Validation of the measurement of 3D left ventricular strains

using image warping and untagged MRI images.

AI Veress, JA Weiss, GC Klein, and GT Gullberg

Introduction: Motivation for Study Assessing regional heart wall

motion (wall motion, thickening, strain, etc.) provides quantitative estimates of local wall function.

Extent of ischemic myocardial disease

Extent of impairment of cardiac function due to hypertrophic and dilated cardiomyopathies.

Determining Deformation from Medical Images

Template Image Target Image

Deformation,X)

Static pressure load of 120 mmHg was applied.

Image-BasedContinuum Mechanics Analysis

WarpingFE Model

ImageData

Stress/StrainMaterialProperties Deformation Map

CCBoundaryConditions

Methods

The image-based body force depends on template and target intensities and their gradients:

UT S

T S

X X X X, ,

Template IntensityImage-basedForce

Target Intensity Template and TargetIntensity Gradients

Manual Segmentation

Segmented curves used to define surfaces

Model Created from surface definitions

Images are 64 x 64 x 8 pixels

Finite Element Model Creation

Template Image (base slice)

Validation of Warping for use With Cardiac MRI

Imaging Template image was mapped onto displacement mesh

producing a target image.

Forward and warping models had fiber angles vary from -90o at the epicardium, 0o at midwall and 90o degrees to the endocardium.

55 mmHg (7333 Pa) internal pressure load was placed on the endocardial surface of heart to provide the physiological loading so that forward so that the stretch distribution was similar to that found in the

literature*.

* Tseng et al. Radiology 2000

Forward Validation Model

Wall material properties determined from curve fit of Humphrey et al. biaxial data.

Humphrey et al. JBME 1990

Internal pressure load 55 mmHg (7333 Pa)

Warping Cardiac MRI Images

Fiber Stretch = final fiber length / initial fiber length= f/o

1.14

0.85

Comparison of Forward with Warping Nodal

Solutions Fiber Stretch Results

1

1.05

1.1

1.15

1 1.05 1.1 1.15

Forward Model Stretch

Wa

rpin

g M

od

el

Str

etc

h y = 7

y = 6

y = 5

y = 4

y = 3

y = 2

y = 1

Every 3 nodes were averagedto provide a comparison of smallregions in the mesh.

Discussion

Using regional average values provides a better method for comparison.

The average of three nodes were used in the present work.

Comparison of the stretches at the nodal locations showed that the nodes were not in the same location in each deformed state.

Conclusion

Initial validation results seems to indicate that reasonably good agreement will be reached.

Strain distributions look reasonable accurate for the resolution of the images.

Acknowledgments

Dr. Grant Gullberg

Dr. Jeffrey Weiss

Dr Gregory Klein

Dr. Richard Rabbitt

Anton Bowden