• Vincent Denolin, Céline Azizieh, and Thierry Metens.
• Unité de Résonance Magnétique, Imagerie Médicale, Hôpital Erasme, Université Libre de Bruxelles, Belgium. vdenolin@ulb.ac.be
• Magn Reson Med. 2005 Oct 1; 54 (4): 937-54.

AbstractRF spoiling is a well established method to produce T(1)-weighted images with short repetition-time gradient-echo sequences, by eliminating coherent transverse magnetization with appropriate RF phase modulation. This paper presents 2 novel approaches to describe signal formation in such sequences. Both methods rely on the formulation of RF spoiling as a linear increase of the precession angle between RF pulses, which is an alternative to the commonly used quadratic pulse phase scheme. The first technique demonstrates that a steady state signal can be obtained by integrating over all precession angles within the voxel, in spite of the lack of a genuine steady-state for separate isochromats. This clear mathematical framework allows a straightforward incorporation of off-resonance effects and detector phase settings. Moreover, it naturally introduces the need for a large net gradient area per repetition interval. In the second step, a modified partition method including RF spoiling is developed to obtain explicit expressions for all signal components. This provides a physical interpretation of the deviations from ideal spoiling behavior in FLASH and echo-shifted sequences. The results of the partition method in the small flip angle regime are compared with numerical simulations based on a Fourier decomposition of magnetization states. Measurements performed with in vitro solutions were in good agreement with numerical simulations at short relaxation times (T(1)/TR = 32 and T(2)/TR = 4); larger deviations occurred at long relaxation times (T(1)/TR = 114 and T(2)/TR = 82).Copyright 2005 Wiley-Liss, Inc.

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