A Method to measure arbitrary k‐space trajectories for rapid MR imaging

A method to measure arbitrary k‐space trajectories was developed to compensate for nonideal gradient performance during rapid magnetic resonance (MR) imaging with actively or nonactively shielded gradients at a magnetic field strength of 4.1 T. Accurate MR image reconstruction requires knowledge of the k‐trajectory produced by the gradient waveforms during k‐space sampling. Even with shielded gradients, residual eddy currents and imperfections in gradient amplifier performance can cause the true k‐space trajectory to deviate from the ideal trajectory. The k‐space determination was used for spiral gradient‐echo imaging of the human brain. While individual calibrations are needed for new pulse sequences, the method of k‐space determination can be used for any sequence of preparation pulses and readout gradient waveforms and should prove useful for other trajectories, including the rastered lines of echo‐planar imaging.