We present as novel method for the exploration of multiple overlapping volumes that provides flexibility to merge data in different ways in different regions. In each region, either one of the modalities is rendered alone or the fusion of two modalities is shown. In the regions where data is fused, the relative weights of each modality are defined with a 2D transfer function depending on the voxel’s pair of property values. The regions can be defined interactively by painting on the volume. Alternatively, when one of the modalities has been pre-classified, a graph representation of the dataset is constructed, and regions can be defined as sets of voxels fulfilling a specific combination of classification criteria. In both cases, a different fusion and shading function can be defined for each region. In this way, illustrative images of the dataset can be easily generated applying effects of cutting away, ghosting and modality enhancement.