Jones Tyler B, Bandettini Peter A, Birn Rasmus M
Laboratory of Brain and Cognition, National Institute of Mental Health, NIH, Bethesda, MD 20892-1148, USA.
Neuroimage. 2008 Aug 15;42(2):582-90. doi: 10.1016/j.neuroimage.2008.05.019. Epub 2008 May 21.
Physiological fluctuations resulting from the heart beat and respiration are a dominant source of noise in fMRI, particularly at high field strengths. Commonly used physiological noise correction techniques, such as RETROspective Image CORrection (RETROICOR), rely critically on the timing of the image acquisition relative to the heart beat, but do not account for the effects of subject motion. Such motion affects the fluctuation amplitude, yet volume registration can distort the timing information. In this study, we aimed to systematically determine the optimal order of volume registration, slice-time correction and RETROICOR in their traditional forms. In addition, we evaluate the sensitivity of RETROICOR to timing errors introduced by the slice acquisition, and we develop a new method of accounting for timing errors introduced by volume registration into physiological correction (motion-modified RETROICOR). Both simulation and resting data indicate that the temporal standard deviation is reduced most by performing volume registration before RETROICOR and slice-time correction after RETROCIOR. While simulations indicate that physiological noise correction with regressors constructed on a slice-by-slice basis more accurately modeled physiological noise compared to using the same regressors for the entire volume, the difference between these regression techniques in subject data was minimal. The motion-modified RETROICOR showed marked improvement in simulations with varying amounts of subject motion, reducing the temporal standard deviation by up to 36% over the traditional RETROICOR. Though to a lesser degree than in simulation, the motion-modified RETROICOR performed better in nearly every voxel in the brain in both high- and low-resolution subject data.
由心跳和呼吸引起的生理波动是功能磁共振成像（fMRI）中主要的噪声源，在高场强下尤为明显。常用的生理噪声校正技术，如回顾性图像校正（RETROICOR），严重依赖于图像采集相对于心跳的时间，但没有考虑受试者运动的影响。这种运动会影响波动幅度，而体积配准会扭曲时间信息。在本研究中，我们旨在系统地确定传统形式下体积配准、切片时间校正和RETROICOR的最佳顺序。此外，我们评估了RETROICOR对切片采集引入的时间误差的敏感性，并开发了一种新方法，将体积配准引入的时间误差纳入生理校正（运动修正的RETROICOR）。模拟和静息数据均表明，在RETROICOR之前进行体积配准，在RETROCIOR之后进行切片时间校正，可最大程度地降低时间标准差。虽然模拟表明，与对整个体积使用相同的回归变量相比，基于逐片构建的回归变量进行生理噪声校正能更准确地模拟生理噪声，但在受试者数据中，这些回归技术之间的差异很小。在不同程度的受试者运动模拟中，运动修正的RETROICOR表现出显著改善，与传统RETROICOR相比，时间标准差降低了36%。尽管程度不如模拟中明显，但在高分辨率和低分辨率受试者数据中，运动修正的RETROICOR在大脑几乎每个体素中的表现都更好。
