¥ ÒNoiseÓ in FMRI is caused by several factors, not completely characterized
H MR thermal noise (well understood)
H Cardiac and respiratory cycles (partly
understood)
² In principle, could measure these
sources of noise separately and then try to
regress them out
H Scanner fluctuations (e.g., thermal
drift)
H Small subject head movements
H Very low frequency fluctuations (periods
longer than 100 s)
¥ Data analysis should try to remove what can be removed and allow for the statistical
effects of what canÕt be removed
H ÒSerial correlationÓ in the noise time
series affects the t- and F-statistics calculated by 3dDeconvolve
H At present, nothing is done to correct
for this effect