Ghost/Object

Referenceless Nyquist Ghost Correction for Echo Planar Imaging (EPI)


EPI is subject to Nyquist (or N/2) ghosts caused by eddy currents, imperfect gradients, and/or timing errors. Nyquist ghosts are typically corrected using a 3-line navigator to measure the 1st-order phase difference [1]. However, several alternative ghost correction strategies can estimate the 1st-order correction parameters using a cost function calculated on the data itself, rather than any reference acquisition. One method is Ghost/Object (G/O) minimization [2], which defines the cost function as the summation over the entire image divided by a ½-FOV-shifted version of the image.


Software


A demonstration of the algorithm is provided in Matlab format, available for download here.

The code provided here demonstrates 1st-order ghost correction using G/O minimization and has the option to test other referenceless methods (entropy [3,4], SVD [5], image energy). The optimization can be done using a discrete or simplex search.

Citation

If you publish or present results obtained using the software or sequences in this package, please acknowledge the researchers who developed the sequences using the following language:

McKay JA, et al. Nyquist ghost correction of breast diffusion weighted imaging using referenceless methods. Magn Reson Med. 2019; 81:2624-2631. doi: 10.1002/mrm.27563

Contact

If you have noticed a bug or have a request for a new feature in a future release, please contact

Patrick Bolan. Be sure to include the sequence variant and the model of scanner you are using in the problem description.

Download

Version 1


References

  1. Heid, O. Method for the phase correction of nuclear magnetic resonance signals. US Patent 6,043,651. 2000.

  2. McKay JA, et al. Nyquist ghost correction of breast diffusion weighted imaging using referenceless methods. Magn Reson Med. 2019; 81:2624-2631. doi: 10.1002/mrm.27563

  3. "Clare, S. Iterative Nyquist ghost correction for single and multi-shot EPI using an entropy measure. In Proceedings of ISMRM. 2003;p.1041."

  4. "Skare S, Clayton DB, Newbould R, Moseley M, and Bammer R. A fast and robust minimum entropy based non-interactive Nyquist ghost correction algorithm. In Proceedings of ISMRM. 2006;p.2349."

  5. "Peterson E, Aksoy M, Maclaren J, and Bammer R. Acquisition-free Nyquist ghost correction for parallel imaging accelerated EPI. In Proceedings of ISMRM. 2015;p.0075."

Patents

US6043651A 
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