1. An apparatus for examining with an interventional tool and visualizing an object of interest, the apparatus comprising a display, an input device, and a calculation unit, the apparatus configured for performing the following steps: acquiring a first data set; acquiring a second data set; fusing the first and second data sets; determining image parameters entered from the input device, related to at least one of an image plane, an angle of view, a contrast and a transparency; and rendering an image on the basis of the data sets and the determined parameters, resulting in a combined image with selected areas of transparency and selected areas of visible contrast information, wherein the image is visualized on the display; wherein the rendering of an image comprises setting up a stencil buffer that enables all enabled slices; rendering contrast information that is situated behind an active slice by changing a Z-buffer depth test to allow those pixels to pass that are further away than the existing slices, and write-protecting a depth buffer corresponding to the stencil buffer; drawing transparent soft tissue slices; adding volume rendered context information, wherein areas of zero density that are transparent provide local 3D volume context information, thereby providing 3D interior to cavities, and wherein the volume rendered context information is added with a transparent presentation of volume information that is hidden by otherwise opaque slices using two window width/level transfer functions; using a third volume rendered context presentation of skin and bone landmarks wherein volume halve spaces having a camera position that is not at the visible side of the slab are added to the 3D context information; adding a skin-like surface surrounding the portions of the object of interest which are not cut away; displaying real-time interventional 2D fluoro data and registering and projecting the real-time interventional 2D fluoro data over 3D vascular or anatomical information of the image; and coupling the orientation of the image to the orientation of the real-time interventional 2D fluoro data; wherein the active slice is selected by a single click and moved along its normal to show different parts of the real-time interventional 2D fluoro data, and wherein the active slice can be rotated by selection of a rotation point graphic; wherein the position of the slices is user selected or determined by 3D localization of the tip of an interventional tool; and thereby creating a high contrast, real time medical image having fully transparent zero density regions that allows the interventional tool to be guided through the fully transparent regions while avoiding regions of less transparency.