¥Data Preparation: Parameter Normalization
HParameters quantifying
activation must be normalized before group comparisons.
åFMRI signal amplitude varies
for different subjects, runs, scanning sessions, regressors, image reconstruction
software, modeling strategies, etc.
HAmplitude measures
(regression coefficients) can be turned to percent signal change from
baseline (do it before individual analysis Ð 3dDeconvolve).
åEquations to use with 3dcalc to calculate percent signal
change
í100 bi / b0 (basic formula)
í100 bi / b0 * c (mask out the outside of the brain)
bi
= coefficient for regressor i (output from 3dDeconvolve)
b0 = baseline estimate (output from 3dTstat -mean)
c = threshold
value generated from running 3dAutomask
-dilate
HOther normalization methods,
such as z-score transformations of statistics, can also be used.