Dual-echo EPI for non-equilibrium fMRI - Implications of different echo combinations and masking procedures
Dual-echo EPI for non-equilibrium fMRI - Implications of different echo combinations and masking procedures
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DOI：
10.1016/j.neuroimage.2010.04.243
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发表时间：
2010-08-15
期刊：
影响因子：
5.7
通讯作者：
Deichmann, Ralf
中科院分区：
文献类型：
--
作者：
Beissner, Florian;Baudrexel, Simon;Deichmann, Ralf
双回波EPI基于每次激发的不同回波时间的两幅图像的采集，从而允许计算纯T-2（中心点）加权数据。该技术可用于测量功能活化，当恒定平衡磁化的先决条件不能满足，由于可变的体积间延迟。后者是由生理参数（如心脏门控）或受试者的反应触发图像采集的情况。尽管它的应用频繁，但目前还没有标准化的方法来结合从两个获取的回波中获得的信息。本研究的目的是量化不同回波组合方法（回波商、量化和计算方式）的含义，无论是在组合前对数据进行预平滑，还是对未平滑的组合数据进行屏蔽（无屏蔽、按体积屏蔽、联合屏蔽）。对BOLD反应的理论预测信噪比（SNR）和两组fMRI实验的激活结果进行了比较，其中一组（n = 5）采用手指敲击和视觉刺激，另一组（n = 21）采用不同的运动范式激活皮层和脑干的运动区域。发现回波组合和掩蔽程序对信噪比和激活结果都有显著影响。推荐的选择是直接计算T-2（中心点）值，或者在未平滑的数据上使用联合掩蔽，或者在T-2（中心点）计算之前预平滑图像。这种方法在靠近大脑表面或脑室附近的区域最有效，可能与脑干功能磁共振成像特别相关。(C) 2010爱思唯尔公司版权所有。
Dual-echo EPI is based on the acquisition of two images with different echo times per excitation, thus allowing for the calculation of purely T-2(center dot) weighted data. The technique can be used for the measurement of functional activation whenever the prerequisite of constant equilibrium magnetization cannot be fulfilled due to variable inter-volume delays. The latter is the case when image acquisition is triggered by physiological parameters (e.g. cardiac gating) or by the subject's response. Despite its frequent application, there is currently no standardized way of combining the information obtained from the two acquired echoes. The goal of this study was to quantify the implication of different echo combination methods (quotients of echoes and quantification of and calculation modalities, either pre-smoothing data before combination or subjecting unsmoothed combined data to masking (no masking, volume-wise masking, joint masking), on the theoretically predicted signal-to-noise ratio (SNR) of the BOLD response and on activation results of two fMRI experiments using finger tapping and visual stimulation in one group (n = 5) and different motor paradigms to activate motor areas in the cortex and the brainstem in another group (n = 21).A significant impact of echo combination and masking procedure was found for both SNR and activation results. The recommended choice is a direct calculation of T-2(center dot) values, either using joint masking on unsmoothed data, or pre-smoothing images prior to T-2(center dot) calculation. This method was most beneficial in areas close to the surface of the brain or adjacent to the ventricles and may be especially relevant to brainstem fMRI. (C) 2010 Elsevier Inc. All rights reserved.