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-Based Continuum Mechanics Analysis

Methods  The image-based body force depends on template and target intensities and their gradients: Template IntensityImage-based Force Target IntensityTemplate and Target Intensity 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 -90 o at the epicardium, 0 o at midwall and 90 o 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

Comparison of Forward with Warping Nodal Solutions Fiber Stretch Results Every 3 nodes were averaged to provide a comparison of small regions 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