Factors influencing flip angle mapping in MRI: RF pulse shape, slice-select gradients, off-resonance excitation, and B0 inhomogeneities

Jinghua Wang, Weihua Mao, Maolin Qiu, Michael B. Smith, R. Todd Constable

Research output: Contribution to journalArticle

41 Scopus citations

Abstract

To understand the various effects that influence actual flip angles, and correct for these effects, it is important to precisely quantify the MRI parameters (such as T1, T2, and perfusion). In this paper actual flip angle maps are calculated using a conventional gradient-echo (GRE) sequence with different radiofrequency (RF) pulse shapes (Gaussian, sinc, and truncated-sinc), slice-selection gradients, off-resonance excitations, and B0 field inhomogeneities. The experimental results demonstrate that RF pulse shapes significantly affect the flip angle distribution and calibration factors. Off-resonance RF excitations, B0 nonuniformities, and slice-selection gradients can lead to degradations in the signal intensities of the images used to map the flip angle, and potentially introduce a bias and increased variance in the measured flip angles.

Original languageEnglish (US)
Pages (from-to)463-468
Number of pages6
JournalMagnetic resonance in medicine
Volume56
Issue number2
DOIs
StatePublished - Aug 1 2006

Keywords

  • High-field MRI
  • Off-resonance excitation
  • RF pulse
  • RF uniformity
  • Selection gradient

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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