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Mapping of the radio frequency magnetic field with a MR snapshot FLASH technique
Author(s) -
Klose Uwe
Publication year - 1992
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.596828
Subject(s) - amplitude , magnetic field , pixel , physics , optics , excitation , nuclear magnetic resonance , snapshot (computer storage) , acoustics , computer science , quantum mechanics , operating system
A fast method to measure the radio frequency magnetic field intensity distribution during magnetic resonance examinations within objects or patients is proposed. Using a snapshot FLASH sequence, several images are obtained with different transmitter amplitudes for the single prepulse prior to the imaging sequence. The signal intensity at each pixel within a selected slice is diminished by this prepulse, unless the pulse angle is 0° or a multiple of 360°. This condition can be used to measure that transmitter amplitude U max for each pixel which causes an excitation of 360° by the prepulse. The values of U max can be visualized in an image and are inversely proportional to the radio frequency magnetic field strength at each position within the image. The method can also be used for in ‐ vivo measurements, where it may be difficult to realize prepulses with sufficient high flip angles. In these cases, signal corresponding to a 180° prepulse can be used for calculating U max .