Artifact-free volume clipping algorithm for real-time 3D ultrasound

Three-dimensional (313) ultrasound has become a useful tool in cardiac imaging, OB/GYN and other clinical applications. It enables clinicians to visualize the acquired volume and/or planes that are not easily accessible using 2D ultrasound, in addition to providing an intuitive understanding of the structural anatomy in three dimensions. One effective way to examine the acquired volumetric data is by clipping away parts of the volume using cross-sectional cuts to reveal the underlying anatomy masked by other structures. Ideally, such boundaries should reflect the orientation and location of the clip surfaces without altering the information content of the original data. Because of the artificial surface introduced by the clip boundary, shading employed to enhance the surfaces of the object gets modified, resulting in inconsistent shading and noticeable artifacts in the case of ultrasound data. Consistent shading of clip surfaces was previously studied for graphics hardware-based volume rendering, and an algorithm was developed and demonstrated in MRI, CT and non-medical datasets. However, that algorithm cannot be applied directly to fast software-based rendering approaches such as the shear-warp algorithm. Furthermore, ultrasound data require a different clipping approach due to their fuzzy nature, lower signal-to-noise ratios, and real-time requirements. In this paper, we present a software-based volume clipping technique that can effectively and efficiently overcome the difficulties associated with the shading of the clip boundaries in ultrasound data using shear-warp. Our technique improves the viewer's comprehension of the clip boundary without altering the original information content within the volume. The method has been implemented on programmable processors while maintaining the interactive speed in rendering.