Two-dimensional strain imaging of controlled rabbit hearts.

Ultrasound strain imaging using 2-D speckle tracking has been proposed to quantitatively assess changes in myocardial contractility caused by ischemia. Its performance must be demonstrated in a controlled model system as a step toward routine clinical application. In this study, a well-controlled 2-D cardiac elasticity imaging technique was developed using two coplanar and orthogonal linear probes simultaneously imaging an isolated retroperfused rabbit heart. Acute ischemia was generated by left anterior descending (LAD) artery ligation. An excitation-contraction decoupler, 2,3-butanedione monoxime, was applied at a 4-mM concentration to reversibly reduce myocardial contractility. Results using a single probe demonstrate that directional changes in the in-plane principal deformation axes can help locate the bulging area as a result of LAD ligation, which matched well with corresponding Evans Blue staining, and strains or strain magnitude, based on principal stretches, can characterize heart muscle contractility. These two findings using asymmetric displacement accuracy (i.e., normal single-probe measurements with good axial but poor lateral estimates) were further validated using symmetric displacement accuracy (i.e., dual-probe measurements using only accurate axial tracking estimates from each). However, the accuracy of 2-D cardiac strain imaging using a single probe depends on the probe's orientation because of the large variance in lateral displacement estimates.