Anisotropy of the backscatter coefficient of formalin-fixed ovine myocardium

Toward 3-D Echocardiographic Determination of Regional Myofiber Structure

As a step toward the goal of relating changes in underlying myocardial structure to observed altered cardiac function in the hearts of individual patients, this study addresses the feasibility of creating echocardiography-derived maps of regional myocardial fiber structure for entire, intact, excised sheep hearts. Backscatter data were obtained from apical echocardiographic images acquired with a clinical ultrasonic imaging system and used to determine local fiber orientations in each of seven hearts. Systematic acquisition across the entire heart volume provided information sufficient to give a complete map for each heart. Results from the echocardiography-derived fiber maps compare favorably with corresponding results derived from diffusion tensor magnetic resonance imaging. The results of this study provide evidence of the feasibility of using echocardiographic methods to generate individualized whole heart fiber maps for patients.

Echocardiographic-based assessment of myocardial fiber structure in individual, excised hearts

The objective of this study was to assess the feasibility of using echocardiographic imaging as an approach for determining the myocardial fiber structure of intact, individual hearts. Seven formalin-fixed, ex vivo sheep hearts were imaged using a commercially available echocardiographic imaging system, and the intrinsic fiber structure for the reconstructed short-axis cross section was determined for a specific distance from the apex of each heart. Diffusion tensor magnetic resonance (DT-MR) images of each heart were acquired and fiber maps were created for comparison with the fiber structure obtained from the corresponding reconstructed echocardiographic images. These two methods of obtaining the fiber structure showed relatively good agreement, suggesting that measurements of fiber orientation for individual hearts can be derived from echocardiographic images. Further development of this method may provide a clinically useful approach for mapping the fiber orientation in individual patients over the heart cycle.

Echocardiographic tissue characterization demonstrates differences in the left and right sides of the ventricular septum

The left and right ventricular function of the heart are influenced by the complex structure of the ventricular septum. The cyclic variation of ultrasonic backscatter over the cardiac cycle is known to be sensitive to both structural and functional characteristics of the myocardium. The objective of this study was to investigate differences in the measured magnitude and normalized delay of cyclic variation between the left and right sides of the ventricular septum in normal adult subjects (N = 31). The measured mean magnitudes of cyclic variation were found to be 4.9 ± 0.4 dB and 2.4 ± 0.3 dB (mean ± SE; p < 0.0001) and the corresponding normalized delay values were found to be 0.94 ± 0.05 and 1.59 ± 0.12 (mean ± SE; p < 0.0001) for the left and right sides, respectively. These results show significant differences in the measured magnitude and normalized delay of cyclic variation between the left and right sides of the ventricular septum in normal subjects that appear consistent with predictions based on previously described models of cyclic variation of backscatter and reported measurements of transmural differences in strain properties of the septum.