Hadamard-Encoded FMRI for Reduced Susceptibility Dropout

Gary H. Glover¹, Catherine E. Chang¹

The susceptibility difference between air and tissue induces intravoxel dephasing that causes signal dropout in BOLD fMRI. Thin slices can mitigate some of this loss but at a severe SNR efficiency penalty that is only partially offset by summing adjacent slices together. We propose a method that uses Hadamard encoding of two thin subslices per slice subsequently combined incoherently with UNFOLD to recover signal at no loss of SNR in uniform regions. Results using 2 2mm subslices and a hypercapnic challenge demonstrate a 10% increase in activation volume in frontal-orbital regions when compared with conventional 4 mm slice acquisitions.