¥ ÒNoiseÓ in FMRI is caused by several factors, not completely characterized
H MR thermal noise (well understood)
H Cardiac and respiratory cycles (partly
understood)
o In
principle, could measure these sources of noise separately and then try to
regress them out
å RETROICOR
program in progress (Rasmus Birn of FIM)
H Scanner fluctuations (e.g., thermal
drift of hardware)
H Small subject head movements (10-100 mm)
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 (by us)