Combining spin echoes with gradient echoes in the context of the global coherent free precession pulse sequence

Wolfgang G. Rehwald, Michael Salerno, Enn Ling Chen, Burkhard Sievers, Raymond J. Kim, Robert M. Judd

Research output: Contribution to journalArticlepeer-review


To extend the signal longevity of magnetically excited spins in flowing fluids while in a state of global coherent free precession (GCFP), a refocusing radiofrequency (RF) pulse and bipolar gradient waveforms were combined with the GCFP sequence. The data demonstrate that RF refocusing in the presence of flowing blood is possible, but the improvement in signal amplitude depends on the static magnetic field homogeneity along the direction of motion and the displacement of the spins between the excitation and the RF refocusing pulse, as well as displacement during subsequent RF refocusing pulses. The least amount of phase dispersion and thus the longest lasting signal is obtained with the shortest echo spacing where only one line of data is recorded between two RF refocusing pulses. This approach was successfully used in a phantom and in vivo to image fast and slow blood flow. Depending on the experimental conditions, signal persistence is improved significantly compared to playing the same sequence without RF refocusing, but the improvement is limited by the product of blood flow velocity and the time between RF refocusing pulses.

Original languageEnglish (US)
Pages (from-to)82-91
Number of pages10
JournalMagnetic resonance in medicine
Issue number1
StatePublished - Jul 2007


  • Angiography
  • Flow
  • GCFP
  • Phase coherence
  • Spin echo

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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