发表机构
Institute for Biomedical Engineering, ETH Zurich and University of Zurich（苏黎世联邦理工学院与苏黎世大学生物医学研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文提出一个正式框架，建模3D BOLD fMRI序列时序效应，定义关键图像和时空滤波器算子，揭示高频信号受损更重，并解释3D序列对生理噪声更敏感的原因。
AI 中文摘要
3D序列为BOLD fMRI提供了2D或多波段序列之外的另一种选择。对于2D或多波段序列，切片间采集时间差异的影响已被充分理解。对于3D序列，k空间被划分为多个段，最终图像取决于在较长时间内采集的样本。任何精确的时序信息在重建过程中都会丢失。文献中缺乏关于序列时序如何影响3D BOLD fMRI数据特性的理论描述。我们提出了一个正式框架来建模序列时序效应，并与现有文献建立联系。该框架基于自旋系统的统计描述，允许纳入BOLD信号变化，并通过空间编码和图像重建的一般描述来完成。利用这一表述，我们定义了三个关键图像：从分段3D采集中重建的实际图像、不受序列时序影响的最优参考图像，以及表示两者差异的误差图像。定义了两组算子来描述这些图像的生成，使我们能够独立于对象分析序列时序的影响。所有算子均采用时空滤波器的形式，它们在空间上并根据时间波形混合信号内容。高频BOLD信号内容比低频内容受到更强的影响。模拟表明，虽然3D图像时间序列的总方差可以降低，但时空保真度逐渐丧失。此外，我们假设3D序列对生理噪声的更高敏感性（与2D相比）是由于序列时序对热噪声的抑制强于对生理波动的抑制。运动和系统不稳定性对图像时间序列的影响需要进一步研究。
英文摘要
3D sequences provide an alternative to 2D or multiband sequences for BOLD fMRI. The impact of acquisition time differences between slices is well understood for 2D or multiband sequences. For 3D sequences, k-space is partitioned into multiple segments and the final image depends on samples taken over an extended period of time. Any precise timing information is lost during reconstruction. A theoretical description of how sequence timing impacts 3D BOLD fMRI data properties is lacking in the literature. We present a formal framework that models sequence timing effects and draw connections to existing literature. The framework rests on the statistical description of a spin system that allows incorporation of BOLD signal changes and is completed by a general description of spatial encoding and image reconstruction. Using this formulation, we define three key images: the actual image reconstructed from a segmented 3D acquisition, an optimal reference image unaffected by sequence timing, and an error image representing their difference. Two sets of operators are defined that describe the generation of these images and allow us to analyse the effects of sequence timing independent of the object. All operators take the form of spatio-temporal filters. They mix signal content spatially and based on its temporal waveform. High-frequency BOLD signal content is affected more strongly compared to low-frequency content. Simulations demonstrate that while the total variance of 3D image time series can be reduced, spatio-temporal fidelity is increasingly lost. Furthermore, we hypothesize that the heightened sensitivity of 3D sequences to physiological noise (compared to 2D) is caused by sequence timing damping thermal noise more strongly than physiological fluctuations. The impact of motion and system instabilities on image time series needs to be studied further.
