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On T 2 ‐shortening by weakly magnetized particles: The chemical exchange model †
Author(s) -
Brooks Rodney A.,
Moiny Francis,
Gillis Pierre
Publication year - 2001
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.1135
Subject(s) - physics , limit (mathematics) , relaxation (psychology) , range (aeronautics) , diffusion , phase (matter) , spherical model , echo (communications protocol) , nuclear magnetic resonance , statistical physics , condensed matter physics , quantum mechanics , mathematical analysis , mathematics , materials science , psychology , social psychology , composite material , computer network , computer science
Chemical exchange (CE) theory is compared with two theories of T 2 ‐shortening caused by microscopic magnetic centers: inner‐ and outer‐sphere relaxation theory (long‐echo limit) and mean gradient diffusion theory (short‐echo limit). The CE equation is shown to be identical to these theories in the respective limits and appropriate parameter relationships are derived for spherical particles. The theories are then compared with computer simulations of spherical particles and with a recent general theory, with good agreement in the asymptotic regions. The CE model also reproduces the essential relaxation characteristics in the intermediate range. Finally, good agreement of a CE model with simulations for magnetized cylinders is also demonstrated. The discussion is limited to weakly magnetized particles such that the maximum phase shift during an echo interval is less than one radian, permitting the use of the Luz‐Meiboom CE equation. Magn Reson Med 45:1014–1020, 2001. Published 2001 Wiley‐Liss, Inc.