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New spatial localization method using pulsed high‐order field gradients (SHOT: Selection with high‐order gradient)
Author(s) -
Oh C. H.,
Hilal S. K.,
Cho Z. H.,
Mun I. K.
Publication year - 1991
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.1910180108
Subject(s) - pulse sequence , pulse (music) , volume (thermodynamics) , field (mathematics) , signal (programming language) , selection (genetic algorithm) , imaging phantom , nuclear magnetic resonance , physics , flip angle , computer science , optics , computational physics , algorithm , materials science , mathematics , artificial intelligence , magnetic resonance imaging , medicine , quantum mechanics , detector , pure mathematics , radiology , programming language
A new spatial localization method using an additional set of high‐order magnetic field gradients is described. The method uses a nonlinear part of high‐order magnetic field gradient patterns which allows us to select a volume in conjunction with the selective radiofrequency (RF) pulse. Unlike the other existing volume selection methods such as ISIS or SPARS, the proposed selection method requires only one RF‐gradient pulse pair to select a volume in two directions. The center of the selected volume can be moved to any arbitrary location within the body by the addition of precalculated lower order gradients which are simultaneously pulsed with the high‐order gradient. The method also has the potential for localized spectroscopy from the FID signal which can be realized by using oscillating second‐ and first‐order gradients for 3D selection with a single RF pulse. By using the proposed localization method, it is possible to design more flexible pulse sequences, e.g., the shorter echo‐time spectroscopic pulse sequence. We have designed and constructed a six‐loop r 2 (or x 2 + y 2 ) gradient coil for initial application. By simultaneously applying this second‐order gradient and proper x, y , and/or z gradients, 2D selections were achieved in arbitrarily selected positions in conjunction with a single selective RF pulse. Phantom and animal experiments have been performed and the results appear promising, especially in areas of NMR spectroscopic imaging applications where spatial localization is essential. © 1991 Academic Press. Inc.