Department of Cognitive Neuroscience, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands; Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, The Netherlands.
Centre for Functional MRI of the Brain, University of Oxford, Oxford, United Kingdom.
Neuroimage. 2014 Sep;98:513-20. doi: 10.1016/j.neuroimage.2014.04.030. Epub 2014 Apr 18.
When defining an MRI protocol, brain researchers need to set multiple interdependent parameters that define repetition time (TR), voxel size, field-of-view (FOV), etc. Typically, researchers aim to image the full brain, making the expected FOV an important parameter to consider. Especially in 2D-EPI sequences, non-wasteful FOV settings are important to achieve the best temporal and spatial resolution. In practice, however, imperfect FOV size estimation often results in partial brain coverage for a significant number of participants per study, or, alternatively, an unnecessarily large voxel-size or number of slices to guarantee full brain coverage. To provide normative FOV guidelines we estimated population distributions of brain size in the x-, y-, and z-direction using data from 14,781 individuals. Our results indicated that 11mm in the z-direction differentiate between obtaining full brain coverage for 90% vs. 99.9% of participants. Importantly, we observed that rotating the FOV to optimally cover the brain, and thus minimize the number of slices needed, effectively reduces the required inferior-superior FOV size by ~5%. For a typical adult imaging study, 99.9% of the population can be imaged with full brain coverage when using an inferior-superior FOV of 142mm, assuming optimal slice orientation and minimal within-scan head motion. By providing population distributions for brain size in the x-, y-, and z-direction we improve the potential for obtaining full brain coverage, especially in 2D-EPI sequences used in most functional and diffusion MRI studies. We further enable optimization of related imaging parameters including the number of slices, TR and total acquisition time.
在定义 MRI 方案时，脑研究人员需要设置多个相互依赖的参数，这些参数定义了重复时间（TR）、体素大小、视野（FOV）等。通常，研究人员的目标是对整个大脑进行成像，因此预期的 FOV 是一个需要考虑的重要参数。特别是在 2D-EPI 序列中，非浪费性的 FOV 设置对于实现最佳的时间和空间分辨率非常重要。然而，在实践中，由于不完善的 FOV 大小估计，每一项研究中都有相当数量的参与者的大脑只有部分被覆盖，或者，为了保证全脑覆盖，不得不采用不必要的大体素大小或切片数量。为了提供规范的 FOV 指南，我们使用来自 14781 个人的数据估计了大脑在 x、y 和 z 方向上的大小的人群分布。我们的结果表明，在 z 方向上增加 11mm，可以区分出 90%和 99.9%的参与者是否能获得全脑覆盖。重要的是，我们观察到，旋转 FOV 以最佳地覆盖大脑，从而减少所需切片的数量，实际上可以有效地减少所需的上下 FOV 大小约 5%。对于一个典型的成人成像研究，当使用 142mm 的上下 FOV 时，99.9%的人群可以实现全脑覆盖，假设最佳的切片方向和最小的扫描内头部运动。通过提供大脑在 x、y 和 z 方向上的大小的人群分布，我们提高了获得全脑覆盖的可能性，特别是在大多数功能和扩散 MRI 研究中使用的 2D-EPI 序列中。我们进一步优化了相关的成像参数，包括切片数量、TR 和总采集时间。
