Biomedical Engineering Reference
In-Depth Information
strain maps that are local measures of nonrigid deformation. The results show that, in
the case of simulated data, the quadratic Cartesian NURBS models with the cylindrical
and prolate spheroidal parameter assignments outperform their counterparts in predicting
normal strain. The decreased complexity associated with the Cartesian model with the
cylindrical parameter assignment prompted its use for subsequent calculations. Lagrangian
strains in three sets of canine data, a normal human, and a patient with a history of myocardial
infarction are presented. Eulerian strains for the normal human are also included.
1.
INTRODUCTION
Noninvasive imaging techniques for assessing the dynamic behavior of the
myocardial tissue, such as tissue tagging with magnetic resonance imaging (MRI),
are invaluable in the characterization of heart disease [1]. The advantages of tagged
MRI have encouraged significant research in the area of quantitative analysis of
myocardial deformation via physical and mathematical models [2, 3]. While most
relevant work has focused exclusively on the left ventricle, promising results have
been obtained from myocardial tag analysis of the right ventricle [4-7]. Our
coupled biventricular NURBS model is capable of providing comprehensive 3D
analysis of both the left and right ventricles using tag and contour information
from tagged MR images.
1.1. Magnetic Resonance Tagging
1.1.1. Overview
MR tagging methods allow for noninvasive measurement of intramural heart
wall motion by combining the high spatiotemporal resolution of MRI with tissue
tagging techniques [8, 9]. By altering the magnetization of the myocardial tissue
with special RF and gradient pulses, planes of hypointense signal, or tag planes,
are placed orthogonal to the image plane at end-diastole, producing a grid pattern
in the short-axis (Figure 1a) or long-axis (Figure 1b) image planes.
The intersections of the image planes with the tag planes are known as tag
lines. These tag lines deform in conjunction with the myocardial tissue facilitating
the visualization of deformation (Figure 2). The tag plane geometry consists of
a sequence of horizontal and a sequence of vertical tag planes placed orthogonal
to the short-axis image planes. Since displacement information with these two
sets of tag planes is only within the short-axis plane, a third set of tag planes is
placed orthogonal to the longitudinal set of images to capture motion normal to
the short-axis image plane. Thus, all three sets of tag planes are used to measure
3D motion.
1.1.2. Imaging protocol
For the canine studies presented in this chapter, the following imaging protocol
was utilized on a 1.5-T Sonata (Siemens Medical Solutions, Erlangen, Germany)
