Spatio-temporal encoding by quadratic gradients in magnetic resonance imaging

Abstract

Spatio-temporal encoding (SPEN) MRI is a non-Fourier imaging technique that encodes the spatial information in such a way that there is a direct relation between the signal intensity recorded during the acquisition and the spin density at a given position. In current spatio-temporal encoding methods, the first crucial step requires imparting a quadratic phase onto the transverse magnetization. Usually, this is achieved by simultaneous application of a frequency-swept (chirp) pulse and a linear magnetic field gradient. In this work, we show that a quadratic phase can be imparted by using quadratic encoding gradients. This leads to smaller specific absorption rates (SARs). Furthermore, the proposed sequence can be used for multi-slice applications similar to ordinary multi-slice sequences, but without the limitations of traditional SPEN.