Multi-volume rendering is a technique that renders and displays multiple volumes simultaneously. In ultrasound
imaging, multi-volume rendering is used for mixing 3D anatomical structures from B-mode imaging with blood flow
information from power Doppler imaging (PDI) or color Doppler imaging (CDI). A variety of multi-volume rendering
techniques have been proposed, such as post fusion (PF), composite fusion (CF) and progressive fusion (PGF). PF,
which combines independently-rendered volumes, is unable to depict a spatial relationship between B-mode images (i.e.,
tissue structure) and PDI/CDI images (i.e., blood flow). The CF technique suffers from color distortion due to
intermixing of hue values. In our recent study, the PGF technique was found to better retain and display tissue structures,
vasculature and their depth relationship. However, the disadvantages of PGF include its high computational cost due to
the requirement of maintaining a separate rendering pipeline for each volume (i.e., B-mode and power/color Doppler)
and potential artifacts of depth-order ambiguity. In this paper, we present a new flexible computationally efficient multivolume
rendering technique, named volume fusion (VF), and compare it with existing techniques. We have evaluated
the VF method and other multi-volume rendering techniques with data acquired from a commercial ultrasound machine
and found that the VF technique can preserve the spatial relationships well amongst multiple volumes without color
distortion while the same rendering pipeline can be used to support both PDI and CDI volume fusion.
Volume rendering in 3D ultrasound is a challenging task due to the large amount of computation required for real-time rendering. The shear-warp algorithm has been traditionally used for 3D ultrasound rendering for its effectiveness in lowering computing cost. However, this lowered computing cost does come at the price of reduced image quality due to (a) the presence of final warp interpolation, which smoothes out fine details and (b) sampling only at discrete slice locations, which introduces aliasing, e.g., staircase artifacts. For 3D ultrasound, we have merged pre-integration with the shear-image-order algorithm to overcome both limitations of shear-warp while still enjoying the computational savings. Pre-integration overcomes the aliasing artifacts while shear-image-order preserves details. We have also developed a technique to integrate shading coefficient into pre-integrated rendering. This pre-integrated shear-image-order algorithm, with slightly higher computation than what is required to support the shear-warp algorithm, improves the quality of the rendered image significantly. In this paper, we discuss the pre-integrated shear-image-order algorithm and present the results of subjective quality evaluation on several data sets. We have also analyzed how this algorithm can be implemented on an advanced digital signal processor (DSP) to achieve real-time performance.