par Denolin, Vincent 
;Azizieh, Céline ;Metens, Thierry
Référence Magnetic resonance in medicine, 54, 10, page (937-954)
Publication Publié, 2005-10
;Azizieh, Céline ;Metens, Thierry Référence Magnetic resonance in medicine, 54, 10, page (937-954)
Publication Publié, 2005-10
Article révisé par les pairs
| Résumé : | RF spoiling is a well established method to produce T1-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 (T1/TR = 32 and T2/TR = 4); larger deviations occurred at long relaxation times (T1/TR = 114 and T2/TR = 82). Magn Reson Med, 2005. © 2005 Wiley-Liss, Inc. |
