期刊
MAGNETIC RESONANCE IN MEDICINE
卷 64, 期 4, 页码 983-994出版社
WILEY
DOI: 10.1002/mrm.22372
关键词
contrast imaging; rotating frame; fictitious field; relaxation; adiabatic pulse
资金
- NIH [P30 NS057091, P41 RR008079, R01 NS061866, R21 NS059813]
- Instrumentarium Science Foundation
- Orion Corporation Research Foundation
- Finnish Cultural Foundation Northern Savo
A new method to measure rotating frame relaxation and to create contrast for MRI is introduced. The technique exploits relaxation along a fictitious field (RAFF) generated by amplitude- and frequency-modulated irradiation in a subadiabatic condition. Here, RAFF is demonstrated using a radiofrequency pulse based on sine and cosine amplitude and frequency modulations of equal amplitudes, which gives rise to a stationary fictitious magnetic field in a doubly rotating frame. According to dipolar relaxation theory, the RAFF relaxation time constant (T-RAFF) was found to differ from laboratory frame relaxation times (T-1 and T-2) and rotating frame relaxation times (T-1p and T-2p). This prediction was supported by experimental results obtained from human brain in vivo and three different solutions. Results from relaxation mapping in human brain demonstrated the ability to create MRI contrast based on RAFF. The value of T-RAFF was found to be insensitive to the initial orientation of the magnetization vector. In the RAFF method, the useful bandwidth did not decrease as the train length increased. Finally, as compared with an adiabatic pulse train of equal duration, RAFF required less radiofrequency power and therefore can be more readily used for rotating frame relaxation studies in humans. Magn Reson Med 64:983-994, 2010. (C) 2010 Wiley-Liss, Inc.
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