Dephased MRI

Abstract

In this work gradient dephasing is treated as a mechanism for manipulating contrast in otherwise conventional MR images. The paper provides a theoretical and experimental framework for this approach. It starts from the observation that dephasing gradients invoke a shift in k-space. From this it is inferred that the effects of in-plane and through-plane dephasing can be systematically explored in the context of any given imaging experiment by sampling k-space more widely and densely than dictated by the field of view (FOV) and the spatial resolution of the desired images. The oversampled k-space allows an ensemble of lower-resolution dephased images to be reconstructed in which the degree and direction of dephasing are determined by the off-center position of the reconstruction window. The efficacy of this approach is demonstrated for standard gradient-echo acquisitions in a phantom. The results indicate the potential of the proposed methodology for evaluating 3D image data and optimizing gradient dephasing in applications that rely on the exploitation of partial volume and susceptibility effects (e.g., tracking interventional devices and tracing magnetically labeled substances).