A method for correctly setting the rf flip angle
作者:
William H. Perman,
Matt A. Bernstein,
John C. Sandstrom,
期刊:
Magnetic Resonance in Medicine
(WILEY Available online 1989)
卷期:
Volume 9,
issue 1
页码: 16-24
ISSN:0740-3194
年代: 1989
DOI:10.1002/mrm.1910090104
出版商: Wiley Subscription Services, Inc., A Wiley Company
数据来源: WILEY
摘要:
AbstractCurrently 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 user to accurately adjust the relative amplitudes of the four rf pulse types within a single pulse sequence. © 1989 Ac
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