Department of Medical Radiology, Division of Radiological Physics, University of Basel Hospital, Basel, Switzerland.
Magn Reson Med. 2011 Mar;65(3):858-62. doi: 10.1002/mrm.22661. Epub 2010 Oct 14.
Magnetization transfer and finite radiofrequency (RF) pulses affect the steady state of balanced steady state free precession. As quantification of transverse relaxation (T2) with driven equilibrium single pulse observation of T2 is based on two balanced steady state free precession acquisitions, both effects can influence the outcome of this method: a short RF pulse per repetition time (TRF/TR≪1) leads to considerable magnetization transfer effects, whereas prolonged RF pulses (TRF/TR>0.2) minimize magnetization transfer effects, but lead to increased finite pulse effects. A correction for finite pulse effects is thus implemented in the driven equilibrium single pulse observation of T2 theory to compensate for reduced transverse relaxation effects during excitation. It is shown that the correction successfully removes the driven equilibrium single pulse observation of T2 dependency on the RF pulse duration. A reduction of the variation in obtained T2 from over 50% to less than 10% is achieved. We hereby provide a means of acquiring magnetization transfer-free balanced steady state free precession images to yield accurate T2 values using elongated RF pulses.
磁化传递和有限射频（RF）脉冲会影响平衡稳态自由进动的稳态。由于驱动平衡稳态自由进动观测 T2 的横向弛豫（T2）定量基于两个平衡稳态自由进动采集，因此这两种效应都会影响该方法的结果：重复时间（TRF/TR≪1）内的短 RF 脉冲会导致相当大的磁化传递效应，而延长 RF 脉冲（TRF/TR>0.2）会最小化磁化传递效应，但会导致有限脉冲效应增加。因此，在驱动平衡稳态自由进动观测 T2 理论中实施了有限脉冲效应的校正，以补偿激发过程中横向弛豫效应的降低。结果表明，校正成功地消除了驱动平衡稳态自由进动观测 T2 对 RF 脉冲持续时间的依赖性。获得的 T2 的变化从超过 50%减少到小于 10%。我们在此提供了一种获取无磁化传递平衡稳态自由进动图像的方法，以使用伸长的 RF 脉冲获得准确的 T2 值。
