Premium
Accelerated radiation damping for increased spin equilibrium (ARISE): A new method for controlling the recovery of longitudinal magnetization
Author(s) -
Huang Susie Y.,
Witzel Thomas,
Wald Lawrence L.
Publication year - 2008
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.21702
Subject(s) - magnetization , spins , physics , relaxation (psychology) , bloch equations , imaging phantom , radiation damping , field (mathematics) , precession , spin (aerodynamics) , flip angle , damping factor , phase (matter) , function (biology) , nuclear magnetic resonance , condensed matter physics , computational physics , magnetic resonance imaging , magnetic field , optics , mathematics , quantum mechanics , voltage , medicine , radiology , input impedance , pure mathematics , thermodynamics , evolutionary biology , biology
Control of the longitudinal magnetization in fast gradient‐echo (GRE) sequences is an important factor in enabling the high efficiency of balanced steady‐state free precession (bSSFP) sequences. We introduce a new method for accelerating the return of the longitudinal magnetization to the + z ‐axis that is independent of externally applied RF pulses and shows improved off‐resonance performance. The accelerated radiation damping for increased spin equilibrium (ARISE) method uses an external feedback circuit to strengthen the radiation damping (RD) field. The enhanced RD field rotates the magnetization back to the + z ‐axis at a rate faster than T 1 relaxation. The method is characterized in GRE phantom imaging at 3T as a function of feedback gain, phase, and duration, and compared with results from numerical simulations of the Bloch equations incorporating RD. A short period of feedback (10 ms) during a refocused interval of a crushed GRE sequence allowed greater than 99% recovery of the longitudinal magnetization when very little T 2 relaxation had time to occur. An appropriate application might be to improve navigated sequences. Unlike conventional flip‐back schemes, the ARISE “flip‐back” is generated by the spins themselves, thereby offering a potentially useful building block for enhancing GRE sequences. Magn Reson Med 60:1112–1121, 2008. © 2008 Wiley‐Liss, Inc.