Consistent non-Cartesian off-axis MRI quality: Calibrating and removing multiple sources of demodulation phase errors

Youngkyoo Jung, Yogesh Jashnani, Richard Kijowski, Walter F. Block

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


The consistency of off-axis MRI with non-Cartesian sequences across a large number of scanners is highly variable. Improper timing alignment of the gradient fields, data acquisition system, and real-time frequency demodulation reference signal, which are necessary for off-axis imaging, is an important source of this variability. In addition, eddy currents and anisotropic gradient delays cause deviations in k-space trajectories that in turn make the demodulation reference signals inaccurate. A method is presented to quickly measure the timing error in the frequency demodulation reference signal and separate it from anisotropic gradient delays. k-Space deviations, as measured with a previous gradient calibration technique, are shown to be a second source of demodulation phase errors that degrade image quality. Using the timing delay and k-space deviations, a retrospective phase correction is applied to each k-space sample before the data are regridded during reconstruction. The timing delays of four MR scanners were measured to be 4.2-7.5 μs below the manufacturer's suggested delay. Significant degradation in 3D radial (3D projection reconstruction (PR)) knee and breast images are retrospectively corrected while a partial prospective correction is applied for spiral imaging. The method allows for more consistent performance of non-Cartesian sequences across multiple scanners without operator intervention.

Original languageEnglish (US)
Pages (from-to)206-211
Number of pages6
JournalMagnetic Resonance in Medicine
Issue number1
StatePublished - Jan 1 2007
Externally publishedYes


  • k-space deviation
  • Non-Cartesian
  • Off-axis
  • Real-time frequency demodulation
  • Timing discrepancy

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging


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