Biventricular Cardiac Mechanics in Healthy Subjects using 3D Spiral Cine DENSE and Mesh-Free Strain Analysis

Jonathan D Suever^{1,2}, Gregory J Wehner^{3}, Christopher M Haggerty^{1,2}, Linyuan Jing^{1,2}, David K Powell^{3}, Sean M Hamlet^{4}, Jonathan D Grabau^{2}, Dimitri Mojsejenko^{2}, and Brandon K Fornwalt^{1,2,3}

3D Spiral cine DENSE was performed on 40 healthy
subjects (age: 27±8 years; 53% female) at 3T (Siemens Trio). Short-axis images
were prescribed to cover both the right and left ventricles at end-diastole.
Additional acquisition parameters included: 12 spiral interleaves, 360x360 mm2
FOV, 180x180 acquisition matrix, 8 mm slice thickness, TE/TR = 1.08/17 ms and
0.04 cycles/mm encoding frequency.^{2,3} Three-point phase cycling was used for
artifact suppression. All imaging was performed using a respiratory navigator.

RV and LV endocardial boundaries and an epicardial boundary were manually delineated on all cardiac phases using custom software (Figure 1A). The X, Y, and Z phase data within the myocardium were unwrapped using a quality-based phase unwrapping algorithm. Radial basis functions (RBFs) were fit to the raw Eulerian displacements and analytical spatial derivatives were computed directly from the coefficients of the RBFs. Using these derivatives, a 3D deformation gradient tensor and subsequently a 3D Cartesian Lagrangian strain tensor could be computed at any point within the myocardium.

The geometry of both the RV and LV was
defined by fitting a triangular surface mesh to the manually-delineated endocardial
contours at end-diastole (Figure 1B). The local coordinate system was defined for
any point on the mesh: the radial direction was the inward normal of the
endocardial mesh, the longitudinal direction was tangent to the surface and
pointed towards the manually-defined ventricular apex, and the circumferential
direction was the cross product of the radial and longitudinal directions. The
Cartesian strain tensors were transformed to correspond with the local
coordinate system to obtain radial, circumferential, and longitudinal strains
(Err, Ecc, and Ell). Torsion was defined as the circumferential-longitudinal
shear angle. Regional activation times were computed by performing
cross-correlation between regional 2^{nd} principal strain curves and the
average curve.

1. Stanton, T., Leano, R., & Marwick, T. H. (2009). Prediction of all-cause mortality from global longitudinal speckle strain: comparison with ejection fraction and wall motion scoring. Circulation. Cardiovascular Imaging, 2(5), 356–64.

2. Zhong, X., Helm, P. a, & Epstein, F. H. (2009). Balanced multipoint displacement encoding for DENSE MRI. Magnetic Resonance in Medicine, 61(4), 981–8.

3. Zhong, X., Spottiswoode, B. S., Meyer, C. H., Kramer, C. M., & Epstein, F. H. (2010). Imaging three-dimensional myocardial mechanics using navigator-gated volumetric spiral cine DENSE MRI. Magnetic Resonance in Medicine, 64(4), 1089–97.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)

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