Cine DENSE MRI with Dual Displacement Encoding

Introduction Cine DENSE (Displacement Encoding with Stimulated Echoes) MRI acquires a temporal sequence of images where the phase of each image is encoded for tissue displacement. More specifically, the phase of the DENSE stimulated-echo signal is given by θ = keΔx, where Δx is the tissue displacement and ke is the userspecified displacement-encoding frequency (a parameter analagous to the “venc” in velocity-encoded phase contrast MRI). The selected value for ke determines the degree of the phase shift for a given displacement (and, consequently, whether or not phase wrapping occurs), and the ke value also affects the degree of intravoxel dephasing and associated signal loss in tissues that deform such as cardiac and skeletal muscle (1). Thus, an optimal value for ke depends on the magnitude of the tissue displacement and deformation, where larger ke values provide greater sensitivity for smaller displacements and deformations and smaller ke values provide less phase wrapping and intravoxel dephasing for larger displacements and deformations. Since cine DENSE typically acquires a temporal sequence of images, often with smaller tissue displacements early in the sequence and larger displacements later, no single value of ke is optimal for all times. The purpose of the present study was to develop a cine DENSE sequence with dual displacement encoding, where two distinct stimulated echoes with different displacement-encoding frequencies are simultaneously stored along the longitudinal axis, and where either can be recalled at any particular time to provide a better match between ke and Δx.