Distributionally Accurate FMRI Phase Activation

Music City Center 

In fMRI, voxel time series are complex-valued after image reconstruction due to magnetic fields inhomogeneities and a lack of k-space Hermitian symmetry. It is well-known that real and imaginary parts of k-space measurements from ADCs are normally distributed and because the IDFT is linear, real and imaginary parts of voxel measurements are normally distributed. A transformation from real and imaginary Cartesian coordinates to magnitude and phase along with marginalizing out the magnitude results in a non-normal unfriendly distribution for the phase. A large SNR assumption is generally made on the phase or it is approximated for use. Here, the exact distribution of the phase will be used for detecting task activation within phase time series and compared to the large SNR normal approximation.

FMRI

Phase

Activation 

Section on Statistics in Imaging