The mean of the overall timeseries is The scaling method is based on the SPM approach to specifying the General Linear Model. FIGURE 1: Simulated block design output showing a baseline signal of 100, and block amplitude estimated as a 2% signal change. This note describes the quantitative scaling laws that make the General Linear Model (GLM) estimation output from SPM consistent with this definition. Our objective is to quantify the imaging pipeline starting from this collected data.
However, percent signal change is easily defined for an fmri block design experiment when the noise is small and the response is relatively flat (Figure 1). Percent signal change for fmri is limited in applicability because it is difficult to relate measured signals to neuronal excitations. Thus, a quantitative check on measured effect size can be used to screen abnormally large values likely caused by artifacts in the data. While cognitive effects give signal changes on the order of 1% (and larger in the visual and auditory cortices), signal variations of over 10% may arise from motion and other artifacts in the data. 23, 2009 Quantitative scaling into percent signal change is helpful to detect and eliminate bad results with abnormal extreme values. 1 Percent Signal Change for fmri calculations Paul Mazaika, Feb.
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