Two-Step Rigid and Non-Rigid Image Registration for the Alignment of Three-Dimensional Echocardiography Sequences From Multiple Views

Ultrasound is a widely used imaging modality, which provides continuous real-time imaging of the human heart, brain, liver, and many other organs. Accurate cardiovascular evaluation plays an important role in early disease diagnosis. Real-time 3D echocardiography (RT3DE) imaging allows better three-dimensional (3D) imaging by extracting spatial features along with temporal information, thus improving clinical decision making. Although there have been technological advances, the majority of acquired RT3DE images tend to be of low quality, characterized by the absence of anatomical information, decreased spatial and temporal resolution, speckle noise, and a limited field of view (FOV). By registering RT3DE images obtained from several windows, it is possible to enhance the recognition of structures and achieve a substantial improvement in image quality as well as it is also useful in the fusion of echo images to image the entire heart. This study proposes a fully automatic point-based rigid registration technique, followed by nonrigid B-spline registration, to align four-dimensional (4D) echocardiogram images acquired from various sonographic windows. The methodology was evaluated using scans acquired from seven volunteers. The accuracy of registration was visually and quantitatively assessed by delineating the left ventricle in each scan and computing the Dice score overlap metric and the Hausdorff distance mutual proximity measure between the first scan and the rest. The overall findings demonstrate that the suggested registration method improves image alignment compared to the initial scans, which might be helpful in the fusion of echocardiographic images.