3D cardiac strain imaging using plane wave excitation and feature tracking

Evaluation of myocardial motion is important in diagnosis of heart diseases. Myocardial strain imaging is desired when assessing myocardial functions, but its clinical applications are mainly limited to two dimensions. As the heart is a fastest-moving organ, it is necessary to develop real-time 3D cardiac strain imaging methods so that complex deformation information can be acquired. Plane wave excitation can provide very high image frame rates. On the other hand, feature tracking, which selectively extract easily identifiable parts of a speckle pattern, can speed up computation time compared to conventional speckle tracking. Thus, the purpose of this study is to investigate whether accurate evaluation of cardiac deformation can be achieved with real-time 3D ultrasound imaging using plane-wave excitation and feature tracking. In this study, we simulated three-dimensional plane-wave excitation (PWE) images with object motion on which speckle tracking and feature tracking methods are applied and compared. Although the image quality of PWE images is lower, we demonstrated that PWE imaging has similar tracking errors in axial displacements when compared with two-way focused images. The computation time for feature tracking is about 500 to 800 times faster than speckle tracking. In terms of the tracking accuracy, the average tracking error for speckle tracking is less than 1%, and the tracking error range for feature tracking is 2 to 10%. If the threshold or the kernel size were larger, the tracking accuracy will be higher. Finally, we apply feature tracking to clinical 3D echocardiographic data of a three-month-old baby. The feature patterns of endo- and epi-cardium were captured partially successful, however, they are not representative of the overall movement of the heart due to limited image quality. It is important to find other ways to identify features and reducing the rate of signal decorrelation on lower quality images in order to improve performance of strain calculations in clinical applications.