The Signal Intensity MUST Be Modulated by the Determinant of the Jacobian When Correcting for Eddy Currents in Diffusion MRI

Derek K. Jones¹

Eddy currents plague diffusion MRI. When they produce a stretch / compression of the image along the phase encode direction, the resultant change in voxel volume leads to a reduction/ increase in signal intensity. Many eddy current correction packages fail to account for this signal change. Here we show that the consequences can be drastic for diffusion tensor MRI, with biases in fibre orientation being as big as 5 degrees in regions of low anisotropy. We conclude that the signal intensity must be modulated by the volumetric change, in order to obtain meaningful and robust results from diffusion MRI.