Balanced steady-state free precession imaging has recently been suggested for chemical exchange detection (bSSFPX). The objective of this work is to investigate the contributions of microstructural, chemical shift and chemical exchange effects to the asymmetry of the bSSFP profile at field strengths of 3 T and 9.4 T. To this end, in vitro bSSFPX experiments are performed for a range of repetition times and flip angles in glucose water solutions with different MnCl2 concentrations and tissue homogenates obtained from the brainstem of pig brains. The experimental results are compared to multi-pool Bloch-McConnell simulations. Additionally, the influence of white matter tract geometry is analyzed ex vivo in pig brain hemispheres measured at two different angles with respect to B0 . The detectable bSSFP profile asymmetry in glucose solutions with tissue-like relaxation times and white matter homogenates was consistent with Bloch-McConnell simulations but relatively small. In intact white matter tracts, the asymmetry was dominated by structural effects with a strong dependency on tract orientation relative to B0 . In tracts perpendicular to B0 , the asymmetry was ≈ 3-4 times higher than in the homogenates, thus barely affected by chemical exchange effects. In conclusion, chemical exchange-related bSSFP profile asymmetries are detectable in tissue homogenates, however, the observed asymmetry level is generally low and prone to confounding structural effects rendering in vivo chemical exchange detection with bSSFP challenging in the brain.

中文翻译：

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结构还是交换？关于组织中平衡的稳态自由进动进行化学交换检测的可行性-体外研究。

最近有人建议将平衡的稳态自由进动成像用于化学交换检测（bSSFPX）。这项工作的目的是研究在3 T和9.4 T的场强下，微观结构，化学位移和化学交换效应对bSSFP轮廓不对称性的贡献。为此，在一定范围内进行了体外bSSFPX实验具有不同MnCl2浓度的葡萄糖水溶液中的重复时间和翻转角以及从猪脑干获得的组织匀浆。将实验结果与多池Bloch-McConnell模拟进行了比较。另外，在相对于B 0的两个不同角度测量的猪脑半球中，离体分析了白质束几何形状的影响。具有类似组织的弛豫时间和白质匀浆的葡萄糖溶液中可检测到的bSSFP轮廓不对称性与Bloch-McConnell模拟结果一致，但相对较小。在完整的白质束中，不对称性主要受结构效应的影响，相对于B0而言，其强烈依赖于束取向。在垂直于B0的区域中，不对称度比均质物中的≈高3-4倍，因此几乎不受化学交换作用的影响。总之，在组织匀浆中可检测到与化学交换相关的bSSFP轮廓不对称性，但是，观察到的不对称水平通常较低，并且容易混淆结构效果，从而使bSSFP的体内化学交换检测在脑中具有挑战性。