ALFF calculation (resting-state)

Dear all,
I like to write a matlab script to calculate fractional-ALFF and ALFF (Amplitude of low-frequency fluctuations).

  1. What is the right order for calculation:
    Temporally band-pass filtered (0.01–0.0.8Hz) and then FFT
    FFT and then to obtain the power spectrum across 0.01–0.08 Hz

  2. Should I apply linearly detrend on the input functional file? (for ALFF)
    Can i apply melodic (ICA decomposition) and removal of noise components (with fsl_regfilt) and next to apply FFT?

  3. For fALFF should I calculate the entire frequency range of the whole brain or only the gray matter?

  4. For fALFF, should I divide by the entire frequency range (0-0.5 Hz, Nyquist frequency) my TR=1sec?

  5. For group comparison ALFF, f/ALFF should be both

  • Divided by the global mean
  • transformed into Z-scores


look at (2.2.3): Percent amplitude of fluctuation: A simple measure for resting-state fMRI signal at single voxel level