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Potential problems with selective pulses in NMR imaging systems
Author(s) -
Joseph Peter M.,
Axel Leon,
O'Donnell Matthew
Publication year - 1984
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 - 10.1118/1.595579
Subject(s) - imaging phantom , fourier transform , nuclear magnetic resonance , relaxation (psychology) , physics , optics , plane (geometry) , medical imaging , computational physics , magnetic resonance imaging , computer science , mathematics , artificial intelligence , medicine , psychology , social psychology , quantum mechanics , radiology , geometry
Most nuclear magnetic resonance (NMR) imaging systems require pulses whose frequency spectrum is shaped so as to selectively excite a given plane in the presence of a magnetic field gradient. We demonstrate by both computer simulation and experiment that linear Fourier transform theory is not a reliable guide to the uniformity of flip angle in the slice. We show by simulation that the nonuniformity can have serious implications for the measurement of relaxation time T 1 if selective 180° pulses are used; the exact results depend also on the details of data analysis and criteria for adjusting the rephasing gradients. We describe an experiment and a phantom in which the axial nonuniformity can be demonstrated on clinical NMR imaging machines.