Myocardial 3D strain calculation by combining cine displacement encoding with stimulated echoes (DENSE) and cine strain encoding (SENC) imaging

Abstract

Three-dimensional (3D) strain maps of the myocardium provide a coordinate-system-independent quantification of myocardial deformation and kinematics. We combine two MRI techniques, displacement encoding with stimulated echoes (DENSE) and strain encoding (SENC), to fully formulate a 3D strain map in a single slice of myocardium. The method utilizes 2D DENSE in-plane displacement measurements in two adjacent slices in conjunction with a single SENC through-plane strain measure to calculate the 3D strain tensor. Six volunteers were imaged and the technique demonstrated 3D strain measures in all volunteers that are consistent with those reported in the literature from 3D tagging. The mean peak strain (+/- standard deviation [SD]) for six healthy volunteers for the first, second, and third principal strains are 0.42 +/-0.11, -0.10 +/-0.03, and -0.21 +/-0.02, respectively. These results show that this technique is capable of reliably quantifying 3D cardiac strain.

Figure 1

A single 16mm cine SENC slice encompasses two 8mm slices imaged with cine DENSE.

Figure 2

a) Image timing demonstrating acquisition of three imaging groups in one breathhold. b) Sequence timing diagram for cine SENC imaging

Figure 3

Depiction of how a segment of myocardium deforms into the Cartesian imaging grid of two contiguous DENSE imaged slices. Vectors are formed between these imaged voxels: V_(2,1), V_(2,3), V_(2,4). The change of these vectors from the reference time to the imaging time are described by F. All vector X and Y components are determined from DENSE. The Z component of V_(2,3), V_(2,4) is determined from the SENC tag plane tilt (spatial gradient of phase), and the Z component of V_(2,1) from using f_enc and f_SENC.

Figure 4

A cluster of voxels through which a 3 element kernel is rotated to form an average deformation gradient for the central voxel.

Figure 5

End systolic principal strains for one volunteer depicted on a colour map overlaid with the vector orientation

Figure 6

Principal mid-ventricular strain averaged across subjects. The temporal resolution is 44ms with a total of 572ms displayed. The dotted lines above and below the average strain are plotted at +/− 1 standard deviation.

Figure 7

RMS error plotted as a function of strain for the simulation that explores the effects of variability in the myocardial position between breathholds. The error for each of the 12 input strain values is plotted on a separate line for each strain component in the RCL system. Err is the radial normal strain, Ecc the circumferential, Ell the Longitudinal, Erc the radial circumferential shear strain, Erl the radial longitudinal shear strain, and Ecl is the circumferential longitudinal shear strain.