A system for visualizing a flow within a volume of a 3-dimensional (3-D) image includes a first transfer unit for applying a first transfer function, which assigns a renderable property to each location of a first plurality of locations within the volume based on a flow pattern assigned to the location. A second transfer unit is provided for applying a second transfer function, which assigns a renderable property to each location of a second plurality of locations within the volume based on a value of the 3-D image assigned to the location. Further, the system also includes a mixing unit for computing a 2-dimensional (2-D) image based on the renderable property assigned to each location of the first plurality of locations and on the renderable property assigned to each location of the second plurality of locations, where the 2-D image visualizes the flow pattern and the 3-D image.