Point spread function mapping for distortion correction of spinal cord diffusion weighted MRI

Introduction Diffusion Weighted Magnetic Resonance Imaging (DWMRI) is a promising method to assess axonal integrity in the spinal cord in vivo [1]. However, the fast imaging sequences required for in vivo DWMRI are sensitive to B0-field inhomogeneities caused by susceptibility differences around vertebral structures and lungs. Those inhomogeneities cause voxel shift that corrupt the anatomical evaluation. Point Spread Function (PSF) mapping is a nobel method developed for correction of single shot EPI [2,3]. By the use of separate reference scan with a phase prewinder before a conventional EPI readout an additional distortion free dimension in k-space is introduced that can be Fourier transformed into the PSF for each voxel. A voxel displacement map is found as the peaks of the PSFs. We demonstrate that PSF mapping can be used as a correction technique for DWMRI of the human cervical spinal cord.