A method for correctly setting the rf flip angle

W. H. Perman, Matthew A Bernstein, J. C. Sandstrom

Research output: Contribution to journalArticle

39 Scopus citations

Abstract

Currently the accepted method for setting the correct rf power levels to achieve 90° and 180 ° rf pulses for Mr imaging is to peak the echo amplitude of a rf spin-echo sequence. The echo amplitude of this α-2α pulse sequence is proportional to sin3 (α) and has a relatively broad maximum. Recently another method for setting the rf flip angle by maximizing the ratio of the stimulated echo to the primary echo amplitudes (in a 3α sequence) demonstrated accuracy similar to that of the spin-echo method using a shorter repetition time. We present a new, more sensitive, and more accurate method for setting the correct rf power levels for 90° and 180° rf pulses. In this method, based upon the stimulated echo pulse sequence, we are able to accurately set the rf power to within ±0.1 dB by minimizing the signal amplitude of the third spin echo. This null method works for both selective and nonselective rf pulses of flip angle 90° or 180°, allowing the use to accurately adjust the relative amplitudes of the four rf pulse types within a single pulse sequence.

Original languageEnglish (US)
Pages (from-to)16-24
Number of pages9
JournalMagnetic Resonance in Medicine
Volume9
Issue number1
StatePublished - 1989
Externally publishedYes

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging
  • Radiological and Ultrasound Technology

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