Three-dimensional regional ventricular wall strains calculated from
magnetic resonance imaging tagging: validation with finite element
analysis.
Moulton, Michael J., Lawrence L. Creswell, Stephen W. Downing, Ricardo
L. Actis, Barna A. Szabo, Michael W. Vannier, Michael K. Pasque.
Department of Surgery, Division of Cardiothoracic Surgery,
[acute]athe Department of Mechanical Engineering, and the
Mallinckrodt Institute of Radiology, Washington University, St.
Louis, Missouri
APStracts 2:0288H, 1995.
A method is developed and validated for approximating continuous,
smooth distributions of finite strains in the ventricles from the
deformations of magnetic resonance imaging (MRI) tissue-tagging
"tag lines" or "tag surfaces." Tag lines and
intersections of orthogonal tag lines are determined using a semi
-automated algorithm. Three-dimensional (3- D) reconstruction of the
displacement field on tag surfaces is performed using two orthogonal
sets of MRI images and employing spline surface interpolation. Three
-dimensional regional ventricular wall strains are computed from an
initial reference image to a deformed image in diastole or systole by
defining a mapping or transformation of space between the two states.
The resultant mapping is termed the measurement analysis solution and
is defined by determining a set of coefficients for the approximating
functions that best fit the measured tag surface displacements.
Validation of the method is performed by simulating tag line or
surface deformations with a finite element (FE) elasticity solution
of the heart and incorporating the measured root mean squared (RMS)
errors of tag line detection into the simulations. The FE-computed
strains are compared with strains calculated by the proposed
procedure. The average difference between two-dimensional (2-D) FE
-computed strains and strains calculated by the measurement analysis
was 0.022 0.009 or 14.2 3.6% of the average FE elasticity strain
solution. Three- dimensional displacement reconstruction errors
averaged 0.087 0.002 mm or 2.4 0.1% of the average FE solution and 3
-D strain fitting errors averaged 0.024 0.011 or 15.9 2.8% of the
average 3-D FE elasticity solution. When the RMS errors in tag line
detection were included in the 2-D simulations, the agreement between
FE solution and fitted solution was 24.7% for the 2-D simulations and
19.2% for the 3-D simulations. We conclude that the 3-D displacements
of MRI tag lines may be reconstructed accurately; however, the strain
solution magnifies the small errors in locating tag lines and
reconstructing 3-D displacements.
Received 26 August 1994; accepted in final form 26 June 1995.
APS Manuscript Number H773-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.