Alex Veress, Ph.D.
Department of Bioengineering (University of Utah)
Visiting Scholar ( UW Department of Bioengineering)
E-mail: averess@u...


TITLE:

"Quantifying Diastolic Function of the Left Ventricle Using a Finite Element Model with Hyperelastic Warping"


ABSTRACT:

The assessment of regional heart wall motion can localize ischemic myocardial
disease, evaluate myocardial viability, and identify impaired cardiac function due to
hypertrophic or dilated cardiomyopathies. The objectives of this research was to assess
applicability of a technique known as hyperelastic warping for the measurement of local
strains in the left ventricle (LV) directly from PET 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, PET 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 PET image dataset from a normal WKY rat 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. Regression
analysis revealed significant correlations between the forward FE and Warping
predictions for fiber stretch (R^2 = 0.96), circumferential strain (R^2 = 0.96), radial strain
(R^2 = 0.93), and longitudinal strain (R^2 = 0. 0.76) (p<0.001 for all cases).

    An application of this technology is illustrated in the determination of the
differences in diastolic function over the life spans in two spontaneously hypertensive
rats (SHR) and a Wistar Kyoto (WKY) control as documented by gated micro-PET
images. Warping was performed on all of the usable images data sets acquired for the
three rats over the subjects two year life spans at 10 week intervals.  The average 1st
principal strain of the SHR left ventricle were higher in the second year of life than that
of the of WKY control. Regional analysis revealed that, in general, the lateral freewall in
the SHR subjects showed the greatest deformation compared with the other wall
segments while the control showed a similar tendency but of lower magnitude.