Zero-gradient-excitation ramped hybrid encoding (zGRF-RHE) sodium MRI

Yasmin Blunck, Bradford A. Moffat, Scott C. Kolbe, Roger J. Ordidge, Jon O. Cleary, Leigh A. Johnston

Research output: Contribution to journalArticleResearchpeer-review

4 Citations (Scopus)

Abstract

Purpose: Fast bi-exponential transverse signal decay compounds sodium image quality. This work aims at enhancing image characteristics using a special case of ramped hybrid encoding (RHE). Zero-gradient-excitation (zGRF)-RHE provides (1) gradient-free excitation for high flip angle, artifact-free excitation profiles and (2) gradient ramping during dead-time for the optimization of encoding time (tenc) to reduce T2 * signal decay influence during acquisition. Methods: Radial zGRF-RHE and standard radial UTE were investigated over a range of receiver bandwidths in simulations, phantom and in vivo brain experiments. Central k-space in zGRF-RHE was acquired through single point measurements at the minimum achievable TE. T2 * blurring artifacts and image SNR and CNR were assessed. Results: zGRF -RHE enabled 90° flip angle artifact-free excitation, whereas gradient pre-ramping provided greater tenc efficiency for any readout bandwidths. Experiments confirmed simulation results, revealing sharper edge characteristics particularly at short readout durations (TRO). Significant SNR improvements of up to 4.8% were observed for longer TRO. Conclusion: zGRF -RHE allows for artifact-free high flip angle excitation with time-efficient encoding improving on image characteristics. This hybrid encoding concept with gradient pre-ramping is trajectory independent and can be introduced in any center-out UTE trajectory design.

Original languageEnglish
Pages (from-to)1172-1180
Number of pages9
JournalMagnetic Resonance in Medicine
Volume81
Issue number2
DOIs
Publication statusPublished - 1 Feb 2019
Externally publishedYes

Keywords

  • hybrid encoding
  • PETRA
  • RHE
  • sodium (Na) MRI
  • UTE
  • zero echo time (zTE)

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