Visibility driven visualization of 3D cardiac ultrasound data on the GPU

Direct volume rendering (DVR) has become a widely used technique for visualizing anatomical structures in medical 3D datasets The aim of this study was to locally adapt the opacity transfer function (OTF) in order to improve the results achieved when rendering 3D echocardiographic datasets using DVR. A novel approach for defining locally adaptive OTFs has been tested and adapted to echo data and implemented on the GPU. The local OTF is modeled as a truncated second order polynomial. The algorithm locates significant transitions along the ray profile (feature detection along the ray) in order to estimate an opacity threshold (below which all values are considered transparent) and the steepness of the polynomial for each ray. A reference global OTF and the locally adaptive algorithm have been implemented on a GPU using OpenCL and tested on a dataset of nine 3D echo recordings. The rendering resolution is 512×512×300, while average timing is 28ms, 104ms for the reference and the new method respectively. The locally adaptive OTFs were able to compensate for high variations in tissue (and such reducing wall drop-outs) and blood pool signal (reducing spurious structures inside the cavity). The method depends on a number of user defined parameters, determining these values robustly is subject of ongoing research.