Reduced MR Acquisition Time with the CROCUS Technique

A technique to reduce magnetic resonance (MR) image acquisition time by approximately 50% is introduced. The conjugate reconstruction by off-center under-sampling (CROCUS) method samples only every other phase-encoded line in raw data space and uses the conjugate symmetry of the data to reconstruct a real image. If acquisition and image reconstruction were done in the simplest manner, this under-sampling would produce unacceptable image aliasing. However, if the phase-encoded lines are offset from the origin, the assumption of conjugate symmetry allows the image to be calculated without aliasing. Unfortunately, information from all practical MR systems contain phase-shift errors that produce deviations from conjugate symmetry. The CROCUS method incorporates a correction technique, similar to that used in other half-Fourier methods, which uses low-resolution phase-shift information obtained from a few extra lines of phase-encoded data. This paper provides a theoretical derivation of the reconstruction algorithm and correction technique and illustrates the results. Excellent image quality is obtained with no loss of spatial resolution. Image signal-to-noise ratio is reduced by a factor of approximately 1.4 because of the reduced acquisition time. When the imaging circumstances are such that a high signal level is available, CROCUS imaging can be an effective means of reducing imaging time.