MEASUREMENT OF PULSATILE FLOW USING MRI AND A BAYESIAN TECHNIQUE OF PROBABILITY ANALYSIS

This work shows that complete spatial information of periodic pulsatil e fluid flows can be rapidly obtained by Bayesian probability analysis of flow encoded magnetic resonance imaging data, These data were acqu ired as a set of two-dimensional images (complete two-dimensional samp ling of k-space or reciprocal position space) but with a sparse (six p oint) and nonuniform sampling of q-space or reciprocal displacement sp ace, This approach enables more precise calculation of fluid velocity to be achieved than by conventional two q-sample phase encoding of vel ocities, without the significant time disadvantage associated with the complete flow measurement required for Fourier velocity imaging, For experimental comparison with the Bayesian analysis applied to nonunifo rmly sampled q-space data, a Fourier velocity imaging technique was us ed with one-dimensional spatial encoding within a selected slice and a uniform sampling of q-space using 64 values of the pulsed gradients t o encode fluid flow, Because the pulsatile flows were axially symmetri c within the resolution of the experiment, the radial variation of flu id velocity, in the direction of the pulsed gradients, was reconstruct ed from one-dimensional spatial projections of the velocity by exploit ing the central slice theorem, Data were analysed for internal consist ency using linearised flow theories, The results show that nonuniform q-space sampling followed by Bayesian probability analysis is at least as accurate as the combined uniform q-space sampling with Fourier vel ocity imaging and projection reconstruction method, Both techniques gi ve smaller errors than a two-point sampling of q-space (the convention al flow encoding experiment).