Band pass filtering for BOLD image.

This function works for a BOLD time-series data

frequencyFilterfMRI(boldmat, tr, freqLo = 0.01, freqHi = 0.1, opt = "butt")

Arguments

boldmat	Time series matrix for bold image
tr	The sequence's TR value , typically 3 or 4.
freqLo	The lower frequency limit, e.g. 0.01 in band-pass filter
freqHi	The higher frequency limit, e.g. 0.1 in band-pass filter
opt	one of 'trig','butt','stl' Type of filter to use: butterworth, trigonometric, stl.

Value

output is the filtered time series.

Author

Avants BB

Examples

fmat<-replicate(1000, rnorm(200))
k<-1
tr = 4
for ( ftype in c("butt","stl","trig") ) {
  myres <- frequencyFilterfMRI( fmat, tr = tr, freqLo = 0.01, freqHi = 0.05, opt = ftype )
  comparemat <- cbind( fmat[,k], myres[,k] )
  plot( ts( comparemat ), main=ftype )
  Sys.sleep(0.3)
  # uncomment below to visualize effect of frequency filtering
  # temp = spectrum( ts(fmat[,k], frequency=1/tr ) )
  # plot( temp$freq, temp$spec, type='l' )
  # temp = spectrum( ts(myres[,k], frequency=1/tr ) )
  # plot( temp$freq, temp$spec, type='l' )
}