Optimal z-Encoding Frequency for zHARP: In-vivo Validation and Comparison with SF-CSPAMM

Introduction: Quantitative functional cardiac imaging can be used to characterize healthy and diseased myocardial tissues. Imaging protocols that measure 3D motion of the heart can lead to more accurate characterization than 2D approaches. However, 3D protocols are often too time-consuming for clinical feasibility. zHARP is a fast imaging technique that can quantify 3D myocardial motion from a single slice. The technique is based on slice-following CSPAMM tagging, adding a z-gradient to encode the through-plane displacement of the tagged CINE images. Although zHARP has demonstrated promising 3D displacement results, no research has been done on either the optimality of the z-encoding frequency for through-plane displacement measurement or its effect on the measurement of in-plane displacements. The purpose of this work is to establish the mathematical framework for studying the intravoxel dephasing effect of the z-encoding on zHARP 3D displacement and in-plane strain measures. The optimal z-gradient strength is determined from this work by experimental comparison of the in-plane and through-plane displacement and strain maps.