Simultaneous mapping of B0, B1 and T1 for the correction of CEST-MRI contrast

化学交换饱和转移法(CEST)是一种较新的、用途广泛的磁共振成像方法。在CEST磁共振成像中，具有可交换质子的外源或内源化合物选择性地饱和。在将磁性从化合物转移到周围的水分子之后，可以间接检测到化合物，因为与直接检测相比，降低了大量水的信号，提高了灵敏度。除了代谢物浓度和pH值等生理参数外，检测到的CEST效应还取决于被检查对象的T1弛豫时间以及MR系统的静磁场(B0)和/或RF激励场(B1)可能的不均匀性。因此，这些参数的定量映射对于采集的CEST数据的后续像素校正是必要的。通常，这三个参数图是使用三个单独的MR脉冲序列来采集的，这伴随着实现的大量工作以及基本上延长的采集时间。因此，本项目的思路是开发一种同时获取所有三个参数图的方法。所提出的方法是基于先前开发的用于B0和B1的量化的方法，该方法将被扩展并结合使用神经网络来实现T1的额外映射。该方法与常规的CEST脉冲序列兼容，可在不到2分钟的时间内提供B0、B1和T1的3D参数图，从而有助于无偏CEST MRI在临床中的推广。

Chemical exchange saturation transfer (CEST) MRI is a relative new and versatile MR method. In CEST MRI, exogenous or endogenous compounds with exchangeable protons are selectively saturated. After the transfer of magnetization from the compound to surrounding water molecules, the compound can be detected indirectly as a reduction of the bulk water signal with increased sensitivity compared to a direct detection. Besides physiological parameters like metabolite concentrations and pH value, the detected CEST effect further depends on the T1 relaxation time of the examined object as well as on possible inhomogeneities of the static magnetic (B0) and/or RF excitation field (B1) of the MR system. Thus, quantitative mapping of these parameters is necessary for a subsequent pixel-wise correction of the acquired CEST data. Usually these three parameter maps are acquired using three separate MR pulse sequences, which comes along with a lot of effort for the implementation as well as essentially prolonged acquisition times. Therefore, the idea of this project is to develop a method for the simultaneous acquisition of all three parameter maps. The proposed method is based on a previously developed approach for the quantification of B0 and B1 that will be extended and combined with the utilization of a neuronal network to enable the additional mapping of T1. The method is compatible with conventional CEST pulse sequences, will provide 3D parameter maps of B0, B1 and T1 in less than two minutes and therefore contribute to the dissemination of unbiased CEST MRI in the clinical routine.