Three-dimensional myocardial deformations: calculation with displacement field fitting to tagged MR images.

Abstract

PURPOSE:To reconstruct three-dimensional (3D) myocardial deformations from orthogonal sets of parallel-tagged magnetic resonance (MR) images. MATERIALS AND METHODS:Displacement information in the direction normal to the undeformed tag planes was obtained at points along tag lines. Three independent sets of onedimensional displacement data were used to fit an analytical series expression to describe 3D displacement as a function of deformed position. The technique was demonstrated with computergenerated models of the deformed left ventricle with data from healthy human volunteers. RESULTS:Model deformations were reconstructed with a 3D tracking error of less than 0.3 mm. Error between estimated and observed one-dimensional displacements along the tags in 10 human subjects was 0.00 mm ± 0.36 (mean ± standard deviation). Robustness to noise in the tag displacement data was demonstrated by using a Monte Carlo simulation. CONCLUSION:The combination of rapidly acquired parallel-tagged MR images and field-fitting analysis is a valuable tool in cardiac mechanics research and in the clinical assessment of cardiac mechanical function. KeywordsHeart, function, 51.91; Magnetic resonance (MR), physics, 511.1214; Myocardium, MR, 511.1214 MAGNETIC resonance (MR) imaging tagging (1-7) and fast, breath-hold imaging (8,9) are promising tools for noninvasive study of the function of the heart wall in both research and clinical settings. The objective of this study was to measure noninvasively the threedimensional (3D) deformation field within the heart wall at many time points in the heart cycle.Myocandial tags are regions where the magnetization has been perturbed before imaging and that, therefore, produce a signal intensity difference relative to that of nontagged regions for a time proportional to T1. Because the tags result from perturbations of the magnetization of the tissue itself, the deformation of the tags accurately reflects the motion of the underlying tissue (10-12). Special techniques are needed to reconstruct the 3D motion of the heart from MR image planes that are fixed in space, because different sections of tissue are sampled at different times.Correspondence to: Elliot R. McVeigh.Address reprint requests to E.R.M.. NIH Public Access Author ManuscriptRadiology. Author manuscript; available in PMC 2008 May 26. Published in final edited form as:Radiology. 1995 June ; 195(3): 829-835. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptThe movement of the heart through short-axis image planes, known as cardiac through-plane motion, is typically 10 mm at the base of the left ventricle (13). (This was confirmed with the analysis of 10 healthy human subjects discussed in this article.) Correction for this is crucial, even for two-dimensional analysis of wall deformation (14). This correction was achieved by combining information from both long-and short-axis sets of tagged heart images into a unified expression for the 3D displacement field.Previously presented motion reconstruction sc...

Combined tag tracking and strain reconstruction from tagged cardiac MR images without user‐defined myocardial contours

“…The second type of error is caused when a deformation model is fit to the tag line data; the model does not fit the tag lines exactly. The RMS difference between the tracked tag lines and synthetic tag lines generated by the deformation model is used to assess the quality of the deformation reconstruction (6,8,13,14,23). The RMS tag line errors reported in this article are a combination of these two errors, because the deformation model is used to track the tag lines.…”

“…For consistency with previously published results (6,8,14,15), we rotate the Lagrangian strain tensor E to prolate spheroidal coordinates for analysis. The strain tensor E is computed on a set of 324 material points (6), a 3 radial ϫ 12 circumferential ϫ 6 longitudinal mesh of material points equally spaced around the myocardium from the most basal short-axis imaging plane to the most apical short-axis imaging plane.…”

“…For comparison purposes, we also computed the strains from the user-defined tag line points using a published user-supervised strain reconstruction method (3,6,18). This method required user-supervised identification of myocardial contours and tag lines in each image in the study.…”

“…The COTTER algorithm produced reproducible strains between two independent users (Table 3) for E rr , E cc , E ll and E min in all three layers. Table 4 shows the correlation coefficients between end-systolic E rr , E cc , E ll and E min strains computed using the COTTER algorithm and the user-supervised reconstruction method (6). Pooled data from the eight human imaging studies show that the COTTER algorithm and user-supervised method showed good correlation in E cc and E min in all three layers.…”

“…The strains computed using our algorithm were compared to those computed from a previously published user-supervised strain reconstruction method (6).…”