Functional MRI (second edition) -- 8. Signal, Noise, and Preprocessing of fMRI Data
2015-08-07 10:32
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Experimental Design 分为:
blocked designs: 用于detection,即确定task激活的区域
event-related designs: 用于estimation,即确定时间上的变化
Analysis分为:
voxelwise analysis
region-of-analysis(ROI) analysis
衡量方法:
structural MRI(T1T_{1}): contrast-to-noise ratio(CNR)
fMRI(T∗2T_{2}^{*}): functional signal-to-noise ratio(functional SNR)(SNR指有刺激和baseline之间的信号比)
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磁场强度影响:
磁场线性增长,信号平方增长,噪声线性增长,physiological noise平方增长
磁场增强会improve spatical specificity和spatial extent
磁场增强会造成susceptibility artifacts增强
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噪声来源
热噪声
系统噪声:field imhomogeneities, instabilities in the gradient field, off-resonace or loading effects, scanner drift(永磁体磁性逐渐减弱)
Motion and physiological noise
Non-task-related neural variability: 与task无关的其他连带神经变化。
个体差异:如每个人完成任务的时候想法步骤不同
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预处理:
Quality assurance:把不满足要求的图像挑出去
slice acquisition time correction:隔行扫描造成的时间差,通过插值解决。
head motion:rigid-body correction
distortion correction:shimming coils,magnetic field map
blocked designs: 用于detection,即确定task激活的区域
event-related designs: 用于estimation,即确定时间上的变化
Analysis分为:
voxelwise analysis
region-of-analysis(ROI) analysis
衡量方法:
structural MRI(T1T_{1}): contrast-to-noise ratio(CNR)
fMRI(T∗2T_{2}^{*}): functional signal-to-noise ratio(functional SNR)(SNR指有刺激和baseline之间的信号比)
——————————————————————————————–
磁场强度影响:
磁场线性增长,信号平方增长,噪声线性增长,physiological noise平方增长
磁场增强会improve spatical specificity和spatial extent
磁场增强会造成susceptibility artifacts增强
————————————————————————————————
噪声来源
热噪声
系统噪声:field imhomogeneities, instabilities in the gradient field, off-resonace or loading effects, scanner drift(永磁体磁性逐渐减弱)
Motion and physiological noise
Non-task-related neural variability: 与task无关的其他连带神经变化。
个体差异:如每个人完成任务的时候想法步骤不同
—————————————————————————————-
预处理:
Quality assurance:把不满足要求的图像挑出去
slice acquisition time correction:隔行扫描造成的时间差,通过插值解决。
head motion:rigid-body correction
distortion correction:shimming coils,magnetic field map