Reproducing Gradient Field Application to Localize Magnetic Resonance Signals Using MRI Simulation

Abstract

This study aimed to reproduce, through MRI simulation, the process by which gradient fields are applied during signal acquisition to obtain spatial information in MR signals. A digital phantom containing three cylinders filled with the simulated material was used to acquire MR signals by gradient echo using MRI simulations, performed using a pulsesequence diagram. MR signals were acquired under three different conditions: a) without a gradient field applied, b) with only a gradient field applied, and c) with a dephasing lobe and gradient field applied. The MR signal acquired under (a) was time-domain data that, after Fourier transformation (FT), yielded a single spectral data corresponding to the resonance frequency. However, when gradient field is applied to obtain spatial information, phase dispersion (dephasing) inevitably occurs over time; furthermore, this dephasing is superimposed. Consequently, the MR signals acquired in b) and c) were confirmed to be frequency-domain data after FT, as they were obtained under gradient field application. Furthermore, the necessity of the dephasing lobe was confirmed, as data reflecting the nature of the k-space could not be obtained without its inclusion during gradient field application during signal acquisition.