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TECHNICAL PAPERS: Soft Tissue

Measurement of Strain in the Left Ventricle during Diastole with cine-MRI and Deformable Image Registration

[+] Author and Article Information
Alexander I. Veress

Department of Bioengineering, and Scientific Computing and Imaging Institute,  University of Utah, Salt Lake City, UT

Grant T. Gullberg

 E. O. Lawrence Berkeley National Laboratory, Berkeley, CA

Jeffrey A. Weiss1

Department of Bioengineering, and Scientific Computing and Imaging Institute,  University of Utah, 50 South Central Campus Drive, Room 2480, Salt Lake City, Utah 84112-9202jeff.weiss@utah.edu

1

Corresponding author.

J Biomech Eng 127(7), 1195-1207 (Jul 29, 2005) (13 pages) doi:10.1115/1.2073677 History: Received December 14, 2004; Revised July 26, 2005; Accepted July 29, 2005

The assessment of regional heart wall motion (local strain) can localize ischemic myocardial disease, evaluate myocardial viability, and identify impaired cardiac function due to hypertrophic or dilated cardiomyopathies. The objectives of this research were to develop and validate a technique known as hyperelastic warping for the measurement of local strains in the left ventricle from clinical cine-magnetic resonance imaging (MRI) image datasets. The technique uses differences in image intensities between template (reference) and target (loaded) image datasets to generate a body force that deforms a finite element (FE) representation of the template so that it registers with the target image. To validate the technique, MRI image datasets representing two deformation states of a left ventricle were created such that the deformation map between the states represented in the images was known. A beginning diastolic cine-MRI image dataset from a normal human subject was defined as the template. A second image dataset (target) was created by mapping the template image using the deformation results obtained from a forward FE model of diastolic filling. Fiber stretch and strain predictions from hyperelastic warping showed good agreement with those of the forward solution (R2=0.67 stretch, R2=0.76 circumferential strain, R2=0.75 radial strain, and R2=0.70 in-plane shear). The technique had low sensitivity to changes in material parameters (ΔR2=0.023 fiber stretch, ΔR2=0.020 circumferential strain, ΔR2=0.005 radial strain, and ΔR2=0.0125 shear strain with little or no change in rms error), with the exception of changes in bulk modulus of the material. The use of an isotropic hyperelastic constitutive model in the warping analyses degraded the predictions of fiber stretch. Results were unaffected by simulated noise down to a signal-to-noise ratio (SNR) of 4.0 (ΔR2=0.032 fiber stretch, ΔR2=0.023 circumferential strain, ΔR2=0.04 radial strain, and ΔR2=0.0211 shear strain with little or no increase in rms error). This study demonstrates that warping in conjunction with cine-MRI imaging can be used to determine local ventricular strains during diastole.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Target (top) and template (bottom) image datasets used in the warping analysis. The Target image dataset was created by mapping the template image dataset with displacements determined from a forward FE simulation of passive diastolic filling.

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Figure 2

(Color) Left: Forward FE model used to create target image. Right: Detail of the LV. Blue arrows indicate that external pressure was applied on the endocardial surface.

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Figure 3

Effect of increasing levels of additive noise on the appearance of one slice from the template image dataset. (A) SNR=0.5, (B) SNR=1, (C) SNR=4, (D) SNR=8, and (E) SNR=16.

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Figure 4

(Color) Fiber stretch distribution for the forward FE (left) and warping (right) analyses. The fiber stretch distributions show good agreement between the FE and the warping analyses.

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Figure 5

Forward and FE predictions of several measures of local wall deformation at end diastole as a function of distance through the myocardial wall (mean±standard deviation). A: local fiber stretch. B: circumferential Green-Lagrange strain. C: radial Green-Lagrange strain. D: in-plane Green-Lagrange shear strain (circumferential∕radial). 0% denotes endocardial surface and 100% denotes epicardial surface. Results are presented for image cross-sectional slices at 1 cm (light gray), 7 cm (dark gray), and as an average over all slices (black). 7 cm corresponds to the base of the LV and 1 cm is near the apex of the heart. Solid lines indicate results for the forward FE model and dashed lines indicate results for hyperelastic warping. Error bars show standard deviations. All values are referenced to the undeformed geometry (beginning diastole).

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Figure 6

Scatter plots of forward FE versus warping stretch∕strains. A: fiber stretch. B: circumferential strain. C: radial strain. D: in-plane shear strain. Symbols represent different axial image slices. 7 cm corresponds to the base of the LV and 1 cm is near the apex of the heart.

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Figure 7

Bland-Altman plots of the validation stretch and strain comparison. A: fiber stretch. B: circumferential strain. C: radial strain. D: in-plane shear strain. The plots show good agreement between the forward and warping solutions. The central solid line indicates the mean difference in the data while the heavy dashed lines indicate the boundary of ±2 standard deviations.

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Figure 8

Effect of signal-to-noise ratio on A: coefficient of determination; and B: the RMS error (units of strain) for the four measures of deformation

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