A HOMOGENEITY CORRECTION METHOD FOR MAGNETIC-RESONANCE-IMAGING WITH TIME-VARYING GRADIENTS

When time-varying gradients are used for imaging, the off-resonance behavior does not just cause geometric distortion as is the case with spin-warp imaging, but changes the shape of the impulse response and causes blurring. This effect is well known for projection reconstruction and spiral kappa-space scanning sequences. We introduce here a reconstruction and homogeneity correction method to correct for the zeroth order effects of inhomogeneity using a priori knowledge of the inhomogeneity. In this method, the data are segmented according to collection time, reconstructed using some fast, linear algorithm, corrected for inhomogeneity and then superimposed to yield a homogeneity corrected image. This segmented method is compared to a conjugate phase reconstruction in terms of degree of correction and execution time. We apply this method to in vivo images using projection-reconstruction and spiral-scan sequences.