Lineshape of Magnetic Resonance and its Effects on Free Induction Decay and Steady-State Free Precession Signal Formation

Abstract

Magnetic resonance imaging based on steady-state free precision (SSFP) sequences is a fast method to acquire T1, T2, and T2∗-weighted images. In inhomogeneous tissues such as lung tissue or blood vessel networks, however, microscopic field inhomogeneities cause a nonexponential free induction decay and a non-Lorentzian lineshape. In this work, the SSFP signal is analyzed for different prominent tissue models. Neglecting the effect of non-Lorentzian lineshapes can easily result in large errors of the determined relaxation times. Moreover, sequence parameters of SSFP measurements can be optimized for the nonexponential signal decay in many tissue structures.

Quantitative platform for accurate and reproducible assessment of transverse (T2) relaxation time

“…The EMC technique maps T 2 relaxation times. We note that relaxation times, in some cases, can be treated as complex numbers, particularly in inhomogeneous tissues such as the lungs, 14 where the real part describes the signal attenuations, and the imaginary part describes phase oscillations 38 . This interpretation is, for example, common with T 2 * and magnetic susceptibility mapping, where the phase images are used for background field removal and phase unwrapping 39 …”