¥ 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