Transfer Functions in DRR Volume Rendering

Digital Reconstruction Radiography (DRR) is an important technique in radiotherapy imaging applications. DRR volume rendering aims to render DRR images using CT or other tomographic data set. Besides appropriate optical model and sampling, realistic DRR volume rendering mainly depends on an accurate attenuation transfer function, which is usually a piecewise function. In this paper, we discuss different methods to interpolate the transfer function in the intersection domain. The continuity of transfer function is critical to render a smooth and well defined boundary between different materials. As a result, interpolation of the attenuation coefficient performs better than interpolation of the mass attenuation coefficient. Attenuation coefficient cubic spline supplies a better result than other interpolation methods.