Liimatainen Timo, Hakkarainen Hanne, Mangia Silvia, Huttunen Janne M J, Storino Christine, Idiyatullin Djaudat, Sorce Dennis, Garwood Michael, Michaeli Shalom
A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland.
Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, USA.
Magn Reson Med. 2015 Jan;73(1):254-62. doi: 10.1002/mrm.25129. Epub 2014 Feb 12.
MRI relaxation measurements are performed in the presence of a fictitious magnetic field in the recently described technique known as RAFF (Relaxation Along a Fictitious Field). This method operates in the 2(nd) rotating frame (rank n = 2) by using a nonadiabatic sweep of the radiofrequency effective field to generate the fictitious magnetic field. In the present study, the RAFF method is extended for generating MRI contrasts in rotating frames of ranks 1 ≤ n ≤ 5. The developed method is entitled RAFF in rotating frame of rank n (RAFFn).
RAFFn pulses were designed to generate fictitious fields that allow locking of magnetization in rotating frames of rank n. Contrast generated with RAFFn was studied using Bloch-McConnell formalism together with experiments on human and rat brains.
Tolerance to B0 and B1 inhomogeneities and reduced specific absorption rate with increasing n in RAFFn were demonstrated. Simulations of exchange-induced relaxations revealed enhanced sensitivity of RAFFn to slow exchange. Consistent with such feature, an increased grey/white matter contrast was observed in human and rat brain as n increased.
RAFFn is a robust and safe rotating frame relaxation method to access slow molecular motions in vivo.
在最近描述的称为RAFF（沿虚拟场的弛豫）的技术中，在虚拟磁场存在的情况下进行MRI弛豫测量。该方法通过对射频有效场进行非绝热扫描以生成虚拟磁场，在第二旋转框架（秩n = 2）中运行。在本研究中，RAFF方法被扩展用于在秩1≤n≤5的旋转框架中生成MRI对比度。所开发的方法被称为秩n旋转框架中的RAFF（RAFFn）。
设计RAFFn脉冲以生成虚拟场，从而使秩n的旋转框架中的磁化锁定。使用Bloch-McConnell形式主义以及对人和大鼠大脑的实验研究了RAFFn产生的对比度。
证明了RAFFn对B0和B1不均匀性的耐受性以及随着n增加比吸收率降低。交换诱导弛豫的模拟显示RAFFn对缓慢交换的敏感性增强。与该特征一致，随着n增加，在人和大鼠大脑中观察到灰质/白质对比度增加。
RAFFn是一种强大且安全的旋转框架弛豫方法，可用于获取体内缓慢的分子运动。
