¥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 the individual
analysis in 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
åThis
will be included into 3dDeconvolve
in a future release
HOther
normalization methods, such as z-score transformations of statistics,
can also be used.