Experimental assessment of angle-independent myocardial elastography performance using a left-ventricular phantom undergoing physiologic motion

Abstract

Echocardiography is the most prevalent imaging modalities in clinical cardiology. However, current diagnostic techniques rely on qualitative image analysis, ignoring the quantitative data inherent to this modality. We seek to develop a quantitative system for analyzing echocardiographic images. In this study, the performance of Myocardial Elastography was tested under motion-induced decorrelation noise using a tissue-mimicking phantom of the human left ventricle (LV) that underwent physiologic, cardiac motion configurations. A Terason system (Teratech Corp., Burlington, MA, USA.) with a phased array transducer (128 elements, 3.5 MHz) was utilized to acquire radiofrequency (RF) data in a short-axis view of a cylindrical Polyacrylamide phantom with geometric (R0 = 28mm, Ri = 15mm, L = 15cm) and mechanical properties (Ewall = 50 kPa + agar scatterers; Ecore = 10 kPa) similar to those of an adult, healthy LV. The phantom underwent two motion configurations - either pure rotation, with the non-rotating end of the phantom being free, or torsion with the non-rotating end being fixed; the latter in order to simulate the "wringing" action of the LV This provided a realistic motion pattern for decorrelation noise and rotational motion analysis. RF data were acquired at multiple slices to assess differential displacements under these motion configurations. In-plane (lateral and axial) displacements were iteratively estimated using a 1D cross-correlation and recorrelation technique in a 2D search (4.10 mm window with 75% overlap) and then radial, circumferential, and angular displacements were calculated via a coordinate transformation. Second, in-plane strains were calculated using a least-squares strain estimator. Radial and circumferential strains were then computed based on a similar coordinate transformation. The observed displacement estimates were in accordance with the theoretically predicted results. During pure rotation, all regions of the phantom exhibited similar displacements and minute strains. In the case of torsion, in-plane strains were again insignificant, but analysis of multiple slices revealed differential motion resulting from the imposed constraint on rotation. Ongoing studies aim at investigating the reproducibility of the measurements as well as studying more complex motion configurations, including simultaneous radial deformation and flow. © 2007 IEEE.