acceleration factors.